Alkaline alpha-galactosidase 2 (CsAGA2) plays a pivotal role in mediating source-sink communication in cucumber

文献类型： 外文期刊

第一作者： Liu, Huan

作者： Liu, Huan;Zhao, Yalong;Nie, Jing;Yao, Xuehui;Lv, Lijun;Yang, Junwei;Ma, Ning;Guo, Yicong;Li, Yaxin;Lin, Tao;Sui, Xiaolei;Liu, Xin;Yang, Xueyong;Liu, Xin

作者机构：

期刊名称：PLANT PHYSIOLOGY （ 影响因子：8.005； 五年影响因子：9.115 ）

ISSN： 0032-0889

年卷期： 2022 年 189 卷 3 期

页码：

收录情况： SCI

摘要： Sugars are necessary for plant growth and fruit development. Cucumber (Cucumis sativus L.) transports sugars, mainly raffinose family oligosaccharides (RFOs), in the vascular bundle. As the dominant sugars in cucumber fruit, glucose and fructose are derived from sucrose, which is the product of RFO hydrolysis by alpha-galactosidase (alpha-Gal). Here, we characterized the cucumber alkaline alpha-galactosidase 2 (CsAGA2) gene and found that CsAGA2 has undergone human selection during cucumber domestication. Further experiments showed that the expression of CsAGA2 increases gradually during fruit development, especially in fruit vasculature. In CsAGA2-RNA interference (RNAi) lines, fruit growth was delayed because of lower hexose production in the peduncle and fruit main vascular bundle (MVB). In contrast, CsAGA2-overexpressing (OE) plants displayed bigger fruits. Functional enrichment analysis of transcriptional data indicated that genes related to sugar metabolism, cell wall metabolism, and hormone signaling were significantly downregulated in the peduncle and fruit MVBs of CsAGA2-RNAi plants. Moreover, downregulation of CsAGA2 also caused negative feedback regulation on source leaves, which was shown by reduced photosynthetic efficiency, fewer plasmodesmata at the surface between mesophyll cell and intermediary cell (IC) or between IC and sieve element, and downregulated gene expression and enzyme activities related to phloem loading, as well as decreased sugar production and exportation from leaves and petioles. The opposite trend was observed in CsAGA2-OE lines. Overall, we conclude that CsAGA2 is essential for cucumber fruit set and development through mediation of sugar communication between sink strength and source activity. Alkaline alpha-galactosidase 2 hydrolyzes raffinose family oligosaccharides in companion cells of cucumber fruit to initiate phloem unloading of sugars for fruit growth and source-sink communication.

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