A systematic analysis of the role of GGDEF-EAL domain proteins in virulence and motility in Xanthomonas oryzae pv. oryzicola

Abstract

The second messenger c-di-GMP is implicated in regulation of various aspects of the lifestyles and virulence of Gram-negative bacteria. Cyclic di-GMP is formed by diguanylate cyclases with a GGDEF domain and degraded by phosphodiesterases with either an EAL or HD-GYP domain. Proteins with tandem GGDEF-EAL domains occur in many bacteria, where they may be involved in c-di-GMP turnover or act as enzymatically-inactive c-di-GMP effectors. Here, we report a systematic study of the regulatory action of the eleven GGDEF-EAL proteins in Xanthomonas oryzae pv. oryzicola, an important rice pathogen causing bacterial leaf streak. Mutational analysis revealed that XOC_2335 and XOC_2393 positively regulate bacterial swimming motility, while XOC_2102, XOC_2393 and XOC_4190 negatively control sliding motility. The ΔXOC_2335/XOC_2393 mutant that had a higher intracellular c-di-GMP level than the wild type and the ΔXOC_4190 mutant exhibited reduced virulence to rice after pressure inoculation. In vitro purified XOC_4190 and XOC_2102 have little or no diguanylate cyclase or phosphodiesterase activity, which is consistent with unaltered c-di-GMP concentration in ΔXOC_4190. Nevertheless, both proteins can bind to c-di-GMP with high affinity, indicating a potential role as c-di-GMP effectors. Overall our findings advance understanding of c-di-GMP signaling and its links to virulence in an important rice pathogen.

Mechanistic insights into host adaptation, virulence and epidemiology of the phytopathogenXanthomonas

“…oryzicola (Xoc) and Xoo. The effects of deletion/mutation of the genes encoding some of these proteins have been reported to effect virulence and biofilm formation (Wei et al 2016;Yang et al 2016;Su et al 2016b;Li et al 2018;Xue et al 2018). The majority of these proteins contain further domains that have a role in recognition of different environmental cues or comprise regulatory elements of two-component systems, such as the HD-GYP domain protein RpfG introduced above.…”

AmrZ is a major determinant of c-di-GMP levels in Pseudomonas fluorescens F113

“…GGDEF and EAL domains are often present in the same protein 14 . In these cases, proteins can either be bi-functional 15 or only one of the domains possesses catalytic activity 16 . Other proteins implicated in c-di-GMP related functions contain sensor or receptor domains, such as the PilZ domain 17 , among others.…”

A Symphony of Cyclases: Specificity in Diguanylate Cyclase Signaling

“…As this paradigm was examined in a progressively larger number of bacteria, many microbes were found to contain a surprising number of DGCs and PDEs, numbering past 60 in some cases (23). Critically, despite the sheer number of DGCs at work, many studies have demonstrated that most DGCs appear to specifically signal for one or two c-di-GMP-dependent processes, indicating some kind of mechanism(s) that allows a given DGC to activate a specific effector (25, 43, 47, 66, 67). These observations gave rise to tension between the idea that effectors can sense the c-di-GMP signal from a specific DGC, and the idea that any one DGC is making the same small, diffusible molecule as its sibling enzymes in the open space of the bacterial cytoplasm.…”