Asparagine synthetase genes (AsnS1 and AsnS2) in durum wheat: structural analysis and expression under nitrogen stress
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Wheat is one of the most widely grown cereal crops based on the amount of calories it provides in the human diet. Durum wheat (Triticum turgidum ssp. durum) 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 (AsnS) gene family. Phylogenetic inference clustered the Ttu-AsnS1 (1.1 and 1.2) and Ttu-AsnS2 (2.1 and 2.2) genes in AsnS 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 AsnS genes was investigated at three developmental stages (seedling, booting, and late milk development), crucial for N absorption, assimilation and remobilization. AsnS1 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. AsnS2 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 Ttu-AsnS1 genes to chromosome 5 and Ttu-AsnS2 to chromosome 3. These findings provide a better understanding of the role of ASN genes in response to N stress in durum wheat.
KeywordsAsnS gene family BAC library High-throughput sequencing Triticum turgidum ssp. durum
We thank Anita Morgese (CNR-IBBR, Bari, Italy), Joëlle Fourment, Nathalie Rodde and Nadine Gautier (CNRGV, Toulouse, France) for technical support.
This work was supported by the Italian Ministry MIUR projects: PON01_01145 ISCOCEM “Sviluppo tecnologico e innovazione per la sostenibilità e competitività della cerealicoltura meridionale”; PRIN 2010–2011 prot. 2010Z77XAX_004 “Identificazione e caratterizzazione di geni utili ad incrementare la produttività e sostenibilità del frumento duro”, and by Italian Ministry MiPAAF project “Implementazione nazionale trattato FAO Risorse Genetiche Vegetali III triennio 2011–2013”.
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