Four members of the maize beta-tubulin gene family are expressed in the male gametophyte.

Four different beta-tubulin cDNA clones have been identified in maize pollen cDNA libraries. Three of the four cDNA clones represent new maize beta-tubulin genes that have been designated tub3, tub4 and tub5. It is shown that the beta-tubulin gene family in maize is more complex than originally anticipated and more complex than those in vertebrates. In the maize beta-tubulin gene family the tub3, tub4 and tub5 genes are shown to represent small beta-tubulin gene subfamilies. Differences in the abundance of the tub3, tub4 and tub5 transcripts are seen among vegetative and reproductive tissues. The tub3 and tub4 transcripts are most abundant in pollen. In spikelet development, abundance of the tub3 transcript increases markedly from the 0.7 cm to the 1.0 cm spikelets whilst the levels of tub4 transcript closely resemble those of total beta-tubulin transcript in the organs examined. The tub3 and tub4 genes appear to have diverged recently in the evolution of the maize beta-tubulin gene family. The tub5 gene is expressed in pollen but its transcript is most abundant in maize vegetative tissues.