Characterization of an A-type cyclin-dependent kinase gene from Dendrobium candidum

Cyclin-dependent kinases (CDKs) play an essential role in cell cycle regulation during the embryonic and postembryonic development of organisms. To better understand the molecular mechanisms of CDKs involved in embryogenesis regulation in the endangered medicinal plant Dendrobium candidum Wall. ex Lindl., a 1229-bp full-length cDNA of an A-type CDK gene, Denca; CDKA; 1, was identified using 3' rapid amplification of cDNA end (RACE) PCR. Denca; CDKA; 1 was predicted to encode a 294 amino acid residue-long protein of 33.76 kDa with an isoelectric point of 7.72. The deduced Denca; CDKA; 1 protein contained a conserved serine/threonine-protein kinase domain (S-TKc) and a canonical cyclin-binding "PSTAIRE" motif. Multiple sequence alignment indicated that members of CDKA family from various plants exhibited a high degree of sequence identity ranging from 82% to 93%. A neighbor-joining phylogenetic tree showed that Denca; CDKA; 1 was clustered into the plant group and was distant from the animal and fungal groups. The modeled three-dimensional structure of Denca; CDKA; 1 exhibited the similar functional structure of a fold consisting of beta-sheets and alpha-helices joined by discontinuous random coils forming two relatively independent lobes. Quantitative real-time PCR analysis revealed that Denca; CDKA; 1 transcripts were the most abundant in protocorm-like bodies with 4.76 fold, followed by that in roots (4.19 fold), seeds (2.57 fold), and stems (1.57 fold). This study characterized the novel Denca; CDKA; 1 gene from D. candidum for the first time and the results will be useful for further functional determination of the gene.