biosynthesis of xylans. In eukaryotes, GTs represent about 1% to 2% of gene products. GTs are assembled into complexes existing in the Golgi apparatus. However, no xylan synthase complexes have been isolated from Arabidopsis tissues (dicot). The first gene involved in the biosynthesis of xylan was revealed on xylem mutants (irx) in Arabidopsis thaliana because of some mutation affecting xylan biosynthesis genes. As a result, abnormal plant growth due to thinning and weakening of secondary xylem cell walls was seen. Arabidopsis mutant irx9 (At2g37090), irx14 (At4g36890), irx10/gut2 (At1g27440), irx10-L/gut1 (At5g61840) showed defect in xylan backbone biosynthesis. Arabidopsis mutants irx7, irx8, and parvus are thought to be related to the reducing end oligosaccharide biosynthesis. Thus, many genes have been associated with xylan biosynthesis but their biochemical mechanism is still unknown. Zeng et al. (2010) immuno-purified xylan synthase activity from etiolated wheat (Triticum aestivum) microsomes. Jiang et al. (2016) reported a xylan synthase complex (XSC) from wheat that has a central core formed of two members of the GT43 and GT47 families (CAZy database). They purified xylan synthase activity from wheat seedlings through proteomics analysis and showed that two members of TaGT43 and TaGT47 are sufficient for the synthesis of a xylan-like polymer in vitro. Breakdown Xylanase convert xylan into xylose. Given that plants contain a up to 30% xylan, xylanase is important to the nutrient cycle. The degradation of xylan and other hemicelluloses is relevant to the production of biofuels. Being less crystalline and more highly branched, these hemicelluloses are particularly susceptible to hydrolysis. Research As a major component of plants, xylan is potentially a significant source of renewable energy especially for second generation biofuels. However, xylose (backbone of xylan) is a pentose sugar that is hard to ferment during biofuel conversion because microorganisms like yeast cannot ferment pentose naturally. References Polysaccharides Cell biology