Integrated NIRS and QTL assays reveal minor mannose and galactose as contrast lignocellulose factors for biomass enzymatic saccharification in rice
Abstract Background: Identifying lignocellulose recalcitrant factors and exploring their genetic properties are essential for enhanced biomass enzymatic saccharification in bioenergy crops. Despite genetic modification of major wall polymers has been implemented for reduced recalcitrance in engineered plant, it could most cause a penalty of plant growth and biomass yield. Alternatively, it is increasingly considered to improve minor wall components, but an applicable approach is required for efficient assay of large population of biomass samples. Hence, this study collected total 100 rice straw samples and characterized all minor wall monosaccharides and biomass enzymatic saccharification by integrating NIRS modeling and QTL profiling. Results: By performing classic chemical analyses and establishing optimal NIRS equations, this study examined a diversity of four minor wall monosaccharides and major wall polymers (acid-soluble lignin/ASL, acid-insoluble lignin/AIL, three lignin monomers, crystalline cellulose), which led to largely varied hexoses yields achieved from enzymatic hydrolyses after two alkali pretreatments were conducted with all rice straws. Correlation analyses indicated that mannose and galactose could play a contrast role for biomass enzymatic saccharification at P < 0.0l level (n=100). Meanwhile, this study found that QTLs controlling mannose, galactose, lignin-related traits and biomass saccharification were co-located. Notably, by combining NIRS assay with QTLs maps, this study interpreted that the mannose-rich hemicellulose may assist AIL disassociation for enhanced biomass enzymatic saccharification, whereas the galactose-rich polysaccharides should be effectively extracted with ASL from alkali pretreatment for condensed AIL association with cellulose microfibrils against enzymatic hydrolysis. Conclusions: By integrating NIRS assay with QTL profiling for large population of rice straw samples, this study identified that the mannose of wall polysaccharides could positively affect biomass enzymatic saccharification, whereas the galactose had a significantly negative impact. It also sorted out that two minor monosaccharides should distinctively associate with lignin deposition for wall network construction. Hence, this study has demonstrated an applicable approach for fast assessments of minor lignocellulose recalcitrant factors and biomass enzymatic saccharification in rice, and it has also provided a potential strategy for bioenergy crop breeding.