Cellulose Synthase Mutants Distinctively Affect Cell Growth and Cell Wall Integrity for Plant Biomass Production in Arabidopsis

Cellulose is the most characteristic component of plant cell walls, and plays a central role in plant mechanical strength and morphogenesis. Despite the fact that cellulose synthase (CesA) mutants exhibit a reduction in cellulose level, much remains unknown about their impacts on cell growth (elongation and division) and cell wall integrity that fundamentally determine plant growth. Here, we examined three major types of AtCesA mutants (rsw1, an AtCesA1 mutant; prc1-1 and cesa6, AtCesA6-null mutants; and IRX3, an AtCesA7 mutant) and transgenic mutants that overexpressed AtCesA genes in the background of AtCesA6-null mutants. We found that AtCesA6-nullmutants showed a reduced cell elongation of young seedlings with little impact on cell division, which consequently affected cell wall integrity and biomass yield of mature plants. In comparison, rsw1 seedlings exhibited a strong defect in both cell elongation and division at restrictive temperature, whereas the IRX3 mutant showed normal seedling growth. Analyses of transgenic mutants indicated that primary wall AtCesA2, AtCesA3, AtCesA5 and AtCesA9 genes played a partial role in restoration of seedling growth. However, co-overexpression of AtCesA2 and AtCesA5 in AtCesA6-null mutants could greatly enhance cell division and fully restore wall integrity, leading to a significant increase in secondary wall thickness and biomass production in mature plants. Hence, this study has demonstrated distinct functions of AtCesA genes in plant cell growth and cell wall deposition for biomass production, which helps to expalin our recent finding that only three AtCesA6-like genes, rather than other AtCesA genes of the AtCesA family, could greatly enhance biomass production in transgenic Arabidopsis plants.