Comparative Chloroplast Genomes and Phylogenetic Relationships of True Mangrove Species Brownlowia tersa and Brownlowia argentata (Malvaceae)

Brownlowia tersa and Brownlowia argentata are two true mangroves in the genus Brownlowia in Malvaceae, and they are a near-threatened and a data-deficient species, respectively. However, the genomic resources of Brownlowia have not been reported for studying their phylogeny and evolution. Here, we report the chloroplast genomes of B. tersa and B. argentata based on stLFR data that were 159,478 and 159,510 base pairs in length, respectively. Both chloroplast genomes contain 110 unique genes and one infA pseudogene. Sixty-eight RNA-editing sites were detected in 26 genes in B. argentata. A comparative analysis with related species showed similar genome sizes, genome structures, and gene contents as well as high sequence divergence in non-coding regions. Abundant SSRs and dispersed repeats were identified. Five hotspots, psbI-trnS, trnR-atpA, petD-rpoA, rpl16-rps3, and trnN-ndhF, were detected among four species in Brownlowioideae. One hotspot, rps14-psaB, was observed in the two Brownlowia species. Additionally, phylogenetic analysis supported that the Brownlowia species has a close relationship with Pentace triptera. Moreover, rpoC2 was a candidate gene for adaptive evolution in the Brownlowia species compared to P. triptera. Thus, these chloroplast genomes present valuable genomic resources for further evolutionary and phylogenetic studies of mangroves and plant species in Malvaceae.