摘要Drought and low temperature are two key envi-ronmental factors that induce adult citrus flow-ering. However, the underlying regulation mecha-nism is poorly understood. The bZIP transcription factor FD is a key component of the florigen acti-vation complex (FAC) which is composed of FLOWERING LOCUS T (FT), FD, and 14-3-3 pro-teins. In this study, isolation and characterization of CiFD in citrus found that there was alternative splicing (AS) of CiFD, forming two different pro-teins (CiFDα and CiFDβ). Further investigation found that their expression patterns were similar in different tissues of citrus, but the subcellular localization and transcriptional activity were dif-ferent. Overexpression of the CiFD DNA sequence (CiFD-DNA), CiFDα, or CiFDβin tobacco and citrus showed early flowering, and CiFD-DNA transgenic plants were the earliest, followed by CiFDβ and CiFDα. Interestingly, CiFDα and CiFDβ were in-duced by low temperature and drought, re-spectively. Further analysis showed that CiFDαcan form a FAC complex with CiFT, Ci14-3-3, and then bind to the citrus APETALA1 (CiAP1) pro-moter and promote its expression. However, CiFDβ can directly bind to the CiAP1 promoter independently of CiFT and Ci14-3-3. These results showed that CiFDβ can form a more direct and simplified pathway that is independent of the FAC complex to regulate drought-induced flowering through AS. In addition, a bHLH transcription factor (CibHLH96) binds to CiFD promoter and promotes the expression of CiFD under drought condition. Transgenic analysis found that CibHLH96 can promote flowering in transgenic tobacco. These results suggest that CiFD is in-volved in drought- and low-temperature-induced citrus flowering through different regulatory patterns.