Isolation and characterisation of cytosolic glutamine synthetase (GSe) genes and association with grain protein content in durum wheat

Glutamine synthetase (GS) enzyme (EC 6.3.1.2) plays a central role in assimilating ammonia produced in the leaf from metabolic processes, spanning from assimilation to transamination reactions and catabolic processes. GS is located in both cytoplasm (GS1, GSe and GSr) and plastids (GS2) of plant cells. Glutamine and glutamate, produced by the concerted action of GS and glutamate synthase, are then transported from the leaf to the developing sinks or grain in wheat. The goal of the present study was to characterise GSe genes and to assess the linkage with grain protein content, an important quantitative trait controlled by multiple genes. Here, we report the isolation of the complete cytosolic GS gene sequences of the durum wheat cvv. 'Ciccio' and 'Svevo' (characterised by low and high protein content, respectively). GSe-A4 located on 4A chromosome comprises 12 exons separated by 11 introns, while the GSe-B4 gene on 4B chromosome comprises 11 exons separated by 10 introns. Quantitative real-time PCR indicated different expression levels of GSe-A4 and GSe-B4 genes in the two wheat cvv. 'Ciccio' and 'Svevo'. The two GSe genes were significantly associated to quantitative trait loci for grain protein content.