Comparative Analysis and Phylogenetic Implications of Plastomes of Five Genera in Subfamily Amyridoideae (Rutaceae)

In the most recent classification of Rutaceae, Amyridoideae is the largest and most diverse subfamily. In Amyridoideae, the genera Phellodendron, Tetradium, Toddalia and Zanthoxylum were proposed as "proto-Rutaceae"due to substantial phytochemical similarities. In this study, we investigated the plastome varia-tions in eight species representing these four genera and Melicope. All plastomes exhibited a typical quadripartite structure with four regions (LSC, SSC, IRa and IRb). The whole chloroplast genome size ranged from 158,383 bp to 159,014 bp and the gene number ranged from 115 to 116. By comparative analyses, we found that there were structural variations at the LSC/IR and SSC/IR borders of the plastomes in the five genera, especially in Melicope. Three most divergent regions (trnH-psbA, trnE-trnT and psaB) were found from the LSC region, which had great potential for developing effective genetic markers. In addition, we conducted a phylogenomic analyses of the "proto-Rutaceae"and related taxa with plastomes data from 36 species. Our results showed that (1) Phellodendron, Tetradium, Toddalia and Zanthoxylum were confirmed as close relatives and grouped together as the 'proto-Rutaceae', (2) Phellodendron was sister to Tetradium, and Toddalia was deeply nested within Zanthoxylum, and (3) Toddalia asiatica was closely related to the Southwest Pacific and East Asian species of Zanthoxylum, and Melicope pteleifolia was more closely related to Acronychia than it is to Tetradium. This study provided new insights into the plastome structural varia-tions in subfamily Amyridoideae, and demonstrated that the plastomes data were sufficiently robust to explore implications of the phylogeny for the previous phylogenetic hypotheses.