Department of Plant Sciences, University of California, Davis, CA 95616, USA.
Departamento de Ciências Biológicas, Instituto de Ciências Exatas e Biológicas, Núcleo de Pesquisas em Ciências Biológicas, Universidade Federal de Ouro Preto, Ouro Preto 35400-000, MG, Brazil.
Int J Mol Sci. 2021 Sep 26;22(19):10374. doi: 10.3390/ijms221910374.
Walnut blight is a significant above-ground disease of walnuts caused by pv. (Xaj). The secreted form of chorismate mutase (CM), a key enzyme of the shikimate pathway regulating plant immunity, is highly conserved between plant-associated beta and gamma proteobacteria including phytopathogens belonging to the Xanthomonadaceae family. To define its role in walnut blight disease, a dysfunctional mutant of chorismate mutase was created in a copper resistant strain Xaj417 (XajCM). Infections of immature walnut (Jr) fruit with XajCM were hypervirulent compared with infections with the wildtype Xaj417 strain. The in vitro growth rate, size and cellular morphology were similar between the wild-type and XajCM mutant strains, however the quantification of bacterial cells by dPCR within walnut hull tissues showed a 27% increase in XajCM seven days post-infection. To define the mechanism of hypervirulence, proteome analysis was conducted to compare walnut hull tissues inoculated with the wild type to those inoculated with the XajCM mutant strain. Proteome analysis revealed 3296 Jr proteins (five decreased and ten increased with FDR ≤ 0.05) and 676 Xaj417 proteins (235 increased in XajCM with FDR ≤ 0.05). Interestingly, the most abundant protein in Xaj was a polygalacturonase, while in Jr it was a polygalacturonase inhibitor. These results suggest that this secreted chorismate mutase may be an important virulence suppressor gene that regulates Xaj417 virulence response, allowing for improved bacterial survival in the plant tissues.
核桃黑斑病是一种重要的地上部病害，由 pv. （Xaj）引起。色氨酸途径中关键酶分支酸变位酶（CM）的分泌形式在与植物相关的β和γ变形菌中高度保守，包括属于黄单胞菌科的植物病原菌。为了确定其在核桃黑斑病中的作用，在铜抗性菌株 Xaj417（XajCM）中创建了分支酸变位酶的功能失调突变体。与感染野生型 Xaj417 菌株相比，感染未成熟核桃（Jr）果实的 XajCM 具有超毒力。野生型和 XajCM 突变菌株之间的体外生长速率、大小和细胞形态相似，然而通过 dPCR 在核桃壳组织内定量细菌细胞显示 XajCM 在感染后七天内增加了 27%。为了定义超毒力的机制，进行了蛋白质组分析以比较用野生型接种的核桃壳组织与用 XajCM 突变菌株接种的核桃壳组织。蛋白质组分析显示 3296 个 Jr 蛋白（五个减少，十个增加，FDR≤0.05）和 676 个 Xaj417 蛋白（235 个在 XajCM 中增加，FDR≤0.05）。有趣的是，Xaj 中最丰富的蛋白是多聚半乳糖醛酸酶，而 Jr 中最丰富的蛋白是多聚半乳糖醛酸酶抑制剂。这些结果表明，这种分泌的分支酸变位酶可能是一个重要的毒力抑制基因，它调节 Xaj417 的毒力反应，允许细菌在植物组织中更好地存活。
