The HD-ZIP Ⅳ transcription factors have been identified and functional characterized in many plant species. However, no tobacco HD-ZIP IV gene has been isolated, and it is not yet known whether HD-ZIP IV genes are involved in controlling flavonols accumulation in plants. Here, we cloned a HD ZIP gene named NtHDG2 from Nicotiana tabacum, which belongs to the class IV of HD-ZIP family, and the NtHDG2-GFP fusion protein is localized to the nucleus. We further observed that the flavonols contents in the NtHDG2 overexpression leaves increase to 1.9-4.5 folds of that in WT plants, but in the NtHDG2-RNAi plants the flavonols contents reduce to 20.9%-52.7% of that in WT plants. The transcriptions of one regulatory gene NtMYB12, and three structural genes (NtPAL, NtF3'H, NtF3GT), contributing to flavonols biosynthesis, were significantly induced by NtHDG2. However, the transcription level of NtNAC002, a flavonols biosynthesis repressor, was also significantly up-regulated in NtHDG2-overexpression lines, but significantly down-regulated in the RNAi lines, indicating that HDG2 regulates the synthesis of flavonols as a complex regulatory network. Moreover, ectopic expression of NtHDG2 gene promoted the transcription of several AP2/ERF genes, including NtERF1-5, NtERF109, NtDREB1, and NtCIPK11, which participate in regulating root development and resistance to abiotic stresses. Our findings reveal the new function of HD-ZIP IV transcription factors in flavonoids biosynthesis, and indicate that HD-ZIP IV members may play an important role in plant resistance to abiotic stress. The NtHDG2 gene provides a promising target for genetically manipulating to increase the amounts of flavonols in tobacco leaves.

中文翻译：

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HD-ZIP IV 转录因子 NtHDG2 在调节烟草黄酮醇生物合成中的功能表征。


HD-ZIP IV 转录因子已在许多植物物种中得到鉴定和功能表征。然而，尚未分离出烟草HD-ZIP IV基因，并且尚不清楚HD-ZIP IV基因是否参与控制植物中黄酮醇的积累。本研究从烟草中克隆了一个HD ZIP基因NtHDG2，该基因属于HD-ZIP家族IV类，NtHDG2-GFP融合蛋白定位于细胞核。我们进一步观察到，NtHDG2过表达叶片中的黄酮醇含量增加至WT植物的1.9-4.5倍，但在NtHDG2-RNAi植物中，黄酮醇含量降低至WT植物的20.9%-52.7%。 NtHDG2 显着诱导了有助于黄酮醇生物合成的一个调控基因 NtMYB12 和三个结构基因（NtPAL、NtF3'H、NtF3GT）的转录。然而，黄酮醇生物合成阻遏物 NtNAC002 的转录水平在 NtHDG2 过表达株系中也显着上调，但在 RNAi 株系中显着下调，表明 HDG2 作为一个复杂的调控网络来调节黄酮醇的合成。此外，NtHDG2基因的异位表达促进了多个AP2/ERF基因的转录，包括NtERF1-5、NtERF109、NtDREB1和NtCIPK11，这些基因参与调节根发育和抵抗非生物胁迫。我们的研究结果揭示了HD-ZIP IV转录因子在类黄酮生物合成中的新功能，并表明HD-ZIP IV成员可能在植物抵抗非生物胁迫中发挥重要作用。 NtHDG2 基因为基因操作增加烟叶中黄酮醇的含量提供了一个有前景的靶标。