Characterization of a Novel Annexin Gene from Cotton (Gossypium hirsutumcv CRI 35) and Antioxidative Role of its Recombinant Protein

Plant annexins represent a multigene family involved in cellular elongation and development. A cDNA encoding a novel annexin was isolated from a cotton (Gossypium hirsutum) fiber cDNA library and designated GhAnx1. This gene encodes a 316 amino acid protein with a theoretical molecular mass of 36.06 kDa and a theoretical pI of 6.19. At the amino acid level, it shares high sequence similarity and has evolutionary relationships with annexins from higher plants. The purified recombinant protein expressed in Escherichia coli was used to investigate its physicochemical properties. Circular dichroism spectrum analyses showed a positive peak rising to the maximum at 196 nm and a broad negative band rounding 215 nm, suggesting that the GhAnx1 protein was prominently alpha-helical. The fluorescence measurements indicated that it could bind to Ca2+ in vitro. These results demonstrated that GhAnx1 was a typical annexin protein in cotton. A bioassay experiment was conducted to analyze its potential function and showed that E. coli cells expressing GhAnx1 were protected from tert-butyl hydroperoxide (tBH) stress, suggesting that it had a potential antioxidative role. Northern blot analyses revealed that GhAnx1 was highly expressed in fibers, especially during the elongation stage, suggesting that it might be important for fiber elongation.