Chlamydomonas ODA10 is a conserved axonemal protein that plays a unique role in outer dynein arm assembly

Assembly of outer dynein arms (ODAs) requires multiple steps and involves multiple proteins in addition to dynein subunits. The Chlamydomonas ODA10, ODA5, and ODA8 loci genetically interact and are hypothesized to function as an axonemal accessory complex, but only ODA5p was previously characterized. We positionally cloned ODA10 and identified the gene by rescuing an oda10 mutant with a hemagglutinin-tagged cDNA. ODA10 sequence predicts a conserved coiled-coil protein homologous to mouse ccdc151. ODA10p is present in cytoplasm and flagella, remains axonemal after detergent treatment, and is extracted with 0.6 M NaCl. Both outer arm dynein and ODA10p rebound to the axonemes when desalted extracts are mixed with oda10-mutant axonemes. Sucrose gradient separation of these extracts shows that ODA10p sediments near the top of the gradient, not with 23S outer dynein arm proteins. Unexpectedly, dynein and ODA10p fractions are able to bind individually to oda10 axonemes. ODA10p is present on oda8-mutant flagella at wild-type levels. However, ODA10p does not assemble into oda5 flagella and is absent from oda5 cytoplasm, suggesting a necessity of ODA5p for stability of ODA10p in vivo. The results suggest that ODA10p does not function as a part of a traditionally defined docking complex.