Transcription factors with basic helix–loop–helix (bHLH) structures regulate plant growth, epidermal structure development, metabolic processes, and responses to stress extensively. Sea lavender (Limonium bicolor) is a recretohalophyte with unique salt glands in the epidermis that make it highly resistant to salt stress, and contribute to improve saline lands. However, the features of the bHLH transcription factor family in L. bicolor are largely unknown. Here, we systematically analyzed the characteristics, localization, and phylogenetic relationships of 187 identified bHLH family genes throughout the L. bicolor genome, as well as their cis-regulatory promoter elements, expression patterns, and key roles in salt gland development or salt tolerance by genetic analysis. Nine verified L. bicolor bHLH genes are expressed and the encoded proteins function in the nucleus, among which the proteins encoded by Lb2G14060 and Lb1G07934 also localize to salt glands. Analysis of CRISPR-Cas9-generated knockout mutants and overexpression lines indicated that the protein encoded by Lb1G07934 is involved in the formation of salt glands, salt secretion and salt resistance, indicating that bHLH genes strongly influence epidermal structure development and stress responses. The current study lays the foundation for further investigation of the effects and functional mechanisms of bHLH genes in L. bicolor and paves the way for selecting salt-tolerance genes that will enhance salt resistance in crops and for the improvement of saline soils.

中文翻译：

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bHLH 转录因子的全基因组鉴定和泌盐植物海薰衣草（Limium bicolor）盐腺发育的功能分析


具有基本螺旋-环-螺旋（bHLH）结构的转录因子广泛调节植物生长、表皮结构发育、代谢过程和对胁迫的反应。海薰衣草（Limium bicolor）是一种泌盐植物，其表皮具有独特的盐腺，使其对盐胁迫具有高度抵抗力，有助于改善盐碱地。然而，双色乳杆菌中 bHLH 转录因子家族的特征很大程度上未知。在这里，我们通过系统分析了整个 L. bicolor 基因组中 187 个已鉴定的 bHLH 家族基因的特征、定位和系统发育关系，以及它们的顺式调控启动子元件、表达模式以及在盐腺发育或耐盐性中的关键作用。遗传分析。九个经过验证的双色乳杆菌 bHLH 基因得到表达，其编码的蛋白质在细胞核中发挥作用，其中 Lb2G14060 和 Lb1G07934 编码的蛋白质也定位于盐腺。对CRISPR-Cas9生成的敲除突变体和过表达系的分析表明，Lb1G07934编码的蛋白参与盐腺的形成、盐分泌和盐抗性，表明bHLH基因强烈影响表皮结构发育和应激反应。本研究为进一步研究二色草bHLH基因的作用和功能机制奠定了基础，为筛选增强作物抗盐性的耐盐基因和改良盐渍土铺平了道路。