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CELL BIOLOGY AND SIGNAL TRANSDUCTION

Overexpression of Pectin Methylesterase Inhibitors in Arabidopsis Restricts Fungal Infection by Botrytis cinerea^1,[C],[W]

Dipartimento di Biologia Vegetale, Università di Roma "La Sapienza," 00185 Rome, Italy (V.L., F.C., D.B.); Dipartimento Territorio e Sistemi Agro-Forestali, Research Group Plant Pathology, Università di Padova, 35020 Legnaro, Padua, Italy (A.R., F.F.); Istituto di Biochimica delle Proteine, Consiglio Nazionale delle Ricerche, 80131 Naples, Italy (L.C.); Dipartimento di Biochimica e Biofisica, Seconda Università degli Studi di Napoli, 80138 Naples, Italy (A.G.); European Patent Office, 80339 Munich, Germany (N.O.); and Michigan State University/United States Department of Energy Plant Research Laboratory, Michigan State University, East Lansing, Michigan 48824–1312 (M.P.)

Pectin, one of the main components of plant cell wall, is secreted in a highly methylesterified form and is demethylesterified in muro by pectin methylesterase (PME). The action of PME is important in plant development and defense and makes pectin susceptible to hydrolysis by enzymes such as endopolygalacturonases. Regulation of PME activity by specific protein inhibitors (PMEIs) can, therefore, play a role in plant development as well as in defense by influencing the susceptibility of the wall to microbial endopolygalacturonases. To test this hypothesis, we have constitutively expressed the genes AtPMEI-1 and AtPMEI-2 in Arabidopsis (Arabidopsis thaliana) and targeted the proteins into the apoplast. The overexpression of the inhibitors resulted in a decrease of PME activity in transgenic plants, and two PME isoforms were identified that interacted with both inhibitors. While the content of uronic acids in transformed plants was not significantly different from that of wild type, the degree of pectin methylesterification was increased by about 16%. Moreover, differences in the fine structure of pectins of transformed plants were observed by enzymatic fingerprinting. Transformed plants showed a slight but significant increase in root length and were more resistant to the necrotrophic fungus Botrytis cinerea. The reduced symptoms caused by the fungus on transgenic plants were related to its impaired ability to grow on methylesterified pectins.

² These authors contributed equally to the paper.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Daniela Bellincampi (daniela.bellincampi{at}uniroma1.it).

^[C] Some figures in this article are displayed in color online but in black and white in the print edition.

^[W] The online version of this article contains Web-only data.

www.plantphysiol.org/cgi/doi/10.1104/pp.106.090803

^* Corresponding author; e-mail daniela.bellincampi{at}uniroma1.it; fax 39–06–49912446.

Received October 5, 2006; accepted January 26, 2007; published February 2, 2007.

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