Evidence for duplication of the structural genes coding plastid and cytosolic isozymes of triose phosphate isomerase in diploid species of clarkia

Formal genetic analyses of the mode of inheritance of the multiple plastid and cytosolic isozymes of triose phosphate isomerase (TPI, EC 5.3.1.1) in annual diploid species of Clarkia (Onagraceae), native to California, suggest that each set of isozymes is specified by duplicate structural genes. In contrast, most diploid plant species possess one plastid and one cytosolic TPI isozyme each coded by a single locus. Linkage tests revealed that the two genes coding the plastid TPIs assort independently. Although the number of individuals sampled per species was small, the plastid isozymes were electrophoretically more variable than the cytosolic isozymes. The two gene duplications are the first reported that characterize an entire plant genus. Initial electrophoretic surveys of TPI in other genera of Onagraceae revealed that the duplication of the gene coding the plastid isozyme is apparently restricted to Clarkia, whereas that of the gene coding the cytosolic isozyme is present in most genera of the family. The separate phylogenetic distributions of the two duplications suggest that the processes that gave rise to them were unrelated.