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The transcription factor FgStuA influences spore development,
pathogenicity and secondary metabolism in Fusarium graminearum
Erik Lysøe1, Matias Pasquali2, Andrew Breakspear2, Sonja S. Klemsdal1, and H. Corby Kistler2,3
1Bioforsk
- Norwegian Institute of Agricultural and Environmental Research, Ås, Norway;
of Plant Pathology, University of Minnesota, St. Paul, MN 55108, USA;
3USDA ARS Cereal Disease Laboratory, University of Minnesota, St. Paul, MN 55108, USA
2Department
Abstract
We deleted the FgStuA gene in Fusarium
graminearum and demonstrate its involvement
in spore development, pathogenicity and
secondary metabolism. The FgStuA protein is a
member of the APSES family which regulate
morphogenesis and virulence in ascomycetes.
FgStuA is closely related to FoStuA in F.
oxysporum and stuA in Aspergillus, but unlike
FoStuA mutants, the FgStuA mutants were
greatly reduced in pathogenicity on wheat and
colonization of apple slices. The mutant
produces no detectable trichothecenes on the
wheat cultivar Bobwhite, and <1% levels of
wildtype in culture. Trichothecenes have shown
to be pathogenicity factors in wheat, and this
could be the reason for loss of ability to produce
disease in the FgStuA mutants. The mutant was
also greatly decreased in sporulation and
produced no perithecia in culture. Thus both
sporulation and trichothecene synthesis may be
regulated under the control of FgStuA.
ΔFgStuA
Wildtype
20 μm
ΔFgStuA
20 μm
Phialide
A
Wildtype
ΔFgStuA
A
20 μm
1/10 sec
20 μm
1 sec
20 μm
1/10 sec
B
Wheat
WT StuA
ppm
800
600
400
B
0
<1%
WT
ΔFgStuA
WT
StuA
WT
StuA
Mock
nd
296
nd
DON concentration (ppm) in wheat
200
SecMet Wheat
ΔFgStuA
StuA
SecMet Wheat
WT
StuA
WT
StuA
C
1000
StuA
20 μm
1 sec
Wildtype
CMC
15 ADON in culture
CMC
WT
WT
A
Wildtype
C
Pathogenicity and trichothecene production
of wildtype PH-1 and ΔFgStuA mutant.
A. Wheat heads inoculated with wildtype PH-1
(center) show tissue bleaching and deformed
awns. No symptoms are seen in mock inoculated
plants (right) or ones inoculated with ΔFgStuA
(left). Deoxynivalenol (DON) concentrations
(ppm) of inoculated spikelets are indicated (nd =
not detected). B. Production of 15 ADON in
culture. The ΔFgStuA mutant produced <1% the
level of wildtype (WT). C. Expression heat map
of trichothecene genes 72h after wheat
infection. None of the trichothecene genes are
expressed in ΔFgStuA, while most are highly
expressed in WT. Grey signal = not detected.
FgStuA is a transcription factor and a
predicted APSES helix loop helix DNA binding
protein. A. The ΔFgStuA mutant has a greatly
reduced sporulation rate and altered spore
morphology. The mutant lacks conidiophores and
phialides and produces spores directly from
hyphea. This way of spore production seems
slow and inefficient. On the spore-producing
medium CMC for 62h, only 100 macroconidia
could be found in ΔFgStuA, in contrast to 1x106
in the wildtype. The mutant macroconidia also
germinate at a slower rate than wildype, about
4h later at 25C in liquid complete medium
(CM). B. The chitin binding stain calcofluor
shows diminished affinity for spores and
germlings of the ΔFgStuA mutant compared to
wildtype, and that septa are lacking from
mutant macroconidia. C. The expression heat
map shows relative expression levels of chitinrelated genes in wildtype PH-1 and ΔFgStuA
during three different experiments, on sporeproducing CMC medium, on a secondary
metabolite producing medium (SecMet) and
during the infection process of wheat. Grey
signal = not detected. The spore characteristics
correlate well with reduced transcript levels in
the mutant for genes related to chitin synthesis,
especially on CMC and during wheat infection.
B
The red pigment aurofusarin.
A. Production of the red pigment aurofusarin is
highly reduced in the ΔFgStuA mutant on
different growth media, such as V8 and PDA.
B. Expression heat map of aurofusarin genes in
wildtype PH-1 and ΔFgStuA during three
different experiments. The lack of pigmentation
in the mutant was reflected in the sporeproducing CMC medium, where 17 adjoining
probesets, including the known aurofusarin
genes, where highly down-regulated or not
detected in ΔFgStuA. Grey signal = not
detected.
Summary - ΔFgStuA mutant characteristics:
1. Pathogenicity
- Non-pathogenic on wheat
- Reduced colonization of apple slices
2. Sporulation
- Reduced sporulation rate, no perithecia
- Lacks conidiophores and phialides
- Altered spore morhology
3. Secondary metabolism
- No trichothecene production in wheat
- Very low 15ADON production in culture
- Reduced pigmentation
Acknowledgements
We thank Karen Hilburn (USDA-ARS Cereal
Disease Laboratory) for outstanding technical
assistance. This project was supported by the
National Research Initiative of the USDA
Cooperative State Research, Education and
Extension Service, grant 2004-35604-14327 and
the BILAT project 173277 supported by the
Research Council of Norway.