Ralstonia solanacearum Alters Root Developmental Programmes in Auxin-Dependent and -Independent Manners

Microbial pathogens and other parasites can modify the development of their hosts, either as a target or a side effect of their virulence activities. The plant-pathogenic bacterium Ralstonia solanacearum, causal agent of the devastating bacterial wilt disease, is a soilborne microbe that invades host plants through their roots and later proliferates in xylem vessels. In this work, we studied the early stages of R. solanacearum infection in the model plant Arabidopsis thaliana, using an in vitro infection system. In addition to the previously reported inhibition of primary root length and increase in root hair formation at the root tip, we observed an earlier xylem differentiation during R. solanacearum infection that occurs in a HrpG-dependent manner, suggesting that the pathogen actively promotes the development of the vascular system upon invasion of the root. Moreover, we found that the phytohormone auxin, of which the accumulation is promoted by the bacterial infection, is required for the R. solanacearum-triggered induction of root hair formation but not earlier xylem differentiation. Altogether, our results shed light on the capacity of R. solanacearum to induce alterations of root developmental pathways and on the role of auxin in this process.