Polyglutamylase that forms polyglutamate side chains on tubulin (By similarity). Acts when complexed with other proteins (Probable). Appears to be dispensable for polar spindle formation in dividing embryonic cells, for cilia-dependent osmotic avoidance and for male mating behavior (PubMed:27635036). Probably by regulating microtubule stability via the glutamylation of tubulin, regulates PLM axon developmental growth (PubMed:23000142). Expressed in head sensory neurons. Expressed in embryos and adults. Belongs to the tubulin--tyrosine ligase family.