Heat-induced HpbHLH43 involves in promoting floral bud induction via activating HpSOC1 in pitaya

Pitaya, belonging to the genus Hylocereus of Cactaceae family, is increasingly cultivated in tropical and subtropical regions due to its high tolerance to drought and heat stresses. The transition from the vegetative to reproductive stage significantly impacts the fruit yield, therefore it is essential to unravel the flowering regulatory mechanism of pitaya. In present work, a HpbHLH43 transcription factor was identified, which is related to stress tolerance and flowering induction. To further investigate the biological function of HpbHLH43, a 747 bp full length coding sequence (CDS) was obtained from pitaya. Under high-temperature stress (42 °C), the expression of HpbHLH43 were up-regulated in stem and floral buds of pitaya. Transient expression showed that HpbHLH43 was located in the nucleus and had transcriptional activity at the N-terminal. Biologically, heat induced the HpbHLH43 promoter to activate GUS gene expression in leaves and flowers. Overexpression of HpbHLH43 in Arabidopsis thaliana significantly accelerated flowering time and was more tolerant to high temperature than the wild-type. Yeast one-hybrid and dual-luciferase assays showed that HpbHLH43 can interact with HpSOC1. Conclusively, high-temperature inducible HpbHLH43 directly targets HpSOC1, accordingly, promotes the floral bud induction in pitaya, which provides an insight into the molecular regulations of floral induction in pitaya.