Cloning, biochemical identification, and expression analysis of a gene encoding S-adenosylmethionine decarboxylase in navel orange (Citrus sinensis Osbeck)

SummaryPolyamines have been shown to be involved in a variety of plant physiological processes such as growth, development, and stress responses. As S-adenosylmethionine decarboxylase (SAMDC) is the rate-limiting enzyme for polyamine biosynthesis, efforts were made to isolate the gene encoding SAMDC from ‘Newhall’ navel orange (Citrus sinensis Osbeck). RT-PCR, in combination with a bioinformatics approach, produced a cDNA (CsSAMDC) containing an intact open reading frame (ORF) of 1,095 bp. The deduced amino acid sequence shared high homology (>75%) with four selected plant SAMDCs and possessed several highly-conserved amino acid residues or motifs. Expression of CsSAMDC in Escherichia coli gave rise to a protein of the expected size, which was shown to have biochemical activity via a SAMDC assay. The expression pattern of the CsSAMDC gene in ‘Newhall’ callus tissue broadly matched the growth of callus cells and the fluctuation in endogenous polyamine levels. Levels of transcription of CsSAMDC in ‘Newhall’...