MdERDL6-mediated glucose efflux to the cytosol promotes sugar accumulation in the vacuole through up-regulating TSTs in apple and tomato.

Lingcheng Zhu, Baiyun Li, Limin Wu, Huixia Li, Zhengyang Wang, Xiaoyu Wei, Baiquan Ma, Yanfeng Zhang, Fengwang Ma, Yong-Ling Ruan, Mingjun Li

Proceedings of the National Academy of Sciences of the United States of America 2021 Jan 05

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Sugar transport across tonoplasts is essential for maintaining cellular sugar home ostasis and metabolic balance in plant cells. It remains unclear, however, how this process is regulated among different classes of sugar transporters. Here, we identified a tonoplast H+/glucose symporter, MdERDL6-1, from apples, which was highly expressed in fruits and exhibited expression patterns similar to those of the tonoplast H+/sugar antiporters MdTST1 and MdTST2. Overexpression of MdERDL6-1 unexpectedly increased not only glucose (Glc) concentration but also that of fructose (Fru) and sucrose (Suc) in transgenic apple and tomato leaves and fruits. RNA sequencing (RNA-seq) and expression analyses showed an up-regulation of TST1 and TST2 in the transgenic apple and tomato lines overexpressing MdERDL6-1 Further studies established that the increased sugar concentration in the transgenic lines correlated with up-regulation of TST1 and TST2 expression. Suppression or knockout of SlTST1 and SlTST2 in the MdERDL6-1-overexpressed tomato background reduced or abolished the positive effect of MdERDL6-1 on sugar accumulation, respectively. The findings demonstrate a regulation of TST1 and TST2 by MdERDL6-1, in which Glc exported by MdERDL6-1 from vacuole up-regulates TST1 and TST2 to import sugars from cytosol to vacuole for accumulation to high concentrations. The results provide insight into the regulatory mechanism of sugar accumulation in vacuoles mediated by the coordinated action of two classes of tonoplast sugar transporters. Copyright © 2021 the Author(s). Published by PNAS.

Citation

Lingcheng Zhu, Baiyun Li, Limin Wu, Huixia Li, Zhengyang Wang, Xiaoyu Wei, Baiquan Ma, Yanfeng Zhang, Fengwang Ma, Yong-Ling Ruan, Mingjun Li. MdERDL6-mediated glucose efflux to the cytosol promotes sugar accumulation in the vacuole through up-regulating TSTs in apple and tomato. Proceedings of the National Academy of Sciences of the United States of America. 2021 Jan 05;118(1)