Plastome phylogenomic and systematic study on the tribe Sophoreae (Fabaceae), with special reference to East Asian genera

초록

The phylogenetic analyses have been proved the heterogeneity of the tribe Sophoreae sensu lato (s.l.), an early-branching group of papilionoid legumes. The recent systematic studies and re-circumscription of the tribe (i.e. the merger of Euchresteae and Thermopsideae into Sophoreae) have improved our understanding of its taxonomy. Nonetheless, definitions and inter- and intra-taxonomic issues of Sophoreae remain unclear because actual synapomorphy is lacking. Moreover, the complete generic-level phylogeny was never conducted for the tribe. Thus, the composition and validity of newly suggested Sophoreae is remained to be tested. Within the field of legume systematics, the molecular characteristics of a plastid genome (plastome) also have an important role in helping to define taxonomic groups. Here, we examined the plastome of an East Asian endemic genus Maackia, belonging to Sophoreae sensu stricto (s.s.), to elucidate the molecular characteristic of Sophoreae. Additionally, sequence data from the nuclear internal transcribed spacer (ITS) and the plastid matK region were used to infer evolutionary relationships of Sophoreae, with special reference to East Asian genera. The gene contents of Maackia are similar to the plastomes of other typical legumes. However, the plastome has a novel 24-kb inversion in its large single copy region in addition to the 50-kb and 36-kb inversions that were already known. The 36-kb inversion was shared by the core genistoids while the 24-kb inversion was distributed throughout eight genera in the Northern Hemisphere. Although the 24-kb inversion can be used as a putative synapomorphic character for the newly circumscribed Sophoreae, its presence suggests a slightly narrower taxonomic group. The phylogenetic analyses based on ITS and matK were concordantly agreed with the monophyly of the taxa that has 24-kb inversion in their plastome. However, there was some topological incongruence between ITS and matK phylogeny. As a main result, it