Characterization of the complete chloroplast genome of Aquilaria sinensis, an endangered agarwood-producing tree

The complete chloroplast genome sequence of Durio oxleyanus (Malvaceae) and its phylogenetic position

Durio oxleyanus (Griff) of Malvaceae is considered a natural heritage by the countries that produce it, including Peninsular Malaysia, Sumatra, and Borneo. Even though the species is regarded as a commercially valuable fruit, cultivation of this species is uncommon. The dwindling population of this species in the wild has put its survival in jeopardy. Conservation efforts are required for this species, which are limited. In this study, the complete chloroplast (cp) genome of D. oxleyanus was assembled and characterized as a genomic resource for conservation programs. The complete cp genome size was 164,831 bp in length, with a pair of inverted repeats of 23,782 bp each, separating the 96,446-bp large and the 20,823-bp small single copies. A total of 135 genes were predicted, which consisted of 90 protein-coding, 37 tRNA, and eight rRNA genes. The overall GC content was 35.8%. The phylogenetic analysis based on the maximum-likelihood and Bayesian inference methods revealed that D. oxleyanus is closely related to D. zibethinus. The genomic data obtained will be useful for future studies of Malvaceae’s phylogenetics and evolution.

Comparison of eight complete chloroplast genomes of the endangered Aquilaria tree species (Thymelaeaceae) and their phylogenetic relationships

Aquilaria tree species are naturally distributed in the Indomalesian region and are protected against over-exploitation. They produce a fragrant non-timber product of high economic value, agarwood. Ambiguous species delimitation and limited genetic information within Aquilaria are among the impediments to conservation efforts. In this study, we conducted comparative analysis on eight Aquilaria species complete chloroplast (cp) genomes, of which seven were newly sequenced using Illumina HiSeq X Ten platform followed by de novo assembly. Aquilaria cp genomes possess a typical quadripartite structure including gene order and genomic structure. The length of each of the cp genome is about 174 kbp and encoded between 89 and 92 proteins, 38 tRNAs, and 8 rRNAs, with 27 duplicated in the IR (inverted repeat) region. Besides, 832 repeats (forward, reverse, palindrome and complement repeats) and nine highly variable regions were also identified. The phylogenetic analysis suggests that the topology structure of Aquilaria cp genomes were well presented with strong support values based on the cp genomes data set and matches their geographic distribution pattern. In summary, the complete cp genomes will facilitate development of species-specific molecular tools to discriminate Aquilaria species and resolve the evolutionary relationships of members of the Thymelaeaceae family.