Genome-wide identification and expression analysis of bHLH transcription factors reveal their putative regulatory effects on petal nectar spur development in Aquilegia

The basic helix-loop-helix (bHLH) transcription factors (TFs) control a diversity of organ morphogenesis involved in cell division and cell expansion processes. The development of petal nectar spur, which plays important roles in plant-pollinator interaction and adaptive radiation, comprised cell division and cell expansion phases in Aquilegia. Here, we conducted a genome-wide identification of the bHLH gene family in Aquilegia to determine the characteristics and the expression profiles of this gene family during the development of petal nectar spur. A total of 120 AqbHLH proteins were identified from the Aquilegia coerulea genome. The phylogenetic tree showed that AqbHLH members were divided into 15 subfamilies, among which S7 and S8 subfamilies occurred marked expansion. Nineteen residues with conservation of more than 50% were found in the four conserved regions. The publicly RNA-Seq data and qRT-PCR results showed that AqbHLH027, AqbHLH083, AqbHLH046, and AqbHLH092 would be associated with the development of petal nectar spur by regulating cell division and cell cycle in phase I. While AqbHLH036 might participate the spur cell elongation and cell expansion in phase . This study provides useful insights for further probing on the function of AqbHLH TFs in the regulation of petal nectar spur development.