Microbial pathogens deliver effectors into plant cells to suppress plant immune responses and modulate host metabolism in order to support infection processes. We sought to determine if the Acidovorax avenae rice-virulent K1 strain can suppress pathogen-associated molecular pattern–triggered immunity (PTI) induced by flagellin isolated from the rice-avirulent N1141 strain. The flagellin-triggered PTI, including H₂O₂ generation, callose deposition, and expression of several immune-related genes were strongly suppressed in K1 preinoculated cultured rice cells in a type III secretion system (T3SS)-dependent manner. By screening 4,562 transposon-tagged mutants based on their suppression ability, we found that 156 transposon-tagged K1 mutants lost the ability to suppress PTI induction. Mutant sequence analysis, comprehensive expression analysis using RNA sequencing, and the prediction of secretion through T3SS showed that a protein named A. avenae K1 suppression factor 1 (AKSF1) suppresses flagellin-triggered PTI in rice. Translocation of AKSF1 protein into rice cells is dependent on the T3SS during infection, an AKSF1-disruption mutant lost the ability to suppress PTI responses, and expression of AKSF1 in the AKSF1-disruption mutant complemented the suppression activity. When AKSF1-disruption mutants were inoculated into the host rice plant, reduction of the disease symptoms and suppression of bacterial growth were observed. Taken together, our results demonstrate that AKSF1 is a novel effector that can suppress the PTI in a host rice plant.

The author(s) have dedicated the work to the public domain under the Creative Commons CC0 “No Rights Reserved” license by waiving all of his or her rights to the work worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law. 2021

微生物病原体将效应子传递到植物细胞中，以抑制植物免疫反应并调节宿主代谢，从而支持感染过程。我们试图确定酸食单胞菌水稻毒力K1菌株是否能抑制从水稻无毒力N1141菌株中分离出的鞭毛蛋白诱导的病原体相关分子模式触发的免疫（PTI）。鞭毛触发的PTI，包括H ₂ O ₂K1预接种的水稻细胞以III型分泌系统（T3SS）依赖的方式强烈抑制了其产生，愈伤组织沉积和几种免疫相关基因的表达。通过基于抑制能力筛选4,562个转座子标记的突变体，我们发现156个转座子标记的K1突变体失去了抑制PTI诱导的能力。突变序列分析，使用RNA测序的全面表达分析以及通过T3SS进行的分泌预测表明，一种名为A. avenae K1抑制因子1（AKSF1）的蛋白可抑制鞭毛蛋白触发的水稻PTI。在感染过程中，AKSF1蛋白向水稻细胞的转运依赖于T3SS，破坏AKSF1的突变体失去了抑制PTI反应的能力，而AKSF1-破坏突变体中的AKSF1补充了抑制活性。当将破坏AKSF1的突变体接种到寄主水稻植物中时，观察到疾病症状的减轻和细菌生长的抑制。两者合计，我们的结果表明，AKSF1是一种新型效应子，可以抑制寄主水稻植株中的PTI。

作者根据知识共享CC0“无保留权利”许可，将作品专用于公共领域，在一定程度上放弃了著作权法规定的他对世界范围内作品的所有权利，包括所有相关和邻近权利法律允许。2021年