Distinct and Overlapping Functions of Miscanthus sinensis MYB Transcription Factors SCM1 and MYB103 in Lignin Biosynthesis.

Philippe Golfier,Emily K Murphy,Jan U Lohmann,Sebastian Wolf,Olga Ermakova,Wan Zhang,Jianbo Xie,Feng He,Shawn D Mansfield,Thomas Rausch,Faride Unda

doi:10.3390/ijms222212395

Abstract

Cell wall recalcitrance is a major constraint for the exploitation of lignocellulosic biomass as a renewable resource for energy and bio-based products. Transcriptional regulators of the lignin biosynthetic pathway represent promising targets for tailoring lignin content and composition in plant secondary cell walls. However, knowledge about the transcriptional regulation of lignin biosynthesis in lignocellulosic feedstocks, such as Miscanthus, is limited. In Miscanthus leaves, MsSCM1 and MsMYB103 are expressed at growth stages associated with lignification. The ectopic expression of MsSCM1 and MsMYB103 in N. benthamiana leaves was sufficient to trigger secondary cell wall deposition with distinct sugar and lignin compositions. Moreover, RNA-seq analysis revealed that the transcriptional responses to MsSCM1 and MsMYB103 overexpression showed an extensive overlap with the response to the NAC master transcription factor MsSND1, but were distinct from each other, underscoring the inherent complexity of secondary cell wall formation. Furthermore, conserved and previously described promoter elements as well as novel and specific motifs could be identified from the target genes of the three transcription factors. Together, MsSCM1 and MsMYB103 represent interesting targets for manipulations of lignin content and composition in Miscanthus towards a tailored biomass.

Highlights

Lignocellulosic biomass, which largely exists in the form of plant secondary cell walls (SCW), holds enormous potential as a renewable feedstock for a sustainable economy [1]
In Miscanthus, the NAC transcription factors (TFs) MsSND1 has been previously characterized as a master regulator orchestrating SCW formation, and MsSCM1, a MYB TF related to MYB20/43/85 [18], has been proposed as specific regulator of lignin biosynthesis [30]
In order to explore the potential of lignocellulosic biomass as a sustainable resource, lignin engineering has become a focus of research with the goal to either decrease recalcitrance or to produce more valuable lignin with enhanced utility

Summary

Introduction

Lignocellulosic biomass, which largely exists in the form of plant secondary cell walls (SCW), holds enormous potential as a renewable feedstock for a sustainable economy [1]. The processing of lignocellulosic biomass into bio-based products and energy is still hampered by the inherent resistance of cell walls to deconstruction, which is largely conferred by the aromatic polyphenol lignin [1,2]. The mechanical importance of lignin is highlighted by lignin-deficient mutants that manifest dwarfism, collapsed xylem vessels, or higher susceptibility to pathogens, some of those phenotypes can be the result of signaling-mediated secondary responses [3]. It is important to understand the mechanisms of lignin biosynthesis and its regulation to harness the potential of lignocellulosic biomass as a renewable resource for biorefineries

Methods

Results

Conclusion