Demethylesterification of the Primary Wall by PECTIN METHYLESTERASE35 Provides Mechanical Support to the Arabidopsis Stem

Abstract

Secondary cell walls, which contain lignin, have traditionally been considered essential for the mechanical strength of the shoot of land plants, whereas pectin, which is a characteristic component of the primary wall, is not considered to be involved in the mechanical support of the plant. Contradicting this conventional knowledge, loss-of-function mutant alleles of Arabidopsis thaliana PECTIN METHYLESTERASE35 (PME35), which encodes a pectin methylesterase, showed a pendant stem phenotype and an increased deformation rate of the stem, indicating that the mechanical strength of the stem was impaired by the mutation. PME35 was expressed specifically in the basal part of the inflorescence stem. Biochemical characterization showed that the activity of pectin methylesterase was significantly reduced in the basal part of the mutant stem. Immunofluorescence microscopy and immunogold electron microscopy analyses using JIM5, JIM7, and LM20 monoclonal antibodies revealed that demethylesterification of methylesterified homogalacturonans in the primary cell wall of the cortex and interfascicular fibers was suppressed in the mutant, but lignified cell walls in the interfascicular and xylary fibers were not affected. These phenotypic analyses indicate that PME35-mediated demethylesterification of the primary cell wall directly regulates the mechanical strength of the supporting tissue.

Xyloglucan Deficiency Disrupts Microtubule Stability and Cellulose Biosynthesis in Arabidopsis, Altering Cell Growth and Morphogenesis

“…A remaining challenge is to precisely determine how alteration of wall composition and organization alters wall mechanical properties in the xxt1 xxt2 mutant, given that recent data have shown that wall stiffness is also decreased in two Arabidopsis cellulose-deficient mutants, prc1-1 and prc1-1/the1 , and that pectin modification, especially pectin demethylation, can likewise alter mechanical strength in Arabidopsis stems (Hongo et al, 2012). xxt1 xxt2 walls are more extensible than Col walls upon treatment with pectindegrading enzymes (Park and Cosgrove, 2012a), further supporting the function of pectins in regulating wall biomechanics.…”

A Rice PECTATE LYASE-LIKE Gene Is Required for Plant Growth and Leaf Senescence

“…Pectins are major components of the plant primary cell wall and middle lamella and have several functions, including involvement in maintaining plant growth and development, promoting cell-to-cell adhesion, providing structural support in soft tissues, defense responses, and influencing wall porosity and thickness, etc (Ridley et al, 2001;Iwai et al, 2002;Ogawa et al, 2009;Wolf et al, 2009;Hongo et al, 2012). Pectins may be the most complex polysaccharide family in the living world, being composed of as many as 17 different monosaccharides and having more than 20 different linkages (Bonnin et al, 2014).…”

Cell wall polysaccharide distribution in Miscanthus lutarioriparius stem using immuno-detection

“…5l). The demethylesterification of HG in the base stem of Arabidopsis can strengthen the support structure (Hongo et al 2012). Thus, we suspected a similar function of partially Me/deesterified HG in the strength of M. lutarioriparius stem.…”

“…For example, the signal of less methyl-esterified HG recognized by JIM5 monoclonal antibody shows stronger intensity in the basal cortical than upper cortical of Arabidopsis stem, and the pme35-1 mutant involved in demethylesterification of HG in the basal cortical exhibits a pendant stem phenotype, suggesting that ME (methyl esterification) degree of HG could regulate the mechanical strength of Arabidopsis stem (Hongo et al 2012). The presence or absence of weakly ME-HGs and fucosylated xyloglucans in intervessel pit membranes might contribute to Pierce's disease susceptibility in grapevine (Sun et al 2011).…”