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

Using a novel rice Osfc9/myb103 mutant and OsMYB103L-RNAi transgenic line, this study examined that down-regulations of OsMYB103L could not significantly affect plant growth and development, but remarkably reduced cellulose level, crystallinity and polymerization without significant impacts in other major wall polymers (hemicellulose, lignin), which thereby resulted in distinct cellulose nanofiber assembly in plant cell walls. These consequently improved lignocellulose recalcitrance for much enhanced biomass enzymatic saccharification in mature rice straws. By performing multi-omics analyses integrated with DAP-seq assay, this work further demonstrated that OsMYB103L could act as an active transcription factor to specifically mediate cellulose biosynthesis and deposition by regulating OsCesAs genes and other genes associated with microfibril orientation and assembly. Hence, this study has not only provided insights into cellulose biosynthesis, but it also offered a powerful strategy for genetic modification of plant cell walls in bioenergy crops.

本研究以新型水稻Osfc9/myb103突变体与OsMYB103L-RNAi转基因株系为实验材料，探究发现：下调OsMYB103L的表达不会对水稻植株的生长发育造成显著影响，但可显著降低纤维素含量、结晶度与聚合度，且对其他主要细胞壁聚合物（半纤维素、木质素）无明显作用，进而使植物细胞壁内的纤维素纳米纤维组装模式发生显著改变。上述变化最终提升了木质纤维素抗降解性，显著增强了成熟水稻秸秆的生物质酶解糖化效率。本研究通过整合多组学分析与DNA亲和纯化测序（DAP-seq）实验，进一步证实OsMYB103L可作为活性转录因子，通过调控OsCesAs基因以及其他与微纤丝取向和组装相关的基因，特异性介导纤维素的生物合成与沉积过程。综上，本研究不仅为纤维素生物合成机制研究提供了新的见解，同时也为能源植物的细胞壁遗传改良提供了一种高效策略。