α- and β-tubulin C-terminal tails with distinct modifications are crucial for ciliary motility and assembly

alpha-and beta-tubulin have an unstructured glutamate-rich region at their C-terminal tails (CTTs). The function of this region in cilia and flagella is still unclear, except that glutamates in CTTs act as the sites for post -translational modifications that affect ciliary motility. The unicellular alga Chlamydomonas possesses only two alpha-tubulin and two beta-tubulin genes, each pair encoding an identical protein. This simple gene organization might enable a complete replacement of the wild-type tubulin with its mutated version. Here, using CRISPR/Cas9, we generated mutant strains expressing tubulins with modified CTTs. We found that the mutant strain in which four glutamate residues in the alpha-tubulin CTT had been replaced by alanine almost completely lacked polyglutamylated tubulin and displayed paralyzed cilia. In contrast, the mutant strain lacking the glutamate-rich region of the beta-tubulin CTT assembled short cilia without the central apparatus. This phenotype is similar to mutant strains harboring a mutation in a subunit of katanin, the function of which has been shown to depend on the beta-tubulin CTT. Therefore, our study reveals distinct and important roles of alpha-and beta-tubulin CTTs in the formation and function of cilia.

Automated summary

The glutamate-rich region at the C-terminal tails of alpha- and beta-tubulin plays important roles in cilia formation and function. Post-translational modifications of the glutamate residues in this region affect ciliary motility and the assembly of cilia.