NAM-1gene polymorphism and grain protein content in Hordeum

Grain protein content (GPC) is a key quality factor for malting and brewing process. In wheat, a QTL explaining a large part of GPC variation was identified, which co-localizes with a gene encoding a NAC transcription factor (TtNAM-B1). NAC transcription factors influence GPC by their role in the regulation of senescence and in protein remobilization. An orthologous gene was discovered on barley chromosome 6H where a GPC QTL was mapped. In this study, we identify allelic variation of the NAM-1 gene for three species of Hordeum representing wild and cultivated barley and we investigate the possible link with GPC. Three haplotypes were identified, one corresponds to the sequences of 11 European varieties representing H. vulgare, one corresponds to the sequence found in H. spontaneum and one represents the sequence of H. bulbosum. Three SNPs were identified between H. spontaneum sequence and H. vulgare sequence. One of the H. bulbosum polymorphisms leads to the introduction of a stop codon and a non-functional protein. Differences in GPC between the 11 varieties were found but no polymorphism in the NAM-1 gene was observed, suggesting that differences in expression of the HvNAM-1 gene or other genes should play a role in GPC regulation. Nevertheless based on published values for GPC of H. bulbosum and H. spontaneum compared to GPC measured here in H. vulgare, the non-functional protein is associated with the lower GPC, suggesting that loss of functionality of the NAM-1 gene in Hordeum is related to lower GPC. Moreover H. spontaneum GPC seems to be higher than H. vulgare GPC, suggesting also that allelic variation of the functional NAM-1 gene could be associated with GPC variation within the genus Hordeum.