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Abstract

Cell wall recalcitrance is a major limitation hindering the exploitation of the enormous potential of lignocellulosic biomass as a renewable resource for energy and bio-based products. In the last decades, C4 grasses from the genus Miscanthus have emerged as a most promising energy crop for the production of lignocellulosic biomass in temperate climates. Secondary cell walls, which represent the largest proportion of lignocellulosic biomass are formed in specialised cells after cessation of growth. In higher plants, the formation of secondary cell walls is tightly regulated, both spatially and temporally, by a complex network of transcription factors. However, in Miscanthus only little is known about molecular players regulating secondary cell wall formation and lignin biosynthesis. In this study, application of the herbicide isoxaben was shown to trigger ectopic lignification in Miscanthus seedling roots. The chemical treatment may be exploited in the future to identify regulators and biosynthetic genes involved in lignification in Miscanthus. In addition, Miscanthus sinensis transcription factors related to SECONDARY WALLASSOCIATED NAC DOMAIN1 (SND1) and SECONDARY CELLWALL MYBs 1-4 (SCM1-4) were identified in the Miscanthus transcriptome, which act as regulators of secondary cell wall formation and lignin biosynthesis. During Miscanthus development, expression of MsSND1 and MsSCMs coincided with the onset of secondary cell wall formation and lignification of vascular tissue and sclerenchyma fibers. MsSND1 and MsVND7 were capable to fully restore growth in a SCW-deficient Arabidopsis thaliana mutant, suggesting they are the Miscanthus orthologues of the well characterised Arabidopsis determinants of SCW formation in fibers and vessels. Ectopic expression of MsSND1 and MsVND7 in tobacco leaves prompted the formation of patterned deposition of lignin, cellulose, and hemicellulose reminiscent of xylem elements. This observation was in sharp contrast to uniform lignification after transient expression of various MsSCMs. Expression of particular Miscanthus TFs led to specific cell wall compositions, providing attractive targets for biomass improvements. Transgenic Arabidopsis lines carrying an inducible system of MsSND1 revealed that MsSND1 regulates directly or indirectly the expression of a broad range of genes involved in secondary cell wall formation.