Down-regulation of OsMYB103L distinctively alters beta-1,4-glucan polymerization and cellulose microfibers assembly for enhanced biomass enzymatic saccharification in rice

Mingliang Zhang,Zi Luo,Liangcai Peng,Leiming Wu,Jingyang Li,Lin Li,Hailang Wang,Yanting Wang,Zhen Hu,Lingqiang Wang,Haizhong Yu,Ran Zhang,Tao Xia,Youmei Wang

doi:10.1186/s13068-021-02093-8

Abstract

BackgroundAs a major component of plant cell walls, cellulose provides the most abundant biomass resource convertible for biofuels. Since cellulose crystallinity and polymerization have been characterized as two major features accounting for lignocellulose recalcitrance against biomass enzymatic saccharification, genetic engineering of cellulose biosynthesis is increasingly considered as a promising solution in bioenergy crops. Although several transcription factors have been identified to regulate cellulose biosynthesis and plant cell wall formation, much remains unknown about its potential roles for genetic improvement of lignocellulose recalcitrance.ResultsIn this study, we identified a novel rice mutant (Osfc9/myb103) encoded a R2R3-MYB transcription factor, and meanwhile generated OsMYB103L-RNAi-silenced transgenic lines. We determined significantly reduced cellulose levels with other major wall polymers (hemicellulose, lignin) slightly altered in mature rice straws of the myb103 mutant and RNAi line, compared to their wild type (NPB). Notably, the rice mutant and RNAi line were of significantly reduced cellulose features (crystalline index/CrI, degree of polymerization/DP) and distinct cellulose nanofibers assembly. These alterations consequently improved lignocellulose recalcitrance for significantly enhanced biomass enzymatic saccharification by 10–28% at p < 0.01 levels (n = 3) after liquid hot water and chemical (1% H2SO4, 1% NaOH) pretreatments with mature rice straws. In addition, integrated RNA sequencing with DNA affinity purification sequencing (DAP-seq) analyses revealed that the OsMYB103L might specifically mediate cellulose biosynthesis and deposition by regulating OsCesAs and other genes associated with microfibril assembly.ConclusionsThis study has demonstrated that down-regulation of OsMYB103L could specifically improve cellulose features and cellulose nanofibers assembly to significantly enhance biomass enzymatic saccharification under green-like and mild chemical pretreatments in rice. It has not only indicated a powerful strategy for genetic modification of plant cell walls in bioenergy crops, but also provided insights into transcriptional regulation of cellulose biosynthesis in plants.

Highlights

As a major component of plant cell walls, cellulose provides the most abundant biomass resource convertible for biofuels
OsMYB103L has been reported with potential binding with OsCesAs genes of secondary cell wall [17], it has not been reported about specific regulation of any transcription factors (TFs) for cellulose biosynthesis in rice, to underlie impacts on cellulose feature and microfibrils assembly in plant cell walls
This study observed that the myb103 mutant had a normal plant growth with similar grain yield to the wild type (WT) (Fig. 2A; Additional file 1: Fig. S1D), but it was of obvious fragile-culm phenotype and remarkably reduced plant height which should be the major cause accounting for significantly decreased lodging index examined in the mutant (Fig. 2B; Additional file 1: Fig. S1B, C)

Summary

Introduction

As a major component of plant cell walls, cellulose provides the most abundant biomass resource convertible for biofuels. Several transcription factors have been identified to regulate cellulose biosynthesis and plant cell wall formation, much remains unknown about its potential roles for genetic improvement of lignocellulose recalcitrance. MYB103 and OsMYB103L have been examined as an R2R3-MYB transcriptional factor for regulating secondary cell wall synthesis in Arabidopsis and rice, respectively [15, 16]. OsMYB103L has been reported with potential binding with OsCesAs genes of secondary cell wall [17], it has not been reported about specific regulation of any TFs for cellulose biosynthesis in rice, to underlie impacts on cellulose feature and microfibrils assembly in plant cell walls

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