Microtubules are important components of the cytoskeleton of plant cells and play key roles in plant growth and morphogenesis. Recent molecular studies have begun to elucidate the structure and expression of plant genes coding for the major components of microtubules, a-and 0-tubulin. Tubulin amino acid sequences deduced from the DNA sequences of eight higher plant tubulin genes are 79-87 % homologous with constitutively expressed mammalian tubulins. The genome of the model plant system Arabidopsis thulium contains four dispersed a-tubulin sequences and at least seven 0-tubulin sequences, only two of which appear to be linked. Of the five A. thaliuna genes whose expression has been analyzed, the transcripts of one a-tubulin and one 0-tubulin gene are constitutively expressed in roots, leaves, and flowers. A second a-tubulin gene is expressed predominately in flowers; the transcripts of the second and third 0-tubulin genes are found predominately in leaves or in roots, respectively.