Asparagine synthetase genes (<em>AsnS1</em> and <em>AsnS2</em>) in durum wheat: structural analysis and expression under nitrogen stress

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anglais. Wheat is one of the most widely grown cereal crops based on the amount of calories it provides in the human diet. Durum wheat (<em>Triticum turgidum</em> ssp.<em> durum</em>) is largely used for production of pasta and other products. In order to use genetic knowledge to improve the understanding of N-use efficiency, we carried out, for the first time in durum wheat, the isolation and the characterization of four members of the asparagine synthetase (<em>AsnS</em>) gene family. Phylogenetic inference clustered the <em>Ttu-AsnS1</em> (1.1 and 1.2) and <em>Ttu-AsnS2</em> (2.1 and 2.2) genes in <em>AsnS</em> gene class I, which is present in monocots and dicots. Class I genes underwent a subsequent duplication leading to the formation of two subgroups. Plants of Svevo cultivar were grown under N-stress conditions and expression of the four <em>AsnS</em> genes was investigated at three developmental stages (seedling, booting, and late milk development), crucial for N absorption, assimilation and remobilization. <em>AsnS1</em> genes were down-regulated in N-stressed roots, stems and leaves during seedling growth and booting, but seemed to play a role in N remobilization in flag leaves during grain filling. <em>AsnS2</em> genes were scarcely expressed in roots, stems, and leaves. In N-stressed spikes there was no differential expression in any of the genes. The genes were mapped in silico using a durum wheat SNP map, assigning <em>Ttu-AsnS1</em> genes to chromosome 5 and <em>Ttu-AsnS2</em> to chromosome 3. These findings provide a better understanding of the role of ASN genes in response to N stress in durum wheat.