CsAGA1 and CsAGA2 Mediate RFO Hydrolysis in Partially Distinct Manner in Cucumber Fruits.
A Raffinose family oligosaccharides (RFOs) is one of the major translocated sugars in the vascular bundle of cucumber, but little RFOs can be detected in fruits. Alpha-galactosidases (α-Gals) catalyze the first catabolism step of RFOs. Six α-Gal genes exist in a cucumber genome, but their spatial functions in fruits remain unclear. Here, we found that RFOs were highly accumulated in vascular tissues. In phloem sap, the stachyose and raffinose content was gradually decreased, whereas the content of sucrose, glucose and fructose was increased from pedicel to fruit top. Three alkaline forms instead of acid forms of were preferentially expressed in fruit vascular tissues and alkaline forms have stronger RFO-hydrolysing activity than acid forms. By inducible gene silencing of three alkaline forms of , stachyose was highly accumulated in RNAi- plants, while raffinose and stachyose were highly accumulated in RNAi- plants. The content of sucrose, glucose and fructose was decreased in both RNAi- and RNAi- plants after β-estradiol treatment. In addition, the fresh- and dry-weight of fruits were significantly decreased in RNAi- and RNAi- plants. In cucurbitaceous plants, the non-sweet motif within the promoter of is widely distributed in the promoter of its homologous genes. Taken together, we found RFOs hydrolysis occurred in the vascular tissues of fruits. and played key but partly distinct roles in the hydrolysis of RFOs.