Abstract
Sorghum (Sorghum bicolor) is an important bioenergy crop. Its biomass mainly consists of the cellulosic and non-cellulosic polysaccharides, both which can be converted to biofuels. The biosynthesis of non-cellulosic polysaccharides involves several glycosyltransferases (GT) families including GT47. However, there was no systemic study on GT47 family in sorghum to date. Here, we identified 39 sorghum GT47 family members and showed the functional divergences of MURUS3 (MUR3) homologs. Sorghum GT47 proteins were phylogenetically clustered into four distinct subfamilies. Within each subfamily, gene structure was relatively conserved between the members. Ten gene pairs were identified from the 39 GT47 genes, of which two pairs might be originated from tandem duplication. 25.6% (10/39) of sorghum GT47 genes were homologous to Arabidopsis MUR3, a xyloglucan biosynthesis gene in primary cell walls. SbGT47_2, SbGT47_7, and SbGT47_8, three most homologous genes of MUR3, exhibited different tissue expression patterns and were selected for complementation into Arabidopsis mur3-3. Physiological and cell wall analyses showed that SbGT47_2 and SbGT47_7 may be two functional xyloglucan galactosyltransferases in sorghum. Further studies found that MUR3-like genes are widely present in the seed plants but not in the chlorophytic alga Chlamydomonas reinhardtii. Our results provide novel information for evolutionary analysis and functional dissection of sorghum GT47 family members.
Highlights
Sorghum(Sorghum bicolor), a highly productive C4 photosynthetic grass, is the fifth most cultivated cereal crop globally due to its huge biomass yield, high nitrogen utilization efficiency and remarkable adaptability on marginal land (Taylor et al, 2010; Byrt et al, 2011)
To identify GT47 proteins in ten representative species namely green alga (Chlamydomonas reinhardtii), moss (Physomitrella patens), sorghum (S. bicolor), stiff brome (Brachypodium distachyon), rice (Oryza sativa), switchgrass (Panicum virgatum), Arabidopsis (Arabidopsis thaliana), grape (Vitis vinifera), alfalfa (Medicago truncatula) and poplar (Populus trichocarpa), Pfam (PF03016) analysis was employed to search against their corresponding genome database1
Arabidopsis MUR3 transforms the galactosyl residue from UDPgalactose to the third xylose (L side chain) of XXXG-type, forming XXLG subunits (Madson et al, 2003; Jensen et al, 2012)
Summary
Sorghum(Sorghum bicolor), a highly productive C4 photosynthetic grass, is the fifth most cultivated cereal crop globally due to its huge biomass yield, high nitrogen utilization efficiency and remarkable adaptability on marginal land (Taylor et al, 2010; Byrt et al, 2011). In comparison to lignocellulosic biomass crops such as switchgrass and Miscanthus, sorghum has a Functional Divergences of MUR3-Like Genes in Sorghum smaller genome (∼730 Mb) and more fermentable soluble sugars, making it an ideal model for functional analysis of C4 grasses (Paterson et al, 2009). Sorghum biomass consists of 24–38% cellulose, 12–22% noncellulosic polysaccharides, 17–22% lignin, and 1–22% starch (Corredor et al, 2009). Non-cellulosic polysaccharides generally interact with cellulose and lignin, contributing to the strength of plant cell walls (Scheller and Ulvskov, 2010). In dicots and non-commelinoid monocotyledons, the major non-cellulosic polysaccharides of primary walls are xyloglucans and a range of pectic polysaccharides, with lower levels of heteroxylans and heteromannans. Primary walls of grasses have much lower levels of xyloglucans and pectins, which are replaced by higher amounts of heteroxylans and, in some cases, with (1,3; 1,4)-β-glucans (Burton and Fincher, 2012). Charactirization of Arabidopsis mutants shows that a battery of glycosyltransferases (GTs) from family GT2, GT8, GT34, GT37, GT43, and GT47 are involved in the biosynthesis of non-cellulosic polysaccharides (Perrin et al, 1999; Faik et al, 2002; Madson et al, 2003; Bauer et al, 2006; Burton et al, 2006; Brown et al, 2007, 2009; Cocuron et al, 2007; Lee et al, 2007)
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