TaNAM-6A is essential for nitrogen remobilisation and regulates grain protein content in wheat (Triticum aestivum L.).

Grain protein content (GPC) is a crucial quality trait in bread wheat, which is influenced by the key transcription factor TaNAM. However, the regulatory mechanisms of TaNAM have remained largely elusive. In this study, a new role of TaNAM was unveiled in regulating nitrogen remobilisation which impacts GPC. The TaNAM knockout mutants generated by clustered regularly interspaced short palindromic repeats/Cas9 exhibited significantly delayed senescence and lower GPC, while overexpression of TaNAM-6A resulted in premature senility and much higher GPC. Further analysis revealed that TaNAM directly activates the genes TaNRT1.1 and TaNPF5.5s, which are involved in nitrogen remobilisation. This activity aids in the transfer of nitrogen from leaves to grains for protein synthesis. In addition, an elite allele of TaNAM-6A, associated with high GPC, was identified as a candidate gene for breeding high-quality wheat. Overall, our work not only elucidates the potential mechanism of TaNAM-6A affecting bread wheat GPC, but also highlights the significance of nitrogen remobilisation from senescent leaves to grains for protein accumulation. Moreover, our research provides a new target and approach for improving the quality traits of wheat, particularly the GPC.

Two dwarfing genes Rht-B1b and Rht-D1b show pleiotropic effects on grain protein content in bread wheat (Triticum aestivum L.).

KEY MESSAGE: Five QTL for wheat grain protein content were identified, and the effects of two dwarfing genes Rht-B1b and Rht-D1b on grain protein content were validated in multiple populations. Grain protein content (GPC) plays an important role in wheat quality. Here, a recombinant inbred line (RIL) population derived from a cross between Yangmai 12 (YM12) and Yanzhan 1 (YZ1) was used to identify quantitative trait loci (QTL) for GPC. Two hundred and five RILs and their parents were grown in three years in randomized complete blocks each with two replications, and genotyped using the wheat 55 K SNP array. Five QTL were identified for GPC on chromosomes 1A, 1B, 2D, 4B, and 4D. Notably, QGpc.yaas-4B (co-located with Rht-B1) and QGpc.yaas-4D (co-located with Rht-D1) were consistently detected across all experiments and best linear unbiased estimating, accounting for 6.61-8.39% and 6.05-10.21% of the phenotypic variances, respectively. The effects of these two dwarfing alleles Rht-B1b and Rht-D1b on reducing GPC and plant height were validated in two additional RIL populations and one natural population. This study lays a foundation for further investigating the effects of dwarfing genes Rht-B1b and Rht-D1b on wheat GPC.

Storage protein activator controls grain protein accumulation in bread wheat in a nitrogen dependent manner.

The expression of cereal grain storage protein (GSP) genes is controlled by a complex network of transcription factors (TFs). Storage protein activator (SPA) is a major TF acting in this network but its specific function in wheat (Triticum aestivum L.) remains to be determined. Here we generated an RNAi line in which expression of the three SPA homoeologs was reduced. In this line and its null segregant we analyzed GSP accumulation and expression of GSP and regulatory TF genes under two regimes of nitrogen availability. We show that down regulation of SPA decreases grain protein concentration at maturity under low but not high nitrogen supply. Under low nitrogen supply, the decrease in SPA expression also caused a reduction in the total quantity of GSP per grain and in the ratio of GSP to albumin-globulins, without significantly affecting GSP composition. The slight reduction in GSP gene expression measured in the SPA RNAi line under low nitrogen supply did not entirely account for the more significant decrease in GSP accumulation, suggesting that SPA regulates additional levels of GSP synthesis. Our results demonstrate a clear role of SPA in the regulation of grain nitrogen metabolism when nitrogen is a limiting resource.