A Pectin Methylesterase Inhibitor Enhances Resistance to Wilt.

Pectins are major components of the primary plant cell wall, which functions as the primary barrier against pathogens. Pectin methylesterases (PMEs) catalyze the demethylesterification of the homogalacturonan domains of pectin in the plant cell wall. Their activity is regulated by PME inhibitors (PMEIs). Here, we provide evidence that the pectin methylesterase-inhibiting protein GhPMEI3 from cotton () functions in plant responses to infection by the fungus GhPMEI3 interacts with PMEs and regulates the expression of a specific fungal polygalacturonase (VdPG1). Ectopic expression of GhPMEI3 increased pectin methyl esterification and limited fungal disease in cotton, while also modulating root elongation. Enzymatic analyses revealed that GhPMEI3 efficiently inhibited the activity of cotton GhPME2/GhPME31. Experiments using transgenic Arabidopsis () plants expressing the gene under the control of the CaMV 35S promoter revealed that GhPMEI3 inhibits the endogenous PME activity in vitro. Moreover, the enhanced resistance to was associated with altered expression. Virus-induced silencing of resulted in increased susceptibility to Further, we investigated the interaction between GhPMEI3 and GhPME2/GhPME31 using inhibition assays and molecular docking simulations. The peculiar structural features of GhPMEI3 were responsible for the formation of a 1:1 stoichiometric complex with GhPME2/GhPME31. Together, these results suggest that GhPMEI3 enhances resistance to wilt. Moreover, GhPMEI3-GhPMEs interactions would be needed before drawing the correlation between structure-function and are crucial for plant development against the ever-evolving fungal pathogens.