The Arabidopsis TUBULIN-FOLDING COFACTOR A Gene Is Involved in the Control of the α/β-Tubulin Monomer Balance

The control of the stoichiometric balance of alpha- and beta-tubulin is important during microtubule biogenesis. This process involves several tubulin-folding cofactors (TFCs), of which only TFC A is not essential in mammalian in vitro systems or in vivo in yeast. Here, we show that the TFC A gene is important in vivo in plants. The Arabidopsis gene KIESEL (KIS) shows sequence similarity to the TFC A gene. Expression of the mouse TFC A gene under the control of the 35S promoter rescues the kis mutation, indicating that KIS is the Arabidopsis ortholog of TFC A. kis plants exhibit a range of defects similar to the phenotypes associated with impaired microtubule function: plants are reduced in size and show meiotic defects, cell division is impaired, and trichomes are bulged and less branched. Microtubule density was indistinguishable from that of the wild type, but microtubule organization was affected in trichomes and hypocotyl cells of dark-grown kis plants. The kis phenotype was rescued by overexpression of an alpha-tubulin, indicating that KIS is involved in the control of the correct balance of alpha- and beta-tubulin monomers.