A plant sugar transporter contributes to powdery mildew resistance in legumes

Obligate biotrophic fungal pathogens establish long-term feeding relationships with their plant host, during which they siphon sugars from host cells through haustoria. The Arabidopsis hexose transporter, STP13 (sugar transport protein 13), was previously shown to confer resistance against hemi-biotrophic and necrotrophic pathogens by limiting sugar flux towards these pathogens. By contrast, expression of Lr67res, a transport-deficient STP13 variant carrying two amino acid substitutions, conferred resistance against biotrophic fungi in wheat and barley. A research article published in Plant and Cell Physiology by Dr. Chandran’s group provides novel insights into the role of STP13 and its variant in powdery mildew resistance in legumes.

The study showed that the Medicago truncatula STP13.1 is a proton-hexose symporter involved in basal resistance against the pea powdery mildew Erysiphe pisi, and that Lr67res-mediated resistance, so far reported only in monocots, is transferable to legumes. Among the 30 MtSTP genes, MtSTP13.1 exhibited the the highest fold-induction in leaves challenged by powdery mildew. Functional assays in yeast showed that the introduction of the Lr67res-specific G144R mutation but not V388L abolished MtSTP13.1’s hexose uptake ability. Virus-induced gene silencing of MtSTP13 repressed expression of defense-associated genes and enhanced PM susceptibility in M. truncatula whereas transient overexpression of MtSTP13.1 or MtSTP13.1^G144R in pea induced the expression of defense genes and enhanced PM resistance. Based on the findings, a model in which STP13.1-mediated sugar signaling triggers defense responses against PM in legumes is proposed. This is the first report which demonstrates the role of the Lr67res-specific mutation in a dicot plant, indicating its broad applicability in powdery mildew disease management.

Full article: https://doi.org/10.1093/pcp/pcab021