Alkaline α-galactosidase 2 (CsAGA2) plays a pivotal role in mediating source-sink communication in cucumber
Alkaline α-galactosidase 2 (CsAGA2) plays a pivotal role in mediating source-sink communication in cucumber
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DOI：
10.1093/plphys/kiac152
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发表时间：
2022-03-31
期刊：
影响因子：
7.4
通讯作者：
Sui, Xiaolei
中科院分区：
文献类型：
--
作者：
Liu, Huan;Liu, Xin;Sui, Xiaolei
糖是植物生长和果实发育所必需的。黄瓜（Cucumis sativus L.）在维管束中运输糖，主要是棉子糖家族寡糖（RFO）。葡萄糖和果糖是黄瓜果实中的主要糖，它们来源于蔗糖，蔗糖是α-半乳糖苷酶（α-Gal）水解RFO的产物。在这里，我们的特点是黄瓜碱性α-半乳糖苷酶2（CsAGA 2）基因，并发现CsAGA 2在黄瓜驯化过程中经历了人为选择。进一步的实验表明，CsAGA 2的表达在果实发育过程中逐渐增加，特别是在果实维管系统中。在CsAGA 2-RNA干扰（RNAi）系，果实生长延迟，因为较低的己糖生产的花序梗和果实主维管束（MVB）。与此相反，CsAGA 2过表达（OE）的植物表现出更大的果实。转录数据的功能富集分析表明，与糖代谢，细胞壁代谢和激素信号转导相关的基因在CsAGA 2-RNAi植物的花序和果实MVB中显著下调。此外，CsAGA 2的下调还引起了源叶的负反馈调节，表现为光合效率降低，叶肉细胞与中间细胞（IC）之间或IC与筛管分子之间的胞间连丝减少，与韧皮部负载相关的基因表达和酶活性下调，以及叶片和叶柄糖的产生和输出减少。在CsAGA 2-OE系中观察到相反的趋势。综上所述，CsAGA 2通过调节库强度和源活性之间的糖通讯对黄瓜座果和发育至关重要;碱性α-半乳糖苷酶2水解黄瓜果实伴胞中的棉子糖家族寡糖，启动韧皮部糖的卸载，促进果实生长和源库通讯。
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.