Interactions between MUR10/CesA7-Dependent Secondary Cellulose Biosynthesis and Primary Cell Wall Structure

Abstract

Primary cell walls are deposited and remodeled during cell division and expansion. Secondary cell walls are deposited in specialized cells after the expansion phase. It is presently unknown whether and how these processes are interrelated. The Arabidopsis (Arabidopsis thaliana) MUR10 gene is required for normal primary cell wall carbohydrate composition in mature leaves as well as for normal plant growth, hypocotyl strength, and fertility. The overall sugar composition of young mur10 seedlings is not significantly altered; however, the relative proportion of pectin side chains is shifted toward an increase in 1 / 5-a-arabinan relative to 1 / 4-b-galactan. mur10 seedlings display reduced fucogalactosylation of tightly cell wall-bound xyloglucan. Expression levels of genes encoding either nucleotide sugar interconversion enzymes or glycosyl transferases, known to be involved in primary and secondary cell wall biosynthesis, are generally unaffected; however, the CesA7 transcript is specifically suppressed in the mur10-1 allele. The MUR10 locus is identical with the CesA7 gene, which encodes a cellulose catalytic subunit previously thought to be specifically involved in secondary cell wall formation. The xylem vessels in young mur10 hypocotyls are collapsed and their birefringence is lost. Moreover, a fucogalactosylated xyloglucan epitope is reduced and a 1 / 5-a-arabinan epitope increased in every cell type in mur10 hypocotyls, including cells that do not deposit secondary walls. mur10 also displays altered distribution of an arabinogalactan-protein epitope previously associated with xylem differentiation and secondary wall thickening. This work indicates the existence of a mechanism that senses secondary cell wall integrity and controls biosynthesis or structural remodeling of primary cell walls and cellular differentiation.

A Peroxidase-Dependent Apoplastic Oxidative Burst in Cultured Arabidopsis Cells Functions in MAMP-Elicited Defense

“…Although significant changes in the cross-linking of Hyp-rich glycoproteins following elicitor treatment have not been observed (Brisson et al, 1994;Wojtaszek et al, 1995;Brown et al, 1998), it is possible that the knockdown of basal levels of PRX33 and PRX34 leads to cell expansion by diminishing peroxidase-catalyzed crosslinking of cell wall polymers, which in turn affects the regulation of genes involved in cell expansion. A similar compensatory mechanism has also been observed in mutants lacking the cellulose synthase gene CESA3, where a reduction of cellulose content affected the pectin and xyloglucan composition of the cell wall (Cañ o-Delgado et al, 2003;Bosca et al, 2006). These data together with our proteomic data suggest a sensing mechanism that monitors the integrity of the cell wall.…”

Complexes with Mixed Primary and Secondary Cellulose Synthases Are Functional in Arabidopsis Plants

“…Overexpression of a mutant allele of the Arabidopsis CESA7 gene, named fra5, resulted in changes in cellulose synthesis during primary wall formation (reduced thickness of the cell wall and cell elongation) as well as causing a dominant-negative effect on cellulose synthesis during secondary wall formation (Zhong et al, 2003), as was also suggested in the case of the widely recognized secondary wall-specific AtCESA7 (MUR10), being required for normal primary cell wall carbohydrate composition in mature leaves, normal plant growth, hypocotyl strength, and fertility (Bosca et al, 2006). Another study shows that despite CESA9 having already been classified as a primary cell wall CESA (Desprez et al, 2007;Persson et al, 2007), a nonredundant role was shown in secondary cell wall thickening in the seed coat (Stork et al, 2010).…”

Functional analysis of complexes with mixed primary and secondary cellulose synthases

“…15,[17][18][19] The molecular details of the primary to secondary cell wall transition and mechanisms that underlie the cross talk between primary and secondary cell wall biosynthesis are largely unknown.…”