Characterization of petB and petD genes of the Populus deltoides Chloroplast psbB operon

Abstract

Using a heterologous probe, we localized the petB and petD genes on a 2.4-kbp BamH I fragment of Populus deltoides ctDNA. The fragment was cloned and characterized by means of nucleotide sequencing. Analysis of the complete nucleotide sequence of this fragment revealed the presence of a 213-codon exon exhibiting more than 90% homology with the petB gene nucleotide sequence of higher plants. We identified a mini-exon and intron of the petD gene downstream from this exon. The presence of conserved splice site sequences suggests that the poplar petB and petD genes contain group II introns. Furthermore, these genes constitute an operon with PSII genes, psbB, psbT, and psbH, and cotranscribe with them as a polycistronic message. Northern hybridization analysis with total RNA prepared from leaves at different developmental stages revealed a quantitative increase in the primary transcript in mature leaves.