Cloning and nucleotide sequence analysis ofpsbD/C operon from chloroplasts of Populus deltoides

Abstract

We report the cloning and nucleotide sequence analysis of psbD/C operon from a dicotyledonous tree species,Populus deltoides (poplar). The coding regions of psbD and psbC and deduced amino acid sequences show very high homology with those from other higher plants. In pairwise alignment of the gene sequences,P. deltoides clustered with dicotyledonous annuals rather than with Pinus, the only other tree whose psbD/C nucleotide sequence is available. Comparison of several reported sequences showed that synonymous substitutions were distributed in both psbD and psbC uniformly, throughout the length of the genes. The frequency of nonsynonymous substitutions located in the amino-terminal end of psbD was distinctly higher, suggesting a lower degree of structural constraints in this region of the encoded D2 protein. The arrangement of reading frames and Northern analysis suggest that organization and expression of psbD/C operon in P. deltoides is similar to that in other higher plants.