Methyl 3-Hydroxymyristate, a Diffusible Signal Mediating phc Quorum Sensing in Ralstonia solanacearum

Ralstonia solanacearum, a plant pathogenic bacterium causing bacterial wilt on crops, uses a quorum sensing (QS) system consisting of phc regulatory elements to control its virulence. Methyl 3-hydroxypalmitate (3-OH PAME) was previously identified as the QS signal in strain AW1. However, 3-OH PAME has not been reportedly detected from any other strains, and this suggests that they produce another unknown QS signal. Here we identify (R)-methyl 3-hydroxymyristate [(R)-3-OH MAME] as a new QS signal that regulates the production of virulence factors and secondary metabolites. (R)-3-OH MAME was synthesized by the methyltransferase PhcB and sensed by the histidine kinase PhcS. The phylogenetic trees of these proteins from R.solanacearum strains were divided into two groups, according to their QS signal types(R)-3-OH MAME or (R)-3-OH PAME. These results demonstrate that (R)-3-OH MAME is another crucial QS signal and highlight the unique evolution of QS systems in R.solanacearum.