Agrobacteria reprogram virulence gene expression by controlled release of host-conjugated signals.

It is highly intriguing how bacterial pathogens can quickly shut down energy-costly infection machinery once successful infection is established. This study depicts that mutation of repressor SghR increases the expression of hydrolase SghA in , which releases plant defense signal salicylic acid (SA) from its storage form SA β-glucoside (SAG). Addition of SA substantially reduces gene expression of bacterial virulence. Bacterial genes and are differentially transcribed at early and later infection stages, respectively. Plant metabolite sucrose is a signal ligand that inactivates SghR and consequently induces expression. Disruption of leads to increased expression and enhances tumor formation whereas mutation of decreases expression and tumor formation. These results depict a remarkable mechanism by which taps on the reserved pool of plant signal SA to reprogram its virulence upon establishment of infection.