Increased grain yield and micronutrient concentration in transgenic winter wheat by ectopic expression of a barley sucrose transporter

Optimising assimilate partitioning to spikes is important to increase wheat yield potential. Novel winter wheat lines (HOSUT), ectopically expressing barley sucrose transporter HvSUT1 controlled by the barley Hordein B1 promoter were used to evaluate the potential of improved sucrose uptake capacity on grain yield and quality under field-like conditions. Three independent HOSUT lines were grown over three years in micro-plots. Grain yield per plot was significantly increased by 28%, together with higher protein yield per plot and higher iron and zinc concentration when compared to the non-transformed control wheat Certo. Thousand grain weight was enhanced, indicating that expression of HvSUT1 increases individual grain sink strength. HOSUT grains are larger, display increased grain width and to a lesser extent grain length, indicating transgene effects at a stage when grains grow under filial control. Grain number per spike was decreased by 15% and protein contents by 5%, on average, especially that of glutenins. Overall, despite some compensating effects on grain number per spike and protein contents, HOSUT lines generate a significant yield advantage. The findings can contribute to understanding determinants of grain size and number and its relationship to grain sink strength and might identify limitations of wheat yield potential.