J Integr Plant Biol. ›› 2023, Vol. 65 ›› Issue (3): 674-691.DOI: 10.1111/jipb.13390

• Abiotic Stress Responses • Previous Articles     Next Articles

A bZIP transcription factor (CiFD) regulates drought- and low-temperature-induced flowering by alternative splicing in citrus

Li-Xia Ye1,2†, Yan-Mei Wu1†, Jin-Xia Zhang1, Jin-Xin Zhang1, Huan Zhou1, Ren-Fang Zeng1, Wei-Xuan Zheng1, Mei-Qi Qiu1, Jing-Jing Zhou1, Zong-Zhou Xie1, Chun-Gen Hu1 and Jin-Zhi Zhang1*   

  1. 1. Key Laboratory of Horticultural Plant Biology (Ministry of Education), College of Horticulture and Forestry Science, Huazhong Agricultural University, Wuhan 430070, China;
    2. Institute of Fruit and Tea, Hubei Academy of Agricultural Sciences, Wuhan 430064, China
    These authors contributed equally to this work.
    *Correspondence: Jin‐Zhi Zhang (jinzhizhang@mail.hzau.edu.cn)
  • Received:2022-06-23 Accepted:2022-10-13 Online:2022-10-17 Published:2023-03-01

Abstract: Drought and low temperature are two key environmental factors that induce adult citrus flowering. However, the underlying regulation mechanism is poorly understood. The bZIP transcription factor FD is a key component of the florigen activation complex (FAC) which is composed of FLOWERING LOCUS T (FT), FD, and 14-3-3 proteins. In this study, isolation and characterization of CiFD in citrus found that there was alternative splicing (AS) of CiFD, forming two different proteins (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 different. Overexpression of the CiFD DNA sequence (CiFD-DNA), CiFDα, or CiFDβ in tobacco and citrus showed early flowering, and CiFD-DNA transgenic plants were the earliest, followed by CiFDβ and CiFDα. Interestingly, CiFDα and CiFDβ were induced by low temperature and drought, respectively. Further analysis showed that CiFDα can form a FAC complex with CiFT, Ci14-3-3, and then bind to the citrus APETALA1 (CiAP1) promoter 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 involved in drought- and low-temperature-induced citrus flowering through different regulatory patterns.

Key words: alternative splicing, citrus, CiFD, drought, flowering, low temperature

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