PF19 encodes the p60 catalytic subunit of katanin and is required for assembly of the flagellar central apparatus in Chlamydomonas.

For all eukaryotic cilia the basal bodies provide a template for the assembly of the doublet microtubules, and intraflagellar transport provides a mechanism for transport of axonemal components into the growing cilium. What is not known is how the central pair of microtubules is nucleated or how their associated polypeptides are assembled. Here we report that the Chlamydomonas pf19 mutation results in a single amino acid change within the p60 catalytic subunit of katanin, and that this mutation prevents microtubule severing activity. The pf19 mutant has paralyzed flagella that lack the central apparatus. Using a combination of mutant analysis, RNAi-mediated reduction of protein expression and in vitro assays, we demonstrate that the p60 catalytic subunit of the microtubule severing protein katanin is required for central apparatus assembly in Chlamydomonas. In addition, we show that in Chlamydomonas the microtubule severing activity of p60 katanin is not required for stress-induced deflagellation or cell cycle progression as has been previously reported.