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

Abstract

Abstract Background Burseratrees are conspicuous elements of the tropical dry forests in the Neotropics, which have a significant cultural value due to their fragrant resins (incense), wood sources (handcrafts), and ecological benefits. Despite its relevance, genetic resources developed for the genus are scarce. Methods and results We sequenced and analyzed the complete chloroplast genome structure and functional annotation of three Bursera species of the Bullockia section: Bursera cuneata, B. palmeri, and B. bipinnata. The chloroplast (Cp) genome sizes ranged from 159,824 to 159,872 bp in length, including a large single-copy (LSC) region from 87,668 to 87,656 bp, a small single-copy (SSC) from 18,581 to 18,571 bp, and two inverted repeats regions (IRa and IRb) of 26,814 bp each. The three Cp genomes consisted of 135 genes, of which 90 were functional, 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 to 591 simple sequence repeats were identified. Phylogenetic relationships within Burseraceae for each Cp region (LSC, SSC, IRa, and IRb) using Bayesian inference confirmed that Commiphora is the sister taxa of Bursera. Only the phylogenetic trees based on the SSC and LSC regions resolved the close relationship between B. bipinnata and B. palmeri within Bursera. Conclusion Our work contributes to the development of Bursera's genomic resources for taxonomic, evolutionary, and ecological-genetic studies.