Agrobacterium tumefaciens ExoR Controls Acid Response Genes and Impacts Exopolysaccharide Synthesis, Horizontal Gene Transfer, and Virulence Gene Expression
Agrobacterium tumefaciens ExoR Controls Acid Response Genes and Impacts Exopolysaccharide Synthesis, Horizontal Gene Transfer, and Virulence Gene Expression
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DOI：
10.1128/jb.01751-14
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发表时间：
2014-09-01
影响因子：
3.2
通讯作者：
Fuqua, Clay
中科院分区：
文献类型：
--
作者：
Heckel, Brynn C.;Tomlinson, Amelia D.;Fuqua, Clay
根癌农杆菌是一种兼性植物病原菌，是引起根癌病的病原菌。感染的初始阶段涉及附着于植物组织，随后，生物膜可在这些部位形成。本研究的重点是周质ExoR调节剂，这是基于严重的生物膜缺陷的A。根癌农杆菌exoR突变体进行全基因组表达分析以阐明完整的ExoR调节子。外泌多糖琥珀聚糖的过度产生是exoR突变体的显著表型。比较表达分析显示，核心ExoR调节子不受琥珀聚糖合成的影响。几个发现与以前的观察结果是一致的：参与琥珀聚糖的生物合成，运动性和VI型分泌的基因在Delta exoR突变体中差异表达。此外，这些研究揭示了受ExoR调控的新功能类别，包括与毒力、pAtC 58巨质粒的接合、ABC转运蛋白和细胞包膜结构相关的基因。为了解决ExoR如何从其周质位置对基因表达产生广泛影响，进行遗传筛选以分离减轻exoR运动表型的抑制突变体并鉴定ExoR调节途径的下游组分。这种抑制分析确定了酸敏感的双组分系统ChvG-ChvI，和抑制突变体表型表明，所有或大部分的特征exoR的属性是通过ChvG-ChvI介导的。随后的分析表明，exoR突变体模拟了对酸性条件的响应，即使在中性培养基中也是如此。本工作扩展了A. tumefaciens，并强调了这种调节剂在基因表达中的全球作用。
Agrobacterium tumefaciens is a facultative plant pathogen and the causative agent of crown gall disease. The initial stage of infection involves attachment to plant tissues, and subsequently, biofilms may form at these sites. This study focuses on the periplasmic ExoR regulator, which was identified based on the severe biofilm deficiency of A. tumefaciens exoR mutants. Genome-wide expression analysis was performed to elucidate the complete ExoR regulon. Overproduction of the exopolysaccharide succinoglycan is a dramatic phenotype of exoR mutants. Comparative expression analyses revealed that the core ExoR regulon is unaffected by succinoglycan synthesis. Several findings are consistent with previous observations: genes involved in succinoglycan biosynthesis, motility, and type VI secretion are differentially expressed in the Delta exoR mutant. In addition, these studies revealed new functional categories regulated by ExoR, including genes related to virulence, conjugation of the pAtC58 megaplasmid, ABC transporters, and cell envelope architecture. To address how ExoR exerts a broad impact on gene expression from its periplasmic location, a genetic screen was performed to isolate suppressor mutants that mitigate the exoR motility phenotype and identify downstream components of the ExoR regulatory pathway. This suppression analysis identified the acid-sensing two-component system ChvG-ChvI, and the suppressor mutant phenotypes suggest that all or most of the characteristic exoR properties are mediated through ChvG-ChvI. Subsequent analysis indicates that exoR mutants are simulating a response to acidic conditions, even in neutral media. This work expands the model for ExoR regulation in A. tumefaciens and underscores the global role that this regulator plays on gene expression.