Functional analysis of three quorum sensing systems in Burkholderia plantarii , the causal agent of rice seedling blight

Numerous Gram-negative bacteria possess N-acyl-L-homoserine lactone (AHL)-mediated quorum-sensing (QS) systems that regulate the activation of specific genes. Burkholderia plantarii causes rice seedling blight by producing the phytotoxin tropolone. In this study, we investigated multiple AHL-type QS systems in B. plantarii MAFF 301723T and their involvement in virulence regulation. MAFF 301723 harbors three AHL-mediated QS systems, designated plaI1/plaR1, plaI2/plaR2, and plaI3/plaR3. The plaI1/plaR1 system, which produces N-octanoyl-l-homoserine lactone, is functional and essential for swarming motility. When forced expression of plaI2 induces the biosynthesis of 3-OH-C10-HSL, it was suggested that expression is rarely observed in wild-type MAFF 301723. The plaI3 gene directs the synthesis of the putative C16:2-HSL, which is a rare AHL bearing two double bonds in the hexadecanoyl chain that has not been previously reported in Burkholderia spp. The plaI3/plaR3-QS system is crucial for tropolone production. These findings suggest that multiple QS systems collectively contribute to the complex virulence regulation of B. plantarii, thereby providing new insights into the development of QS-targeted biocontrol strategies for agriculture.