Glucomannans are based on a linear β-1,4-linked glucosyl (Glc) and mannosyl (Man) polymer that can be substituted by galactosyl (Gal) side chains (Figure 1). The composition of the glucosyl and mannosyl polymer backbone as well as the side chain substitution varies between tissues and species.
Figure 1: Structure of Galacto(gluco)mannan
Our recent work on the biosynthesis of glucomannan in Arabidopsis thaliana characterises a group of genes of the CSLA family that are required for glucomannan biosynthesis. There are nine members of the CSLA family in Arabidopsis, which are differentially expressed throughout development. Analysis of knock-out mutants reveals that CSLA2/CSLA3/CSLA9 are the major components required for glucomannan in stems, whereas CSLA7 seems to synthesise glucomannan in the embryo. Even though there is a lack of glucomannan in stems in the CSLA2/CSLA3/CSLA9 triple mutant (Figure 2A), no effect on stem development and strength can be detected. In contrast, altering the glucomannan levels by mutating CSLA7 or by expressing CSLAs using a strong and ubiquitous promotor (35Spro) interferes with embryo development (Figure 2B), suggesting a role of glucomannan in signalling processes.
Figure 2: Immunofluorescence labelling of Arabidopsis stem sections and analysis of embryo lethality in csla mutants and CSLA overexpressing lines