Glutamine Synthetase Genes: Expression in Two Durum Wheat Cultivars Different for Grain Protein Content

 Glutamine synthetase (GS) is a key enzyme for nitrogen (N) assimilation in plants, which catalyses the ATP-dependent condensation of ammonium and glutamate into glutamine, the principal precursor for the synthesis of most nitrogenous cellular compounds. GS exists in different isoforms classified into groups according to their localization within the cell: a cytosolic form, GS1, responsible for assimilating the ammonium produced by reduction of nitrate in roots and for synthesizing Glnfor the transport of N between different organs; a chloroplastic form, GS2, involved into the reassimilation of ammonia endogenously released by photorespiration.

RT-real time PCR was conducted for plastidic (GS2-A2 and GS2-B2) and cytosolic isoforms (GSe1 and GSe2) in two durum wheat cultivars, Ciccio and Svevo, characterized respectively by high and low kernel protein content. The analysis was conducted on several tissues and developmental stages normalized against three housekeeping genes, CDC (Cell Division Control), ADP-RF (ADP-Ribosilation Factor) and RLI (RNase L Inhibitor-like protein ). In particular, total RNA was extracted and cDNA synthesized from leaves and roots collected from ten wheat plants. qRT-PCR in leaves from Svevo detected an increase of GSe expression and a contemporary decrease of GS2 transcript level in the different phenological stages, reflecting the transition from photosynthetic to senescing leaves.

The higher expression level of all the GS isoforms detected in Svevo compared to Ciccio could suggest a more efficient nitrogen metabolism in the cv. characterized by a high GPC. This result could validate the role of GSgene in controlling the grain protein content in durum wheat.