The OsNAC24‐OsNAP protein complex activates OsGBSSI and OsSBEI expression to fine‐tune starch biosynthesis in rice endosperm

作者：Su‐Kui Jin, Lina Xu, Yujia Leng, Mingqiu Zhang, Qingqing Yang, Shuilian Wang, Shuwen Jia, Tao Song, Ruo‐An Wang, Tao Tao, Qiaoquan Liu, Xiuling Cai, Jiping Gao · 发表于：Plant Biotechnology Journal · 年份：2023 · DOI：10.1111/pbi.14124 · 被引用次数：49 · 研究领域：Plant nutrient uptake and metabolism、Food composition and properties、Biofuel production and bioconversion

Starch accounts for up to 90% of the dry weight of rice endosperm and is a key determinant of grain quality. Although starch biosynthesis enzymes have been comprehensively studied, transcriptional regulation of starch-synthesis enzyme-coding genes (SECGs) is largely unknown. In this study, we explored the role of a NAC transcription factor, OsNAC24, in regulating starch biosynthesis in rice. OsNAC24 is highly expressed in developing endosperm. The endosperm of osnac24 mutants is normal in appearance as is starch granule morphology, while total starch content, amylose content, chain length distribution of amylopectin and the physicochemical properties of the starch are changed. In addition, the expression of several SECGs was altered in osnac24 mutant plants. OsNAC24 is a transcriptional activator that targets the promoters of six SECGs; OsGBSSI, OsSBEI, OsAGPS2, OsSSI, OsSSIIIa and OsSSIVb. Since both the mRNA and protein abundances of OsGBSSI and OsSBEI were decreased in the mutants, OsNAC24 functions to regulate starch synthesis mainly through OsGBSSI and OsSBEI. Furthermore, OsNAC24 binds to the newly identified motifs TTGACAA, AGAAGA and ACAAGA as well as the core NAC-binding motif CACG. Another NAC family member, OsNAP, interacts with OsNAC24 and coactivates target gene expression. Loss-of-function of OsNAP led to altered expression in all tested SECGs and reduced the starch content. These results demonstrate that the OsNAC24-OsNAP complex plays key roles in fine-tuning ...