One-component systems were the simplest and the most effective signaling mechanism in bacteria. Per-ARNT-Sim (PAS) domains were important modules that play crucial roles in light or oxygen or redox signaling in bacteria, and most characterized GGDEF proteins involved in cyclic di-GMP (c-di-GMP) synthesis played crucial roles in c-di-GMP signaling in bacteria. In Xanthomonas campestris pv. Campestris (Xcc), xvgA encoded a protein containing both a PAS and a GGDEF domains. Deletion of xvgA altered bacterial morphology and significantly reduced not only Xcc virulence but also bacterial growth, the growth assays under different light conditions indicated that XvgA involved in light (red or far-red) signaling in Xcc. XvgA had been shown to possess diguanylate cyclase (DGC) activity that converted GTP to c-di-GMP in vitro. Moreover, the PAS domain was necessary for its DGC activity, and glutamic acid 98 (E98) site in the PAS domain was an active site, which was verified with bioinformatics and biochemical assays in vitro. These findings indicated that XvgA was an important one-component system involved in c-di-GMP and light signaling, which contributed to regulate Xcc growth, motility and virulence.
Key words: Xcc, PAS domain, c-di-GMP, one-component system.
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