CHARACTERIZATION OF THE CATALASE ANTIOXIDANT DEFENSE GENE CAT1 OF MAIZE, AND ITS DEVELOPMENTALLY REGULATED EXPRESSION IN TRANSGENIC TOBACCO

A genomic clone containing the maize Cat1 gene nas been isolated and its complete DNA sequence determined. The start of transcription has been mapped by primer extension. Six introns were identified in the Cat1 coding region. In order to determine the tissue-specific expression pattern of the Cat1 gene, promoter-reporter gene fusion constructs were made consisting of 2.5 kb and 0.8 kb of the 5' Cat1 sequence fused to the coding region of the beta-glucuronidase (GUS) gene. These fusion constructs were introduced into Nicotiana tabacum cv. Burley 21 and the expression of Cat1-GUS in various tissues was examined. In transgenic tobacco, the Cat1 promoter can drive GUS expression at relatively high levels in mature seeds. GUS activity starts to accumulate at about 10 days after flowering, reaching a maximum at about 22 days after flowering, and decreases thereafter, but persists until after seed desiccation through early germination. Low levels of GUS activity can be detected in pollen. This corresponds to the Cat1 expression pattern observed in maize.