Temperature-sensitive yellow mutants of Chlamydomonas reinhardtii

Abstract

We have isolated and genetically characterized 10 mutants of Chlamydomonas reinhardtii carrying single, mendelian, temperature-sensitive yellow mutations. The mutants have a yellow phenotype at the restrictive temperature (33°C), but have a wildtype phenotype at the permissive temperature (25°C). Based on complementation and recombination tests, the ten mutations include alleles of two previously described yellow loci (y-1 and y-6) and three new yellow loci (y-8, y-9, and y-10). At the restrictive temperature, y-8, y-9, and y-10 are physiologically similar to other yellow mutants. They accumulate small amounts of protochlorophyllide when grown under dim light, but synthesize normal amounts of chlorophyll when grown in the light. Linkage tests indicate that the three new mutations are not linked to each other. y-8 is linked to y-7 on linkage group III, and y-10 is linked to y-5 and y-6 on linkage group I. y-9 is located on linkage group II. We conclude that the control of light-independent protochlorophyllide reduction is complex, involving several genetic loci which are scattered in the genome and which code for gene products able to complement in trans. Temperature-sensitive alleles at several of the yellow loci suggest that the gene products made by these loci are proteins.