青枯菌效应蛋白RipAF1对植物PTI的诱导作用

The role of Ralstonia solanacearum typeⅢeffector RipAF1 in the induction of host PTI response

青枯雷尔氏菌(Ralstonia solanacearum)利用Ⅲ型分泌系统(Type three secretion system, T3SS)将自身合成的100多个效应蛋白注入寄主植物细胞引起免疫反应的变化。本文报道青枯菌GMI1000效应蛋白RipAF1对寄主植物先天免疫反应的诱导作用。在本氏烟草植物上瞬时表达RipAF1,显著地诱导了PTI标志基因NbAcre31、NbPti5和NbGras2的增强表达,伴随着胼胝质的累积。酵母双杂交实验从烟草cDNA文库中筛选到与RipAF1互作的NbBAK1的C端序列,随后的荧光素酶和双分子荧光互补实验表明RipAF1与BAK1在植物体内相互作用。在GMI1000菌株中将ripAF1缺失突变,在营养丰富和基本培养基中生长与野生型没有明显区别,灌根接种番茄后致病力增强,在番茄植物体内的繁殖速度变快。这些结果表明RipAF1是一个诱导寄主植物PTI反应的效应蛋白,并且负向影响青枯菌的致病力。

Ralstonia solanacearum injects a repertoire of effectors into host cells to modulate plant immune response via a typeⅢsecretion system.Our work reports the role of typeⅢeffector RipAF1 from GMI1000 in the induction of host immune response.Transient overexpression of RipAF1 in Nicotiana benthamiana resulted in the enhanced expression levels of PTI marker genes NbAcre31,NbPti5 and NbGras2.Simultaneously,a large amount of callose was accumulated.In a yeast two-hybrid experiment,a RipAF1-interacting C-terminal of BAK1 was screened from a cDNA library of N.benthamiana.Subsequent split-luciferase and bimolecular fluorescence complementation experiments showed that RipAF1 was interacted with NbBAK1 in vivo.A deletion mutantΔripAF1 was constructed in GMI1000,which showed no difference from wild type in growth in both nutrient rich and minimal media.However,the mutant showed increased virulence on tomato plants,as well as the replication in planta.These results demonstrated that RipAF1 is an effector able to induce plant PTI and exerts a negative role for virulence.