Complete Chloroplast Genomes and Phylogenetic Relationships of Bougainvillea spectabilis and Bougainvillea glabra (Nyctaginaceae)

Bougainvillea L. (Nyctaginaceae) is a South American native woody flowering shrub of high ornamental, economic, and medicinal value which is susceptible to cold damage. We sequenced the complete chloroplast (cp) genome of B. glabra and B. spectabilis, two morphologically similar Bougainvillea species differing in cold resistance. Both genomes showed a typical quadripartite structure consisting of one large single-copy region, one small single-copy region, and two inverted repeat regions. The cp genome size of B. glabra and B. spectabilis was 154,520 and 154,542 bp, respectively, with 131 genes, including 86 protein-coding, 37 transfer RNA, and 8 ribosomal RNA genes. In addition, the genomes contained 270 and 271 simple sequence repeats, respectively, with mononucleotide repeats being the most abundant. Eight highly variable sites (psbN, psbJ, rpoA, rpl22, psaI, trnG-UCC, ndhF, and ycf1) with high nucleotide diversity were identified as potential molecular markers. Phylogenetic analysis revealed a close relationship between B. glabra and B. spectabilis. These findings not only contribute to understanding the mechanism by which the cp genome responds to low-temperature stress in Bougainvillea and elucidating the evolutionary characteristics and phylogenetic relationships among Bougainvillea species, but also provide important evidence for the accurate identification and breeding of superior cold-tolerant Bougainvillea cultivars.