Molecular cloning, characterization and expression of a novel Asr gene from Ginkgo biloba

A new abscisic acid, stress and ripening (Asr) gene was cloned from Ginkgo biloba by rapid amplification of cDNA ends (RACE) method. The full-length cDNA of G. biloba Asr (designated as GbAsr) was 952 bp long and it contained a 543 bp open reading frame encoding a protein of 181 amino acids. GbASR was found to be rich in His, Lys, Glu and Ala, and it had extensive homology with those of other plant Asr genes via multiple alignment analysis. Phylogenetic tree analysis indicated that the GbASR had a closer relationship with ASR from pine, another gymnosperm species, than with angiosperm ASRs. Southern blot analysis indicated that GbAsr belonged to a small multigene family. RT-PCR analyses revealed that GbAsr had a distinct up-regulated transcript pattern in root, stem and leaf under mannitol, NaCl and ABA treatments. The recombinant GbASR protein was successfully expressed in E. coli strain with pET-32a vector, and the result showed that the molecular weight of the recombinant protein was about 20 kDa, a size in agreement with that of the predicted by bioinformatic analysis. The expression of the GbAsr in E. coli will facilitate further research on this gene.