The CsMYB36-CsSWEET17 module mediates the calcium-induced sucrose accumulation in citrus

Abstract

Sugar content serves as a crucial determinant of fruit flavor quality and nutritional value. Calcium plays extensive regulatory roles in fruit development and quality formation, yet the molecular mechanisms underlying calcium-mediated sugar accumulation remain poorly understood. In this study, we demonstrate that calcium treatment enhances sugar accumulation in both citrus fruits and calli, concomitant with upregulated expression of the sucrose transporter gene CsSWEET17. Functional characterization revealed that the membrane-localized CsSWEET17 protein exhibits sucrose transport activity. Transgenic overexpression of CsSWEET17 in citrus juice sacs, calli and heterologous tomato systems consistently elevated sucrose levels. Conversely, suppression of CsSWEET17 expression through either virus-induced gene silencing or RNA interference significantly reduced sucrose content in citrus. Further investigation identified CsMYB36 as a calcium-responsive transcription factor that directly activates CsSWEET17 expression. Transgenic validation demonstrated that both calcium signaling and CsMYB36-mediated sucrose accumulation strictly depend on CsSWEET17 transcriptional regulation. Our findings elucidate a novel calcium-MYB36-SWEET17 regulatory module controlling sucrose accumulation, providing molecular insights into calcium-based strategies in citrus quality improvement and informing fundamental mechanisms of sugar transporter regulation in fruit crops.

Acknowledgments

We thank Prof. Ruth Stadler at the University Erlangen-Nürnberg for S. cerevisiae strain CSY4000. We thank Core Facilities in National Key Laboratory for Germplasm Innovation and Utilization of Horticultural Crops in Huazhong Agricultural University for technical support. This work was supported by National Key Research and Development Program of China (2023YFD2300603, 2022YFF1003100), the National Natural Science Foundation of China (32322073), Foundation of Hubei Hongshan Laboratory (2021hszd016), Fundamental Research Funds for the Central Universities (2662025YLPY003) and the Huazhong Agricultural University (start-up funding to C.L.)

Author contributions

C.L. and J.H.L. conceived and designed the research. X.S. performed most of the experiments and analyzed the data, M.L., Y.L., Z.M. and X.Z. assisted with the experiments. X.S. and C.L. wrote the manuscript draft, C.L. and J.H.L. finalized writing and revision of the manuscript.

Data availability

All data is available within the manuscript and its supporting materials.

Conflict of interest statement

The authors declare no conflict of interest.

Supplementary data

Supplementary data is available at Horticulture Research online.

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