Genome-wide systematic characterization of the NRT2 gene family and its expression profile in wheat (Triticum aestivum L.) during plant growth and in response to nitrate deficiency.

BACKGROUND: Wheat (Triticum aestivum L.) is a major cereal crop that is grown worldwide, and it is highly dependent on sufficient N supply. The molecular mechanisms associated with nitrate uptake and assimilation are still poorly understood in wheat. In plants, NRT2 family proteins play a crucial role in NO3- acquisition and translocation under nitrate limited conditions. However, the biological functions of these genes in wheat are still unclear, especially their roles in NO3- uptake and assimilation. RESULTS: In this study, a comprehensive analysis of wheat TaNRT2 genes was conducted using bioinformatics and molecular biology methods, and 49 TaNRT2 genes were identified. A phylogenetic analysis clustered the TaNRT2 genes into three clades. The genes that clustered on the same phylogenetic branch had similar gene structures and nitrate assimilation functions. The identified genes were further mapped onto the 13 wheat chromosomes, and the results showed that a large duplication event had occurred on chromosome 6. To explore the TaNRT2 gene expression profiles in wheat, we performed transcriptome sequencing after low nitrate treatment for three days. Transcriptome analysis revealed the expression levels of all TaNRT2 genes in shoots and roots, and based on the expression profiles, three highly expressed genes (TaNRT2-6A.2, TaNRT2-6A.6, and TaNRT2-6B.4) were selected for qPCR analysis in two different wheat cultivars ('Mianmai367' and 'Nanmai660') under nitrate-limited and normal conditions. All three genes were upregulated under nitrate-limited conditions and highly expressed in the high nitrogen use efficiency (NUE) wheat 'Mianmai367' under low nitrate conditions. CONCLUSION: We systematically identified 49 NRT2 genes in wheat and analysed the transcript levels of all TaNRT2s under nitrate deficient conditions and over the whole growth period. The results suggest that these genes play important roles in nitrate absorption, distribution, and accumulation. This study provides valuable information and key candidate genes for further studies on the function of TaNRT2s in wheat.

[Pedigree and development of wheat varieties in Sichuan Province].

Variety pedigree contains a lot of information, including parental origin, breeding methods, genetic relationship, and so on. Studying them could reveal the evolution characteristics and rules of breeding and ultimately guide practice. The pedigrees of 326 wheat varieties from 1936 to 2017 in the history of the Sichuan Province was collected and analyzed in terms of breeding methods, parental composition, changes of high frequency parents and backbone parents, genetic contribution, distribution of translocation lines and synthetic germplasms. Over the past 80 years since 1930s, breeders have selected 387 direct parents from a large number of materials, made 256 combinations by means of cross breeding, and have released 314 varieties from them, which contributed directly to wheat breeding and production in Sichuan. Wheat breeding experienced a process from utilizing landraces, introducing foreign germplasm to creating breeding materials independently; high-frequency parents and backbone parents used for breeding gradually changed in different stage of the breeding history. Synthetic germplasms contributed greatly to wheat breeding in recent years. The consistency of breeding objectives will inevitably lead to the loss of genetic diversity and the fragility of genetic basis. In the future, the protection and utilization of genetic resources should be strengthened. In this review, the development of wheat breeding in Sichuan was summarized through pedigree analysis, in order to provide a reference for future research.