Departamento de Biología, Universidad Autónoma de Madrid, Campus de Cantoblanco, 28049, Madrid, Spain.
Department of Molecular Microbiology, John Innes Centre. Colney Lane, Norwich, UK.
Sci Rep. 2019 May 30;9(1):8096. doi: 10.1038/s41598-019-44554-z.
Flagellum mediated motility is an essential trait for rhizosphere colonization by pseudomonads. Flagella synthesis is a complex and energetically expensive process that is tightly regulated. In Pseudomonas fluorescens, the regulatory cascade starts with the master regulatory protein FleQ that is in turn regulated by environmental signals through the Gac/Rsm and SadB pathways, which converge in the sigma factor AlgU. AlgU is required for the expression of amrZ, encoding a FleQ repressor. AmrZ itself has been shown to modulate c-di-GMP levels through the control of many genes encoding enzymes implicated in c-di-GMP turnover. This cyclic nucleotide regulates flagellar function and besides, the master regulator of the flagellar synthesis signaling pathway, FleQ, has been shown to bind c-di-GMP. Here we show that AdrA, a diguanylate cyclase regulated by AmrZ participates in this signaling pathway. Epistasis analysis has shown that AdrA acts upstream of SadB, linking SadB with environmental signaling. We also show that SadB binds c-di-GMP with higher affinity than FleQ and propose that c-di-GMP produced by AdrA modulates flagella synthesis through SadB.
鞭毛介导的运动是假单胞菌在根际定殖的一个重要特征。鞭毛合成是一个复杂且能量消耗大的过程，受到严格的调控。在荧光假单胞菌中，调控级联反应从主调控蛋白 FleQ 开始，反过来又通过 Gac/Rsm 和 SadB 途径受到环境信号的调控，这两个途径在 sigma 因子 AlgU 中汇聚。AlgU 是编码 FleQ 抑制剂的 amrZ 表达所必需的。AmrZ 本身通过控制许多参与 c-di-GMP 周转的酶的基因表达来调节 c-di-GMP 水平。这种环核苷酸调节鞭毛功能，此外，鞭毛合成信号通路的主调控因子 FleQ 已被证明与 c-di-GMP 结合。在这里，我们表明，受 AmrZ 调控的二鸟苷酸环化酶 AdrA 参与了这一信号通路。上位性分析表明，AdrA 在 SadB 之前起作用，将 SadB 与环境信号联系起来。我们还表明，SadB 与 c-di-GMP 的结合亲和力高于 FleQ，并提出由 AdrA 产生的 c-di-GMP 通过 SadB 调节鞭毛合成。
