Expression of Heat-Stable Starch Synthase Genes Increase Yield Potential of Heat Stressed Wheat

Several global climate models predict that global temperatures will continue to rise this century, which is a major concern for wheat production worldwide. Wheat is a temperate cereal with an optimum growth temperature range of 15-22°C. During the grain filling stage of development, for every 1°C rise above the optimum temperature, yield is reduced ~3-6%. This heat stress reduces the kernal weight of wheat seeds by decreasing starch production. The soluble starch synthase (SSS), a key heat-labile enzyme, plays an important role in regulating the conversion of sucrose to starch in the wheat endosperm. Expression of putative thermostable SSS in genetically engineered wheat could increase the productivity under heat stress. We demonstrated that the grain weight of transgenic wheat was significantly improved under high temperature conditions by independently expressing three different thermostable SSS genes under the regulatory control of either the maize ubiquitin or wheat high molecular weight glutenin promoter. Under optimum growing conditions all agronomic traits evaluated (seed size, seed number, tiller number, and physiological maturity) had no significant variations. However, under heat-stress conditions the concentration of soluble starch in transgenic lines was significantly higher compared to the controls.  Transgenic lines demonstrated up to a 34% increase in thousand seed weight compared to non-transgenic controls under heat stress conditions ranging from 31/24°C (d/n) to 34/28°C (d/n) during the grain filling period. Further analysis of transgenic wheat plants is in the process in hope to provide a novel strategy for improving heat tolerance for cool season crop plants.