NADP-dependent isocitrate dehydrogenase exists as a low-copy, nuclear-encoded gene family with mitochondrial, plastid, cytosolic, and, in some plants, peroxzome isoenzymes. cDNA sequences of putative mitochondrial and cytosolic forms representing a few angiosperm families have been reported previously. The phylogenetic potential of this region has not been explored, however, and nDNA sequences that reveal gene organization (exon and intron lengths and numbers) have not heretofore been published. We have sequenced two nDNA IDH loci from representative members of Polemoniaceae to identify regions with sufficient variability to resolve relationships within this family. Comparison of exon sequences with reported cDNAs suggests these loci encode cytosolic paralogs that diverged recently relative to multiple cytosolic forms observed in other angiosperm families. Intron lengths differ, sometimes dramatically, between copies and gene organization is not wholly conserved within Polemoniaceae.

Key words: gene structure, IDH sequences, nuclear markers, phylogeny, Polemoniaceae