Our previous study demonstrated that the expression of GhNAC4, a NAC transcription factor from cotton was induced by abiotic stresses and abscisic acid (ABA) treatment. In the present study, we investigated the molecular mechanisms underlying ABA and stress response of GhNAC4. Over-expression of GhNAC4 in transgenic tobacco conferred tolerance to salinity and drought treatments with associated enhanced expression of several stress-responsive marker genes. GhNAC4 is a nuclear protein that exhibits transcriptional activation property and the C-terminal transcriptional regulatory (TR) domain is responsible for it. GhNAC4 also forms homo-dimers and the N-terminal NAC-domain is essential for this activity. The structure-function relationship of NAC transcription factors, particularly with respect to abiotic stress tolerance remains largely unclear. In this study, we investigated the domains essential for the biochemical functions of GhNAC4. We developed transgenic tobacco plants overexpressing the GhNAC4 NAC-domain and the TR-domain separately. NAC-domain transgenics showed hypersensitivity to exogenous ABA while TR-domain transgenics exhibited reduced sensitivity. Abiotic stress assays indicated that transgenic plants expressing both the domains separately were more tolerant than wild-type plants with the NAC-domain transgenics showing increased tolerance as compared to TR-domain transgenics. Expression analysis revealed that various stress-responsive genes were upregulated in both NAC-domain and TR-domain transgenics as compared to wild-type under salinity and drought treatments. These results suggest that the stress tolerance ability of GhNAC4 is associated with both the component domains while the ABA responsiveness is largely associated with N-terminal NAC-domain.

中文翻译：

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陆地棉NAC转录因子，GhNAC4与ABA和非生物胁迫反应的结构-功能关系

我们以前的研究表明，GhNAC4的表达，棉花的NAC转录因子是通过非生物胁迫和脱落酸（ABA）处理诱导的。在本研究中，我们调查了ABA和GhNAC4应激反应的分子机制。GhNAC4在转基因烟草中的过表达赋予了对盐分和干旱处理的耐受性，并增强了几种胁迫反应性标记基因的表达。GhNAC4是一种核蛋白，具有转录激活特性，其C端转录调节（TR）结构域负责其中。GhNAC4还形成同型二聚体，而N端NAC结构域对该活性至关重要。NAC转录因子的结构-功能关系，特别是关于非生物胁迫耐受性的关系尚不清楚。在这个研究中，我们研究了GhNAC4的生化功能必不可少的域。我们开发了分别过表达GhNAC4 NAC域和TR域的转基因烟草植物。NAC域转基因对外源ABA表现出超敏性，而TR域转基因则表现出降低的敏感性。非生物胁迫测定表明，分别表达两个结构域的转基因植物比野生型植物具有更大的耐受性，其中NAC结构域转基因与TR结构域转基因相比具有更高的耐受性。表达分析显示，与盐和干旱处理下的野生型相比，NAC域和TR域转基因中的各种胁迫响应基因均上调。