Download Genetic control of broad-spectrum resistance to turnip mosaic virus

Journal of General Virology (2007), 88, 3177–3186
DOI 10.1099/vir.0.83194-0
Genetic control of broad-spectrum resistance to
turnip mosaic virus in Brassica rapa (Chinese
cabbage)
Rachel L. Rusholme,1,2,33 Erin E. Higgins,1 John A. Walsh2
and Derek J. Lydiate1,3
Correspondence
John A. Walsh
[email protected]
1
Agriculture and Agri-Food Canada, 107 Science Place, Saskatoon, SK S7N 0X2, Canada
2
Warwick HRI, University of Warwick, Wellesbourne, Warwick CV35 9EF, UK
3
John Innes Centre, Colney Lane, Norwich NR4 7UH, UK
Received 29 May 2007
Accepted 19 July 2007
The Brassica rapa line RLR22 was resistant to eight diverse turnip mosaic virus (TuMV) isolates. A
B. rapa genetic map based on 213 marker loci segregating in 120 first back-cross (B1) individuals
was established and aligned with the B. rapa genome reference map using some of the RFLP
probes. B1 individuals were self-pollinated to produce B1S1 families. The existence of two loci
controlling resistance to TuMV isolate CDN 1 was established from contrasting patterns of
segregation for resistance and susceptibility in the B1S1 families. The first gene, recessive TuMV
resistance 01 (retr01), had a recessive allele for resistance, was located on the upper portion of
chromosome R4 and was epistatic to the second gene. The second gene, Conditional TuMV
resistance 01 (ConTR01), possessed a dominant allele for resistance and was located on the
upper portion of chromosome R8. These genes also controlled resistance to TuMV isolate CZE 1
and might be sufficient to explain the broad-spectrum resistance of RLR22. The dominant
resistance gene, ConTR01, was coincident with one of the three eukaryotic initiation factor 4E
(eIF4E) loci of B. rapa and possibly one of the loci of eIF(iso)4E. The recessive resistance gene
retr01 was apparently coincident with one of the three loci of eIF(iso)4E in the A genome of
Brassica napus and therefore, by inference, in the B. rapa genome. This suggested a mode of
action for the resistance that is based on denying the viral RNA access to the translation initiation
complex of the plant host. The gene retr01 is the first reported example of a recessive resistance
gene mapped in a Brassica species.
INTRODUCTION
Turnip mosaic virus (TuMV; genus Potyvirus) infects a
wide range of cultivated plant species (Edwardson &
Christie, 1991) and causes significant economic losses in
Brassica crops (Shattuck, 1992). TuMV is a positive-strand
RNA virus with a genome comprising 9830–9835 nt
(Nicolas & Laliberté, 1992; Ohshima et al., 1996; Jenner
et al., 2000) and is the subject of advanced molecular
characterization (Revers et al., 1999; Jenner et al., 2000;
Walsh & Jenner, 2002). Plant genes for resistance to TuMV
have been mapped in lettuce (Tu, Robbins et al., 1994),
Brassica napus (TuRB01, Walsh et al., 1999; TuRB03,
Hughes et al., 2003; TuRB04 and TuRB05, J. A. Walsh & D.
J. Lydiate, unpublished) and Brassica rapa (TuRB01b,
Rusholme et al., 2007). All are dominant resistance genes
(R genes) that control resistance to narrow spectra of
3Present address: University of East Anglia, School of Biological
Sciences, Norwich, Norfolk NR4 7TJ, UK.
0008-3194 G 2007 SGM
TuMV isolates. In the case of TuRB01, TuRB01b and
TuRB04, the cytoplasmic inclusion protein has been
identified as the viral avirulence determinant (Jenner
et al., 2000, 2002; Walsh et al., 2002). For TuRB03 and
TuRB05, the viral avirulence determinant is the P3 protein
(Jenner et al., 2002, 2003).
Plants possess a range of defence responses against viral
pathogens. The best-characterized defence responses lead
to a hypersensitive reaction with localized cell death and
are often associated with activation of systemic acquired
resistance and restriction of the virus to the initial site of
infection (Staskawicz et al., 1995; Yang et al., 1997). This
type of response is strain-specific and is controlled by R
genes that play a role in virus recognition. The N gene,
controlling resistance to tobacco mosaic virus (Erickson
et al., 1999), and Rx, which controls resistance to potato
virus X (Köhm et al., 1993), are well-characterized
examples of dominant R genes. Both genes have a
nucleotide binding site and a leucine-rich repeat motif
(Erickson et al., 1999; Bendahmane et al., 1999) that are
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R. L. Rusholme and others
common to many R genes active not only against viruses,
but also against a wide range of other pathogens (Dangl &
Jones, 2001).
An additional general mechanism by which plants have
developed resistance to viruses is by the modification of
host functions that are involved in the virus life cycle. It has
been shown that the pvr2 locus in pepper, which confers
recessive resistance against the potyviruses potato virus Y
and tobacco etch virus (TEV), corresponds to the
eukaryotic initiation factor 4E gene (eIF4E) (Ruffel et al.,
2002). Similarly, in Arabidopsis thaliana, disrupting the
function of eIF(iso)4E produces plants that are resistant to
TEV (Lellis et al., 2002), TuMV (Duprat et al., 2002; Lellis
et al., 2002) and lettuce mosaic virus (LMV) (Duprat et al.,
2002). The eIF(iso)4E protein of Arabidopsis has also been
shown to interact with the genome-linked protein (VPg,
which is attached to the 59 end of the viral genome and is
assumed to be responsible for recruiting the viral RNA to
the translation initiation complex) of TuMV in the yeast
two-hybrid system (Wittmann et al., 1997). Since these
original findings, a number of recessive resistances to other
members of the Potyviridae have been shown to correspond
to eIF4E or eIF(iso)4E (Robaglia & Caranta, 2006). The
natural role of eIF4E and eIF(iso)4E is in the initiation of
translation of capped mRNAs (Browning, 1996). eIF4E
binds eIF4G, which is a scaffold for other components of
the translation initiation complex.
Several plant genes with recessive alleles that restrict the
cell-to-cell movement (Nicolas et al., 1997) or the systemic
spread (Schaad & Carrington, 1996; Murphy et al., 1998;
Hämäläinen et al., 2000) of viruses have been identified.
One example is a mutant gene of A. thaliana that is
thought to disrupt the interaction of turnip vein clearing
virus with plasmodesmata at the boundary between
vascular and non-vascular tissue (Lartey et al., 1998).
Genes with dominant (wild-type) alleles that restrict virus
movement have also been identified in A. thaliana (RTM1,
RTM2 and RTM3; Chisholm et al., 2001). All of the above
plant defence mechanisms are distinct from virus-induced
gene silencing, which involves the recognition and
sequence-specific degradation of viral RNA by plants
(Vance & Vaucheret, 2001).
B. rapa is grown worldwide as vegetable, oilseed and fodder
crops. In addition, it has contributed the Brassica A
genome to the amphidiploid crop species B. napus and
Brassica juncea (U, 1935). Several accessions of B. rapa
exhibiting broad-spectrum resistance to TuMV have been
identified (Anonymous, 1996; Liu et al., 1996) but the
genetic control of resistance in even the best-characterized
accessions, 0-2 and BP058, is unclear (Yoon et al., 1993;
Suh et al., 1995, 1996; Hughes et al., 2002). This paper
describes the application of established Brassica genetic
marker technology (Parkin et al., 1995; Sharpe et al., 1995)
and the European TuMV pathotyping system (Jenner &
Walsh, 1996) to identify the genes controlling broadspectrum resistance to TuMV in the Chinese cabbage line
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RLR22 and to position these genes on the B. rapa genome.
It establishes a solid foundation for understanding a
mechanism of broad-spectrum resistance to potyviruses
based on modifying the host eIF4E and eIF(iso)4E genes.
METHODS
Parental plant material. The Chinese cabbage accession BP079
exhibits resistance to a wide variety of TuMV isolates (Anonymous,
1996; Liu et al., 1996; Walsh et al., 2002). It was obtained from Dr
Sylvia Green (Asian Vegetable Research and Development Centre,
Shanhua, Tainan, Taiwan). BP079-8 was an inbred line derived from
BP079, and RLR22 was a plant selfed from BP079-8 (Walsh et al.,
2002). R-o-18 was an inbred line of B. rapa ssp. trilocularis (D. J.
Lydiate).
TuMV isolates and disease assays. The origins and propagation
of the eight TuMV isolates used in this study (UK 1, CHN 5, CZE 1,
CDN 1, JPN 1, DEU 7, GK 1 and UK 4, representative of TuMV
pathotypes 1, 3, 3, 4, 7, 8, 9 and 12, respectively) and their phenotypes
on the B. napus differentials of the European pathotyping system have
been described by Jenner & Walsh (1996). In disease assays, the
cotyledons and the first and second leaves of plants were mechanically
inoculated at the two true-leaf stage (Jenner & Walsh 1996) and
resistance (the absence of systemic spread) was established by negative
results from ELISA on the uninoculated third and fourth leaves, 4
weeks post-inoculation (Jenner et al., 1999; Walsh et al., 1999). The
eight TuMV isolates were inoculated separately to batches of six
RLR22S1 plants and batches of three R-o-18 plants. TuMV isolates
UK 1, CZE 1 and CDN 1 were inoculated separately to batches of
seven F1 plants from the cross R-o-186RLR22 (Fig. 1).
DNA extraction and genetic marker analysis. DNA extraction
and Southern blot hybridization were carried out as described by
Sharpe et al. (1995) except that filters were washed only at low
stringency. Genetic marker analysis of the first back-cross (B1)
mapping population (Fig. 1) employed a range of Brassica genomic
and cDNA clones as Southern blot hybridization probes in RFLP
analysis including those described by Thormann et al. (1994) (pW)
Fig. 1. Breeding strategy used to develop the first back-cross
(B1) population segregating for resistance to TuMV, the selfed
progeny of the B1 individuals (B1S1 families) used to assess
resistance/susceptibility to different TuMV isolates and an inbred
line with broad-spectrum resistance to TuMV (RLR22S1). fl, Selfpollination; =, male parent; R, female parent. RLR22 is resistant to
TuMV isolate CDN 1 and R-o-18 is susceptible to TuMV isolate
CDN 1.
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Journal of General Virology 88
Broad-spectrum resistance to turnip mosaic virus
and Sharpe et al. (1995) (pN, pO and pR), new sets of Brassica
genomic clones (pJ and pM; A. Sharpe & D. J. Lydiate, unpublished)
and Z18443 (Sillito et al., 2000). In addition, Brassica microsatellite
markers (A. Sharpe & D. J. Lydiate, unpublished) were used as
described by Naom et al. (1995). The B. rapa/Brassica A genome loci
representing eIF4E and eIF(iso)4E were mapped using B. napus cDNA
clones selected on the basis of homology to the corresponding A.
thaliana genes (A. Sharpe, unpublished). The clone LL61 represented
eIF4E, whilst the clone es2686 represented eIF(iso)4E. The highly
polymorphic SG mapping population of B. napus was also used to
map the various members of the eIF4E and eIF(iso)4E gene families.
The SG population was derived from a resynthesized B. napus6domesticated B. napus cross; it has been used to develop a map of over
1200 microsatellite loci and has been aligned with the established B.
napus genome (Parkin et al., 1995) on the basis of well-characterized
RFLP loci (Parkin et al., 2005) (I. Parkin, personal communication,
and D. J. Lydiate, unpublished).
and the resulting genetic linkage map along with the
framework loci are presented in Fig. 2.
The distribution of interval sizes in the new map was
compared with the distribution expected from an equivalent theoretical population with both markers and crossovers randomly distributed across the genome (Fig. 3) and
the observed and expected distributions were essentially
identical (Kolmogorov–Smirnov statistic50.051, P50.65),
suggesting that neither crossovers nor marker loci were
clustered. The frequency distribution of segregation ratios
at marker loci showed that segregation distortion was not a
problem in the back-cross population (Fig. 4), although a
slight but significant (x2521.1, P54.4261026) bias against
R-o-18 alleles was evident. The above parameters suggested
that the B1 population was near-ideal for genetic analyses.
Statistical analysis of genetic linkage data. Genetic linkage
analysis was performed using MAPMAKER version 3.0 (Lander et al.,
1987). A logarithm of odds (LOD) score of 4.0 was used to associate
genetic loci into linkage groups, and three-point and multipoint
analyses were performed to determine the most probable order of
loci. The final locus order for each linkage group was established by
minimizing double crossovers after proofreading. Recombination
frequencies were converted to map distances using Kosambi’s
mapping function (Kosambi, 1944).
RESULTS
Resistance spectra of RLR22S1, R-o-18 and F1
progeny
Self progeny of RLR22 (RLR22S1), plants of the line R-o-18
and F1 progeny from the R-o-186RLR22 cross were
inoculated with eight diverse isolates of TuMV to establish
the resistance spectra of the three B. rapa genotypes.
Individual plants were inoculated with only one virus
isolate. RLR22S1 exhibited broad-spectrum resistance; all
plants inoculated were immune to JPN 1 and resistant to
systemic spread of the other seven TuMV isolates. All R-o18 plants and all F1 plants from the R-o-186RLR22 cross
were susceptible to the TuMV isolates tested, indicating
that at least one gene controlling resistance to TuMV in
RLR22 was recessive. A single F1 plant was used to pollinate
an RLR22S1 plant to produce a back-cross population (B1)
(Fig. 1) that was expected to segregate for resistance to
TuMV. Each individual of the back-cross population was
self-pollinated to produce a separate B1S1 (Fig. 1) family
that could be tested to infer the resistance of the parental
B1 genotype to a range of TuMV isolates.
Genetic linkage map of the B1 population
One hundred and twenty B1 individuals were assayed at
213 genetic marker loci and the segregation data for these
loci were assembled into ten substantial linkage groups
with no unlinked loci. The linkage groups were unambiguously aligned with those of established maps of the
Brassica A genome (Parkin et al., 1995; Sharpe et al., 1995)
using loci that shared identical or indistinguishable alleles,
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Identifying a recessive gene controlling
resistance to TuMV
Eight individuals from each of 61 B1S1 families (Fig. 1)
were tested for resistance/susceptibility to TuMV isolate
CDN 1 and the results are summarized in Fig. 5. Nineteen
of the B1S1 families were uniformly resistant (no susceptible individuals among the eight plants tested) and these
families were expected to be derived from B1 individuals
homozygous for a recessive resistance gene. Marker data
from the 19 B1 plants from which the uniformly resistant
B1S1 families were derived were surveyed to identify loci
exhibiting an excess of homozygotes. Four loci at the top of
R4 (pN220e3, pW205e1, pN202e1 and pW103e2) were
homozygous in all 19 B1 individuals and this degree of
linkage was highly significant (x2519, P51.3161025).
However, ten B1 individuals also homozygous in the region
associated with control of resistance to TuMV did not
produce uniformly resistant B1S1 families (Fig. 5),
suggesting that at least one more locus was involved in
controlling the trait.
A two-gene model for control of resistance to
TuMV
The expected values for the experimental design described
above were calculated based on a hypothesis invoking a
resistance locus with a recessive allele for resistance on the
upper half of linkage group R4 and epistatic to a second
locus with a dominant allele for resistance. In this model,
RLR22 would be homozygous for the recessive resistance
allele at the first locus (aa) and homozygous for the
dominant resistance allele at the second locus (RR), whilst
R-o-18 would be homozygous for the dominant allele for
susceptibility at the first locus (AA) and homozygous for
the recessive allele for susceptibility at the second locus
(rr). The A locus would be epistatic to the R locus. The F1
would be heterozygous at both loci (AaRr), assuming
balanced segregation ratios and that A and R are unlinked,
and the B1 population would contain equal proportions of
four genotypes: aaRR, aaRr, AaRR and AaRr9. The first B1
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Journal of General Virology 88
Fig. 2. Genetic map of B. rapa. The vertical lines, R1 to R10, represent the ten established linkage groups of the B. rapa genome. Marker loci are to the left of the linkage
groups and interval sizes in cM are to the right of the linkage groups. Locus nomenclatures with prefixes ‘p’ or ‘s’ refer to RFLP markers and microsatellite markers,
respectively. *, Loci used to align and orientate the new linkage groups with those of the established maps; retr01, locus with recessive allele for resistance to TuMV;
ConTR01, locus with dominant allele for resistance to TuMV.
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Broad-spectrum resistance to turnip mosaic virus
Fig. 3. Distribution of interval sizes in the new genetic map ($,
observed) compared with the distribution expected from a
population representing crossovers randomly distributed across
the genome and assayed with genetic markers also randomly
distributed across the genome (—, expected).
genotype (aaRR) would be true-breeding and yield B1S1
families uniformly resistant to TuMV (aaRR), whereas the
other three genotypes (heterozygous at one, the other or
both loci) would yield B1S1 families segregating for
resistant and susceptible individuals. The B1 genotype
aaRr would yield B1S1 families segregating into three
resistant (aaR-) to one susceptible (aarr). The B1 genotype
AaRR would yield B1S1 families segregating into one
resistant (aaRR) to three susceptible (A-RR). The B1
genotype AaRr would yield B1S1 families segregating into
three resistant (aaR-) to 13 susceptible (A— and aarr).
With the above model, the limited sample size of eight
individuals employed to assess the phenotype of each B1S1
family imposed a degree of uncertainty in deducing the
genotypes of B1 individuals. Based on the model, the
majority of those B1S1 families where all eight individuals
were resistant to TuMV would be derived from B1 plants of
the aaRR genotype, although almost 10 % of such families
would be predicted to be derived from B1 plants of the
Fig. 4. Frequency distribution of segregation ratios for the 213
marker loci assayed in the new population. Observed (solid line)
and expected (dashed line) values were calculated based on 1 %
windows taken at 1 % intervals.
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Fig. 5. Observed distribution of resistance/susceptibility phenotypes of B1S1 families challenged with TuMV isolate CDN 1 and
genotypes of the corresponding B1 parents at the pN202e1 locus
on linkage group R4.
aaRr genotype. Similarly, the vast majority of B1S1 families
exhibiting one, two or three susceptible plants amongst the
eight tested would be derived from B1 plants of the aaRr
genotype, whilst those families exhibiting five, six, seven or
eight susceptible individuals would be derived from B1
plants of the AaRR and AaRr genotypes.
Mapping retr01 and ConTR01
Based on the predictions of the above model, almost all of
the B1 plants that gave rise to B1S1 families exhibiting three
or fewer susceptible individuals (amongst the eight tested)
would be homozygous for the recessive resistance allele at
the first locus; 27 of the 61 families tested fell into this class.
Similarly, almost all of the B1 plants that gave rise to B1S1
families exhibiting five or more susceptible individuals
would be heterozygous at the first locus, and 27 of the 61
families fell into this second class. Comparing the
segregation pattern for the predicted genotypes for the
first resistance locus (the hypothetical A locus) with
the segregation at marker loci indicated that the A locus
was closely linked to pN202e1 on chromosome R4 (Fig. 2).
This association was highly significant (x2546.3,
P54.9610210; Table 1) and the resistance locus thus
identified was named retr01 (recessive TuMV resistance
locus 01). The two B1S1 families with phenotypes different
from those anticipated based on the B1 genotype at the
pN202e1 locus were those derived from B1 plants 101 and
102. Plant 101 was homozygous at the pN202e1 locus but
the B1S1 progeny exhibited five out of eight susceptible
individuals, whilst plant 102 was heterozygous at pN202e1
but the B1S1 progeny exhibited three out of eight
susceptible individuals. The phenotypes exhibited by B1S1
families 101 and 102 were both particularly prone to
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R. L. Rusholme and others
misclassification. On testing a further nine individuals of
family 102 for resistance to TuMV isolate CDN 1, eight of
the nine individuals were susceptible, suggesting that
reclassification of the B1 plant 102 to heterozygous at retr01
was appropriate. Limited quantities of B1S1 seed precluded
further testing of 101. These results do not preclude the
possibility that retr01 is coincident with pN202e1.
thus identified was named ConTR01 (Conditional TuMV
Resistance 01). The two B1S1 families with phenotypes
different from those anticipated based on the B1 genotype
at the pO85e1 locus were those derived from B1 plants 43
and 109. Both plants were heterozygous at the pO85e1
locus but the B1S1 progeny exhibited no susceptible
individuals out of eight progeny. This type of discrepancy
was precisely that expected from the inevitable misclassification of a proportion of B1S1 families derived from B1
plants homozygous for the RLR22 allele at retr01 and
heterozygous at ConTR01. On testing a further 12
individuals of family 109 for resistance to TuMV isolate
CDN 1, two of the 12 individuals were susceptible,
indicating that reclassification of the B1 plant 109 to
heterozygous at ConTR01 was appropriate. Limited
quantities of B1S1 seed prevented further testing of family
43. These results do not preclude the possibility that
ConTR01 is coincident with pO85e1.
Again following the predictions of the above model, those
B1 plants that were heterozygous at retr01 would give rise
to B1S1 families for which the influence of variation at the
second resistance locus was unresolvable using the current
experimental system. In contrast, those B1 plants homozygous for the RLR22 allele at retr01 would give rise to B1S1
families that were uniformly resistant when the second
locus was homozygous for the dominant resistance allele,
but would exhibit at least one in eight susceptible
individuals (in 90 % of tests) when the second locus was
heterozygous. Twenty-nine of the 61 B1 plants for which
B1S1 TuMV resistance/susceptibility scoring data were
available were homozygous at pN202e1 (Fig. 5). Of these
29 B1 plants, 19 individuals gave rise to uniformly resistant
B1S1 families (based on the limited sample size employed)
and were presumed to be homozygous for the dominant
resistance allele at the second locus, whilst ten individuals
gave rise to B1S1 families segregating for resistance/
susceptibility and were predicted to be heterozygous at
the second locus. Comparing the predicted genotypes for
the putative second resistance locus (the R locus) with
marker data identified a pair of coincident marker loci on
linkage group R8 (pO52e2 and pO85e1; Fig. 2) with an
identical segregation pattern in all but two of the 29
informative families. This association was highly significant
(x2521.8, P56.761025; Table 1) and the resistance locus
The genetic markers tightly linked to retr01 (pN202e1) and
ConTR01 (pO85e1) were used to test for segregation
distortion in the regions of the B. rapa genome carrying
the resistance genes. Of the 120 B1 plants, 62 were
homozygous and 58 heterozygous at pN202e1 and again
62 were homozygous and 58 heterozygous at pO85e1; these
observed ratios were extremely close to 1 : 1 and demonstrated efficient transmission of the two alleles at each locus
to the B1 progeny. Brassica microsatellite markers known to
detect loci in the region of R4 containing retr01 or the region
of R8 containing ConTR01 were screened to identify those
loci polymorphic in the B1 mapping population. The
segregation patterns of the informative microsatellite
markers in the B1 population were scored, allowing these
markers to be positioned on the genetic linkage map (Fig. 2).
Table 1. x2 tests for linkage of marker allele segregation at loci pN202e1 and pO85e1 to segregation
of the resistance phenotype
Predicted genotype
Genotype*
Observed
pN202e1d
aa
Aa
pO85e1§
RR
Rr
x2
d.f.D
P
Expected
+
”
+
”
1
26
26
1
13.5
13.5
13.5
13.5
46.3
1
4.9610210
2
10
17
0
9.5
5
9.5
5
21.8
1
6.761025
*+, Heterozygous for the RLR22 allele; 2, homozygous for the RLR22 allele.
Dd.f., Degrees of freedom.
dPredicted B1 genotype at the locus with a recessive allele for resistance (a). B1S1 families with ,4/8 susceptible
individuals (aa) and B1S1 families with .4/8 susceptible individuals (Aa).
§Predicted B1 genotype at the locus with a dominant allele for resistance (R). B1S1 families with 0 out of 8
susceptible individuals (RR) and B1S1 families with 1, 2 or 3 out of 8 susceptible (Rr).
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Journal of General Virology 88
Broad-spectrum resistance to turnip mosaic virus
ConTR01 and retr01 control resistance to multiple
TuMV pathotypes
The initial mapping of retr01 and ConTR01 employed
resistance/susceptibility tests based solely on CDN 1, a
pathotype 4 TuMV isolate (Jenner & Walsh, 1996). To test
whether retr01 and ConTR01 were sufficient to control
broad-spectrum resistance, individuals from 17 B1S1
families, tested with CDN 1 in the initial mapping of
retr01 and ConTR01, were tested with CZE 1. CZE 1 is a
representative of TuMV pathotype 3 (Jenner & Walsh,
1996). The results are summarized in Table 2 and clearly
demonstrated that the B1S1 families exhibited the same
resistance/susceptibility phenotypes when tested with CZE
1 as when tested with CDN 1. Thus, retr01 and ConTR01
control resistance to two distinct TuMV pathotypes and
might explain the genetic basis for the broad-spectrum
resistance observed in RLR22.
Association of eIF4E with ConTR01 and of
eIF(iso)4E with retr01
Southern blot hybridization analysis of members of the B.
napus SG mapping population using the LL61 and es2686
clones as probes for the members of the eIF4E and
eIF(iso)4E gene families, respectively, indicated that there
were probably six members of each gene family in B. napus
(three copies of each in the A genome and three copies of
each in the C genome). The six members of the eIF4E gene
family mapped on A genome chromosomes N1, N3 and N8
and on C genome chromosomes N11, N17 and N18 of B.
napus. The eIF4E gene on N8 was closely linked to the
pO85d locus, with only one recombinant in the 90 doubled
haploid (DH) lines of the SG population that were assayed.
The pO85d locus on the SG map was the same as the
pO85e1 locus on the B1 map and was possibly coincident
with ConTR01. LL61 was then used as a probe in RFLP
mapping in the B1 mapping population and identified a
member of the eIF4E gene family that was coincident with
Table 2. Correlation between phenotypes exhibited by B1S1
families when challenged separately with TuMV isolates CDN 1
and CZE 1
Results are shown as the number of families.
CZE 1 phenotype*
X
Y
Z
CDN 1 phenotypeD
X
Y
Z
6
0
0
0
1
0
0
0
10
*Phenotype of B1S1 families tested with TuMV isolate CZE 1: X, 0/8
susceptible; Y, 1/8, 2/8 or 3/8 susceptible; Z, 5/8, 6/8, 7/8 or 8/8
susceptible.
DB1S1 families tested with TuMV isolate CDN 1; data reduced to three
classes as above.
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the pO85e1 and ConTR01 loci. Five members of the
eIF(iso)4E gene family mapped on A genome chromosomes
N4, N5 and N8 and C genome chromosomes N14 and
N16, whilst the remaining gene was provisionally assigned
to another C genome chromosome, N18. The eIF(iso)4E
gene on N4 was closely linked to the pN202b locus with no
recombinants represented in the 90 DH lines. The pN202b
locus on the SG map was the same as the pN202e1 locus on
the B1 map and was possibly coincident with retr01.
Similarly, the eIF(iso)4E gene on N8 was closely linked to
the pO85d locus with only two recombinants in the
population of 90 DH lines. The clone es2686 was then used
as an RFLP probe on the B1 mapping population but none
of the regions containing members of the eIF(iso)4E gene
family was polymorphic in that population.
DISCUSSION
Two genes that act together to confer resistance to the
TuMV isolates CDN 1 (a pathotype 4 isolate) and CZE 1 (a
pathotype 3 isolate) on Chinese cabbage were identified
and positioned in the B. rapa genome. The first resistance
locus, retr01, mapped to the upper portion of chromosome
R4 and was epistatic to the second locus. The second
resistance locus, ConTR01, mapped to the upper region of
chromosome R8. Plants exhibited resistance to TuMV
isolates CDN 1 and CZE 1 when retr01 was homozygous
for the recessive allele and at least one copy of the
dominant allele was present at the ConTR01 locus.
Plants expressing resistance to mechanical inoculation
developed chlorotic blotches in the inoculated leaves, with
no detectable systemic spread of the virus. This indicated
that the resistance mediated by retr01 and ConTR01
operated by limiting viral replication and/or restricting
viral movement to only the few cells surrounding the initial
foci of infection. The same resistance genes were even more
effective against the low levels of inoculum resulting from
aphid-mediated TuMV challenge. This better reflects the
conditions experienced by plants in the field; CDN 1 failed
to establish any detectable infection in the plants with
retr01 and ConTR01 in contrast to the clear infection and
systemic spread of the virus in control plants (J. A. Walsh
& J. M. Bambridge, unpublished).
One of the three copies of initiation factor 4E (eIF4E) in
the B. rapa genome was probably coincident with ConTR01
on chromosome R8. Similarly, one of the three copies of
the isoform of eIF4E [eIF(iso)4E], was probably coincident
with retr01 on chromosome R4, whilst another copy of
eIF(iso)4E was closely linked to (and possibly coincident
with) ConTR01 on chromosome R8. It is difficult to
estimate precisely the significance of these observations as
the phenotypes of B1 plants were deduced from samples of
their self progeny and because the positions of the
eIF(iso)4E genes relative to retr01 and ConTR01 were
determined on the basis of linkage to common marker loci
in two different mapping populations. However, if we
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R. L. Rusholme and others
assume that retr01 and ConTR01 were each definitively
localized within their respective 5 cM segments of the
genome, and we know that there are six copies in total of
eIF4E and eIF(iso)4E and we know that the total length of
the assayed genome was 801 cM, then the chance of eIF4E
or eIF(iso)4E being fortuitously coincident with retr01 or
ConTR01 was 66(5 cM+5 cM)/801 cM, or 7.5 %. After
the first observation that a copy of eIF(iso)4E was
apparently coincident with retr01 on chromosome R4,
then the likelihood of a second copy of eIF4E or eIF(iso)4E
being fortuitously coincident with ConTR01 on chromosome R8 was 565 cM/796 cM, or 3.1 %. The likelihood
of both marker associations occurring by chance was
therefore 7.5 %63.1 %, or 0.23 %.
It has been shown in a number of plant–potyvirus
interactions that the potyvirus VPg is able to bind to the
eIF4E protein and that mutations in members of the eIF4E
gene family can confer resistance to potyviruses (Robaglia
& Caranta, 2006). The exact biochemical role of eIF4E in
potyvirus infection has yet to be defined. The VPg that is
covalently bound to the 59 end of the viral RNA might
mimic the cap of mRNA and recruit the viral RNA to the
translation initiation complex to initiate translation. eIF4E
in pea (Pisum sativum) has been shown to be involved in
movement of the potyvirus pea seed-borne mosaic virus
(PSbMV) from cell to cell, as well as its probable support of
viral translation (Gao et al., 2004). Studies on the binding
of the VPg from the potyvirus LMV with lettuce eIF4E
suggest that this binding increases the strength of
interaction between eIF4E and the eIF4E-binding domain
on eIF4G (the central component of the complex required
for the initiation of protein translation), showing that VPg
is an efficient modulator of eIF4E biochemical functions
(Michon et al., 2006). The potyviral genome is known to
have an alternative mechanism for initiation of translation
(Carrington & Freed, 1990; Levis & Astier-Manifacier,
1993) but this might be of secondary importance to the
VPg–eIF4E/eIF(iso)4E pathway. It is clear that some
potyviruses need at least one member of the eIF4E/
eIF(iso)4E gene family in order to infect plants. TuMV
needs eIF(iso)4E in order to infect Arabidopsis; it does not
appear to be able to use any of the eIF4E gene family in this
species, whereas for another potyvirus, clover yellow vein
virus, the opposite is true (Sato et al., 2005). Where known,
most potyviruses are able to use eIF4E but not eIF(iso)4E,
and other genera of plant viruses use eIF4E (Robaglia &
Caranta, 2006). Our results suggest that TuMV is able to
use only specific members of either the eIF(iso)4E or both
the eIF(iso)4E and eIF4E gene families in B. rapa. It is likely
that the recessive allele of eIF(iso)4E at the retr01 locus is
non-functional for TuMV replication, whereas the dominant allele at this locus is functional for viral replication.
The simplest model to explain the involvement of the
second locus (ConTR01) is that the dominant allele of
eIF(iso)4E or eIF4E at this locus is non-functional for
TuMV, whereas the recessive allele either is only partially
functional for TuMV or is only weakly expressed. As a
3184
consequence, when the retr01 locus is homozygous for the
virus-incompatible allele, TuMV can only achieve replication above the threshold sufficient for full systemic
infection of plants when the virus-compatible allele at the
ConTR01 locus is homozygous.
The TuMV protein VPg is covalently linked to the viral
genome and a mutation in the VPg that abolished the
interaction with eIF(iso)4E in vitro prevented viral infection
in planta (Léonard et al., 2000). The VPg protein has been
implicated in overcoming resistance mediated by these
initiation factors in a range of other plant species (Robaglia
& Caranta, 2006); however, as we have not been able to
identify any TuMV isolates that can overcome the resistance
controlled by retr01 and ConTR01 (Walsh et al., 2002), it is
not currently possible to investigate differences that would
distinguish the VPg proteins from virulent and avirulent
TuMV isolates. Other eIF4E- and eIF(iso)4E-based resistances appear to be strain-specific. The gene sbm-1 with a
recessive allele for resistance to the potyvirus PSbMV has
been reported in pea (Johansen et al., 2001). sbm-1 behaves
in a gene-for-gene manner with the potyvirus pathogen
avirulence gene (VPg) (Keller et al., 1998) and sbm-1 has
been shown to be eIF4E (Gao et al., 2004). This facet of the
behaviour of these recessive resistance genes parallels the
gene-for-gene interactions of classical R genes. The resistance controlled by retr01 and ConTR01 is effective against
two geographically and genetically diverse TuMV isolates
(Jenner & Walsh, 1996; Lehmann et al., 1997; Tomimura
et al., 2003) and indeed the resistance spectrum of the
parental line RLR22 suggests that retr01 and ConTR01
together confer broad-spectrum resistance to TuMV on
Chinese cabbage (Walsh et al., 2002).
Previous investigations into the genetic control of broadspectrum resistance to TuMV in Chinese cabbage have
produced variable results that probably reflect the allelic
differences between the precise parents employed (Yoon et
al., 1993; Suh et al., 1995, 1996). The generation of a new
mapping population by crossing RLR22 to a susceptible
parent of a different genotype could still uncover the
involvement of additional copies of eIF4E and/or
eIF(iso)4E at other loci in the susceptibility and resistance
of B. rapa to TuMV. Similarly, testing B1S1 families with
TuMV isolates representing additional pathotypes could
still identify other resistance genes required for resistance
to different isolates of TuMV.
Based on the hypothesis that retr01 and ConTR01 are
members of the eIF(iso)4E and possibly eIF4E gene
families, it will now be possible to clone these genes and
sequence their allelic variants. This will pave the way for
direct investigation of the interaction between the TuMV
proteins (most notably VPg) and the different copies of
eIF4E and eIF(iso)4E present in the parental B. rapa lines
RLR22 and R-o-18. Such studies will shed light on the
precise molecular mechanism of resistance. Molecular
investigation of the eIF4E and eIF(iso)4E loci in B. rapa
other than retr01 and ConTR01 will determine whether
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Journal of General Virology 88
Broad-spectrum resistance to turnip mosaic virus
TuMV-incompatible alleles for these genes have already
become fixed in both RLR22 and R-o-18. The acquisition
of TuMV-incompatible alleles at retr01 and ConTR01 could
then be seen as the end of a long evolutionary process of
establishing resistance to TuMV.
(iso)4E is dispensable for plant growth but required for susceptibility
to potyviruses. Plant J 32, 927–934.
The broad-spectrum resistance identified in RLR22 is as yet
undefeated. The ability of pathogens to overcome resistance controlled by simply inherited dominant resistance
genes has resulted in a repetitive cycle of developing new
cultivars with new resistance specificities and the consequent mutation of the pathogen to overcome these
resistance genes (Bergelson et al., 2001). Therefore, this
broad-spectrum resistance represents a novel and potentially durable source of resistance to TuMV that can be
deployed in susceptible Brassica crops. The PCR-based
microsatellite markers that have been identified as flanking
the resistance genes retr01 and ConTR01 can be employed
in marker-assisted selection for TuMV resistance, assisting
in the elimination of linkage drag (Tanksley et al., 1989)
and promoting rapid and accurate breeding for these useful
genes. In future, single nucleotide polymorphism markers
that select directly for the resistance alleles at the retr01 and
ConTR01 loci could also be very helpful in this process.
between tobacco mosaic virus and the tobacco N gene. Philos Trans R
Soc Lond B Biol Sci 354, 653–658.
Edwardson, J.R. & Christie, R.G. (1991). The Potyvirus Group. Volumes
I–IV, Florida Agricultural Experiment Station Monograph 16.
Erickson, F. L., Dinesh-Kumar, S. P., Holzberg, S., Ustach, C. V.,
Dutton, M., Handley, V., Corr, C. & Baker, B. J. (1999). Interactions
Gao, Z., Johansen, E., Eyres, S., Thomas, C. L., Ellis, T. H. N. & Maule,
A. J. (2004). The potyvirus recessive gene, sbm1, identifies a novel role
for translation initiation factor eIF4E in cell-to-cell trafficking. Plant J
40, 376–385.
Hämäläinen, J. H., Kekarainen, T., Gebhardt, C., Watanabe, K. N. &
Valkonen, J. P. T. (2000). Recessive and dominant genes interfere with
the vascular transport of potato virus A in diploid potatoes. Mol Plant
Microbe Interact 13, 402–412.
Hughes, S. L., Green, S. K., Lydiate, D. J. & Walsh, J. A. (2002).
Resistance to turnip mosaic virus in Brassica rapa and B. napus and the
analysis of genetic inheritance in selected lines. Plant Pathol 51, 567–573.
Hughes, S. L., Hunter, P. J., Sharpe, A. G., Kearsey, M. J., Lydiate, D. J.
& Walsh, J. A. (2003). Genetic mapping of a novel turnip mosaic virus
resistance gene in Brassica napus. Theor Appl Genet 107, 1169–1173.
Jenner, C. E. & Walsh, J. A. (1996). Pathotypic variation in turnip
mosaic virus with special reference to European isolates. Plant Pathol
45, 848–856.
Jenner, C. E., Keane, G. J., Jones, J. E. & Walsh, J. A. (1999). Serotypic
variation in turnip mosaic virus. Plant Pathol 48, 101–108.
ACKNOWLEDGEMENTS
We are very grateful to Dr Sylvia Green (Taiwan) for providing seed
of the BP079 B. rapa accession, Isobel Parkin for access to the SG
mapping population and mapping data, Andrew Sharpe for access to
the B. napus cDNA clones from the AAFC collection, Judith
Bambridge for technical support, and the UK Biotechnology and
Biological Sciences Research Council, the UK Department for
Environment Food and Rural Affairs, the European Union INCODC programme and Agriculture and Agri-Food Canada for funding.
Jenner, C. E., Sanchez, F., Nettleship, S. B., Foster, G. D., Ponz, F. &
Walsh, J. A. (2000). The cylindrical inclusion gene of turnip mosaic
virus encodes a pathogenic determinant to the Brassica resistance gene
TuRB01. Mol Plant Microbe Interact 13, 1102–1108.
Jenner, C. E., Tomimura, K., Ohshima, K., Hughes, S. L. & Walsh, J. A.
(2002). Mutations in turnip mosaic virus P3 and cylindrical inclusion
proteins are separately required to overcome two Brassica napus
resistance genes. Virology 300, 50–59.
Jenner, C. E., Wang, X., Tomimura, K., Ohshima, K., Ponz, F. & Walsh,
J. A. (2003). The dual role of the potyvirus P3 protein of turnip
mosaic virus as a symptom and avirulence determinant in brassicas.
Mol Plant Microbe Interact 16, 777–784.
REFERENCES
Anonymous (1996). Asian Vegetable Research and Development
Centre Annual Report. Asian Vegetable Research and Development
Centre, Shanhua, Tainan, Taiwan.
Bendahmane, A., Kanyuka, K. & Baulcombe, D. C. (1999). The Rx
gene from potato controls separate virus resistance and cell death
responses. Plant Cell 11, 781–791.
Bergelson, J., Kreitman, M., Stahl, E. A. & Tian, D. (2001).
Evolutionary dynamics of plant R-genes. Science 292, 2281–2285.
Browning, K. S. (1996). The plant translational apparatus. Plant Mol
Johansen, I. E., Lund, O. S., Hjulsager, C. K. & Laursen, J. (2001).
Recessive resistance in Pisum sativum and potyvirus pathotype
resolved in a gene-for-cistron correspondence between host and
virus. J Virol 75, 6609–6614.
Keller, K. E., Johanssen, I. E., Martin, R. R. & Hampton, R. O. (1998).
Potyvirus genome-linked protein (VPg) determines pea seed-borne
mosaic virus pathotype-specific virulence in Pisum sativum. Mol Plant
Microbe Interact 11, 124–130.
Köhm, B. A., Goulden, M. G., Gilbert, J. E., Kavanagh, T. A. &
Baulcombe, D. C. (1993). A potato virus X resistance gene mediates an
Biol 32, 107–143.
induced, nonspecific resistance in protoplasts. Plant Cell 5, 913–920.
Carrington, J. C. & Freed, D. D. (1990). Cap-independent enhance-
Kosambi, D. D. (1944). The estimation of map distances from
ment of translation by a plant potyvirus 59 non-translated region.
J Virol 64, 1590–1597.
recombination values. Ann Eugen 12, 172–175.
Chisholm, S. T., Para, M. A., Anderberg, R. J. & Carrington, J. C.
(2001). Arabidopsis RTM1 and RTM2 genes function in phloem to
restrict long-distance movement of tobacco etch virus. Plant Physiol
127, 1667–1675.
Dangl, J. L. & Jones, J. D. G. (2001). Plant pathogens and integrated
Lander, E. S., Green, P., Abrahamson, J., Barlow, A., Daly, M. J.,
Lincoln, S. E. & Newberg, L. (1987). MAPMAKER: an interactive
computer package for constructing primary genetic linkage maps of
experimental and natural populations. Genomics 1, 174–181.
Lartey, R. T., Ghoshroy, S. & Citovsky, V. (1998). Identification of an
defense responses to infection. Nature 411, 826–833.
Arabidopsis thaliana mutation (vsm1) that restricts systemic movement of tobamoviruses. Mol Plant Microbe Interact 11, 706–709.
Duprat, A., Caranta, C., Revers, F., Menand, B., Browning, K. S. &
Robaglia, C. (2002). The Arabidopsis eukaryotic initiation factor
Lehmann, P., Petrzik, K., Jenner, C., Greenland, A., Spak, J.,
Kozubek, E. & Walsh, J. A. (1997). Nucleotide and amino acid
http://vir.sgmjournals.org
Downloaded from www.microbiologyresearch.org by
IP: 88.99.165.207
On: Mon, 19 Jun 2017 01:08:53
3185
R. L. Rusholme and others
variation in the coat protein coding region of turnip mosaic virus
isolates and possible involvement in the interaction with the Brassica
resistance gene TuRB01. Physiol Mol Plant Pathol 51, 195–208.
Lellis, A. D., Kasschau, K. D., Whitham, S. A. & Carrington, J. (2002).
Loss-of-susceptibility mutants of Arabidopsis thaliana reveal an essential
role for eIF(iso)4E during potyvirus infection. Curr Biol 12, 1046–1051.
Sato, M., Nakahara, K., Yoshii, M., Ishikawa, M. & Uyeda, I. (2005).
Selective involvement of members of the eukaryotic initiation factor
4E family in the infection of Arabidopsis thaliana by potyviruses. FEBS
Lett 579, 1167–1171.
Schaad, M. C. & Carrington, J. C. (1996). Suppression of long-
distance movement of tobacco etch virus in a nonsusceptible host. J
Virol 70, 2556–2561.
Léonard, S., Plante, D., Wittmann, S., Daigneault, N., Fortin, M. G. &
Laliberté, J.-F. (2000). Complex formation between potyvirus VPg
Sharpe, A. G., Parkin, I. A. P., Keith, D. J. & Lydiate, D. J. (1995).
and translation initiation factor 4E correlates with virus infectivity.
J Virol 74, 7730–7737.
Frequent nonreciprocal translocations in the amphidiploid genome of
oilseed rape (Brassica napus). Genome 38, 1112–1121.
Levis, C. & Astier-Manifacier, S. (1993). The 59 untranslated region of
Shattuck, V. I. (1992). The biology, epidemiology and control of
PVY RNA, even located in an internal position, enables initiation of
translation. Virus Genes 7, 367–379.
Liu, X. P., Lu, W. C., Liu, Y. K., Wei, S. Q., Xu, J. B., Liu, Z. R., Zhang,
H. J., Li, J. L., Ke, G. L. & other authors (1996). Occurrence and strain
differentiation of turnip mosaic potyvirus and sources of resistance in
Chinese cabbage in China. Acta Hortic 407, 431–440.
turnip mosaic virus. Plant Breed Rev 14, 199–238.
Sillito, D., Parkin, I. A. P., Mayerhofer, R., Lydiate, D. J. & Good, A. G.
(2000). Arabidopsis thaliana: a source of candidate disease-resistance
genes for Brassica napus. Genome 43, 452–460.
Staskawicz, B. J., Ausubel, F. M., Baker, B. J., Ellis, J. G. & Jones, J. D.
G. (1995). Molecular genetics of plant disease resistance. Science 268,
Michon, T., Estevez, Y., Walter, J., German-Retana, S. & Le Gall, O.
(2006). The potyviral virus genome-linked protein VPg forms a
661–667.
ternary complex with the eukaryotic initiation factors eIF4E and
eIF4G and reduces eIF4E affinity for a mRNA cap analogue. FEBS J
273, 1312–1322.
five strains of turnip mosaic virus in Chinese cabbage. Euphytica 81,
71–77.
Murphy, J. F., Blauth, J. R., Livingstone, K. D., Lackney, V. K. & Jahn,
M. K. (1998). Genetic mapping of the pvr1 locus in Capsicum spp. and
Suh, S. K., Park, H. G. & Green, S. K. (1996). Interactions among
TuMV strains inoculated and their movement in Chinese cabbage.
J Kor Hort Sci 37, 392–398.
evidence that distinct potyvirus resistance loci control responses that
differ at the whole plant and cellular levels. Mol Plant Microbe Interact
11, 943–951.
Suh, S. K., Green, S. K. & Park, H. G. (1995). Genetics of resistance to
Tanksley, S. D., Young, N. D., Paterson, A. H. & Bonierbale, M. W.
(1989). RFLP mapping in plant breeding: new tools for an old science.
Naom, I. S., Mathew, C. G. & Town, M. M. (1995). Genetic mapping
Biol Technol 7, 257–264.
with microsatellites. In DNA Cloning: a Practical Approach 3: Complex
Genomes, pp.195–217. Edited by D. M. Glover & B. D. Hames.
Oxford: IRL Press.
Thormann, C. E., Ferreira, M. E., Camargo, L. E. A., Tivang, J. G. &
Osborn, T. C. (1994). Comparison of RFLP and RAPD markers to
Nicolas, O. & Laliberté, J.-F. (1992). The complete nucleotide
sequence of turnip mosaic potyvirus RNA. J Gen Virol 73, 2785–2793.
Nicolas, O., Dunnington, S. W., Gotow, L. F., Pirone, T. P. & Hellmann,
G. M. (1997). Variations in the VPg protein allow a potyvirus to
overcome va gene resistance in tobacco. Virology 237, 452–459.
Ohshima, K., Tanaka, M. & Sako, N. (1996). The complete nucleotide
sequence of turnip mosaic virus RNA Japanese strain. Arch Virol 141,
1991–1997.
Parkin, I. A. P., Sharpe, A. G., Keith, D. J. & Lydiate, D. J. (1995).
Identification of the A and C genome of amphidiploid Brassica napus
(oilseed rape). Genome 38, 1122–1131.
Parkin, I. A. P., Gulden, S. M., Sharpe, A. G., Lukens, L., Trick, M.,
Osborn, T. C. & Lydiate, D. J. (2005). Segmental structure of the
Brassica napus genome based on comparative analysis with
Arabidopsis thaliana. Genetics 171, 765–781.
estimate genetic relationships within and among cruciferous species.
Theor Appl Genet 88, 973–980.
Tomimura, K., Gibbs, A. J., Jenner, C. E., Walsh, J. A. & Ohshima, K.
(2003). The phylogeny of Turnip mosaic virus; comparisons of 38
genomic sequences reveal a Eurasian origin and a recent ‘emergence’
in east Asia. Mol Ecol 12, 2099–2111.
U, N. (1935). Genome analysis in Brassica with special reference to the
experimental formation of B. napus and peculiar mode of fertilisation
Jpn J Bot 7, 389–452.
Vance, V. & Vaucheret, H. (2001). RNA silencing in plants – defense
and counterdefense. Science 292, 2277–2280.
Walsh, J. A. & Jenner, C. E. (2002). Turnip mosaic virus and the quest
for durable resistance. Mol Plant Pathol 3, 289–300.
Walsh, J. A., Sharpe, A. G., Jenner, C. E. & Lydiate, D. J. (1999).
Revers, F., Le Gall, O., Candresse, T. & Maule, A. J. (1999). New
Characterisation of resistance to turnip mosaic virus in oilseed rape
(Brassica napus) and genetic mapping of TuRB01. Theor Appl Genet
99, 1149–1154.
advances in understanding the molecular biology of plant/potyvirus
interactions. Mol Plant Microbe Interact 12, 367–376.
Walsh, J. A., Rusholme, R. L., Hughes, S. L., Jenner, C. E.,
Bambridge, J. M., Lydiate, D. J. & Green, S. K. (2002). Different
Robaglia, C. & Caranta, C. (2006). Translation initiation factors: a
weak link in plant RNA virus infection. Trends Plant Sci 11, 40–45.
classes of resistance to turnip mosaic virus in Brassica rapa. Eur J
Plant Pathol 108, 15–20.
Robbins, M. A., Witsenboer, H., Michelmore, R. W., Laliberte, J. F. &
Fortin, M. G. (1994). Genetic mapping of turnip mosaic virus
Wittmann, S., Chatel, H., Fortin, M. G. & Laliberté, J.-F. (1997).
resistance in Lactuca sativa. Theor Appl Genet 89, 583–589.
Ruffel, S., Dussault, M.-H., Palloix, A., Moury, B., Bendahmane, A.,
Robaglia, C. & Caranta, C. (2002). A natural recessive resistance gene
Interaction of the viral protein genome linked of turnip mosaic
potyvirus with the transitional eukaryotic initiation factor (iso) 4E of
Arabidopsis thaliana using the yeast two-hybrid system. Virology 234,
84–92.
against potato virus Y in pepper corresponds to the eukaryotic
initiation factor 4E (eIF4E). Plant J 32, 1067–1075.
Yang, Y., Shah, J. & Klessig, D. F. (1997). Signal perception and
Rusholme, R. L., Walsh, J. A. & Lydiate, D. J. (2007). Genetic control
Yoon, J. Y., Green, S. K. & Opena, R. T. (1993). Inheritance of
of immunity to turnip mosaic virus (TuMV) pathotype 1 in Brassica
rapa (Chinese cabbage). Genome (in press).
resistance to turnip mosaic virus in Chinese cabbage. Euphytica 69,
103–108.
3186
transduction in plant defense responses. Genes Dev 11, 1621–1639.
Downloaded from www.microbiologyresearch.org by
IP: 88.99.165.207
On: Mon, 19 Jun 2017 01:08:53
Journal of General Virology 88