Cyclic-di-GMP Regulates Autoaggregation Through the Putative Peptidoglycan Hydrolase, EagA, and Regulates Transcription of the Zinc Uptake Gene Cluster in .

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.