The transcription regulator ChpA affects the global transcriptome including quorum sensing-dependent genes in Ralstonia pseudosolanacearum strain OE1-1

The gram-negative plant-pathogenic p- proteobacterium Ralstonia pseudosolanacearum strain OE1- 1 produces methyl 3-hydroxymyristate as a quorum sensing (QS) signal through methyltransferase PhcB and senses the chemical via the sensor histidine kinase PhcS. This leads to activation of the LysR family transcription regulator PhcA, which regulates the genes (QS-dependent genes) responsible for QS-dependent phenotypes, including virulence. The transcription regulator ChpA, which possesses a response regulator receiver domain and also a hybrid sensor histidine kinase/response regulator phosphore-acceptor domain but lacks a DNA-binding domain, is reportedly involved in QS-dependent biofilm formation and virulence of R. pseudosolanacearum strain GMI1000. To explore the function of ChpA in QS of OE1- 1, we generated a chpA- deletion mutant (?chpA) and revealed that the chpA deletion leads to significantly altered QS-dependent phenotypes. Furthermore, ?chpA exhibited a loss in its infectivity in xylem vessels of tomato plant roots, losing virulence on tomato plants, similar to the phcA- deletion mutant (?phcA). Transcriptome analysis showed that the transcript levels of phcB, phcQ, phcR, and phcA in AchpA were comparable to those in OE1- 1. However, the transcript levels of 89.9% and 88.9% of positively and negatively QS-dependent genes, respectively, were significantly altered in ?chpA compared with OE1- 1. Furthermore, the transcript levels of these genes in ?chpA were positively correlated with those in ?phcA. Together, our results suggest that ChpA is involved in the regulation of these QS-dependent genes, thereby contributing to the behaviour in host plant roots and virulence of OE1- 1.

Automated summary

Research shows that the protein ChpA regulates QS-dependent genes and affects the behavior in host plant roots and virulence of pathogenic bacterium Ralstonia pseudosolanacearum OE1-1.