MAIZE ALPHA-TUBULIN GENES ARE EXPRESSED ACCORDING TO SPECIFIC PATTERNS OF CELL-DIFFERENTIATION

In the past few years many alpha- and beta-tubulin genes of different organisms have been cloned and studied, and in most systems studied th ey constitute multigene families. In plants, most studies have been do ne in Arabidopsis thaliana and Zea mays. In this paper, the study of m RNA accumulation by in situ hybridization and the activity of three ma ize ol-tubulin gene promoters (tua1, tua2 and tua3) in transgenic toba cco plants are described. In maize, the expression of these three tubu lin isotypes differ in the root and shoot apex and is associated with different groups of cells throughout the distinct stages of cell diffe rentiation. In transgenic tobacco plants the promoters of the genes, f used to the uidA reporter gene (GUS), direct expression to the same ti ssues observed by in situ hybridization experiments. The tua1 promoter is mainly active in cortex-producing meristematic cells and in pollen , whereas tua3 is active in cells which are differentiating to form va scular bundles in the root and shoot apices. The accumulation of tua2 mRNA is detected by RNA blot in a similar form as tua1, but at a very much low level. In situ hybridization indicates that the tua2 mRNA spe cifically accumulates in the maize root epidermis. No GUS staining was detected in transgenic tobacco plants with the tua2 promoter. The dif ference in expression of the specific genes may be linked to processes where microtubules have different functions, suggesting that in plant s, as in animals, there are differences in the function of the tubulin isotypes.