Plastome evolution and phylogeny of the tribe Ruteae (Rutaceae)

Rutaceae is a large family, and the genus-level classification in the subfamilies or tribes of this family is not unified based on different taxonomic treatments. Until now, phylogenetic relationships of some genera in traditional tribe Ruteae have not been clearly resolved. In this study, seven new complete plastomes of this tribe were sequenced, and a comparative analysis was performed to investigate their plastome characteristics and evolution. In addition, we inferred the phylogenetic relationships of Ruteae based on complete plastome and nuclear ITS data. All plastomes exhibited a typical quadripartite structure and were relatively conserved in their structure and gene arrangement. Their genome sizes ranged from 154,656 bp to 160,677 bp, and the size variation was found to be associated with differences in IR expansion and gene loss. A total of 112 to 114 genes were identified in the genomes, including 78 to 79 protein-coding genes, 30 tRNA genes, 4 rRNA genes, and 2 pseudogenes. Sequence divergence analysis indicated that non-coding regions exhibited a higher percentage of variable characters, and nine non-coding and six coding regions were identified as divergent hotspots. Phylogenetic results based on different datasets showed that this tribe was divided into three reciprocally exclusive groups. The phylogenetic analyses between plastome and nuclear ITS data were partly incongruent with each other. This study provides new insights into plastome evolution of Ruteae as well as Rutaceae. The availability of these plastomes provides useful genomic resources for molecular DNA barcodes and phylogenetically informative markers and deepens our understanding of the phylogeny in Ruteae.