A YajQ‐LysR‐like, cyclic di‐GMP‐dependent system regulating biosynthesis of an antifungal antibiotic in a crop‐protecting bacterium, Lysobacter enzymogenes

YajQ, a binding protein of the universal bacterial second messenger cyclic di‐GMP (c‐di‐GMP), affects virulence in several bacterial pathogens, including Xanthomonas campestris. In this bacterium, YajQ interacts with the transcription factor LysR. Upon c‐di‐GMP binding, the whole c‐di‐GMP‐YajQ‐LysR complex is found to dissociate from DNA, resulting in virulence gene regulation. Here, we identify a YajQ‐LysR‐like system in the bacterial biocontrol agent Lysobacter enzymogenes OH11 that secretes an antifungal antibiotic, heat‐stable antifungal factor (HSAF) against crop fungal pathogens. We show that the YajQ homologue, CdgL (c‐di‐GMP receptor interacting with LysR) affects expression of the HSAF biosynthesis operon by interacting with the transcription activator LysR. The CdgL‐LysR interaction enhances the apparent affinity of LysR to the promoter region upstream of the HSAF biosynthesis operon, which increases operon expression. Unlike the homologues CdgL (YajQ)‐LysR system in X. campestris, we show that c‐di‐GMP binding to CdgL seems to weaken CdgL‐LysR interactions and promote the release of CdgL from the LysR‐DNA complex, which leads to decreased expression. Together, this study takes the YajQ‐LysR‐like system from bacterial pathogens to a crop‐protecting bacterium that is able to regulate antifungal HSAF biosynthesis via disassembly of the c‐di‐GMP receptor–transcription activator complex.