Utility of NADP-dependent isocitrate dehydrogenase for species-level evolutionary inference in angiosperm phylogeny: A case study in Saltugilia

NADP-dependent isocitrate dehydrogenase is a low-copy nuclear gene family. We have sequenced two regions from an idh gene (idhB) near the 3′ terminal end. The first fragment encodes 4 exons and 3 introns and is between ∼600 and 950 bp in length. The second fragment includes three additional exons and introns and is between ∼1200 and 1500 bp in length. The phylogenetic utility of the two sequence regions was evaluated in Polemoniaceae with a focus on Saltugilia, an incipient species complex that lacks phylogenetic resolution among these same taxa based on nuclear ribosomal ITS and chloroplast trnL. Multiple sequences from several individuals, multiple individuals from several populations, and multiple populations from all Saltugilia species were sampled to evaluate the taxonomic level at which idhB was useful as a phylogenetic marker in this clade. Phylogenies based on idhB sequences were compared with topological resolution and clade composition in ITS and trnL phylogenies. Phylogenies based on idhB and idhB in combination with ITS and trnL are better resolved than any other phylogenies for Saltugilia published to date, and character evolution within Saltugilia is explored.