Olawole Olakunle I, Gleason Mark L, Beattie Gwyn A
Department of Plant Pathology and Microbiology, Iowa State University, Ames, IA, 50011-1101, U.S.A.
Mol Plant Microbe Interact. 2022 Sep;35(9):768-778. doi: 10.1094/MPMI-01-22-0002-R. Epub 2022 Sep 13.
The predicted repertoire of type III secretion system effectors (T3SEs) in , causal agent of cucurbit bacterial wilt, is much larger than in xylem pathogens in the closely related genera and . The genomes of strains BHKY and SCR3, which represent distinct clades, encode at least 6 clade-specific and 12 shared T3SEs. The strains expressed the majority of the T3SE genes examined in planta. Among the shared T3SE genes, was expressed most highly in both strains in squash () and muskmelon () but the clade-specific gene was expressed 40- to 900-fold more than in BHKY. The T3SEs AvrRpm2, Eop1, SrfC, and DspE contributed to BHKY virulence on squash and muskmelon, as shown using combinatorial mutants involving six T3SEs, whereas OspG and AvrB4 contributed to BHKY virulence only on muskmelon, demonstrating host-specific virulence functions. Moreover, Eop1 was functionally redundant with AvrRpm2, SrfC, OspG, and AvrB4 in BHKY, and BHKY mutants lacking up to five effector genes showed similar virulence to mutants lacking only two genes. The T3SEs OspG, AvrB4, and DspE contributed additively to SCR3 virulence on muskmelon and were not functionally redundant with Eop1. Rather, loss of and restored wild-type virulence to the mutant, suggesting that Eop1 suppresses a functionally redundant effector in SCR3. These results highlight functional differences in effector inventories between two clades, provide the first evidence of OspG as a phytopathogen effector, and suggest that Eop1 may be a metaeffector influencing virulence. [Formula: see text] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.
葫芦科细菌性枯萎病的病原菌中预测的III型分泌系统效应蛋白（T3SEs）库比密切相关属中的木质部病原菌大得多。代表不同进化枝的菌株BHKY和SCR3的基因组编码至少6个进化枝特异性和12个共享的T3SEs。这些菌株在植物中表达了所检测的大多数T3SE基因。在共享的T3SE基因中，在南瓜（）和甜瓜（）的两种菌株中表达最高，但进化枝特异性基因在BHKY中的表达比高40至900倍。如使用涉及六个T3SEs的组合突变体所示，T3SEs AvrRpm2、Eop1、SrfC和DspE对BHKY在南瓜和甜瓜上的毒力有贡献，而OspG和AvrB4仅对BHKY在甜瓜上的毒力有贡献，证明了宿主特异性毒力功能。此外，在BHKY中，Eop1与AvrRpm2、SrfC、OspG和AvrB4在功能上是冗余的，缺乏多达五个效应基因的BHKY突变体与仅缺乏两个基因的突变体表现出相似的毒力。T3SEs OspG、AvrB4和DspE对SCR3在甜瓜上的毒力有累加作用，并且与Eop1在功能上不是冗余的。相反，和的缺失使突变体恢复了野生型毒力，这表明Eop1抑制了SCR3中一个功能冗余的效应蛋白。这些结果突出了两个进化枝之间效应蛋白库的功能差异，提供了OspG作为植物病原菌效应蛋白的首个证据，并表明Eop1可能是一种影响毒力的元效应蛋白。[公式：见正文] 版权所有©2022作者。这是一篇根据知识共享署名4.0国际许可协议分发的开放获取文章。
