PHYLOGENETIC-RELATIONSHIPS AMONG THE SECTIONS OF CLARKIA(ONAGRACEAE) INFERRED FROM THE NUCLEOTIDE-SEQUENCES OF PGIC

Paralogous genes PgiC1 and PgiC2 resulting from a single duplication e ncode the cytosolic isozymes of phosphoglucose isomerase (EC 5.3.1.9) in Clarkia. The duplication is ancestral to all extant sections of Cla rkia. Both genes are expressed in species with two active PGIC isozyme s, but species that have a single PGIC isozyme have an expressed PgiC1 and a silenced psi PgiC2. Genomic nucleotide sequences have been obta ined for eight PgiC1 and five PgiC2 genes from species representing si x of the eight presently recognized diploid sections of Clarkia. The s equences include a nearly complete psi PgiC2 from C. mildrediae and a partial psi PgiC2 from C. rostrata. Parsimony analysis using the singl e PgiC of Oenothera mexicana as outgroup places the sequences of Clark ia into two groups corresponding to PgiC1 and PgiC2. The tree is stron gly supported by bootstrapping and the modified Templeton's test. Fitc h-Margoliash and neighbor-joining methods give the same tree. The resu lts for the two genes are in perfect accord and establish the relation ships among the sections. From the base of the genus, the sections bra nch in the following order: sect. Eucharidium, sect. Rhodanthos, sect. Myxocarpa, sect. Phaeostoma, sect. Godetia, and sect. Sympherica. The only ambiguity concerns whether the basal lineage is sect. Eucharidiu m alone or paired with sect. Rhodanthos. Data from PgiC1 alone provide 92.5% bootstrap support for the basal placement of sect. Eucharidium. The phylogenetic tree reveals that PgiC2 has been silenced at least f our times independently. The results demonstrate the value of nuclear PgiC sequences to resolve difficult phylogenetic problems.