Genetics. 2008 Sep 9. [Epub ahead of print]
Secondary Mutations Correct Fitness Defects in Toxoplasma gondii with Dinitroaniline Resistance Mutations
Ma CI, Tran J, Li C, Ganesan L, Wood D, Morrissette NS.
University of California, Irvine.
Dinitroanilines (oryzalin, trifluralin, ethafluralin) disrupt microtubules in protozoa but not vertebrate cells, causing selective death of intracellular Toxoplasma gondii parasites without affecting host cells. Parasites containing alpha1-tubulin point mutations are dinitroaniline resistant but show increased rates of aberrant replication relative to wild type parasites. T. gondii parasites bearing the F52Y mutation were previously demonstrated to spontaneously acquire two distinct intragenic mutations that decrease both resistance levels and replication defects. Parasites bearing the G142S mutation are largely dependent on oryzalin for viable growth in culture. We isolated 46 T. gondii lines that have suppressed microtubule defects associated with the G142S or the F52Y mutations by acquiring secondary mutations. These compensatory mutations were alpha1-tubulin pseudorevertants or extragenic suppressors (the majority alter the beta1-tubulin gene). Many secondary mutations were located in tubulin domains that suggest that they function by destabilizing microtubules. Most strikingly, we identified eight novel mutations that localize to an eight amino acid insert that stabilizes the alpha1-tubulin M loop, including one (P364R) that acts as a compensatory mutation in both F52Y and G142S lines. These lines have reduced dinitroaniline resistance but perform better than parental lines in competition assays, indicating that there is a tradeoff between resistance and replication fitness.
PMID: 18780736 [PubMed - as supplied by publisher]