New genetic resources in wheat breeding for increased grain protein content

Abstract

This review offers an overview of genetic research on grain protein content (GPC) in various Triticum L. and Aegilops L. species. Regularities in the geographic variability of GPC and the results of a longterm screening of accessions from the VIR collection for this trait are considered. Based on these assessments, a core collection of genetic sources with high GPC has been formed. It includes the diploid Aegilops species as donors of B, G, and D genomes for allopolyploid wheats, as well as accessions of di-, tetra-, and hexaploid wheat species. The use of high-protein sources in wheat breeding in the United States and Canada in the 1970s–1980s resulted in the GPC of bread wheat increasing by 0.5–3.0%; however, further attempts at increasing GPC by traditional breeding methods have failed. A breakthrough in increasing the total GPC has been achieved as a result of molecular genetics methods and development of molecular markers. For the first time, a functional locus, or the Gpc-B1 gene (chromosome 6BS) affecting the accumulation of protein, Zn, and Fe in grain, was identified in T. dicoccoides, cloned, and studied in detail. The application of molecular markers has revealed the active allele of this gene in some landraces and old cultivars of T. dicoccum, T. durum, T. spelta, and T. aestivum. Moreover, the Gpc-A1, Gpc-D1, and Gpc-2 wheat genes have been found in chromosomes 6A and 6D and homeologous group 2, respectively. All these genes have been identified as NAC transcription factors, which play an important role in the accelerated senescence of plants and the remobilization of nutrients from leaves to grain. The genes related to Gpc-B1 from T. dicoccoides were found in the G genome of T. timopheevii and B (=S) genome of different species of Aegilops sect. sitopsis. Functional Gpc-B1 alleles have been introduced into commercial tetra- and hexaploid wheat cultivars, which resulted in the creation of new high-protein and high-yield cultivars and series of nearly isogenic lines in different countries. They are promising sources for research and wheat breeding purposes.