Multiple Cellulose Synthase Catalytic Subunits Are Required for Cellulose Synthesis in Arabidopsis

Abstract

The irregular xylem 1 ( irx1 ) mutant of Arabidopsis has a severe deficiency in the deposition of cellulose in secondary cell walls, which results in collapsed xylem cells. This mutation has been mapped to a 140-kb region of chromosome 4. A cellulose synthase catalytic subunit was found to be located in this region, and genomic clones containing this gene complemented the irx1 mutation. IRX1 shows homology to a previously described cellulose synthase (IRX3). Analysis of the irx1 and irx3 mutant phenotypes demonstrates that both IRX1 and IRX3 are essential for the production of cellulose in the same cell. Thus, IRX1 and IRX3 define distinct classes of catalytic subunits that are both essential for cellulose synthesis in plants. This finding is supported by coprecipitation of IRX1 with IRX3, suggesting that IRX1 and IRX3 are part of the same complex.

Patterning of plant cell wall deposition by cortical microtubules

“…Whereas libriform fibres have a uniformly deposited secondary cell wall, tracheary elements have patterned secondary cell wall thickenings. Besides structural support for the plant as a whole, these patterned secondary wall thickenings resist forces during transport, preventing collapse of the vessel as mentioned previously 6,[9][10][11][12] . Secondary cell wall thickenings in tracheary elements are deposited in different patterns, such as rings, spirals, reticulated or pitted patterns 1,13-15 ( Fig.…”

“…Mutants in these secondary CesAs result in dwarfed Arabidopsis plants, caused by collapsed vessel elements indicating the importance of the secondary cell wall thickenings [9][10][11][12] . Tracheary elements are characterized by typical patterned secondary cell wall thickenings.…”

Structure, organization, and functions of cellulose synthase complexes in higher plants

“…In fact, orthologs of AtCesA1, AtCesA3, and AtCesA6 appear to be required for the synthesis of cellulose deposited in the primary cell walls (Fagard et al, 2000;Scheible et al, 2001;Burn et al, 2002;Doblin et al, 2002). In contrast, orthologs of AtCesA4, AtCesA7, and AtCesA8 seem to be essential for cellulose synthesis in the secondary cell walls (Turner and Somerville, 1997;Taylor et al, 1999Taylor et al, , 2000Taylor et al, , 2003Zhong et al, 2003). The latter three CESA isoforms are specific to secondary cell wall formation and they actually physically interact with each other so it is highly probable that they are located in the same CelS as discussed previously (Taylor et al, 2003).…”

Characterization and cloning of a brittle culm mutant (bc88) in rice (Oryza sativa L.)

“…Evidence from CesA mutants in Arabidopsis shows that the CesA gene encodes the enzyme responsible for cellulose synthesis [6]. Arabidopsis mutants, i.e., irx1 (irregular xylem1), irx3 and irx5 genes destroy the function of AtCesA8, AtCesA7 and AtCesA4, respectively [7][8][9][10]. These CesAs form a complex CesA triplex responsible for cellulose synthesis [11].…”