Genome-wide identification and characterization of cucumber bHLH family genes and the functional characterization of CsbHLH041 in NaCl and ABA tolerance in Arabidopsis and cucumber

Jialin Li,Ting Wang,Jing Han,Zhonghai Ren

doi:10.1186/s12870-020-02440-1

Abstract

BackgroundThe 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.).ResultsHere, 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.ConclusionThis 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.

Highlights

The basic/helix-loop-helix transcription factor family exists in all three eukaryotic kingdoms as important participants in biological growth and development
Identification and analysis of cucumber bHLH genes To identify CsbHLH family genes in cucumber, we used the BlastP programme to search against the cucumber genome database by using 166 Arabidopsis bHLH proteins [2, 10] and the consensus protein sequences of the bHLH domain, with Hidden Markov Model (HMM) profile (PF00010) as queries
142 proteins had the corresponding conserved bHLH domain, which were named CsbHLH1 to CsbHLH142 according to their sequence similarity and phylogenies with individual AtbHLH proteins

Summary

Introduction

The basic/helix-loop-helix (bHLH) transcription factor family exists in all three eukaryotic kingdoms as important participants in biological growth and development. Basic helix-loop-helix (bHLH) transcription factors form one of the largest families of TFs and exist widely in all three eukaryotic kingdoms [1, 2]. The bHLH TFs are named for their own structural characteristics [3], which are mostly composed of conserved 60 amino acid residues. The basic region is distributed at the Nterminus of the bHLH conserved domain and contains approximately 15 to 20 residues, which are related to DNA binding [5, 6]. The HLH domain is distributed at the C-terminus of the gene sequence, composing of two amphipathic α-helices mainly constituting of hydrophobic residues linked by a loop region of variable sequence and length. The HLH domain is an essential structure for the formation of homologous or heterologous dimers in bHLH TFs [6, 7]

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Results

Conclusion