Molecular Cloning and Functional Analysis of the Gene and Promoter of IbbHLH2from Purple-Fleshed Sweet Potato

Transcription factors basic helix-loop-helix (bHLH) have been identified as regulators of flavonoid synthesis in flowers, seeds and fruits. Transcription factors IbbHLH2 regulate the expression of structural genes that participated in anthocyanin synthesize of purple-fleshed sweet potato. In this study, IbbHLH2 had been cloned, the expression pattern and function were investigated in purple-fleshed sweet potato. Real-time quantitative PCR was used to determine the expression levels of transcription factors (IbbHLH2, IbMYB1, IbWD40) in different colour and developmental stages of sweet potato. The results showed that the expression ofIbbHLH2 was completely synchronized with the accumulation of anthocyanins in different colour and developmental stages of sweet potato. The IbbHLH2 was introduced into wild-type Arabidopsis thaliana by Agrobacterium-mediated transformation. The cotyledon and epicotyl of the transgenic plants became purple in color, the anthocyanin content was increased and the structural genes (CHS, CHI, F3H, DFR, ANS and 3GT) were upregulated. In addition, the IbbHLH2 promoter sequence of 1020 bp was cloned by hi-TAIL PCR and was shown using a histochemical assay to initiate the expression of the GUS gene. Bioinformatic analysis indicates that the IbbHLH2 promoter contains a TATA-box and a CAAT-box, MYB-binding elements and elements governing responses to light, gibberellic acid (GA), abscisic acid (ABA) and salicylic acid (SA). The expression of IbbHLH2 was regulated by MYB transcription factors and environmental factors.