Non-mendelian mutation affecting ribulose-1, 5-bisphosphate carboxylase structure and activity

Chlamydomonas reinhardii , a haploid unicellular green alga, is the only organism in which the non-mendelian (uniparental) genes thought to reside in chloroplast DNA have been observed to re combine. Thus, genetic mapping by recombination analysis is possible, and a single linkage group with a large number of markers has been characterized 1,2 . Although circumstantial evidence is consistent with the hypothesis that this uniparental linkage group is located in the chloroplast, 1,2 there is no direct evidence associating any of the known markers with chloroplast DNA. As the gene for the large subunit (LS) of ribulose-1, 5-bisphosphate carboxylase (RubPCase) has been located on the physical map of C. reinhardii chloroplast DNA, 3,4 a genetic marker in this same gene would help to prove the relationship between the uniparental linkage group and chloroplast DNA. We have now succeeded in isolating a mutation in a C. reinhardii gene which controls the structure and function of the LS of RubPCase. This new genetic marker will serve as the first reference point in our efforts to correlate the physical and genetic maps for the chloroplast genome. At the same time, the fact that we have obtained this mutant should encourage further attempts to produce genetic modifications of this key photosynthetic enzyme with the goal of improving plant productivity 5 .