Zhejiang Academy of Agricultural Sciences, Institute of Vegetables, Hangzhou, Zhejiang 310021, China.
USDA-Agricultural Research Service, U.S. Vegetable Laboratory, Charleston, SC 29414, USA.
Sci Rep. 2016 Jun 20;6:28146. doi: 10.1038/srep28146.
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.
当感染宿主植物时，真菌尖孢镰刀菌会将几种效应蛋白分泌到木质部组织中，以促进毒力。然而，在具有涉及类似抗性蛋白的先天免疫系统的宿主植物中，真菌效应蛋白可能会触发抗性，而不是促进毒力。目前尚不清楚影响西瓜（Citrullus lanatus）的尖孢镰刀菌 f. sp. niveum（Fon）菌株的效应基因的身份。在这项研究中，在 Fon 菌株 0 和 1 中鉴定出了 SIX6（木质部分泌蛋白 6）基因，但在毒力更强的 Fon 菌株 2 中没有鉴定出。在 Fon 菌株 1 中破坏 FonSIX6 基因不会影响真菌的孢子形成或生长速度，但显着增强了西瓜中的 Fon 毒力，表明突变体ΔFon1SIX6 蛋白允许逃避 R 蛋白介导的宿主抗性。用 FonSIX6 互补野生型菌株 2（缺乏 FonSIX6）降低了其毒力。这些结果为 FonSIX6 是无毒基因的假设提供了证据。将 FonSix6 鉴定为无毒因子可能是了解西瓜中 Fon 毒力和抗性机制的第一步，并进一步阐明 Six6 在镰刀菌-植物相互作用中的作用。
