Pectin methylesterases affect plant resistance to pathogens

Pectin is synthesized in a highly methyl esterified form and is de-esterified in muro by pectin methyl esterases (PMEs). The degree and pattern of methyl esterification affect the cell wall structure and properties with consequences on their resistance to pathogens. We show that PME is required for the initial plant tissue colonization by fungal and bacterial necrotrophs, making pectin more susceptible to the action of the hydrolytic enzymes of the pathogens. We have reduced the susceptibility of plants to pathogens by increasing the methyl esterification of pectin through the overexpression of PME inhibitors (PMEI). A natural Arabidopsis ecotype, showing a higher pectin esterification and lower homogalacturonan content than the reference ecotype Col-0 is more resistant to necrotrophic fungal and bacterial pathogens. PME is also required for viral cell-to-cell and long-distance movement of plant virus. Our results support the notion that PME activity affects the mechanical properties of cell wall and plant resistance against pathogens.