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.

中文翻译：

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热诱导的 HpbHLH43 通过激活火龙果中的 HpSOC1 参与促进花芽诱导


火龙果属于仙人掌科 Hylocereus 属，由于其对干旱和热胁迫的高度耐受性，越来越多地在热带和亚热带地区种植。从营养阶段到生殖阶段的转变对果实产量有显著影响，因此必须解开火龙果的开花调节机制。在本研究中，鉴定出一种 HpbHLH43 转录因子，它与胁迫耐受性和开花诱导有关。为了进一步研究 HpbHLH43 的生物学功能，从火龙果中获得 747 bp 的全长编码序列 （CDS）。高温胁迫 （42 °C） 下，火藤茎芽和花芽中 HpbHLH43 的表达上调。瞬时表达显示 HpbHLH43 位于细胞核中，并在 N 端具有转录活性。在生物学上，热诱导 HpbHLH43 启动子激活叶片和花中的 GUS 基因表达。拟南芥中过表达 HpbHLH43 显著加快了开花时间，并且比野生型更耐高温。酵母单杂交和双荧光素酶测定显示 HpbHLH43 可与 HpSOC1 相互作用。总之，高温诱导型 HpbHLH43 直接靶向 HpSOC1，因此促进了火龙果中的花芽诱导，这为了解火龙果中花诱导的分子调控提供了见解。