Multiple phosphorylation sites on γ‐tubulin are essential and contribute to the biogenesis of basal bodies in Tetrahymena

The mechanisms that regulate γ‐tubulin, including its post‐translational modifications, are poorly understood. γ‐Tubulin is important for the duplication of centrioles and structurally similar basal bodies (BBs), organelles which contain a ring of nine triplet microtubules. The ciliate Tetrahymena thermophila carries hundreds of cilia in a single cell and provides an excellent model to specifically address the role of γ‐tubulin in the BBs assembly and maintenance. The genome of Tetrahymena contains a single γ‐tubulin gene. We show here that there are multiple isoforms of γ‐tubulin that are likely generated by post‐translational modifications. We identified evolutionarily conserved serine and threonine residues as potential phosphosites of γ‐tubulin, including S80, S129, S131, T283, and S360. Several mutations that either prevent (S80A, S131A, T283A, S360A) or mimic (T283D) phosphorylation were conditionally lethal and at a higher temperature phenocopied a loss of γ‐tubulin. Cells that overproduced S360D γ‐tubulin displayed phenotypes consistent with defects in the microtubule‐dependent functions, including an asymmetric division of the macronucleus and abnormalities in the pattern of BB rows, including gaps, fragmentation, and misalignment. In contrast, overexpression of S129D γ‐tubulin affected the orientation, docking, and structure of the BBs, including a loss of either the B‐ or C‐subfibers or the entire triplets. We conclude that conserved potentially phosphorylated amino acids of γ‐tubulin are important for either the assembly or stability of BBs.