GROWTH CONTROL BY PECTIN METABOLISM IN PLANTS – GROWPEC

This project is targeted at elucidating the role of the fine control of the degree of methylesterification (DM) of the pectins of plant cell wall, and its impact on the regulation of the elongation capacity of a given organ. Pectins, which are rich in galacturonic acid, play a major role in regulating the physico-chemical properties of the cell wall, as well as plants' response to pathogen attack. Pectins physico-chemical properties are notably related to their degree of methylesterification, which is regulated within the cell wall, by pectin methylesterases (PMEs) and their inhibitors PMEIs (PME inhibitor). The DM of pectins is an important determinant of their sensitivity to pectic degrading enzymes such as polygalacturonases (PGs) or pectin/pectate lyases (PLs). This pectic turnover can therefore lead to the formation of signalling molecules such as oligo-galacturonides (OGA), which could, in addition, play a role in the regulation of growth processes. It is likely that pectin turnover play as well a major role in modifying the pectic network that could changes the cell wall mechanical properties. The project will investigate the role of each of the three phenomena (DM and/or pectin turnover and/or OGA signalling), acting synergistically or not, in determining cell elongation capacity. Our hypothesis is that the composition and structure of cell wall is, together with the changes in cell turgescence, one of the major events that can determine the capacity of a given cell to elongate at a given rate. For this project, the three partners will use a simple experimental model, Arabidopsis hypocotyl grown in the dark, which easily allows the integration of developmental and cell biology, genetics, biochemistry and biophysics in a single system. This model is characterized by a very localised and regulated cell elongation, in absence of cell division. Preliminary results obtained by the partners have shown that major changes in cell wall structure and in the expression of genes encoding pectin remodelling enzymes (PME, PMEI, PG and PL) occur at very specific phases of cell growth. The project will define the specific role of these enzymes in changing pectin structure at specific developmental stages. The project will allow, using a multidisciplinary approach (from gene regulation and enzyme activities to cell wall structure and mechanical properties) to propose a coherent mechanistic model of the differences, on the basis of pectic network, between slow and rapid elongating cells. This is of the utmost importance, with regards to the current lack of information concerning those aspects in the literature, to understand organ growth regulation in plants. This project is organised with three partners (Univ. Amiens; INRA Versailles and Univ. Rouen), which have been collaborating in the field of pectin research for several years. They will bring their knowledge to complete the project in a timely manner.