Phylogenomic analyses unravel the tangled evolutionary history of Genisteae (Fabaceae)

Abstract

Genisteae, a tribe in the subfamily Papilionoideae (Fabaceae), is characterized by the production of quinolizidine alkaloids that confer pest resistance in most of its members. Many relationships at the generic level remain unresolved due largely to a lack of modern attempts to reconstruct the phylogeny. Previous studies with limited taxon sampling and only a few molecular loci indicated the presence of three clades within the tribe: the Lupinus clade, the Cytisus-Genista complex and the Argyrolobium group. There are also two historical genera, Teline and Chamaecytisus, that have been reclassified over the years with some controversy. Species from Teline are currently classified in Genista, and Chamaecytisus species are placed inside of Cytisus. Sellocharis is another genus with vague placement inside of Genisteae near Anarthrophyllum, based mostly on morphology and cytology. Representative taxa from 24 of the 25 genera of Genisteae, along with species of historical genera Teline and Chamaecytisus, were sampled and utilized in a phylogenomic investigation using both plastid and nuclear data to resolve relationships at the generic level. Whole genomic DNA was sequenced and complete plastomes were assembled and annotated. Low-copy nuclear genes were retrieved from the genomic DNA sequences using a mapping-assembly-scaffold approach. Phylogenetic analyses using maximum likelihood, Bayesian and coalescence methods resulted in fully resolved and strongly supported trees for both nuclear and plastid data that show four major clades inside of Genisteae: Cytisus-Genista complex, Lupinus clade, Argyrolobium group and the novel Anarthrophyllum group. The resulting phylogenetic trees also supported the transfer of the Argyrolobium group from Crotalarieae to Genisteae, and the reclassification of Teline inside of Genista, both of which were previously suggested in literature. The phylogenetic trees also determined a placement for Sellocharis in the new Anarthrophyllum group. Although both nuclear and plastid trees were congruent with respect to the monophyly and relationships among the four major clades, incongruence was detected within some of the major clades and the potential causes are discussed.