Complete chloroplast genomes of three copal trees (Bursera: Bullockia): comparative analysis and phylogenetic relationships.

Abstract

Bursera trees are conspicuous elements of the tropical dry forests in the Neotropics that have significant cultural value due to their fragrant resins (incense), wood sources (handcrafts), and ecological benefits. Despite their relevance, genetic resources developed for the genus are scarce. We obtained the complete chloroplast (Cp) genome sequence, analyzed the genome structure, and performed functional annotation of three Bursera species of the Bullockia section: Bursera cuneata, B. palmeri, and B. bipinnata. The Cp genome sizes ranged from 159,824 to 159,872bp in length, including a large single-copy (LSC) region from 87,668 to 87,656bp, a small single-copy (SSC) from 18,581 to 18,571bp, and two inverted repeats regions (IRa and IRb) of 26,814bp each. The three Cp genomes consisted of 135 genes, of which 90 were protein-coding, 37 tRNAs, and 8 rRNAs. The Cp genomes were relatively conserved, with the LSC region exhibiting the greatest nucleotide divergence (psbJ, trnQ-UCC, trnG-UCC, and petL genes), whereas few changes were observed in the IR border regions. Between 589 and 591 simple sequence repeats were identified. Analysis of phylogenetic relationships using our data for each Cp region (LSC, SSC, IRa, and IRb) and of seven species within Burseraceae confirmed that Commiphora is the sister genus of Bursera. Only the phylogenetic trees based on the SSC and LSC regions resolved the close relationship between B. bipinnata and B. palmeri. Our work contributes to the development of Bursera's genomic resources for taxonomic, evolutionary, and ecological-genetic studies.