The allelic distribution and variation analysis of the NAM-B1 gene in Chinese wheat cultivars

The NAM-B1 gene is a member of the NAC (NAM, ATAF, and CUC) transcription factor family and plays an important role in regulating wheat grain protein content (GPC). The ancestral NAM-B1 allele has been discovered in many tetraploid wild emmer (Triticum turgidum ssp. dicoccoides) accessions and few domesticated emmer accessions (T. turgidum ssp. dicoccum), however, it is rarely found in hexaploid bread wheat (Triticum aestivum L.). There are no systematic reports on the distribution of NAM-B1 alleles in Chinese wheat cultivars. In this study, the NAM-B1 alleles in 218 Chinese cultivars were investigated. The cultivars were collected from five major wheat regions (12 provinces), covering most of the winter wheat growing regions in China. The results showed that the NAM-B1 gene is present in 53 (24.3%) cultivars and absent in the remaining 165 (75.7%) cultivars. Further analysis revealed that in contrast to the wild-type allele, the NAM-B1 gene in Chinese wheat cultivars contained a 1-bp insertion in the coding region. This caused a frame-shift mutation and introduced a stop codon in the middle of the gene, rendering it non-functional. Polymorphisms were detected in DNA sequences of 21 cultivars among these 53 cultivars. However, cDNA sequence analysis suggested that these variations in the exon region were not able to restore NAM-B1 gene (1-bp insertion) function. Thus, exploring the distribution of NAM-B1 gene variations (1-bp insertion and deletion) can provide some information for improving the quality of winter wheat in China and other countries.