# Root exudate monosaccharides modulate the pathogenicity of Ralstonia pseudosolanacearum

## TL;DR

This study shows that galactose, a sugar in plant root exudates, increases the pathogenicity of a soil-borne bacterial pathogen by altering its gene expression and metabolism.

## Contribution

The study reveals that galactose specifically enhances the virulence of Ralstonia pseudosolanacearum through up-regulation of effectors and nitrogen metabolism.

## Key findings

- Galactose up-regulates type III secreted effectors in Ralstonia pseudosolanacearum.
- Galactose induces nitrogen metabolism, producing reactive nitrogen species that may enhance pathogenicity.
- Metabolites from galactose-induced cultures cause cell death in tobacco leaves.

## Abstract

The Ralstonia solanacearum species complex (RSSC) is a devastating soil-borne pathogen that causes bacterial wilt in solanaceous crops. However, the response of RSSC to monosaccharides—key components of root exudates released into the rhizosphere—remains unclear. We supplemented culture media with several typical monosaccharides derived from tobacco root exudates to mimic rhizosphere signals and examined their effect on the expression of bacterial virulence factors. Transcriptome analysis revealed that galactose markedly altered the physiological status of RSSC, inducing a state resembling that during plant infection. Among the monosaccharides tested, galactose specifically up-regulated the expression of type III secreted effectors. Notably, galactose also actively induced nitrogen metabolism, leading to the production of nitrous oxide and other reactive nitrogen species, which may, like reactive oxygen species, enhance pathogenicity. Furthermore, metabolites extracted from galactose-induced RSSC cultures triggered cell death when infiltrated into tobacco leaves.