Sakata Nanami, Fujikawa Takashi, Uke Ayaka, Ishiga Takako, Ichinose Yuki, Ishiga Yasuhiro
Faculty of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba 305-8572, Ibaraki, Japan.
Institute of Plant Protection, National Agriculture and Food Research Organization (NARO), Tsukuba 305-8666, Ibaraki, Japan.
Microorganisms. 2023 Apr 14;11(4):1025. doi: 10.3390/microorganisms11041025.
pv. () causes bacterial blight on cabbage. We previously conducted a screening for reduced virulence using Tn transposon mutants and identified one of the transcriptional factors, HexR, as a potential virulence factor. However, the role of HexR in plant pathogenic virulence has not been investigated well. Here, we demonstrated that the mutant showed reduced disease symptoms and bacterial populations on cabbage, indicating that HexR contributes to virulence. We used RNA-seq analysis to characterize the genes regulated by HexR. We found that several type three secretion system (T3SS)-related genes had lower expression of the mutant. Five genes were related to T3SS machinery, two genes were related to type three helper proteins, and three genes encoded type three effectors (T3Es). We also confirmed that T3SS-related genes, including , , , and , were also down-regulated in the mutant both in culture and in vivo by using RT-qPCR. T3SS functions to suppress plant defense in host plants and induce hypersensitive response (HR) cell death in non-host plants. Therefore, we investigated the expression profiles of cabbage defense-related genes, including and , and found that the expressions of these genes were greater in the mutant. We also demonstrated that the mutant did not induce HR cell death in non-host plants, indicating that HexR contributes in causing HR in nonhost plants. Together, these results indicate that the mutation in leads to a reduction in the T3SS-related gene expression and thus an impairment in plant defense suppression, reducing virulence.
丁香假单胞菌（Pseudomonas syringae pv. ）会导致卷心菜发生细菌性叶枯病。我们之前利用Tn转座子突变体进行了降低毒力的筛选，并鉴定出其中一个转录因子HexR是一种潜在的毒力因子。然而，HexR在植物致病毒力中的作用尚未得到充分研究。在此，我们证明该突变体在卷心菜上表现出减轻的病害症状和细菌数量，表明HexR有助于毒力。我们使用RNA测序分析来表征受HexR调控的基因。我们发现几个三型分泌系统（T3SS）相关基因在突变体中的表达较低。五个基因与T3SS机制相关，两个基因与三型辅助蛋白相关，三个基因编码三型效应子（T3Es）。我们还通过实时定量PCR证实，包括、、和在内的T3SS相关基因在突变体的体外培养和体内均下调。T3SS的功能是抑制宿主植物中的植物防御，并在非宿主植物中诱导超敏反应（HR）细胞死亡。因此，我们研究了卷心菜防御相关基因（包括和）的表达谱，发现这些基因在突变体中的表达更高。我们还证明突变体在非宿主植物中不会诱导HR细胞死亡，表明HexR在非宿主植物中导致HR方面发挥作用。总之，这些结果表明突变导致T3SS相关基因表达降低，从而损害植物防御抑制，降低毒力。
