Clone and expression of CpGAPDH gene in Codonopsis pilosula

Abstract

GAPDH(glyceraldehyde-3-phosphate dehydrogenase) gene is a key enzyme gene in carbohydrate metabolism and always used as reference gene. To clarify and complete the biosynthetic pathway of polysaccharide, the GAPDH gene in Codonopsis pilosula, named CpGAPDH, was cloned according to the transcriptome of pilosula, using the GAPDH gene in potato as query. The CpGAPDH contained a 1 014 bp open reading frame(ORF) and encoded a protein with 337 amino acids. Bioinformatic analysis clearly suggested that CpGAPDH shared high similarity with GAPDH among other plants, and had the closest relatives to potato and danshen. The predicted protein did not have signal peptide, which indicated that it might be located in the cytoplasm. According to the existing of several phosphorylation sites and the conserved domains analysis, we predicted that it belonged to Gp_dh_N superfamily. Prokaryotic expression showed that the recombinant expressed a 44.3 kDa protein, which was corresponding to the theoretical relative molecular mass. However, the relative transcript level of the CpGAPDH did not have significant differences in different tissues and roots at different developmental stages of pilosula. Moreover, the stability of the CpGAPDH was analyzed by BestKeeper, geNorm, and NormFinder and RefFinder software, which showed that the CpGAPDH was more stable and could be used as a new reference gene. All these lay a foundation for the expression analysis of the gene relative to the polysaccharide synthesis.