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.

Methods Taking litchi cultivar ‘Xianjinfeng’ as the experimenta 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 content of endogenous hormones was 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 quantitative real-time PCR (qRT-PCR).

Results During the process of floral bud differentiation, the contents of different hormones showed distinct dynamic patterns. The contents of 1-aminocyclopropane-1-carboxylic acid (ACC, a precursor of ethylene synthesis) and gibberellin (GA) significantly increased at the floral initiation stage, while the ABA content significantly decreased. Endogenous hormone levels in floral buds exhibited an overall increasing trends. Gene expression analysis revealed that the dynamic changes of ABA content were closely associated with the upregulation of Cytochrome P450, family 707, subfamily A, polypeptide 3 (LcCYP707A3) and Cytochrome P450, family 707, subfamily A, polypeptide 6 (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.