Regulation of seed vigor by manipulation of raffinose family oligosaccharides (RFOs) in maize and Arabidopsis
Tao Li, Yumin Zhang, Dong Wang, Ying Liu, Lynnette M.A. Dirk, Jack Goodman, A.Bruce Downie, Jianmin Wang, Guoying Wang, Tianyong Zhao.
Abstract: Raffinose family oligosaccharides (RFOs) accumulate in seeds during maturation desiccation in many plant species. It is still unclear whether RFOs have a role in establishing seed vigor. GALACTINOL-, RAFFINOSE- and STACHYOSE-SYNTHASE (GOLS, RS and STS) are enzymes responsible for RFOs biosynthesis. Only raffinose is detected in maize seeds and a unique maize RS gene (ZmRS) was identified. Two independent mutator (Mu)-interrupted zmrs lines, containing no raffinose but hyper-accumulating galactinol, had significantly reduced seed vigor, compared to null segregant (NS) controls. Unlike maize, Arabidopsis seeds contain several RFOs (raffinose, stachyose and verbascose). Manipulation of Arabidopsis RFOs content by overexpressing ZmGOLS2, ZmRS or AtSTS demonstrated that co-overexpression of ZmGOLS2 and ZmRS, or overexpression of ZmGOLS2 alone, significantly increased total RFOs and enhanced seed vigor. Surprisingly, while over-expression of ZmRS increased raffinose it dramatically decreased seed vigor, galactinol, stachyose and verbascose amounts, while the mutant (atrs5) was similar to WT in all respects except for stachyose, which it accumulated. Total RFOs, RFOs:sucrose ratio, but not absolute individual RFOs amounts, positively correlated with Arabidopsis seed vigor, with stachyose and verbascose contributing more than raffinose. These findings provide new and contrasting information about the requirement for RFOs for seed vigor of a monocot and a dicot.