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

Abstract

ORCID IDs: 0000-0003-4379-4173 (J.Z.W.); 0000-0001-7481-3571 (C.T.A.)Plant cell separation and expansion require pectin degradation by endogenous pectinases such as polygalacturonases, few of which have been functionally characterized. Stomata are a unique system to study both processes because stomatal maturation involves limited separation between sister guard cells and stomatal responses require reversible guard cell elongation and contraction. However, the molecular mechanisms for how stomatal pores form and how guard cell walls facilitate dynamic stomatal responses remain poorly understood. We characterized POLYGALACTURONASE INVOLVED IN EXPANSION3 (PGX3), which is expressed in expanding tissues and guard cells. PGX3-GFP localizes to the cell wall and is enriched at sites of stomatal pore initiation in cotyledons. In seedlings, ablating or overexpressing PGX3 affects both cotyledon shape and the spacing and pore dimensions of developing stomata. In adult plants, PGX3 affects rosette size. Although stomata in true leaves display normal density and morphology when PGX3 expression is altered, loss of PGX3 prevents smooth stomatal closure, and overexpression of PGX3 accelerates stomatal opening. These phenotypes correspond with changes in pectin molecular mass and abundance that can affect wall mechanics. Together, these results demonstrate that PGX3-mediated pectin degradation affects stomatal development in cotyledons, promotes rosette expansion, and modulates guard cell mechanics in adult plants.

Multitrait genome‐wide association analysis of Populus trichocarpa identifies key polymorphisms controlling morphological and physiological traits

“…Downregulation of GAUT4 in P. deltoides resulted in decreased pectic homogalacturonan and rhamnogalacturonan II and increased plant height, diameter, leaf area, and biomass (Biswal et al, 2018a). Additional evidence supporting increased leaf growth with decreases in pectin is provided by reports of increased expansion of Arabidopsis rosette leaves resulting from overexpression of polygalacturonase, an enzyme that degrades pectic homogalacturonan (Rui et al, 2017).…”

Monitoring Polysaccharide Dynamics in the Plant Cell Wall

“…Both PI and the oligosaccharide probes can label HG in less than 20 min to provide an unprecedented resolution of HG dynamics in living cells. Recently, HG dynamics were visualized using COS conjugated with Alexa Fluor 488 (COS 488 ) and PI probes in guard cells lacking or overexpressing the PGX3 polygalacturonase (Rui et al, 2017). Although COS 488 and PI labeled only partially overlapping regions of the wall, they both supported an inverse relationship between the presence of PGX3 and unesterified HG.…”

“…Although COS 488 and PI labeled only partially overlapping regions of the wall, they both supported an inverse relationship between the presence of PGX3 and unesterified HG. Additionally, COS 488 and PI were more sensitive for quantifying GalA epitopes in three dimensions, compared with indirect labeling of fixed cells with mAbs (LM19, LM20, and 2F4; Rui et al, 2017). Therefore, these new probes are compelling alternatives to mAbs and should be exploited further.…”

“…While the egg-box model predicts that PME activity increases the stiffness of the pectic matrix, the atomic force microscopy experiments found that demethylesterification of HG promoted wall loosening and was a prerequisite for organ initiation (Peaucelle et al, 2011). Therefore, unesterified HG in growing cells is likely targeted by pectincleaving enzymes such as the recently identified polygalacturonanses involved in cell expansion (PGX1, PGX2, and PGX3), which are required for the development of multiple Arabidopsis organs (Xiao et al, 2014Rui et al, 2017).…”

A wall with integrity: surveillance and maintenance of the plant cell wall under stress

“…The primary wall of growing cells is a three-dimensional dynamic network composed of cellulose, hemicelluloses, pectins and a small amount of structural proteins (Somerville et al, 2004;Cosgrove, 2005;Lampugnani et al, 2018). Pectin chemistrysuch as HG de-methylesterification, Ca 2+ -mediated HG crosslinking, and borate crosslinking of RG-IIaffects the stiffness of the wall and, as a result, cell and organ growth (O'Neill et al, 2001;Peaucelle et al, 2008Peaucelle et al, , 2011Peaucelle et al, , 2015Qi et al, 2017;Rui et al, 2017;Bou Daher et al, 2018). Each cellulose microfibril is composed of b-1,4-linked glucan chains synthesized at the cell surface by cellulose synthase (CESA) complexes (CSCs), which are highly mobile membrane proteins (Paredez et al, 2006;McFarlane et al, 2014;Kieber & Polko, 2019).…”