Graduate School of Biotechnology and Bioengineering, Yuan Ze University, Taoyuan, Taiwan.
Department of Chemical and Materials Bioengineering, Chang Gung University, Taoyuan, Taiwan.
Biotechnol Bioeng. 2020 Apr;117(4):933-944. doi: 10.1002/bit.27262. Epub 2020 Jan 27.
Rice straw, a common agricultural waste, is used as a potential feedstock for bioethanol production. Currently, bioethanol is made mostly from the microbial fermentation of starch-containing raw materials. Therefore, genetically engineered starch-excess rice straw through interference of starch degradation as a potential strategy to enhance bioethanol production was evaluated in this study. Arabidopsis Starch Excess 4 (SEX4) encodes a chloroplast-localized glucan phosphatase and plays a role in transitory starch degradation. Despite the identification of a SEX4 homolog in rice, OsSEX4, its biological function remains uncertain. Ectopic expression of OsSEX4 complementary DNA complemented the leaf starch-excess phenotype of the Arabidopsis sex4-4 mutant. OsSEX4-knockdown transgenic rice plants were generated using the RNA interference approach. Starch accumulation was higher in OsSEX4-knockdown suspension-cultured cells, leaves, and rice straw compared with the wild type, suggesting that OsSEX4 plays an important role in degradation of transitory starch. The OsSEX4-knockdown rice plants showed normal plant growth and no yield penalty. Starch-excess OsSEX4-knockdown rice straw used as feedstock for fermentation resulted in improved bioethanol yield, with a 50% increase in ethanol production in a vertical mass-flow type bioreactor, compared with that of the wild-type straw.
稻草是一种常见的农业废弃物，可用作生物乙醇生产的潜在原料。目前，生物乙醇主要通过含有淀粉的原料进行微生物发酵生产。因此，本研究评估了通过干扰淀粉降解来遗传工程化过量淀粉的稻草，作为提高生物乙醇产量的潜在策略。Arabidopsis Starch Excess 4（SEX4）编码一种质体定位的葡聚糖磷酸酶，在暂存淀粉降解中发挥作用。尽管在水稻中鉴定到了 SEX4 的同源物 OsSEX4，但它的生物学功能尚不清楚。OsSEX4 cDNA 的异位表达弥补了拟南芥 sex4-4 突变体的叶片淀粉过量表型。利用 RNA 干扰方法生成了 OsSEX4 敲低的转基因水稻植株。与野生型相比，OsSEX4 敲低悬浮培养细胞、叶片和稻草中的淀粉积累更高，表明 OsSEX4 在暂存淀粉的降解中发挥着重要作用。OsSEX4 敲低的水稻植株表现出正常的植物生长，没有产量损失。与野生型稻草相比，用作发酵原料的淀粉过量 OsSEX4 敲低的水稻秸秆在垂直质量流式生物反应器中发酵导致生物乙醇产量提高，乙醇产量提高了 50%。
