National Institute of Plant Genome Research (NIPGR), Aruna Asaf Ali Marg, New Delhi 110067, India.
Mol Biotechnol. 2011 Oct;49(2):138-50. doi: 10.1007/s12033-011-9385-7.
The plant-specific NAC (NAM, ATAF, and CUC) transcription factors have diverse role in development and stress regulation. A transcript encoding NAC protein, termed SiNAC was identified from a salt stress subtractive cDNA library of S. italica seedling (Puranik et al., J Plant Physiol 168:280-287, 2011). This single/low copy gene containing four exons and four introns within the genomic-sequence encoded a protein of 462 amino acids. Structural analysis revealed that highly divergent C terminus contains a transmembrane domain. The NAC domain consisted of a twisted antiparallel beta-sheet packing against N terminal alpha helix on one side and a shorter helix on the other side. The domain was predicted to homodimerize and control DNA-binding specificity. The physicochemical features of the SiNAC homodimer interface justified the dimeric form of the predicted model. A 1539 bp fragment upstream to the start codon of SiNAC gene was cloned and in silico analysis revealed several putative cis-acting regulatory elements within the promoter sequence. Transactivation analysis indicated that SiNAC activated expression of reporter gene and the activation domain lied at the C terminal. The SiNAC:GFP was detected in the nucleus and cytoplasm while SiNAC ΔC(1-158):GFP was nuclear localized in onion epidermal cells. SiNAC transcripts mostly accumulated in young spikes and were strongly induced by dehydration, salinity, ethephon, and methyl jasmonate. These results suggest that SiNAC encodes a membrane associated NAC-domain protein that may function as a transcriptional activator in response to stress and developmental regulation in plants.
植物特异性 NAC（NAM、ATAF 和 CUC）转录因子在发育和应激调节中具有多种作用。从盐胁迫下的甜高粱幼苗消减 cDNA 文库中鉴定出一种编码 NAC 蛋白的转录本，称为 SiNAC（Puranik 等人，J Plant Physiol 168:280-287, 2011）。该单拷贝/低拷贝基因在基因组序列中包含四个外显子和四个内含子，编码一个 462 个氨基酸的蛋白质。结构分析表明，高度变异的 C 端含有一个跨膜结构域。NAC 结构域由一侧的扭曲反平行 β-折叠与 N 端α螺旋相对，另一侧的较短螺旋组成。该结构域被预测为同源二聚体，控制 DNA 结合特异性。SiNAC 同源二聚体界面的物理化学特性证明了预测模型的二聚体形式是合理的。克隆了 SiNAC 基因起始密码子上游的 1539bp 片段，通过计算机分析发现启动子序列内存在几个假定的顺式作用调控元件。转激活分析表明，SiNAC 激活了报告基因的表达，激活结构域位于 C 端。SiNAC:GFP 在细胞核和细胞质中被检测到，而 SiNAC ΔC(1-158):GFP 在洋葱表皮细胞中定位于细胞核。SiNAC 转录本主要在幼穗中积累，并强烈诱导干旱、盐胁迫、乙烯和茉莉酸甲酯。这些结果表明，SiNAC 编码一种膜相关的 NAC 结构域蛋白，可能作为一种转录激活因子，在植物中响应胁迫和发育调节。
