The conserved ciliary protein Bug22 controls planar beating of Chlamydomonas flagella

Abstract

Eukaryotic flagella and cilia may exhibit planar or non-planar beating, the mechanism underlying which is unknown. Chlamydomonas flagella beat in approximately the same plane either in asymmetric ciliary or symmetric flagellar waveforms. Each B tubule of number 1, 5 and 6 doublets of the flagellar axoneme possesses a beak-like structure. The number 5 and 6 beak structures are implicated in conversion of ciliary motion into flagellar motion. Here, we show that a null mutant of Bug22 converts asymmetric ciliary waveform into symmetric flagellar waveforms in three dimensions. Bug22 is localized approximately to the proximal half to two-thirds of the flagellum, similar to localization of beak-like structures. However, Bug22 associates with axonemal microtubules without apparent preference for any doublets shown by immunogold labeling. Interestingly, bug22 lacks all beak-like structures. We propose that one function of Bug22 is to regulate the anchoring of the beak-like structures to the doublet microtubules and confines flagellar beating in a plane.