A LysR-type regulator influencing swimming motility, galactose utilization, and virulence in Ralstonia solanacearum GMI1000

Background LysR-type transcriptional regulators (LTTRs) are one of the largest families of regulators in prokaryotic organism, which help the bacterium adapt to diverse conditions by controlling a wide array of regulons, encompassing genes responsible for nitrogen and carbon fixation, oxidative stress response, bacterial virulence, and the breakdown of diverse compounds. Ralstonia solanacearum strain GMI1000 possesses 80 LTTR genes, yet the precise roles and functional contributions of only three of these LTTRs have been conclusively established among the total. In this work, our group reveal a novel LTTR member LysR7 (RS_RS02375) that exerts multiple regulatory roles in motility, carbon metabolism and virulence. Results In this investigation, an in-frame deletion mutant Delta lysR7 and a complemented strain C Delta lysR7 were prepared. The mutant Delta lysR7 had increased swimming motility on semi-soft medium and showed a reduced replication rate in nutrient-rich medium and in planta. Moreover, Delta lysR7 was unable to grow on nutrient-limited medium, supplemented with galactose as a single carbon resource. RT-qPCR analysis and GUS activity detection indicated that the expression of lysR7 was induced in the presence of galactose. The mutant Delta lysR7 caused weaker wilt disease on either Solanum lycopersicum or Capsicum annuum plants compared to both wild type GMI1000 and C Delta lysR7. Transcriptome analysis revealed that 12 upregulated and 8 downregulated differentially expressed genes (DEGs) in Delta lysR7 were restored in C Delta lysR7 relative to wild type. In particular, the expression of hrpG, a key gene responsible for type III secretion system, was downregulated. KEGG analysis revealed that, except for lysR7 gene, the 19 DEGs were most enriched in microbial metabolism in diverse environments and metabolic pathways. Conclusions The data indicate that LysR7 regulates multiple processes in association with motility, galactose metabolism and virulence in R. solanacearum. The study offers valuable evidence to understand comprehensive regulatory mechanisms mediated by LTTR family members in R. solanacearum.