Tuning of pectin methylesterification: consequences for cell wall biomechanics and development

Abstract

Recent publications have increased our knowledge of how pectin composition and the degree of homogalacturonan methylesterification impact the biochemical and biomechanical properties of plant cell walls, plant development, and plants' interactions with their abiotic and biotic environments. Experimental observations have shown that the relationships between the DM, the pattern of de-methylesterificaton, its effect on cell wall elasticity, other biomechanical parameters, and growth are not straightforward. Working towards a detailed understanding of these relationships at single cell resolution is one of the big tasks of pectin research. Pectins are highly complex polysaccharides abundant in plant primary cell walls. New analytical and microscopy techniques are revealing the composition and mechanical properties of the cell wall and increasing our knowledge on the topic. Progress in plant physiological research supports a link between cell wall pectin modifications and plant development and interactions with the environment. Homogalacturonan pectins, which are major components of the primary cell wall, have a potential for modifications such as methylesterification, as well as an ability to form cross-linked structures with divalent cations. This contributes to changing the mechanical properties of the cell wall. This review aims to give a comprehensive overview of the pectin component homogalacturonan, including its synthesis, modification, regulation and role in the plant cell wall.

Gradients in Wall Mechanics and Polysaccharides along Growing Inflorescence Stems

“…A recent study that combined extensometry with atomic force microscopy and different forms of cell wall strain showed that both cellulose microfibrils and matrix polymers, predominantly pectins, bear the tensile load of elastically stretched onion walls (Zhang et al, 2017). This confirms the mechanical significance of the matrix at the molecular scale and adds impetus to recent interest in the state of pectins in growing cell walls and the need for better models of cell wall mechanics (Peaucelle et al, 2012;Xiao et al, 2014;Levesque-Tremblay et al, 2015).…”

POLYGALACTURONASE INVOLVED IN EXPANSION3 Functions in Seedling Development, Rosette Growth, and Stomatal Dynamics in Arabidopsis thaliana

“…In PGX3 OE plants, HG molecules are smaller due to excessive PGX3 expression and more pectin degradation, which, together with the observation that there is less demethylesterified HG, leads to enhanced pectin fluidity, increased rosette size, and faster stomatal opening. (Amsbury et al, 2016), but it is currently mysterious how PME6 regulates these mechanics because removing methyl groups from pectins might result in either wall stiffening or loosening, depending on the patterns of demethylesterification (Levesque-Tremblay et al, 2015;Hocq et al, 2017). Additionally, PME34 has been implicated in stomatal responses to heat stress in Arabidopsis (Huang et al, 2017), suggesting that multiple pectin methylesterases might modulate pectin cross-linking and/or degradability in guard cell walls, adding an additional layer of complexity and control.…”

Monitoring Polysaccharide Dynamics in the Plant Cell Wall

“…The Arabidopsis genome contains more than 170 HG-related enzymes (Sénéchal et al, 2014), although the precise roles of only a few have been characterized to date. HG methylesterification status plays important roles in various developmental processes and is controlled tightly by pectin methylesterases (PMEs), PME inhibitors (PMEIs), subtilisin-type Ser proteases (SBTs), and at least one E3 ubiquitin ligase (Levesque-Tremblay et al, 2015). Mutants with altered expression of these players have been characterized using mAbs directed against HG domains with different degrees of methylesterification.…”