Improving Wheat Yield Under Heat Stress By Expressing Putative Thermostable Starch Synthase Genes

As global climate shifts worldwide, high temperature becomes one of the major environmental stresses for wheat production. Heat stress during the grain filling stage reduces the kernal weight of the wheat seed by decreasing starch production and soluble starch synthase (SSS), a key heat-labile enzyme that 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. In this study, we demonstrated that the grain weight of transgenic wheat was significantly improved under high temperature conditions by expressing multiple SSS from different plant species, including rice (Oryza sativa), grape (Vitis vinifera), and black cottonwood (Populus trichocarpa), respectively. These genes were selected according to a thermostabililty prediction algorithm, codon optimized for wheat, and expressed in transgenic wheat under regulatory control of either the maize ubiquitin or wheat high molecular weight glutenin promoter (Dy10). 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 during the grain filling period ranging from 31/24 °C (d/n) to 36/28 °C (d/n) demonstrated up to a 34% increase in thousand seed weight in transgenic lines compared to non-transgenic controls grown under the same condition. Starch analysis also confirmed the concentrations of soluble starch in transgenic lines were also significantly higher compared to the controls.