The FonSIX6 gene acts as an avirulence effector in the Fusarium oxysporum f. sp. niveum - watermelon pathosystem.
When infecting a host plant, the fungus Fusarium oxysporum secretes several effector proteins into the xylem tissue to promote virulence. However, in a host plant with an innate immune system involving analogous resistance proteins, the fungus effector proteins may trigger resistance, rather than promoting virulence. Identity of the effector genes of Fusarium oxysporum f. sp. niveum (Fon) races that affect watermelon (Citrullus lanatus) are currently unknown. In this study, the SIX6 (secreted in xylem protein 6) gene was identified in Fon races 0 and 1 but not in the more virulent Fon race 2. Disrupting the FonSIX6 gene in Fon race 1 did not affect the sporulation or growth rate of the fungus but significantly enhanced Fon virulence in watermelon, suggesting that the mutant ΔFon1SIX6 protein allowed evasion of R protein-mediated host resistance. Complementation of the wild-type race 2 (which lacks FonSIX6) with FonSIX6 reduced its virulence. These results provide evidence supporting the hypothesis that FonSIX6 is an avirulence gene. The identification of FonSix6 as an avirulence factor may be a first step in understanding the mechanisms of Fon virulence and resistance in watermelon and further elucidating the role of Six6 in Fusarium-plant interactions.
Zhejiang Academy of Agricultural Sciences, Institute of Vegetables, Hangzhou, Zhejiang 310021, China.
Xiaowei
X
Niu
Zhejiang Academy of Agricultural Sciences, Institute of Vegetables, Hangzhou, Zhejiang 310021, China.
Xiaoqiang
X
Zhao
USDA-Agricultural Research Service, U.S. Vegetable Laboratory, Charleston, SC 29414, USA.
Kai-Shu
KS
Ling
USDA-Agricultural Research Service, U.S. Vegetable Laboratory, Charleston, SC 29414, USA.
Amnon
A
Levi
Zhejiang Academy of Agricultural Sciences, Institute of Vegetables, Hangzhou, Zhejiang 310021, China.
Yuyan
Y
Sun
Zhejiang Academy of Agricultural Sciences, Institute of Vegetables, Hangzhou, Zhejiang 310021, China.
Min
M
Fan
D000595:Amino Acid Sequence / Q000235:genetics; D001483:Base Sequence; D029773:Citrullus / Q000235:genetics / Q000276:immunology* / Q000382:microbiology*; D003001:Cloning, Molecular; D018744:DNA, Plant / Q000235:genetics; D005670:Fusarium / Q000235:genetics* / Q000472:pathogenicity*; D018398:Homeodomain Proteins / Q000235:genetics*; D010935:Plant Diseases / Q000382:microbiology; D018517:Plant Roots / Q000382:microbiology; D017422:Sequence Analysis, DNA; D014774:Virulence / Q000235:genetics
D018744:DNA, Plant; D018398:Homeodomain Proteins