The periplasmic substrate-binding protein ThuE is required for sucrose uptake and multiplication of Pseudomonas syringae pv. tomato DC3000 in tomato leaves

Phytopathogenic bacteria depend on host-derived carbon for successful colonization of plant tissue. While sucrose is among the most abundant sugars in the leaf apoplast, the steps that limit its acquisition by Pseudomonas syringae are not known. In this study, we used base editing to generate mutants of six candidate sucrose utilization genes in P. syringae pv. tomato DC3000 (Pto). Loss of either the sucrose hydrolase ScrB or both levansucrases had no detectable effect, whereas the growth defect in the loss of the outer membrane porin mutant scry was overcome by raising external sucrose. Loss of the periplasmic substrate-binding protein ThuE impaired growth both in vitro and in planta, reducing bacterial populations to approximately two orders of magnitude lower in tomato leaves. Sucrose import through a single non-redundant inner membrane ABC transporter is therefore required for Pto multiplication in planta and serves as a potential target for controlling bacterial speck disease.