A c-di-AMP receptor mediates epithelial adhesion of Lactiplantibacillus plantarum.

Cyclic di-adenosine monophosphate (c-di-AMP) is a crucial second messenger used by bacteria to mediate bacterial-host interactions. However, its roles in Lactiplantibacillus plantarum remain poorly understood. Here, we identify RwpL, which consists solely of an HTH domain, as a c-di-AMP receptor in L. plantarum WCFS1. RwpL mediates epithelial adhesion of L. plantarum WCFS1 and functions as both a transcription inhibitor and activator, with transcriptional output determined by the position of its binding site relative to the transcription start site (TSS) of target genes. Specifically, RwpL inhibits wxlA transcription by binding downstream of its TSS, thus reducing WxlA interaction with fibronectin, a matrix protein on the surface of intestinal epithelia. In contrast, RwpL activates transcription of the matrix-degrading metalloprotease gene mmpL by recruiting the sigma factor RpoA upstream of its TSS. Notably, elevated c-di-AMP levels diminish RwpL binding affinity for both DNA and RpoA, thereby reversing its regulatory functions and enhancing L. plantarum adhesion to host epithelial cells. Together, our findings uncover a dual and reversible regulatory mechanism through which c-di-AMP modulates bacterial-host interactions in L. plantarum.