Structural variation of the complete chloroplast genome and plastid phylogenomics of the genus Asteropyrum (Ranunculaceae)

Two complete chloroplast genome sequences of Asteropyrum, as well as those of 25 other species from Ranunculaceae, were assembled using both Illumina and Sanger sequencing methods to address the structural variation of the cp genome and the controversial systematic position of the genus. Synteny and plastome structure were compared across the family. The cp genomes of the only two subspecies of Asteropyrum were found to be differentiated with marked sequence variation and different inverted repeat-single copy (IR-SC) borders. The plastomes of both subspecies contains 112 genes. However, the IR region of subspecies peltatum carries 27 genes, whereas that of subspecies cavaleriei has only 25 genes. Gene inversions, transpositions, and IR expansion-contraction were very commonly detected in Ranunculaceae. The plastome of Asteropyrum has the longest IR regions in the family, but has no gene inversions or transpositions. Non-coding regions of the cp genome were not ideal markers for inferring the generic relationships of the family, but they may be applied to interpret species relationship within the genus. Plastid phylogenomic analysis using complete cp genome with Bayesian method and partitioned modeling obtained a fully resolved phylogenetic framework for Ranunculaceae. Asteropyrum was detected to be sister to Caltha, and diverged early from subfamily Ranunculoideae.