Kharadi Roshni R, Sundin George W
Department of Plant, Soil and Microbial Sciences, Michigan State University, East Lansing, MI, United States.
Front Microbiol. 2020 Nov 17;11:605265. doi: 10.3389/fmicb.2020.605265. eCollection 2020.
is the causal agent of fire blight, an economically impactful disease that affects apple and pear production worldwide. pathogenesis is comprised of distinct type III secretion-dependent and biofilm-dependent stages. Alterations in the intracellular levels of cyclic-di-GMP (c-di-GMP) regulate the transition between the different stages of infection in . We previously reported that hyper-elevation of c-di-GMP levels in Ea1189, resulting from the deletion of all three c-di-GMP specific phosphodiesterase genes (Ea1189Δ), resulted in an autoaggregation phenotype. The two major exopolysaccharides, amylovoran and cellulose, were also shown to partially contribute to autoaggregation. In this study, we aimed to identify the c-di-GMP dependent factor(s) that contributes to autoaggregation. We conducted a transposon mutant screen in Ea1189Δ and selected for loss of autoaggregation. Our search identified a peptidoglycan hydrolase, specifically, a D, D-endopeptidase of the metallopeptidase class, EagA ( aggregation factor A), that was found to physiologically contribute to autoaggregation in a c-di-GMP dependent manner. The production of amylovoran was also positively affected by EagA levels. An deletion mutant (Ea1189Δ) was significantly reduced in virulence compared to the wild type Ea1189. is part of the zinc uptake gene cluster and is located within an operon downstream of The / gene cluster was transcriptionally regulated by elevated levels of c-di-GMP as well as by the zinc-dependent transcriptional repressor Zur. We also observed that with an influx of Zn in the environment, the transcription of the gene cluster is regulated by both Zur and a yet to be characterized c-di-GMP dependent pathway.
是火疫病的致病因子，火疫病是一种对全球苹果和梨生产有经济影响的疾病。其致病机制由不同的III型分泌依赖性和生物膜依赖性阶段组成。环二鸟苷酸（c-di-GMP）细胞内水平的变化调节了在感染不同阶段之间的转变。我们之前报道过，由于所有三个c-di-GMP特异性磷酸二酯酶基因缺失（Ea1189Δ），Ea1189中c-di-GMP水平的过度升高导致了自聚集表型。两种主要的胞外多糖，聚半乳糖醛酸和纤维素，也被证明部分促成了自聚集。在本研究中，我们旨在鉴定促成自聚集的c-di-GMP依赖性因子。我们在Ea1189Δ中进行了转座子突变体筛选，并选择自聚集丧失的突变体。我们的研究发现了一种肽聚糖水解酶，具体来说，是一种金属肽酶类的D，D-内肽酶，EagA（聚集因子A），它在生理上以c-di-GMP依赖性方式促成自聚集。聚半乳糖醛酸的产生也受到EagA水平的正向影响。与野生型Ea1189相比，EagA缺失突变体（Ea1189Δ）的毒力显著降低。EagA是锌摄取基因簇的一部分，位于基因的下游操纵子内。该基因簇受c-di-GMP水平升高以及锌依赖性转录阻遏物Zur的转录调控。我们还观察到，随着环境中锌的流入，该基因簇的转录受Zur和一条尚未明确的c-di-GMP依赖性途径的调控。
