New insights into the regulation and roles of pectin methylesterases (PMEs)

Abstract: The plant primary cell wall is a complex structure, mainly composed of proteins and polysaccharides that play a central role controlling plant shape and development. Over the recent years, cell wall pectins have been reported as major actors regulating the mechanical properties of the cell wall that can mediate changes in growth. Pectins represent, depending on species and tissues, up to one third of the primary wall dry mass. They are complex polysaccharides rich in galacturonic acids and comprise four main domains: homogalacturonan (HG), rhamnogalacturonan-I (RG-I), rhamnogalacturonan-II (RG-II) and xylogalacturonan (XG). One key feature of HG, a homopolymer of α-1,4-linked-D-galacturonic acid units, is its degree of methylesterification and acetylesterification. In Arabidopsis, HG are indeed synthetized as a highly methylesterified form (up to 80% of methyl ester at the C-6 carboxyl) and a low acetylated form (up to 5-10% of acetyl ester at the O-2 or O-3 residues) in the Golgi apparatus, before being exported to the cell wall. The degree of methylesterification (DM) of pectins is subsequently temporally and spatially modulated in muro by the action of pectin methylesterases (PMEs, EC 3.1.1.11), which are in turn regulated through their 1:1 interaction with proteinaceous inhibitors called Pectin Methylesterase Inhibitors (PMEIs). Both PMEs and PMEIs are encoded by large multigenic families (respectively 66 and 76 members in Arabidopsis) which obviously questions the rationale for such abundance. Over the recent years, PMEs have been shown to play a key role in regulating developmental processes as diverse as primordia emergence at the shoot apical meristem, plant-pathogen interactions, pollen tube elongation, seed development, mucilage production and dark-grown hypocotyl elongation.

Novel elements related to the role and regulation of PMEs will be presented. This will include the biochemical and functional characterization of PME32, a pectin methylesterase which is ubiquitously expressed in dark-grown hypocotyls. In addition, Molecular Dynamics (MD) simulation was shown to be powerful tool to predict functional diversity between PMEIs, allowing the discovery of a strategy that may be used by PMEIs to inhibit PMEs in different micro-environmental conditions and paving the way to identify the specific role of PMEIs’ in muro.

Host: Leonardo Gomez