Genetic loci simultaneously controlling lignin monomers and biomass digestibility of rice straw

Zhen Hu,Youmei Wang,Jonathan D Walton,Lingqiang Wang,Rana Abdul Samad,Liangcai Peng,Yuqing He,Guifen Zhang,Ali Muhammad

doi:10.1038/s41598-018-21741-y

Abstract

Lignin content and composition are crucial factors affecting biomass digestibility. Exploring the genetic loci simultaneously affecting lignin-relevant traits and biomass digestibility is a precondition for lignin genetic manipulation towards energy crop breeding. In this study, a high-throughput platform was employed to assay the lignin content, lignin composition and biomass enzymatic digestibility of a rice recombinant inbred line population. Correlation analysis indicated that the absolute content of lignin monomers rather than lignin content had negative effects on biomass saccharification, whereas the relative content of p-hydroxyphenyl unit and the molar ratio of p-hydroxyphenyl unit to guaiacyl unit exhibited positive roles. Eight QTL clusters were identified and four of them affecting both lignin composition and biomass digestibility. The additive effects of clustered QTL revealed consistent relationships between lignin-relevant traits and biomass digestibility. Pyramiding rice lines containing the above four positive alleles for increasing biomass digestibility were selected and showed comparable lignin content, decreased syringyl or guaiacyl unit and increased molar percentage of p-hydroxyphenyl unit, the molar ratio of p-hydroxyphenyl unit to guaiacyl unit and sugar releases. More importantly, the lodging resistance and eating/cooking quality of pyramiding lines were not sacrificed, indicating the QTL information could be applied to select desirable energy rice lines.

Highlights

Lignocellulosic biomass represents an abundant, renewable source of mixed sugars for fermentation to biofuels[1]
We analyzed the lignin content, lignin composition and biomass digestibility of rice straw samples from a recombinant inbred line (RIL) population composed of different genotypes using a high throughput platform, which allowed us to correlate biomass enzymatic digestibility with various lignin properties at the genetic level
The pyramiding rice lines selected by quantitative trait loci (QTL) information displayed decreased S or G and increased H%, H/G and biomass digestibility as well as normal agronomic traits, which suggested a convenient method for selecting outstanding rice lines at the population scale and a feasible direction for modifying lignin-relevant traits

Summary

Introduction

Lignocellulosic biomass represents an abundant, renewable source of mixed sugars for fermentation to biofuels[1]. One approach to overcome cell-wall recalcitrance is to develop bioenergy feedstock plants that are more susceptible to hydrolysis[2] For this breeding purpose, it is necessary to uncover relationships between cell wall components, identify key cell wall compositional features influencing recalcitrance and discover and manipulate genetic basis involved in biosynthesis, modification and conversion of cell wall[3]. Lignin is a hydrophobic heteropolymer composed of three types of hydroxycinnamyl alcohol precursors: syringyl (S), guaiacyl (G) and p-hydroxyphenyl (H) It has been identified as a major deterrent to enzyme attack on cellulose[4,5]. More studies are required to better define the impact of lignin content and composition on biomass recalcitrance. Studies focusing on detection of QTL associated with lignin-relevant traits or biomass digestibility are very limited. The QTL and candidate genes associated with lignin content and enzymatic digestibility were identified in a recombinant inbred maize population[11]. Further work should be conducted to detect more QTL related to lignin composition and biomass digestibility

Methods

Results

Conclusion