AtPME17 is a functionalArabidopsis thalianapectin methylesterase regulated by its PRO region that triggers PME activity in the resistance toBotrytis cinerea

Pectin is synthesized in a highly methylesterified form in the Golgi cisternae and partially de-methylesterified in muro by pectin methylesterases (PMEs).Arabidopsis thalianaproduces a local and strong induction of PME activity during the infection of the necrotrophic fungusBotrytis cinerea. AtPME17 is a putativeA. thalianaPME highly induced in response toB. cinerea. Here, a fine tuning of AtPME17 expression by different defence hormones was identified. Our genetic evidence demonstrates that AtPME17 strongly contributes to the pathogen-induced PME activity and resistance againstB. cinereaby triggering jasmonic acid-ethylene-dependentPDF1.2expression. AtPME17 belongs to group 2 isoforms of PMEs characterized by a PME domain preceded by an N-terminal PRO region. However, the biochemical evidence for AtPME17 as a functional PME is still lacking and the role played by its PRO region is not known. Using thePichia pastorisexpression system, we demonstrate that AtPME17 is a functional PME with activity favoured by an increase in pH. AtPME17 performs a blockwise pattern of pectin de-methylesterification that favours the formation of egg-box structures between homogalacturonans. Recombinant AtPME17 expression inEscherichia colireveals that the PRO region acts as an intramolecular inhibitor of AtPME17 activity.