ANALYSIS OF A MAIZE ALPHA-TUBULIN GENE PROMOTER BY TRANSIENT EXPRESSION AND IN TRANSGENIC TOBACCO PLANTS

The pattern of expression directed by the promoter of the maize Tubalp ha1 gene was investigated by analysis of chloramphenicol acetyl transf erase (CAT) and beta-glucuronidase (GUS) activities in transient expre ssion experiments of maize and tobacco protoplasts. The same promoter was also investigated by histochemical GUS analysis in transgenic toba cco plants containing promoter gene fusions. As determined by histoche mical tests, the Tubalpha1 promoter gene preferentially directs GUS ex pression in regenerating root tip meristems and pollen. This pattern c orresponds to the distinctive features of natural expression of the ge ne in maize as determined by Northern analysis. However, no expression is observed in other meristematic tissues of the transgenic tobacco p lants, as in shoot apex or in coleoptiles, which is weakly detected in maize. Analysis of the regulatory properties of 5' promoter deletions showed that the proximal region of the promoter, from positions -1410 or -449 to 15 bp upstream of the ATG, is sufficient to establish the qualitative pattern of expression in transgenic tobacco plants. Deleti ons to positions -352 or -117 abolished the expression in roots, but n ot in pollen, suggesting that upstream of these positions there are el ements responsible for the pattern in root. Further deletions abolishe d all the promoter activity, suggesting that this promoter region cont ains the elements essential for expression in pollen. The different pa tterns and levels of transient and stable expression are discussed.