Sakata Nanami, Ishiga Takako, Ishiga Yasuhiro
Faculty of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Japan.
Front Microbiol. 2021 Apr 20;12:659734. doi: 10.3389/fmicb.2021.659734. eCollection 2021.
pv. () causes bacterial leaf spot and blight of Brassicaceae and Poaceae. We previously identified several potential virulence factors with transposon mutagenesis. Among these a mutant disrupted the tryptophan synthase alpha chain, and had an effect on disease symptom development and bacterial multiplication. To assess the importance of TrpA in virulence, we characterized the mutant based on inoculation test and gene expression profiles. The mutant showed reduced virulence when dip- and syringe-inoculated on cabbage and oat. Moreover, epiphytic bacterial populations of the mutant were also reduced compared to the wild-type (WT). These results suggest that TrpA contributes to bacterial multiplication on the leaf surface and in the apoplast, and disease development. Additionally, several Brassicaceae (including Japanese radish, broccoli, and Chinese cabbage) also exhibited reduced symptom development when inoculated with the mutant. Moreover, disruption led to downregulation of bacterial virulence genes, including type three effectors (T3Es) and the phytotoxin coronatine (COR), and to upregulation of tryptophan biosynthesis genes. These results indicate that a trade-off between virulence factor production and multiplication with tryptophan might be regulated in the infection processes.
pv.（）会导致十字花科和禾本科植物的细菌性叶斑病和叶枯病。我们之前通过转座子诱变鉴定了几种潜在的毒力因子。其中一个突变体破坏了色氨酸合酶α链，并对疾病症状发展和细菌繁殖产生了影响。为了评估TrpA在毒力中的重要性，我们基于接种试验和基因表达谱对该突变体进行了表征。当通过浸蘸和注射接种到卷心菜和燕麦上时，该突变体表现出毒力降低。此外，与野生型（WT）相比，该突变体的附生细菌数量也减少了。这些结果表明，TrpA有助于细菌在叶表面和质外体中的繁殖以及疾病发展。此外，几种十字花科植物（包括日本萝卜、西兰花和大白菜）接种该突变体后症状发展也有所减轻。此外，TrpA的破坏导致细菌毒力基因下调，包括III型效应子（T3Es）和植物毒素冠菌素（COR），并导致色氨酸生物合成基因上调。这些结果表明，在感染过程中，毒力因子产生与色氨酸繁殖之间的权衡可能受到调节。
