Ralstonia solanacearumalters root developmental programs in auxin-dependent and independent manners

Abstract

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 soil-borne 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.

A bacterial type III effector targets plant vesicle‐associated membrane proteins

“…Traditional soil‐drenching assays, in which virulence is measured according to the development of wilting symptoms upon bacterial inoculation on the soil, showed a slightly enhanced susceptibility of the ccoaomt1‐1 mutant compared with wild‐type plants (Figures 6a,b and S7 ). In order to enhance the sensitivity and accuracy of R. solanacearum inoculation assays in Arabidopsis, we have recently developed an in vitro inoculation system where bacteria are placed on the root surface near the root tip of Arabidopsis seedlings grown on solid Murashige and Skoog (MS) medium and bacterial colonization is measured by quantifying bacterial numbers in shoot tissues (Dindas et al, 2022 ; Xue et al, 2022 ). Compared with wild‐type plants, the ccoaomt1‐1 mutant showed slightly but significantly enhanced susceptibility to R. solanacearum colonization (Figure 6c ).…”

“…Arabidopsis wild‐type Col‐0 plants and transgenic lines RipD #1 and RipD #2 used in this study were grown under short‐day conditions (10 h light/14 h darkness, 22°C, 100–150 mmol m −2 s −1 ) and long‐day conditions (16 h light/8 h darkness, 22°C, 100–150 mmol m −2 s −1 ) for phenotyping. In the experiments with Arabidopsis seedlings on agar plates, the seedlings in ½× MS medium and MS solid medium (4.4 g/L MS medium with vitamins, 0.5 g/L MES, 8 g/L Bacto agar, pH 5.8) (Lu et al, 2018 ; Xue et al, 2022 ) were kept in a growth chamber (16 h light/8 h darkness, 22°C, 100–150 mmol m −2 s −1 ).…”

“…In vitro inoculation assays to quantify R. solanacearum growth in Arabidopsis seedlings were performed as previously described (Lu et al, 2018 ; Xue et al, 2022 ) with small modifications. Eight‐day‐old Arabidopsis seedlings (5 days on ½× MS solid agar plates and then 3 days on MS solid agar plates) were used for inoculation.…”