Department of Plant Sciences

Human nutrition and health can be improved by enhancing the nutritional value of food crops. Efforts to increase wheat grain protein content (GPC) and micronutrient levels have been hindered by their large environmental dependency and their complex inheritance. We recently cloned the high-grain protein content gene Gpc-B1 from wild wheat (Triticum turgidum ssp. dicoccoides) and showed that it encodes a NAC transcription factor (NAM-B1) associated with differences in senescence. The ancestral wild wheat allele is functional, whereas the allele present in modern wheat varieties is either deleted or has a frame shift mutation and is non-functional. The introgression of the functional allele results in average 5-10% increases in grain protein, Fe and Zn concentration and also in a ~5% increase in total grain N yield (N concentration x grain yield), balanced by a similar decrease in the straw. The functional allele was also associated with a significant decrease in grain Cd in some genotypes. In addition, the functional Gpc-B1 allele accelerates senescence which results in reduced grain filling periods and in some genotypes, smaller grain size (~5%). In some lines, the smaller grains were compensated by other yield components resulting in no significant differences in yield. This suggests that breeding can be used to ameliorate the negative effect of this gene on grain size. Reduction in RNA levels of the multiple NAM homologs by RNA interference delayed senescence by more than 3 weeks and reduced wheat grain protein, zinc, and iron content by more than 30% compared to the non-transgenic control lines. We have also developed TILLING mutants for all the NAM genes and confirmed delayed senescence in some of them. Our results suggest that lines with higher amounts of NAM transcripts (non-transgenic controls) are able to remobilize more minerals, in a shorter time frame. This more efficient remobilization of N and minerals to the grain is the source of the observed increases in total N yield. The absence of the functional NAM-B1 allele in the modern wheat germplasm suggests a broad potential impact of the functional allele in cultivated durum and bread wheat varieties.