Abstract

Ralstonia solanacearum injects type III effectors into host cells to cause bacterial wilt in Solanaceae plants. To identify R. solanacearum effectors that suppress effector-triggered immunity (ETI) in plants, we evaluated R. solanacearum RS1000 effectors for their ability to suppress a hypersensitive response (HR) induced by the avirulence (Avr) effector RipAA in Nicotiana benthamiana. Out of the 11 effectors tested, 4 suppressed RipAA-triggered HR cell death. Among them, RipAC contains tandem repeats of the leucine-rich repeat (LRR) motif, which serves as the structural scaffold for a protein–protein interaction. We found that the LRR domain of RipAC was indispensable for the suppression of HR cell death during the recognition of RipAA and another Avr effector RipP1. By yeast two-hybrid screening, we identified N. benthamiana SGT1, an adaptor protein that forms a molecular chaperone complex with RAR1, as a host factor of the RipAC target. RipAC interacted with NbSGT1 in yeast and plant cells. Upon the formation of the molecular chaperone complex, the presence of RipAC markedly inhibits the interaction between NbSGT1 and NbRAR1. The RipAA- and RipP1-triggered HR cell deaths were not observed in NbSGT1-silenced plants. The introduction of RipAC was complementary to the reduced growth of the R. solanacearum mutant strain in N. benthamiana. These findings indicate that R. solanacearum uses RipAC to subvert the NbSGT1-mediated formation of the molecular chaperone complex and suppress ETI responses during the recognition of Avr effectors.

中文翻译：

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Ralstonia solanacearum III 型效应器 RipAC 靶向 SGT1 抑制效应器触发的免疫

 抽象的

青枯雷尔斯顿菌将 III 型效应子注入宿主细胞，引起茄科植物青枯病。为了鉴定抑制植物中效应子触发免疫（ETI）的青枯菌效应子，我们评估了青枯菌RS1000 效应子抑制本塞姆氏烟草无毒（Avr）效应子 RipAA 诱导的过敏反应（HR）的能力。在测试的 11 个效应器中，有 4 个抑制了 RipAA 触发的 HR 细胞死亡。其中，RipAC 包含富含亮氨酸重复序列 (LRR) 基序的串联重复序列，可作为蛋白质-蛋白质相互作用的结构支架。我们发现，在识别 RipAA 和另一个 Avr 效应子 RipP1 过程中，RipAC 的 LRR 结构域对于抑制 HR 细胞死亡是必不可少的。通过酵母双杂交筛选，我们鉴定出本塞姆氏烟草SGT1（一种与 RAR1 形成分子伴侣复合物的接头蛋白）作为 RipAC 靶标的宿主因子。 RipAC 与酵母和植物细胞中的 NbSGT1 相互作用。在分子伴侣复合物形成后，RipAC 的存在显着抑制 NbSGT1 和 NbRAR1 之间的相互作用。在NbSGT1沉默的植物中没有观察到 RipAA 和 RipP1 触发的 HR 细胞死亡。 RipAC 的引入与本塞姆氏烟草中青枯菌突变株生长的减少相辅相成。这些发现表明，青枯菌使用 RipAC 来破坏 NbSGT1 介导的分子伴侣复合物的形成，并在识别 Avr 效应子期间抑制 ETI 反应。