Tubulin gene expression in maize (Zea mays L.). Change in isotype expression along the developmental axis of seedling root

Two-dimensional gel/western blot analysis was used to characterize α- and β-tubulin isotype expression along the developmental axis of the maize (Zea mays) seedling primary root. We identified four distinct α-tubulin isotypes and a minimum of six β-tubulin isotypes. This analysis showed differences between the α- and β-tubulin isotypes expressed in rapidly dividing tissue at the root tip and differentiated root tissues proximal to the tip. The α1 and α4 isotypes predominated in samples from immature rapidly dividing tissues such as root tips, whereas in mature tissues such as differentiated root and pollen, α2, a3 and α4 isotypes predominated. The β1 and β2 isotypes were more abundant in protein samples from root cortex than in samples from the root tip or vascular cylinder. In contrast, the β4 and β5 isotypes appeared to be more abundant in root tip and vascular cylinder samples than in root cortex samples. Hybridization probes from the 3′ non-coding region of six α-tubulin cDNA clones were used to quantify the levels of corresponding tubulin transcripts in selected tissues, from embryonic to mature and from largely undifferentiated to highly differentiated. The results from these hybridization experiments showed that all of the α-tubulin genes were expressed in all tissues examined, although each gene showed a unique pattern of differential transcript accumulation. A transcript produced from cDNA clone representing the tua5 α-tubulin gene was translated in vitro and produced an α-tubulin that comigrated with the α2 isotype.