Abstract: In this study, a full-length cDNA sequence (GenBank No：KF751654）encoding a bHLH transcription factor GhMYC4 was isolated from Gossypium hirsutism L. via silico cloning. Results of bioinformatic analysis showed that the cDNA sequence contained a complete open reading frame of 1 650 bp, encoding a protein of 549 amino acids. The N-terminal of GhMYC4 protein contained a typical conserved bHLH-MYC-N domain of MYC protein, and its C-terminal contained a typical DNA binding domain bHLH. Results of homologous sequence alignment analysis and phylogenetic tree analysis showed that GhMYC4 protein was most closely related to Gossypium hirsutism L. bHLH and Theobroma cacao bHLH. It had a great similarity with MYC2 family members of other speices. The tissue expression pattern analysis using RT-PCR and Q-PCR showed that GhMYC4 was highly expressed in the root and leaf of cotton, but only faintly expressed in the fiber tissue. Subcellular localization analysis of the transient expression of this gene in Arabidopsis thaliana protoplasts confirmed that the GhMYC4 protein was located in the nucleus. Under the experiments of drought and salt stresses, overexpression of GhMYC4 in Arabidopsis showed a good drought resistance and salt tolerance compared to the control. The contents of relative moisture, soluble sugar and proline in the transgentic arabidopsis thaliana were all significantly higher than those in the control, and the MDA content was significantly lower than that of the control group. The results of this study  provided a new gene source for the cultivation of new drought resistant and salt tolerant cotton varieties.

Key words: Gossypium hirsutism L., bHLH transcription factor, MYC protein, subcellular localization, tissue-specific expression, drought resistant and salt tolerant

摘要： 通过电子克隆技术从陆地棉中分离了一个GhMYC4基因（GenBank登录号：KF751654），该基因编码的蛋白属于bHLH类转录因子。生物信息学分析结果显示：该基因完整开放阅读框有1 650 bp，编码549个氨基酸。GhMYC4蛋白的N-端具有MYC蛋白家族特有的bHLH-MYC-N保守结构域，C端具有高度保守的DNA结合域即bHLH结构域。同源比对和系统进化树分析结果显示GhMYC4蛋白与陆地棉bHLH转录因子和可可bHLH转录因子的亲缘关系最近，与其他物种的MYC2家族成员具有很大的相似性。通过Real time-PCR检测该基因的组织表达特异性，结果显示该基因在陆地棉的根部和叶片中高效表达，纤维中微量表达。在拟南芥原生质体中进行该基因的瞬时表达，证实了GhMYC4蛋白定位于细胞核。转GhMYC4的拟南芥受到高盐和干旱胁迫后相比于对照在表型上表现出很好的抗旱耐盐性能，其叶片相对含水量、可溶性糖含量及脯氨酸含量显著高于对照，MDA含量显著低于对照。该结果为培育抗旱耐盐棉花新品种提供了新的基因来源。

关键词: 陆地棉, bHLH转录因子, MYC蛋白, 亚细胞定位, 组织表达特异性, 抗旱耐盐