National Key Laboratory of Crop Genetic Improvement and National Centre of Plant Gene Research, Huazhong Agricultural University, Wuhan, 430070, China.
BMC Plant Biol. 2013 Sep 12;13:132. doi: 10.1186/1471-2229-13-132.
As the final stage of leaf development, leaf senescence may cause the decline of photosynthesis and gradual reduction of carbon assimilation, which makes it a possible limiting factor for crop yield. NACs are plant-specific transcription factors and some NACs have been confirmed to play important roles in regulating leaf senescence.
In this study, we reported a member of the NAC transcription factor family named OsNAP whose expression is associated with leaf senescence, and investigated its preliminary function during the process of leaf senescence. The results of qRT-PCR showed that the OsNAP transcripts were accumulated gradually in response to leaf senescence and treatment with methyl jasmonic acid (MeJA). A subcellular localization assay indicated that OsNAP is a nuclear-localized protein. Yeast one-hybrid experiments indicated that OsNAP can bind the NAC recognition site (NACRS)-like sequence. OsNAP-overexpressing transgenic plants displayed an accelerated leaf senescence phenotype at the grain-filling stage, which might be caused by the elevated JA levels and the increased expression of the JA biosynthesis-related genes LOX2 and AOC1, and showed enhanced tolerance ability to MeJA treatment at the seedling stage. Nevertheless, the leaf senescence process was delayed in OsNAP RNAi transgenic plants with a dramatic drop in JA levels and with decreased expression levels of the JA biosynthesis-related genes AOS2, AOC1 and OPR7.
These results suggest that OsNAP acts as a positive regulator of leaf senescence and this regulation may occur via the JA pathway.
作为叶片发育的最后阶段，叶片衰老可能导致光合作用下降和碳同化逐渐减少，这使其成为作物产量的一个潜在限制因素。NAC 是植物特异性转录因子，一些 NAC 已被证实在调节叶片衰老中发挥重要作用。
本研究报道了一个 NAC 转录因子家族成员 OsNAP，其表达与叶片衰老有关，并研究了其在叶片衰老过程中的初步功能。qRT-PCR 的结果表明，OsNAP 转录本随着叶片衰老和茉莉酸甲酯(MeJA)处理而逐渐积累。亚细胞定位实验表明，OsNAP 是一种核定位蛋白。酵母单杂交实验表明，OsNAP 可以结合 NAC 识别位点（NACRS）样序列。在灌浆期，过表达 OsNAP 的转基因植株表现出加速的叶片衰老表型，这可能是由于 JA 水平升高和 JA 生物合成相关基因 LOX2 和 AOC1 的表达增加引起的，同时在幼苗期对 MeJA 处理表现出增强的耐受性。然而，在 OsNAP RNAi 转基因植株中，叶片衰老过程被延迟，JA 水平急剧下降，JA 生物合成相关基因 AOS2、AOC1 和 OPR7 的表达水平降低。
这些结果表明，OsNAP 作为叶片衰老的正调控因子发挥作用，这种调控可能通过 JA 途径发生。
