The basic/helix-loop-helix (bHLH) transcription factor family exists in all three eukaryotic kingdoms as important participants in biological growth and development. To date, the comprehensive genomic and functional analyses of bHLH genes has not been reported in cucumber (Cucumis sativus L.). Here, a total of 142 bHLH genes were identified and classified into 32 subfamilies according to the conserved motifs, phylogenetic analysis and gene structures in cucumber. The sequences of CsbHLH proteins were highly conserved based on the results of multiple sequence alignment analyses. The chromosomal distribution, synteny analysis, and gene duplications of these 142 CsbHLHs were further analysed. Many elements related to stress responsiveness and plant hormones were present in the promoter regions of CsbHLH genes based on a cis-element analysis. By comparing the phylogeny of cucumber and Arabidopsis bHLH proteins, we found that cucumber bHLH proteins were clustered into different functional clades of Arabidopsis bHLH proteins. The expression analysis of selected CsbHLHs under abiotic stresses (NaCl, ABA and low-temperature treatments) identified five CsbHLH genes that could simultaneously respond to the three abiotic stresses. Tissue-specific expression profiles of these five genes were also analysed. In addition, 35S:CsbHLH041 enhanced the tolerance to salt and ABA in transgenic Arabidopsis and in cucumber seedlings, suggesting CsbHLH041 is an important regulator in response to abiotic stresses. Lastly, the functional interoperability network among the CsbHLH proteins was analysed. This study provided a good foundation for further research into the functions and regulatory mechanisms of CsbHLH proteins and identified candidate genes for stress resistance in cucumber.

中文翻译：

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黄瓜bHLH家族基因的全基因组鉴定和表征以及拟南芥和黄瓜中NasCl和ABA耐受性中CsbHLH041的功能表征。

基本/螺旋-环-螺旋（bHLH）转录因子家族作为生物生长和发育的重要参与者存在于所有三个真核生物王国中。迄今为止，黄瓜（Cucumis sativus L.）中尚未报道bHLH基因的全面基因组和功能分析。在这里，根据保守的基序，系统发育分析和黄瓜的基因结构，共鉴定了142个bHLH基因并将其分为32个亚科。基于多个序列比对分析的结果，CsbHLH蛋白的序列高度保守。进一步分析了这142个CsbHLHs的染色体分布，同义分析和基因重复。基于顺式元素分析，CsbHLH基因的启动子区域中存在许多与胁迫响应性和植物激素相关的元素。通过比较黄瓜和拟南芥bHLH蛋白的系统发育，我们发现黄瓜bHLH蛋白聚类到拟南芥bHLH蛋白的不同功能进化枝中。在非生物胁迫（NaCl，ABA和低温处理）下选择的CsbHLHs的表达分析确定了五个可同时响应这三个非生物胁迫的CsbHLH基因。还分析了这五个基因的组织特异性表达谱。此外，35S：CsbHLH041增强了转基因拟南芥和黄瓜幼苗对盐和ABA的耐受性，表明CsbHLH041是应对非生物胁迫的重要调节剂。最后，分析了CsbHLH蛋白之间的功能互操作性网络。