Wild emmer wheat as a source for high-grain-protein genes: Map-based cloning of Gpc-B1

The global need to increase the nutritional value of staple crops can be largely met by improving wheat quality. Wheat is a major constituent of diets worldwide and accounts for approximately 20% of all calories consumed by humans. Wild emmer wheat, Triticum turgidum ssp. dicoccoides, the wild progenitor of domesticated wheat, harbors a rich source of allelic diversity for many agronomic traits, including grain protein content (GPC). We review here the map-based cloning of Gpc-B1, a quantitative trait locus (QTL) originated from wild emmer wheat, with pleiotropic effects on whole plant senescence, grain protein, zinc, and iron content. Combining different strategies, the Gpc-B1 QTL was delimited to a 7.4-kb chromosome region containing only one gene that encodes a NAC transcription factor (designated TtNAM-B1). Modern wheat varieties carry a nonfunctional TtNAM-B1 allele attributed to a frame shift mutation caused by an insertion of thymine, while wild emmer wheat carries a functional TtNAM-B1 allele. The absence of the functional TtNAM-B1 allele in modern germplasm suggests a broad potential impact of the functional wild emmer allele in breeding of cultivated durum and bread wheat varieties. A century ago, after A. Aaronsohn discovered wild emmer wheat in Rosh Pinna, Israel, he wrote about wild emmer wheat as a potential source for crop improvement: "It has a practical and economic - I might even say a social - importance". The map-based cloning of TtNAM-B1 is, in fact, a significant step towards the realization of Aaronsohn's vision.