VvPMEI1 GENE ENCODES A NOVEL FUNCTIONAL CELL WALL PECTIN METHYL ESTERASE INHIBITOR INVOLVED IN GRAPE BERRY DEVELOPMENT

Pectin is secreted in a highly methyl esterified form and partially de-methyl esterified in cell wall by pectin methyl esterases (PMEs). PME activity is expressed during plant growth, development and biotic stresses. At post-transcriptional level, PME activity is controlled by proteins named PME inhibitors (PMEIs). We have identified, expressed and characterized VvPMEI1, a new functional PME inhibitor of Vitis vinifera. VvPMEI1 typically affects the activity of plant PMEs and is inactive against microbial PMEs. The kinetics of PMEI-PME interaction, studied by surface plasmon resonance, indicate that the inhibitor strongly interacts with immobilized PME at apoplastic pH while the stability of the complex is reduced by increasing the pH. The analysis of VvPMEI1 expression in different grapevine tissues and during grape fruit development suggests that this inhibitor controls PME activity manly during the earlier phase of berry development. A proteomic analysis performed at this stage identifies a PME isoform as possible target of VvPMEI1.