Mao Zuolin, Li Mengdi, Gao Siyang, Zhao Zeqi, Zhai Xiawan, Liu Ji-Hong, Cheng Lailiang, Li Chunlong
National Key Laboratory for Germplasm Innovation & Utilization of Horticultural Crops, College of Horticulture and Forestry Sciences, Huazhong Agricultural University, Wuhan, China.
Hubei Hongshan Laboratory, Wuhan, China.
Plant Biotechnol J. 2025 Sep 9. doi: 10.1111/pbi.70341.
Abscisic acid (ABA) and calcium respectively work as crucial plant hormones and second signalling molecules in the regulation of fruit development and quality formation, including the sugar content and flavour quality. However, the regulatory mechanisms of fruit sugar accumulation arising from the interaction between ABA and calcium have not yet been fully elucidated. Here, we show that the application of ABA or calcium enhances sugar accumulation in sweet orange (Citrus sinensis) fruit, accompanied by upregulation of the expression level of tonoplast sugar transporter 2 (CsTST2), which mediates the transport of sugars into the vacuole. Based on molecular and transgenic analyses, we identified CsABI5 as the core transcription factor that positively regulates CsTST2 expression for sugar accumulation. Both CsSRK2A, a key player in ABA signalling, and CsCIPK6, a kinase linked to calcium signalling, interact with and phosphorylate CsABI5 at distinct amino acid sites to enhance its transcriptional activity. Interestingly, CsABI5 also activates the expression of CsCIPK6 by binding to its promoter, thereby establishing a positive feedback loop between ABA and calcium signalling that cascades into higher expression of CsTST2 and sugar content. Collectively, these findings uncover a novel molecular network that underlies sugar accumulation in citrus, revealing the intricate coordination between ABA and calcium signalling in regulating tonoplast sugar transport in a non-climacteric fruit.
脱落酸（ABA）和钙分别作为关键的植物激素和第二信号分子，参与果实发育和品质形成的调控，包括糖分含量和风味品质。然而，ABA与钙相互作用导致果实糖分积累的调控机制尚未完全阐明。在此，我们发现施用ABA或钙可促进甜橙（Citrus sinensis）果实中的糖分积累，同时液泡膜糖转运蛋白2（CsTST2）的表达水平上调，该蛋白介导糖分向液泡的转运。基于分子和转基因分析，我们确定CsABI5是正向调控CsTST2表达以促进糖分积累的核心转录因子。ABA信号通路中的关键因子CsSRK2A和与钙信号相关的激酶CsCIPK6均与CsABI5相互作用，并在不同的氨基酸位点使其磷酸化，从而增强其转录活性。有趣的是，CsABI5还通过结合CsCIPK6的启动子来激活其表达，从而在ABA和钙信号之间建立正反馈回路，进而导致CsTST2的更高表达和糖分含量增加。总的来说，这些发现揭示了柑橘果实糖分积累的一个新的分子网络，揭示了非跃变型果实中ABA和钙信号在调控液泡膜糖转运方面的复杂协调作用。
