Glutathione reductase a unique enzyme: molecular cloning, expression and biochemical characterization from the stress adapted C4 plant, Pennisetum glaucum (L.) R. Br.

The generation of excess reactive oxygen species (ROS) is one of the most common consequences of abiotic stress on plants. Glutathione reductase (GR, E.C. 1.6.4.2) and allied enzymes of the ascorbate-glutathione cycle play a crucial role to maintain the homeostatic redox balance in the cellular environment. GR plays an essential role in upholding the reduced glutathione pool under stress conditions. In the present study, a full-length GR cDNA and corresponding genomic clone was isolated from Pennisetum glaucum (L.) R. Br. The PgGR cDNA, encodes a 497-amino acid peptide with an estimated molecular mass of ~53.5 kDa. The PgGR peptide exhibits 54-89% sequence homology with GR from other plants and is cytoplasmic in nature. The PgGR enzyme was purified to near homogeneity, the recombinant protein being relatively thermostable and displaying activity in a broad range of temperature, pH and substrate concentrations. The PgGR transcript level was differentially regulated by heat, cold, salinity and methyl viologen-induced oxidative stress. The heterologously expressed PgGR protein in E. coli showed an improved protection against metal- and methyl viologen-induced oxidative stress. Our overall finding underscores the role of PgGR gene that responds to multiple abiotic stresses and provides stress tolerance in the experimental model (E. coli) which can be potentially used for the improvement of crops under abiotic stress conditions.

Biochemical and molecular analyses of copper-zinc superoxide dismutase from a C4 plant Pennisetum glaucum reveals an adaptive role in response to oxidative stress.

Superoxide dismutases (SODs) form the foremost line of defense against ROS in aerobes. Pennisetum glaucum cDNA library is constructed to isolate superoxide dismutase cDNA clone (PgCuZnSOD) of 798 bp comprising 5'UTR (111 bp), an ORF (459 bp) and 3'UTR (228 bp). Deduced protein of 152 amino acids (16.7 kDa) with an estimated isoelectric point of 5.76 shared highest homology to cytoplasmic CuZnSODs from monocots i.e., maize, rice. Predicted 3D model reveals a conserved eight-stranded ß-barrel with active site held between barrel and two surface loops. Purified recombinant protein is relatively thermo-stable with maximal activity at pH 7.6 and shows inhibition with H(2)O(2) (4.3 mM) but not with azide (10 mM). In Pennisetum seedlings, abiotic stress induced PgCuZnSOD transcript up-regulation directly correlates to high protein and activity induction. Overexpression of PgCuZnSOD confers comparatively enhanced tolerance to methyl viologen (MV) induced oxidative stress in bacteria. Results imply that PgCuZnSOD plays a functional role in conferring oxidative stress tolerance to prokaryotic system and may hold significant potential to impart oxidative stress tolerance in higher plants through transgenic approach.