Basic Helix-Loop-Helix (bHLH) transcription factor family in Yellow horn (Xanthoceras sorbifolia Bunge): Genome-wide characterization, chromosome location, phylogeny, structures and expression patterns.

Yellow horn (Xanthoceras sorbifolia Bunge) is a oil-rich, woody deciduous shrub with exceptional economic and ecological values. Basic Helix-Loop-Helix (bHLH) transcription factor (TF) family fulfills crucial biological functions in plant. However, genome-wide survey of the bHLH genes in yellow horn has not been performed. In this study, 136 putative XsbHLH genes were identified from yellow horn genome which were divided into 26 subfamilies according to the sequence similarity and phylogenetic relationships. 130 XsbHLH genes were unevenly distributed on 15 chromosomes, with six XsbHLH genes locating on the scaffolds. The similar structural compositions of XsbHLHs in the same subfamily suggested that they were relatively conserved and therefore exhibited similar molecular functions. Cis-regulatory elements analysis revealed that most XsbHLH genes had many stress-responsive elements, such as MYB, ARE, ABRE and LTR. In addition, XsbHLHs showed differential expression profiles under various abiotic stresses. Transcriptome analysis revealed that three XsbHLH genes, including XsbHLH 59, XsbHLH 71 and XsbHLH 102, were significantly up-regulated under salt, ABA and low temperature stresses over time, demonstrating their key roles in stress responses. The current study would provide a comprehensive information for further functional research on the stress-responsive bHLH gene candidates in yellow horn.