Abstract
BackgroundIdentifying 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 crops, 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 of 100 rice straw samples and characterized all minor wall monosaccharides and biomass enzymatic saccharification by integrating NIRS modeling and QTL profiling.ResultsBy performing classic chemical analyses and establishing optimal NIRS equations, this study examined 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 large population of rice straws. Correlation analyses indicated that mannose and galactose can play a contrast role for biomass enzymatic saccharification at P < 0.0 l level (n = 100). Meanwhile, we found that the QTLs controlling mannose, galactose, lignin-related traits, and biomass saccharification were co-located. By combining NIRS assay with QTLs maps, this study further 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 the alkali pretreatment for condensed AIL association with cellulose microfibrils.ConclusionsBy integrating NIRS assay with QTL profiling for large population of rice straw samples, this study has identified that the mannose content of wall polysaccharides could positively affect biomass enzymatic saccharification, while the galactose had a significantly negative impact. It has also sorted out that two minor monosaccharides could distinctively associate with lignin deposition for wall network construction. Hence, this study demonstrates an applicable approach for fast assessments of minor lignocellulose recalcitrant factors and biomass enzymatic saccharification in rice, providing a potential strategy for bioenergy crop breeding and biomass processing.
Highlights
Identifying lignocellulose recalcitrant factors and exploring their genetic properties are essential for enhanced biomass enzymatic saccharification in bioenergy crops
All rice straw samples were of the highest xylose contents ranged from 239.74 to 290.25 μg mg−1, whereas they had the second high levels of arabinose from 27.50 to 39.09 μg mg−1 among seven monosaccharides examined, consistent with the previous findings of xylose and arabinose as two major monosaccharides of hemicellulose in grassy plants [6, 31]
Among the rest of monosaccharides examined, the rice straw samples showed largely varied glucose and galactose contents about 27.03– 42.49 μg mg−1 and 9.27–15.4 μg mg−1, with much lower mannose levels from 2.17 to 3.34 μg mg−1, consistent with the previously reported ones in rice and other grassy crops [8, 32]. It suggested that the largest amounts of glucose should be mainly from the -1,3–1,4-glucans, which is the characteristic hemicellulose of rice straw [33]
Summary
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 crops, it could most cause a penalty of plant growth and biomass yield. Attempts have been undertaken by genetic modification of plant cell walls in bioenergy crops along with optimal biomass pretreatments [3, 4]. Hemicellulose is a major wall polysaccharide, but its deposition could reduce cellulose crystallinity for enhanced biomass enzymatic saccharification under various physical and chemical pretreatments in bioenergy grasses examined [8, 9]. It is important to explore the genetic engineering approach for improved lignin-carbohydrate complexes in bioenergy crops
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