Objective To investigate the changes of endogenous hormones and the expression patterns of their regulatory genes during floral bud differentiation of litchi (Litchi chinensis Sonn.), and to elucidate the key role of abscisic acid (ABA) from the floral induction stage to the inflorescence development stage.

Method Taking litchi cultivar ‘Xianjinfeng’ as the experimental material, terminal buds of autumn shoots and the third mature compound leaves were periodically collected from the floral induction stage to the inflorescence development stage (November 2021 to March 2022). The contents of endogenous hormones were determined by ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS), and the expression characteristics of genes related to ABA synthesis, metabolism, and signal transduction were analyzed by qRT-PCR.

Result During the process of floral bud differentiation, the contents of different hormones showed distinct dynamic patterns. During the floral initiation phase, the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) and ABA exhibited opposite dynamic patterns: ACC content increased and reached a peak during the early phase of floral initiation, whereas ABA content remained low; subsequently, ACC content decreased, while ABA content rebounded markedly at the late stage of floral initiation. Different gibberellin (GA) forms showed transient increases during the early phase of floral initiation. Gene expression analysis revealed that the dynamic change of ABA content was closely associated with the upregulation of Cytochrome P450, family 707, subfamily A, polypeptide genes LcCYP707A3 and LcCYP707A6, as well as the downregulation of 9-cis-epoxycarotenoid dioxygenase 1 (LcNCED1). Additionally, the key flowering genes FLOWERING LOCUS T 1 (LcFT1) and FLOWERING LOCUS T 2 (LcFT2) were significantly expressed at the floral initiation stage.

Conclusion The decrease in ABA content at the floral initiation stage is a key signal regulating litchi flowering, and its dynamics are coordinately controlled by ABA synthesis and degradation genes. This study provides a theoretical basis for the construction of the ABA-mediated flowering molecular network and the application of exogenous hormones in litchi production.