Jiangsu Key Laboratory of Crop Genomics and Molecular Breeding/Zhongshan Biological Breeding Laboratory /Key Laboratory of Plant Functional Genomics of the Ministry of Education/Jiangsu Key Laboratory of Crop Genetics and Physiology/Jiangsu Co-Innovation Center for Modern Production Technology of Grain Crops, College of Agriculture, Yangzhou University, Yangzhou, China.
National Key Laboratory of Plant Molecular Genetics, CAS Center for Excellence in Molecular Plant Sciences, Shanghai Institute of Plant Physiology and Ecology, Chinese Academy of Sciences, Shanghai, China.
Plant Biotechnol J. 2023 Nov;21(11):2224-2240. doi: 10.1111/pbi.14124. Epub 2023 Jul 11.
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 starch synthesis in rice endosperm and further suggest that manipulating the OsNAC24-OsNAP complex regulatory network could be a potential strategy for breeding rice cultivars with improved cooking and eating quality.
淀粉占水稻胚乳干重的 90%左右，是决定谷物品质的关键因素。尽管淀粉生物合成酶已被广泛研究，但淀粉合成酶编码基因（SECGs）的转录调控在很大程度上尚不清楚。在本研究中，我们探讨了 NAC 转录因子 OsNAC24 在调节水稻淀粉合成中的作用。OsNAC24 在发育中的胚乳中高度表达。与野生型相比，osnac24 突变体胚乳的外观和淀粉粒形态正常，而总淀粉含量、直链淀粉含量、支链淀粉链长分布以及淀粉的理化性质发生了变化。此外，osnac24 突变体植株中几个 SECG 的表达发生了改变。OsNAC24 是一种转录激活因子，靶向六个 SECG 的启动子；OsGBSSI、OsSBEI、OsAGPS2、OsSSI、OsSSIIIa 和 OsSSIVb。由于 OsGBSSI 和 OsSBEI 的 mRNA 和蛋白丰度在突变体中均降低，因此 OsNAC24 主要通过 OsGBSSI 和 OsSBEI 来调节淀粉合成。此外，OsNAC24 与新鉴定的 TTGACAA、AGAAGA 和 ACAAGA 以及核心 NAC 结合基序 CACG 结合。另一个 NAC 家族成员 OsNAP 与 OsNAC24 相互作用并共同激活靶基因表达。OsNAP 的功能丧失导致所有测试的 SECG 表达发生改变，淀粉含量降低。这些结果表明，OsNAC24-OsNAP 复合物在精细调节水稻胚乳淀粉合成中发挥关键作用，并进一步表明操纵 OsNAC24-OsNAP 复合物调控网络可能是培育具有改良蒸煮和食用品质的水稻品种的一种潜在策略。
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