The Expression Level Of NAM-B1 Gene And Its Effect On Grain Nutritional Quality In Derivatives Between Triticum Turgidum Ssp. Dicoccoides And Common Wheat Cultivar Chuannong 16

Triticum turgidum ssp. dicoccoides, the wild tetraploid ancestor of common wheat, usually have high grain protein content and micronutrient content. By contrast, modern wheat cultivar have high yield but low grain nutrient component. NAM-B1 is functional and expressed after anthesis in T. turgidum ssp. dicoccoides. This allele accelerates senescence and increases nutrient remobilization from leaves to developing grains, therefore promoting the higher nutrient content. However, this gene is deleted or carries a 1-bp insertion that disrupts the reading frame in modern wheat varieties.In this study, NAM-B1 genes in 27 F10 lines derived from crosses between common wheat cultivar Chuannong 16 (CN16) and wild emmer accession Dl or D97 were sequenced and their expression levels were also measured. Once harvested, grain protein content and micronutrient content was measured. We further analyzed the relationship between NAM-B1 gene and grain nutritional quality in these lines. The main results are as follows:Both D1 and D97, and their 12 F10 derivatives carry a functional NAM-B1 allele. Compared with previously reported gene sequence DQ869673, there is only one base mutation but with same amino acid sequence. CN16 and 12 F10 derivatives showed no polymerase chain reaction (PCR) amplification products of the NAM-B1 gene, thus suggesting the absence of this gene. Three out of the 27 F10 lines carry a nonfunctional NAM-B1 allele.The expression of NAM-B1 is at a relatively low level at anthesis, ranging from 1/22 to 1/6 of the expression level of actin gene, and there is no significant difference between lines. The expression of NAM-B1 is at a relatively high level at fifteen days after anthesis, ranging from 1/4.5 to 1/1.5 of the expression level of actin gene, and there are significant differences between lines.The mean grain protein concentration of 12 F10 lines with a functional NAM-B1 allele is significantly higher than that of 15 lines without functional NAM-B1 allele. Out of the 12 F10 lines with a functional allele, four have significantly higher grain protein concentration than CN16. By contrast, only one of 15 lines without functional allele is significantly higher than CN16 in grain protein concentration.The mean grain Fe concentration of 12 F10 lines with a functional NAM-B1 allele is significantly higher than that of 15 F10 lines without the functional allele and parent CN16. However, there is no obvious relationship between NAM-B1 gene and grain Zn concentration.There is no significant difference in the mean thousand kernel weight between F10 lines with and without a functional NAM-B1 allele, although they both are significantly higher than CN16. It probably results from our continually selection on high yield property since F2 generations.In view of a dilution effect caused by larger grains, grain nutrient concentration may not perfectly reflect the ability of nutrient remobilization from leaves to developing grains but total nutrient content in a thousand seeds can. Functional NAM-B1 gene significantly increases total protein and total Fe content in a thousand seeds.Correlation analysis showed a stronger correlation between nutritional quality traits of F10 lines with functional NAM-B1 and a weaker correlation between nutritional quality traits of F10 lines without functional NAM-B1. Grain nutrient concentration has a negative correlation with thousand kernel weight, sometimes significantly. By contrast, total nutrient content in a thousand seeds has a weaker correlation with thousand kernel weight, even positively for F10 lines with a functional NAM-B1 allele. As total nutrient content in a thousand seeds reflects the ability of nutrient remobilization from leaves to developing grains, we believe that selecting lines with high thousand kernel weight in hybrids will not bring about low quality. We conclude that utilization of NAM-B1 gene in combination with phenotypic selection is a useful strategy for development of wheat genotypes with high grain nutritional quality associated with no loss in yield. In addition, a weak relationship between expression levels of NAM-B1 gene and grain nutritional quality indicates that grain protein and micronutrient content is complex quantitative traits, controlled by a series of genes for biochemical, physical and chemical reactions except NAM-B1.