Download Inheritance of Organelle DNA Sequences in a Citrus–Poncirus

Inheritance of Organelle DNA Sequences in a
Citrus–Poncirus Intergeneric Cross
C. D. Moreira, F. G. Gmitter Jr., J. W. Grosser, S. Huang, V. M. Ortega, and
C. D. Chase
From the University of Florida, Horticultural Sciences
Department, Institute of Food and Agricultural Sciences, Gainesville, FL 32611-0690 (Moreira, Ortega, and
Chase), and CREC, P.O. Box 1088, Lake Alfred, FL 33850
(Gmitter, Grosser, and Huang). We thank Drs. K. Cline,
W. Gruissem, D. Pring, and G. Moore for providing the
petA, petD, atp9, and lycopene cyclase clones, respectively. The Phaseolus vulgaris mitochondrial rrn26
cDNA clone was constructed by Dr. B. O. Kim. This
work was supported in part by grant no. 942-27 (to
F.G.G. and J.W.G.) by the Florida Citrus Production Research Advisory Council—Florida Department of Agriculture and Consumer Services. C.D.M. was supported
by Conselho Nacional de Desenvolvimento Cientifico e
Tecnologico/Brasilia-DF/Brazil (CNPq). This research
was approved for publication as Florida Agriculture Experiment Station Journal Series no. R-06487. Address
correspondence to C. D. Chase at the address above
or e-mail: [email protected].
2002 The American Genetic Association 93:174–178
174
Many land plants deviate from the maternal pattern of plastid and mitochondrial
genome inheritance, with some species
demonstrating biparental or even paternal
transmission of one or both genomes (reviewed by Harrison and Doyle 1990; Mogensen 1996; Reboud and Zeyl 1994).
Studies of plant mitochondrial genome inheritance are further complicated by the
complex, multipartite organization of this
genome. Although the entire complexity of
a plant mitochondrial genome can be
physically mapped as a ‘‘master circle,’’
recombination across direct repeats results in subgenomic molecules (reviewed
by Backert et al. 1997; Fauron et al. 1995).
Many plant (mitochondrial DNA [mtDNA])
configurations exist as low-abundance
copies termed sublimons (Small et al.
1987). The relative abundance of a particular mtDNA configuration can vary in different plant lineages, such that a sublimon
in one lineage is the predominant configuration in another lineage (Small et al.
1987, 1989). Furthermore, nuclear genes
regulate mitochondrial genome organization and influence the relative abundance
of the various mitochondrial subgenomes
(Mackenzie and Chase 1990; Sakamoto et
al. 1996; Small et al. 1989).
An additional complication in studies of
organelle genome inheritance is the presence of organelle DNA sequences in the
nuclear genome. Insertions of organelle
DNA into the nuclear genome of plants
and animals have occurred frequently
over the course of evolution (reviewed by
Blanchard and Lynch 2000; Blanchard and
Schmidt 1995; Henze and Martin 2001;
Martin and Herrmann 1998). In the land
plants there are many examples of functional gene transfer from mitochondria to
nucleus. These most likely occur via RNA
intermediates with the subsequent gain of
nuclear promoters and mitochondrial targeting signals (reviewed by Gray 2000;
Palmer et al. 2000). In animals, such functional gene transfers were precluded once
mitochondria evolved a unique genetic
code (Gray 2000). However, nonfunctional
mtDNA sequences are common in animal
nuclear genomes (reviewed by Blanchard
and Schmidt 1996; Henze and Martin 2001;
Shay and Werbin 1992). A notable example
of nonfunctional mtDNA in a plant nuclear
genome is the complete mitochondrial genome copy on chromosome 2 of Arabidop-
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Many land plants deviate from the maternal pattern of organelle inheritance. In this
study, heterologous mitochondrial and chloroplast probes were used to investigate
the inheritance of organelle genomes in the progeny of an intergeneric cross. The
seed parent was LB 1–18 (a hybrid of Citrus reticulata Blanco cv. Clementine ⴛ C.
paradisi Macf. cv. Duncan) and the pollen parent was the cross-compatible species
Poncirus trifoliata (L.) Raf. All 26 progeny examined exhibited maternal inheritance
of plastid petA and petD loci. However, 17 of the 26 progeny exhibited an apparent
biparental inheritance of mitochondrial atpA, cob, coxII, and coxIII restriction fragment length polymorphisms (RFLPs) and maternal inheritance of mitochondrial
rrn26 and coxI RFLPs. The remaining nine progeny inherited only maternal mitochondrial DNA (mtDNA) configurations. Investigations of plant mitochondrial genome inheritance are complicated by the multipartite structure of this genome,
nuclear gene control over mitochondrial genome organization, and transfer of mitochondrial sequences to the nucleus. In this study, paternal mtDNA configurations
were not detected in purified mtDNA of progeny plants, but were present in progeny
DNA preparations enriched for nuclear genome sequences. MtDNA sequences in
the nuclear genome therefore produced an inheritance pattern that mimics biparental inheritance of mtDNA.
sis thaliana ( Lin et al. 1999; Stupar et al.
2001). This insertion is much larger than
any of the previously reported organellenuclear transfers. High levels of sequence
identity between the mitochondrial genome and nuclear copy suggest a very recent transfer event ( Lin et al. 1999).
The present investigation of organelle
DNA inheritance in a Citrus–Poncirus intergeneric cross revealed an unusual pattern
of mtDNA transmission resulting from the
presence of mtDNA in the nuclear genome.
Materials and Methods
ing hybridization, the blots were washed
in 2⫻ SSPE, 0.1% SDS at room temperature
for 10 min. Following a second identical
wash, the blots were washed in 1⫻ SSPE,
0.1% SDS at 60⬚C for 15 min and then in
0.1⫻ SSPE, 0.1% SDS at 60⬚C for 10 min.
Membranes were exposed to Kodak ( XOmat RP XRP-5) film for 7–14 days.
Results and Discussion
To identify DNA polymorphisms between
LB 1–18 and P. trifoliata, total cellular DNA
samples were digested and hybridized
with two chloroplast probes (petA and
petD) and seven mitochondrial probes
(atpA, cob, coxI, coxII, coxIII, rrn26, and
atp9). Most hybridization profiles revealed
polymorphisms, and seven probes were
selected for use in inheritance analysis.
Plastid DNA appeared to exhibit strict
maternal inheritance in the intergeneric
hybrids. The petA probe detected the maternal 13 kb BamHI fragment in all the 26
F1 progeny, and no P. trifoliata (10 kb) fragments were observed in any of the progeny. DNAs from 14 of the analyzed progeny are shown in Figure 1A. Furthermore,
only maternal configurations were observed in the hybrids analyzed with the
chloroplast petD clone (not shown). Although the lack of polymorphisms limited
the number of loci that could be tested,
the results indicated a maternal inheritance of the chloroplast genome.
All intergeneric hybrid progeny carried
abundant maternal mtDNA configurations
for all loci examined ( Figure 1B–F). Hybridization of the atpA mtDNA probe to
HindIII-digested DNAs of 26 progeny trees
revealed an intense 3.4 kb maternal fragment in all 26. However, 17 progeny (progeny 6, 7, 9, 10, 12–16, 18, 23, 27, 28, 30, 33,
36, and 44) also carried a faint 4.3 kb fragment characteristic of P. trifoliata. ( Eight
progeny DNAs of this type are included in
Figure 1B.) The coxIII probe identified a 4.5
kb maternal fragment in HindIII-digested
DNA from all progeny, and those progeny
carrying P. trifoliata atpA configurations
also carried a faint 6 kb P. trifoliata coxIII
fragment ( Figure 1C). All progeny carried
a 10.5 kb maternal cob gene configuration,
and those progeny with P. trifoliata atpA
and coxIII configurations also carried a 2.1
kb P. trifoliata cob configuration ( Figure
1D). This same subset of progeny also carried a faint 16.0 kb P. trifoliata coxII configuration in addition to the 9.0 kb maternal
configuration ( Figure 1E). The atpA, cob,
coxII, and coxIII loci appeared to be
‘‘linked,’’ in that the same 17 individuals
Moreira et al • Organelle DNA Inheritance in Citrus 175
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The intergeneric sexual hybrid family analyzed in this work was developed at the
Citrus Research and Education Center,
University of Florida, Lake Alfred, FL. The
seed parent was LB 1–18, a hybrid of Citrus
reticulata Blanco cv. Clementine ⫻ C. paradisi Macf. Duncan grapefruit. Seeds produced by LB 1–18 are monoembryonic,
containing sexually derived zygotic embryos. The sexually compatible pollen parent was a seed-derived tree of Poncirus trifoliata ( L.) Raf. The paternal tree is no
longer extant and its cultivar is unknown.
Organelle DNA restriction patterns of two
different P. trifoliata varieties (Gainesville
and Rubidoux) were compared and no differences were observed when DNA from
these two varieties was restricted with six
different enzymes and hybridized with two
plastid and two mitochondrial probes. In
subsequent studies, DNA of the cultivar
Rubidoux was used to identify P. trifoliataunique organelle DNA configurations. We
do not know if the paternal tree was identical to Rubidoux in all mtDNA configurations, but the maternal tree was available
for analysis. Therefore progeny mtDNA
configurations matching P. trifoliata cultivar Rubidoux and absent from the maternal tree could be identified as paternally
derived. Seven-year-old progeny trees
from the intergeneric cross were screened
for the inheritance of mitochondria and
chloroplast DNA polymorphisms ( F1 hybrids 3, 4, 6, 7, 9, 10, 12–16, 18, 19, 21–24,
27, 28, 30, 33, 35, 36, 44, 48, and 55). Leaf
material from each tree was collected at
different times of the year, but always at
about 50% leaf expansion.
F1 33 and F1 44 were open-pollinated,
and the resulting progeny were examined
for inheritance of mtDNA configurations.
Nuclear embryony reviewed by Koltunow
(1993) is common in citrus, so random amplified polymorphic DNA (RAPD) markers
(developed as described by Gmitter et al.
1996) were used to verify the zygotic na-
ture of the progeny plants. The primer
that best demonstrated the zygotic nature
of these progeny was H01 (5⬘GGTCGGAGAA3⬘) purchased from Operon Technologies (Alameda, CA). All progeny carried
either nonparental RAPD markers, indicating progeny resulting from outcrossing, or
a subset of the seed parent’s RAPD markers, indicating progeny resulting from either self-pollination or outcrossing.
Total cellular DNA was isolated from 1 g
frozen leaf samples by the phenol-chloroform extraction method of Durham et al.
(1992). MtDNA was recovered from 50 g of
freshly collected leaves as described by
Hsu and Mullin (1988). To prepare DNA enriched for nuclear genome sequences, nuclei were prepared by the Triton washing
procedure of Jofuku and Goldberg (1998).
DNA was extracted from Triton-washed
nuclei by the procedure of Dellaporta et al.
(1983). DNA was digested by restriction
enzymes having six-base recognition sequences (EcoRI, HindIII, PstI, EcoRV,
BamHI, SmaI, DraI, or XbaI) according to
the manufacturer’s instructions ( Life
Technologies Inc.). Restriction fragments
were separated by electrophoresis through
0.8% agarose gels in TPE buffer (30 mM
NaH2PO4, 36 mM Trizma base, and 1 mM
Na2EDTA·2H2O) at 800 V-h.
DNA fragments were transferred to nylon supports and hybridized with radiolabeled mitochondrial and chloroplast
probes. The blots were prehybridized for
at least 1 h in 10⫻ SSPE (1⫻ 0.18 M NaCl,
0.01 M NaH2PO4, 0.001 M Na2EDTA), 50⫻
Denhardts (1⫻ 0.02% w/v bovine serum albumin, 0.02% w/v Ficoll, 0.02% w/v PVP
360), 10% w/v SDS, and 20 ␮g/ml herring
sperm DNA. The source, amplification, recovery, and radiolabeling of plastid petA
and petD; mitochondrial atpA, atp9, cob,
and coxI; and nuclear lycopene cyclase
(lyc) probes were described previously
(Moreira et al. 2000; Wen and Chase 1999).
Primers 5⬘GTAGATCCAAGTCCATGG and
5⬘GCATGATGGGCCCAAGTT (Malek et al.
1996) were used to amplify coxIII coding
sequences from maize mtDNA. Primers
5⬘GCGGAACCATGGCAATTA and 5⬘GGCATGATTAGTTCCACT (Moon et al. 1985) were
used to amplify coxII coding sequences
from maize mtDNA, and universal primers
(5⬘CAGGAAACAGCTATGACC and 5⬘GTAAAACGACGGCCAGT ) were used to amplify
rrn26 coding sequences from a Phaseolus
vulgaris mitochondrial cDNA clone. Following denaturation, radiolabeled probes
were added directly to the prehybridization solution and the blots were hybridized for a minimum of 16 h at 60⬚C. Follow-
carried all four P. trifoliata configurations,
whereas the other 9 progeny carried none
of the P. trifoliata configurations. The intergeneric hybrids were therefore segregating for the presence or absence of the
P. trifoliata mtDNA configurations. This
pattern of inheritance was not observed
for all mitochondrial loci. The rrn26 (not
shown) and coxI ( Figure 1F) probes identified only maternal fragments in all progeny.
Although the P. trifoliata mtDNA configurations were of low abundance in the
176 The Journal of Heredity 2002:93(3)
progeny, these configurations were not
likely the result of partial digestion. P. trifoliata configurations were always reproducible in different DNA preparations from
the same plant, and one of the substoichiometric P. trifoliata configurations, the
2.1 kb cob fragment ( Figure 1D), was of
smaller size than the abundant 10.5 kb maternal fragment. Furthermore, it is improbable that partial digestion products at the
atpA, coxII, and coxIII loci would each comigrate with the major corresponding P.
trifoliata mtDNA configuration.
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Figure 1. Mitochondrial and plastid DNA configurations in the progeny of a Citrus ⫻ Poncirus cross. Autoradiographs of Southern blots containing total DNA from LB 1–18 (maternal parent), P. trifoliata cultivar Rubidoux, and
14 F1 hybrids are shown. DNA samples (5 ␮g/lane) were loaded as follows: 1, P. trifoliata; 2, LB 1–18; 3–16, F1
hybrids 3, 6, 7, 10, 15, 16, 19, 21, 27, 33, 35, 44, 48, and 55, respectively. Enzyme-probe combinations used in the
hybridizations were: panel A, BamHI-petA; panel B, HindIII-atpA; panel C, HindIII-coxIII; panel D, BamHI-cob; panel
E, EcoRI-coxII, panel F, PstI-coxI. PetA is a plastid gene probe; all others are mitochondrial gene probes.
The apparent segregation of the intergeneric F1 progeny with respect to the P.
trifoliata mtDNA configurations suggested
that these configurations resulted from influence of the nuclear genome. Nuclear alleles might alter mtDNA organization in
the progeny, producing P. trifoliata configurations. Alternatively, the P. trifoliata
mtDNA configurations observed in the
progeny might result from nuclear copies
of these mitochondrial genes in the paternal parent, and consequently in the progeny plants. To distinguish between these
two hypotheses, we analyzed mtDNA purified from two of the progeny (progeny 7
and 33) for the presence of P. trifoliata and
LB 1–18 atpA configurations. The 4.3 kb P.
trifoliata atpA configuration was not detected in the purified mtDNA samples ( Figure 2A, lanes 4 and 6). To determine
whether this configuration was present in
the nuclear genome of the F1 progeny, we
compared total DNA preparations with
DNA preparations enriched for nuclear sequences from progeny tree 33 ( Figure 2B–
D). The nuclear-enriched sample was contaminated by organelle DNA, as evidenced
by hybridization to the plastid petD probe
( Figure 2D, lane 4). However, the abundance of single-copy, nuclear lycopene cyclase (lyc) sequences was increased relative to the plastid petD sequences in this
sample ( Figure 2C and D, lanes 3 and 4).
The abundance of the P. trifoliata atpA configuration relative to the maternal ( LB 1–
18) atpA configuration was also increased
in the nuclear-enriched DNA sample ( Figure 2B, lanes 3 and 4).
These observations are consistent with
the hypothesis that low-abundance P. trifoliata atpA, cob, coxII, and coxIII configurations present in the F1 progeny were inherited from a paternal plant hemizygous
for a relatively large mtDNA segment inserted into the nuclear genome. Seventeen
of 26 hybrids carried the P. trifoliata
configurations. The Yates-corrected chisquared test ( Yates 1934) for a 1:1 segregation in this population was 1.9 (P ⬎ .1).
This hypothesis cannot be confirmed directly because the paternal tree is no longer living. Given that P. trifoliata trees are
naturally outcrossing and highly heterozygous ( Durham et al. 1992; Torres et al.
1985), mtDNA transfer into one member of
a chromosome pair would be expected to
remain hemizygous in some individuals.
The fate of P. trifoliata mtDNA configurations in subsequent plant generations
provided additional genetic evidence for
nuclear hemizygosity. Zygotic progeny resulting from the open pollination of inter-
generic hybrids 33 and 44 ( both of which
carried the P. trifoliata configurations)
were analyzed for atpA configurations. Six
of 12 progeny recovered from hybrid 33
and 9 of 12 progeny recovered from hybrid
44 carried the 4.3 kb P. trifoliata configuration in addition to the LB 1–18 configuration, and the relative abundance of the
two atpA configurations was similar between the F1 intergeneric hybrids and this
subsequent generation of progeny (not
shown). Because paternal parents of openpollination progeny are unknown, a specific model for segregation of the P. trifoliata atpA configuration could not be
tested. However, the segregation of both
progenies for the presence or absence of
this configuration was consistent with a
single nuclear copy in the seed parent.
The nuclear copies of the atpA, cob,
coxII, and coxIII genes appear to be linked,
as no recombinant progeny carrying a
subset of these configurations were observed. Whether these genes are, or were
at any time, contiguous in the P. trifoliata
mitochondrial genome is unknown. The
mitochondrial genes transferred as large
multigene segments are unlikely to function in the nucleus due to requirements
for a nuclear promoter, RNA editing, and a
mitochondrial targeting sequence. This is
in contrast to the functional transfer of
References
Adams KL, Daley DO, Qiu Y-L, Whelan J, and Palmer
JD, 2000. Repeated, recent and diverse transfers of a
mitochondrial gene to the nucleus in flowering plants.
Nature 408:354–357.
Backert S, Nielsen BL, and Borner T, 1997. The mystery
of the rings: structure and replication of mitochondrial
genomes from higher plants. Trends Plant Sci 2:477–
483.
Benasson D, Zhang D, and Hewitt GM, 2000. Frequent
assimilation of mitochondrial DNA by grasshopper nuclear genomes. Mol Biol Evol 17:406–415.
Blanchard JL and Lynch M, 2000. Organellar genes—
Moreira et al • Organelle DNA Inheritance in Citrus 177
Downloaded from http://jhered.oxfordjournals.org/ at Pennsylvania State University on February 27, 2014
Figure 2. Location of P. trifoliata mtDNA configurations in Citrus ⫻ Poncirus hybrids. Autoradiographs of Southern
blots containing DNA from LB 1–18 (maternal parent), P. trifoliata cultivar Rubidoux, and F1 hybrids 7 and 33 are
shown. Panel A DNA samples were loaded as follows: 1, P. trifoliata total DNA; 2, LB 1–18 total DNA; 3, F1 hybrid
33 total DNA; 4, F1 hybrid 33 mtDNA; 5, F1 hybrid 7 total DNA; 6, F1 hybrid 7 mtDNA. DNA samples (15 ␮g of total
DNA or 1.5 ␮g of mtDNA) were digested with HindIII and hybridized with the atpA probe. Autoradiographs shown
in panels B, C, and D resulted from the hybridization of a single blot with mitochondrial atpA, nuclear lyc, and
plastid petD probes, respectively. HindIII-digested DNA samples of 15 ␮g/lane were loaded as follows: 1, P. trifoliata
total DNA; 2, LB 1–18 total DNA; 3, F1 hybrid 33 total DNA; 4, F1 hybrid 33 DNA enriched for nuclear genome
sequences.
single plant mitochondrial genes to the
nucleus. Functional transfer involves edited RNA intermediates and the acquisition of nuclear promoters and mitochondrial targeting sequences (Adams et al.
2000).
The occurrence of mitochondrial sequences in the nucleus complicates the
study of mtDNA inheritance. The purification of mtDNA is needed to distinguish nuclear copies from low-abundance mitochondrial configurations. While some
researchers have utilized mtDNA purification to demonstrate maternal (Conde et al.
1979) or biparental ( Erickson and Kemble
1990) inheritance of mtDNA, other reports
of mtDNA inheritance (reviewed by Reboud and Zeyl 1994) have not employed
this technique.
MtDNA sequences in the nucleus also
complicate the use of mtDNA as a molecular marker in natural populations. Our
observations in Citrus, together with those
in Arabidopsis ( Lin 1999; Stupar 2000), indicate that the insertion of large mtDNA
segments into the nuclear genome may be
a relatively frequent event in plant genome evolution. An extensive survey of
angiosperms revealed a high frequency of
functional, single-gene transfers from mitochondrial to nuclear genomes (Adams et
al. 2000; Gray 2000). Computer database
searches estimated 3–7% of plant nuclear
genome sequence files contain short (38–
785 nucleotide) segments of organelle
DNA randomly integrated by nonhomologous end joining ( Blanchard and Schmidt
1995). The mechanism for transfer of large
multigene segments from mitochondria to
nucleus is unknown, and no published surveys address the frequency of such transfers. The study of mtDNA sequences in the
nucleus is of considerable evolutionary interest, providing insight into the dynamics
of genome evolution and intergenomic interactions, as well as a potentially important mechanism for generating genomic
diversity ( Benasson et al. 2000).
why do they end up in the nucleus? Trends Genet 16:
315–320.
tion of mitochondrial DNA from cotton seedlings. Plant
Cell Rep 7:356–360.
Blanchard JL and Schmidt GW, 1995. Pervasive migration of organellar DNA to the nucleus in plants. J Mol
Evol 41:397–406.
Jofuku KD and Goldberg RB, 1988. Analysis of plant
gene structure. In: Plant molecular biology a practical
approach (Shaw CH, ed). Oxford: IRL Press; 37–66.
Blanchard JL and Schmidt GW, 1996. Mitochondrial
DNA migration events in yeast and humans: integration
by a common end-joining mechanism and alternative
perspectives on nucleotide substitution patterns. Mol
Biol Evol 13:537–548.
Koltunow AM, 1993. Apomixis: embryo sacs and embryos formed without meiosis or fertilization in ovules.
Plant Cell 5:1425–1437.
Conde MF, Pring DR, and Levings CS III, 1979. Maternal
inheritance of organelle DNAs in Zea mays–Zea perennis reciprocal crosses. J Hered 70:2–4.
Dellaporta SL, Wood J, and Hicks JB, 1983. A plant DNA
minipreparation: version II. Plant Mol Biol Rep 1:19–21.
Durham RE, Liou PC, Gmitter FG Jr, and Moore GA,
1992. Linkage of restriction fragment length polymorphisms and isozymes in Citrus. Theor Appl Genet 84:
39–48.
Fauron CM-R, Moore B, and Casper M, 1995. Maize as
a model of higher plant mitochondrial genome plasticity. Plant Sci 112:11–32.
Gmitter FG Jr, Xiao SY, Huang S, Hu XL, Garnsey SM,
and Deng Z, 1996. A localized linkage map of the citrus
tristeza virus resistance gene region. Theor Appl Genet
92:688–695.
Gray MW, 2000. Mitochondrial genes on the move. Nature 408:302–304.
Harrison RG and Doyle JJ, 1990. Redwoods break the
rules. Nature 344:295–296.
Mackenzie SA and Chase CD, 1990. Fertility restoration
is associated with loss of a portion of the mitochondrial genome in cytoplasmic male sterile common
bean. Plant Cell 2:905–912.
Malek O, Lating K, Hiesel R, Brennicke A, and Knoop V,
1996. RNA editing in bryophytes and a molecular phylogeny of land plants. EMBO J 15:1403–1411.
Martin W and Herrmann RG, 1998. Gene transfer from
organelles to the nucleus: how much, what happens
and why? Plant Physiol 118:9–17.
Mogensen HL, 1996. The hows and whys of cytoplasmic
inheritance in seed plants. Am J Bot 83:383–404.
Moon E, Kao T, and Wu R, 1985. Pea cytochrome oxidase subunit II gene has no intron and generates two
mRNA transcripts with different 5⬘ termini. Nucleic Acids Res 13:3195–3205.
Henze K and Martin W, 2001. How do mitochondrial
genes get into the nucleus? Trends Genet 17:383–387.
Moreira CD, Chase CD, Gmitter FG Jr, and Grosser JW,
2000. Inheritance of organelle genomes in citrus cybrids. Mol Breed 6:401–405.
Hsu CL and Mullin BC, 1988. A new protocol for isola-
Palmer JD, Adams KL, Cho Y, Parkinson CL, Qiu Y, and
178 The Journal of Heredity 2002:93(3)
Reboud X and Zeyl C, 1994. Organelle inheritance in
plants. J Hered 72:132–140.
Sakamoto W, Kondo H, Murata M, and Motoyoshi F,
1996. Altered mitochondrial gene expression in a maternal distorted leaf mutant of Arabidopsis induced by
chloroplast mutator. Plant Cell 8:1377–1390.
Shay JW and Werbin H, 1992. New evidence for the insertion of mitochondrial DNA into the human genome:
significance for cancer and aging. Mutat Res 275:227–
235.
Small ID, Isaac PG, and Leaver CJ, 1987. Stoichiometric
differences in DNA molecules containing the atpA gene
suggest mechanisms for the generation of mitochondrial genome diversity in maize. EMBO J 6:865–869.
Small I, Suffolk R, and Leaver CJ, 1989. Evolution of
plant mitochondrial genomes via substoichiometric intermediates. Cell 58:69–76.
Stupar RM, Lilly JW, Town CD, Cheng Z, Kaul S, Buell
CR, and Jiang J, 2000. Complex mtDNA constitutes an
approximate 620-kb insertion on Arabidopsis thaliana
chromosome 2: implication of potential sequencing errors caused by large-unit repeats. Proc Natl Acad Sci
USA 98:5099–5103.
Torres AM, Mau-Lastovicka T, Williams TE, and Soost
RK, 1985. Segregation distortion and linkage of Citrus
and Poncirus isozyme genes. J Hered 76:289–294.
Wen L and Chase CD, 1999. Mitochondrial gene expression in developing male gametophytes of male-fertile
and S male-sterile maize. Sex Plant Reprod 11:323–330.
Yates F, 1934. Contingency tables involving small numbers and the ␹2 test. J R Stat Soc 1(suppl):217–235.
Received August 24, 2001
Accepted March 5, 2002
Corresponding Editor: David Wagner
Downloaded from http://jhered.oxfordjournals.org/ at Pennsylvania State University on February 27, 2014
Erickson L and Kemble R, 1990. Paternal inheritance of
mitochondria in rapeseed (Brassica napus). Mol Gen
Genet 222:135–139.
Lin X, Kaul S, Rounsley S, Shea T, Benito M, Town CD,
Fujii CY, Mason T, Bowman CL, Barnstead M, Feldblyum
TV, Buell R, Ketchum KA, Lee J, Ronning CM, Koo HL,
Moffat KS, Cronin LA, Shen M, Pal G, Van Aken S, Umayam L, Tallon LJ, Gill JE, Adams MD, Carrera AJ, Creasy
TH, Goodman HM, Somerville CR, Copenhaver GP,
Preuss D, Nierman WC, White O, Elsen JA, Salzberg SL,
Fraser CM, and Venter JC, 1999. Sequence and analysis
of chromosome 2 of the plant Arabidopsis thaliana. Nature 402:761–769.
Song K, 2000. Dynamic evolution of plant mitochondrial
genomes: mobile genes and introns and highly variable
mutation rates. Proc Natl Acad Sci USA 97:6960–6966.