Complete Chloroplast Genomes of Vachellia nilotica and Senegalia senegal: Comparative Genomics and Phylogenomic Placement in a New Generic System

Vachellia and Senegalia are the most important genera in the subfamily Mimosoideae (Fabaceae). Recently, species from both genera were separated from the long-characterized Acacia due to their macro-morphological characteristics. However, this morpho-taxonomic differentiation struggles to discriminate some species, for example, Vachellia nilotica and Senegalia senegal. Therefore, sequencing the chloroplast (cp) genomes of these species and determining their phylogenetic placement via conserved genes may help to validate the taxonomy. Hence, we sequenced the cp genomes of V. nilotica and S. senegal, and the results showed that the sizes of the genomes are 165.3 and 162.7 kb, respectively. The cp genomes of both species comprised large single-copy regions (93,849~91,791 bp) and pairs of inverted repeats (IR; 26,093~26,008 bp). The total numbers of genes found in the V. nilotica and S. senegal cp genomes were 135 and 132, respectively. Approximately 123:130 repeats and 290:281 simple sequence repeats were found in the S. senegal and V. nilotica cp genomes, respectively. Genomic characterization was undertaken by comparing these genomes with those of 17 species belonging to related genera in Fabaceae. A phylogenetic analysis of the whole genome dataset and 56 shared genes was undertaken by generating cladograms with the same topologies and placing both species in a new generic system. These results support the likelihood of identifying segregate genera from Acacia with phylogenomic disposition of both V. nilotica and S. senegal in the subfamily Mimosoideae. The current study is the first to obtain complete genomic information on both species and may help to elucidate the genome architecture of these species and evaluate the genetic diversity among species.