Enhanced expression of OsNAC5 leads to up-regulation of OsNAC6 and changes rice (Oryza sativa L.) ionome

Abstract NAC transcription factors are plant-specific proteins involved in many processes during the plant life cycle and responses to biotic and abiotic stresses. Previous studies have shown that stress-induced OsNAC5 from rice (Oryza sativa L.) is up-regulated by senescence and might be involved in control of iron (Fe) and zinc (Zn) concentrations in rice seeds. Aiming a better understanding of the role of OsNAC5 in rice plants, we investigated a mutant line carrying a T-DNA insertion in the promoter of OsNAC5, which resulted in enhanced expression of the transcription factor. Plants with OsNAC5 enhanced expression were shorter at the seedling stage and had reduced yield at maturity. In addition, we evaluated the expression level of OsNAC6, which is co-expressed with OsNAC5, and found that enhanced expression of OsNAC5 leads to increased expression of OsNAC6, suggesting that OsNAC5 might regulate OsNAC6 expression. Ionomic analysis of leaves and seeds from the OsNAC5 enhanced expression line revealed lower Fe and Zn concentrations in leaves and higher Fe concentrations in seeds than in WT plants, further suggesting that OsNAC5 may be involved in regulating the ionome in rice plants. Our work shows that fine-tuning of transcription factors is key when aiming at crop improvement.

摘要：NAC转录因子（NAC transcription factors）是一类植物特异性蛋白质，参与植物生命周期的多个进程以及对生物和非生物胁迫的应答。既往研究显示，水稻（Oryza sativa L.）中受胁迫诱导的OsNAC5可被衰老过程诱导上调，且可能参与调控水稻种子中铁（Fe）与锌（Zn）的累积浓度。为深入解析OsNAC5在水稻植株中的生物学功能，本研究分析了一个在OsNAC5启动子区携带T-DNA插入的突变株系，该插入可使该转录因子的表达水平显著增强。OsNAC5表达上调的株系在苗期株高较矮，成熟期产量降低。此外，我们检测了与OsNAC5共表达的OsNAC6的表达水平，发现OsNAC5的表达上调会导致OsNAC6表达量升高，提示OsNAC5可能调控OsNAC6的转录。对该OsNAC5表达上调株系的叶片与种子进行离子组分析发现，相较于野生型（Wild Type, WT）植株，该株系叶片中的铁、锌浓度更低，而种子中的铁浓度更高，进一步表明OsNAC5可能参与调控水稻的离子组稳态。本研究证实，在作物遗传改良中，对转录因子进行精准调控是关键所在。