P-335 - Functional Analysis of Three Quorum Sensing Systems in Burkholderia plantarii, the Causal Agent of Rice Seedling Blight

Many gram-negative bacteria regulate the expression of virulence factors through quorum sensing (QS) mediated by acylhomoserine lactones (AHLs). In plant-pathogenic gram-negative bacteria, QS regulates key pathogenic traits such as toxin production, biofilm formation, and swarming motility. Burkholderia plantarii, the causal agent of rice seedling blight, possesses three QS gene pairs, plaI1/plaR1, plaI2/plaR2, and plaI3/plaR3. Although the plaI1/plaR1 system has been previously characterized, the functions of the other two QS systems remain unclear. In this study, we generated QS-deficient mutants of the B. plantarii type strain MAFF 301723 to investigate the roles of each QS gene pair in AHL biosynthesis and regulation of virulence factors. The plaI1/plaR1 system seems to be the primary QS regulatory pathway in MAFF 301723 and utilizes N-octanoyl-l-homoserine lactone (C8-HSL) to regulate swarming motility and biofilm formation. In contrast, the plaI2/plaR2 system did not regulate any general function, although PlaI2 was found to be capable of producing N-3-hydroxydecanoyl-l-homoserine lactone (3-OH-C10-HSL). Notably, the plaI3/plaR3 system plays a crucial role in the biosynthesis of the phytopathogenic toxin tropolone through the production of putative AHL, such as N-hexadecanoyl-l-homoserine lactone with two double bonds (C16:2-HSL). These findings provide new insights into QS regulatory networks in the virulence regulation of B. plantarii.