Asparagine synthetase genes (AsnS) in durum wheat

Nitrogen (N) is a necessary component of proteins, enzymes, and metabolic products involved in thè synthesis and transfer of energy. Plants require large amounts of it for their growth and survival. At present, thè increase in investment in agriculture is mainly due to thè use of nitrogen fertilizer because it directly affects yield. Plants can only use approximately 30-40% ofthe applied N, and more than 40% ofthe N fertilizer is lost via leakage into thè atmosphere, groundwater, lakes and rivers. Such leakage results in serious environmental pollution. For this reason there is a need to improve nitrogen use efficiency (NUE) in plants. It is well known that many plants rely on thè synthesis and degradation of thè amides asparagine and glutamine to relocate nitrogen within their tissue. In this context, asparagine plays a prominent role in nitrogen transport and Storage in plants. Glutamine-dependent asparagine synthetase (AsnS) catalyses thè transfer of an amide group from glutamine to aspartate-forming asparagine (Asn). In most plant species, AsnS seems to be encoded by a small gene family ranging from one or two in most species (i.e. sunflower, bread wheat, barley) to three and four in some others (i.e. arabidopsis and mais). In order to find AsnS genes in Triticum durum a hybridization of a I durum BAC-library macroarrays was carried out. Probes were developed on cDNA sequences belonging to other grass AsnS genes already present in public databases. Positive BAC clones, two ipotetical homoeologousfor/\snS/ and AsnS2, were chosen for Roche454 next generation sequencing (NGS). Read assembling and gene annotation allowed us to carry out structural and phylogenetic analysis of T. durum AsnS genes comparing them with other AsnS proteins from a wide range of species within both monocots and dicots. Our phylogenetic reconstruction showed that these genes belong to class I, one of thè three major AsnS gene classes. The possible roleof/\snS/ and AsnS2 genes in response to different conditions of N supply is discussed