Functional conservation and divergence of Miscanthus lutarioriparius GT43 gene family in xylan biosynthesis.

Xiaoyu Wang,Qi Tang,Yingzhen Kong,Guo He,Gongke Zhou,Chunlin Jia,Xuanwen Yang,Xun Zhao,Aimin Wu,Ruibo Hu

doi:10.1186/s12870-016-0793-5

Abstract

BackgroundXylan is the most abundant un-cellulosic polysaccharides of plant cell walls. Much progress in xylan biosynthesis has been gained in the model plant species Arabidopsis. Two homologous pairs Irregular Xylem 9 (IRX9)/9L and IRX14/14L from glycosyltransferase (GT) family 43 have been proved to play crucial roles in xylan backbone biosynthesis. However, xylan biosynthesis in grass such as Miscanthus remains poorly understood.ResultsWe characterized seven GT43 members in M. lutarioriparius, a promising bioenergy crop. Quantitative real-time RT-PCR (qRT-PCR) analysis revealed that the expression of MlGT43 genes was ubiquitously detected in the tissues examined. In-situ hybridization demonstrated that MlGT43A-B and MlGT43F-G were specifically expressed in sclerenchyma, while MlGT43C-E were expressed in both sclerenchyma and parenchyma. All seven MlGT43 proteins were localized to Golgi apparatus. Overexpression of MlGT43A-E but not MlGT43F and MlGT43G in Arabidopsis irx9 fully or partially rescued the mutant defects, including morphological changes, collapsed xylem and increased xylan contents, whereas overexpression of MlGT43F and MlGT43G but not MlGT43A-E complemented the defects of irx14, indicating that MlGT43A-E are functional orthologues of IRX9, while MlGT43F and MlGT43G are functional orthologues of IRX14. However, overexpression of all seven MlGT43 genes could not rescue the mucilage defects of irx14 seeds. Furthermore, transient transactivation analyses of MlGT43A-E reporters demonstrated that MlGT43A and MlGT43B but not MlGT43C-E were differentially activated by MlSND1, MlMYB46 or MlVND7.ConclusionThe results demonstrated that all seven MlGT43s are functionally conserved in xylan biosynthesis during secondary cell wall formation but diversify in seed coat mucilage xylan biosynthesis. The results obtained provide deeper insight into xylan biosynthesis in grass, which lay the foundation for genetic modification of grass cell wall components and structure to better suit for next-generation biofuel production.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-016-0793-5) contains supplementary material, which is available to authorized users.

Highlights

Xylan is the most abundant un-cellulosic polysaccharides of plant cell walls
MlGT43 genes rescue the morphological defects of irx9 or irx14 To reveal whether MlGT43 genes perform the same functions as Irregular Xylem 9 (IRX9) and IRX14 orthologues in Arabidopsis, we examined their abilities to rescue the morphological defects of irx9 and irx14
Overexpression of MlGT43F and MlGT43G but not MlGT43A-E in irx14 recovered the levels of cellulose and lignin nearly to the wild type (WT) level (Additional file 3: Figure S1). These results further indicate that MlGT43A-E but not MlGT43F-G can partially restore the xylan biosynthesis in irx9, while MlGT43F-G but not MlGT43A-E are able to rescue the xylan biosynthesis defect in irx14, suggesting that MlGT43A-E are orthologous to IRX9, while MlGT43F and MlGT43G are orthologous to IRX14

Summary

Introduction

Xylan is the most abundant un-cellulosic polysaccharides of plant cell walls. Plant cell walls are complex and dynamic structures composed mainly of polysaccharides GAX is the predominant hemicellulose in grass cell walls, and has sidechains of α-1,2 or α1,3-linked arabinose (Ara) and GlcA residues [3]. GX in angiosperm and GAX in several gymnosperm species contain a tetrasaccharide sequence [β-D-Xyl(1,3)-α-L-Rha-(1,2) -α-D-GalA-(1,4)-D-Xyl] at the reducing end [5,6,7]. No such oligosaccharide has yet been identified for xylans in grasses [8, 9]. It is still in controversy whether this oligosaccharide functions as a primer or as a terminator in xylan backbone biosynthesis [10]

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Conclusion