The diguanylate cyclase AdrA regulates flagellar biosynthesis in Pseudomonas fluorescens F113 through SadB

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 SadBThis work was supported by funding from MINECO/FEDER EU Grant RTI2018 093991-BI00 to R.R. and M.M. C.M. was funded by a FPI fellowship from MINECO. EB-R was the recipient of fellowships from Fundación Tatiana Pérez de Guzmán el Bueno (Medioambiente 2016) and the FPU program from MECD (FPU16/05513). Short stays of R.R. and C.M. at John Innes Centre were funded by MECD (Salvador de Madariaga and FPU, respectively