Development and fertility in Caenorhabditis elegans clk-1 mutants depend upon transport of dietary coenzyme Q₈ to mitochondria

The Caenorhabditis elegans clk-1 mutants lack coenzyme Q₉ and instead accumulate the biosynthetic intermediate demethoxy-Q₉ (DMQ₉). clk-1 animals grow to reproductive adults, albeit slowly, if supplied with Q₈-containing Escherichia coli. However, if Q is withdrawn from the diet, clk-1 animals either arrest development as young larvae or become sterile adults depending upon the stage at the time of the withdrawal. To understand this stage-dependent response to a Q-less diet, the quinone content was determined during development of wild-type animals. The quinone content varies in the different developmental stages in wild-type fed Q₈-replete E. coli. The amounts peak at the second larval stage, which coincides with the stage of arrest of clk-1 larvae fed a Q-less diet from hatching. Levels of the endogenously synthesized DMQ₉ are high in the clk-1(qm30)-arrested larvae and sterile adults fed Q-less food. Comparison of quinones from animals fed a Q-replete or a Q-less diet establishes that the Q₈ present is assimilated from the E. coli. Furthermore, this E. coli-specific Q₈ is present in mitochondria isolated from fertile clk-1(qm30) adults fed a Q-replete diet. These results suggest that the uptake and transport of dietary Q₈ to mitochondria prevent the arrest and sterility phenotypes of clk-1 mutants and that DMQ is not functionally equivalent to Q.