Complete chloroplast genome sequencing of Caralluma quadrangula and comparative analysis of the Asclepiadoideae subfamily (Apocynaceae)

Abstract

Caralluma quadrangula is an herbaceous plant distributed in Saudi Arabia, India, Africa, and the Canary Islands. To assess the phylogenetic and evolutionary relationships among the Asclepiadoideae subfamily in the Apocynaceae family, we carried out a compara-tive chloroplast (cp) genome analysis of four species. The size of the C. quadrangula chloroplast genome is 161,456 bp, while the large single-copy (LSC) is 85,992 bp, the small single-copy (SSC) is 13,380 bp, and the two inverted repeats (IRs) are 31,042 bp each. The genome has a total of 129 genes, among which 19 are located at the inverted repeat region, 85 are protein coding genes, 36 are tRNA genes, and eight are rRNA genes. Visualization of single-copy and inverted repeat borders showed that expansion and contraction have occurred in the cp genomes of the compared species of Ascle-piadoideae. The genome comparative analysis shows that the coding regions are more highly conserved than the non-coding region; thus, the variable hotspot can serve as a barcode for species in the subfamily. Phylogenetic analysis conducted based on cp sequences identified Stapelia as sister to Caralluma, in agreement with previous studies. The current study may facilitate the development of molecular markers to ease the identifi cation and authentication of members of the genus Caralluma in the Apocynaceae.