Phosphorylation and ubiquitination coordinate homeostasis of a tomato transporter responsible for fruit sugar accumulation

Bangqian Song; Yong Kang; Xi Zheng; Zhengguo Li; Yulin Cheng

doi:10.1016/j.jgg.2026.03.019

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Phosphorylation and ubiquitination coordinate homeostasis of a tomato transporter responsible for fruit sugar accumulation

doi: 10.1016/j.jgg.2026.03.019

a. Key Laboratory of Plant Hormones and Molecular Breeding of Chongqing, School of Life Sciences, Chongqing University, Chongqing 401331, China;
b. Center of Plant Functional Genomics and Synthetic Biology, Institute of Advanced Interdisciplinary Studies, Chongqing University, Chongqing 401331, China

Funds:

We thank Ms. Qin Deng from the Analytical and Testing Center of Chongqing University for technological guidance. This study was supported by National Key Research and Development Program of China (2022YFD2100105), National Natural Science Foundation of China (32230092, 32272381, and 32572652), Project of Chongqing Science and Technology Commission (CSTB2025NSCQ-LZX0003), and Fundamental Research Funds for the Central Universities (2024IAIS-ZX005).

Received Date: 2025-12-06
Accepted Date: 2026-03-22
Rev Recd Date: 2026-03-22

Available Online: 2026-03-27

Abstract

Abstract

Sugar transport mediated by different transporters is essential for maintaining sugar homeostasis in plants. Here, we report that phosphorylation and ubiquitination coordinate the homeostasis of a tomato (Solanum lycopersicum) sugar transporter SlSWEET16, revealing a new aspect of plant sugar homeostasis. SlSWEET16 is localized to plasma membrane and functions as a mono- and disaccharide transporter. SlSWEET16 mediates cellular sugar efflux, and CRISPR/Cas9-mediated knockout of SlSWEET16 leads to increased fruit sugar accumulation. Strikingly, SlSWEET16’s C-terminus is subjected to both phosphorylation and ubiquitination. Two protein kinases including SlSnRK2.3 and SlSnRK2.4 associate with SlSWEET16’s C-terminus, resulting into an increase in the stability of SlSWEET16. Meanwhile, SlSWEET16’s C-terminus also interacts with an E3 ubiquitin ligase SlTT3.1L2, which decreases the stability of SlSWEET16. SlSnRK2.3 and SlSnRK2.4 inhibit fruit sugar accumulation, whereas SlTT3.1L2 promotes it. Mutations of phosphorylated or ubiquitinated residues in SlSWEET16’s C-terminus further corroborate the contribution of phosphorylation and ubiquitination to the stability of SlSWEET16 and fruit sugar accumulation. Our results reveal a multiple-protein regulatory module that integrates different post-translational modifications to control transporter-mediated fruit sugar accumulation.
- Tomato fruit,
- SWEET,
- Sugar transporter,
- Post-translational modifications,
- Protein abundance

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