Inner dynein arms but not outer dynein arms require the activity of kinesin homologue protein KHP1FLA10 to reach the distal part of flagella in Chlamydomonas

Abstract

Inner dynein arms, but not outer dynein arms, require the activity of KHP1FLA10 to reach the distal part of axonemes before binding to outer doublet microtubules. We have analyzed the rescue of inner or outer dynein arms in quadriflagellate dikaryons by immunofluorescence microscopy of p28IDA4, an inner dynein arm light chain, or IC69ODA6, an outer dynein arm intermediate chain. In dikaryons two strains with different genetic backgrounds share the cytoplasm. As a consequence, wild-type axonemal precursors are transported to and assembled in mutant axonemes to complement the defects. The rescue of inner dynein arms containing p28 in ida4-wild-type dikaryons progressively occurred from the distal part of the axonemes and with time was extended towards the proximal part. In contrast, the rescue of outer dynein arms in oda2-wild-type dikaryons progressively occurred along the entire length of the axoneme. Rescue of inner dynein arms containing p28 in ida4fla10-fla10 dikaryons was similar to the rescue observed in ida4-wild-type dikaryons at 21°C, whereas it was inhibited at 32°C, a nonpermissive temperature for KHP1FLA10. In contrast, rescue of outer dynein arms in oda2fla10-fla10 dikaryons was similar to the rescue observed in oda2-wild-type dikaryons at both 21° and 32°C and was not inhibited at 32°C. Positioning of substructures in the internal part of the axonemal shaft requires the activity of kinesin homologue protein 1.