EXPRESSION OF A CYTOCHROME-P450 GENE FAMILY IN MAIZE

Maize seedlings, like seedlings of many other plants, are rich in cyto chrome P450 (P450) enzyme activity. Four P450 genes (CYPzm1-4), isolat ed from a seedling-specific cDNA library, are characterised by a trans ient and seedling-specific expression pattern. The maximum steady stat e mRNA levels are reached at 3 days in root and at 7 days in shoot tis sue, respectively. All four genes belong to one gene family and are cl osely related to the CYP71 family of plant P450 genes, which includes the enzymes of the ripening avocado fruit (CYP71A1) and eggplant hypoc otyls (CYP71A2, A3, A4). The expression of these related P450 genes in monocot and dicot plants indicates that these enzymes play a signific ant role in plants; however, the in vivo enzyme functions are unknown. The divergence of the four members of the maize gene family is suffic iently high to account for different substrate and/or reaction specifi city. Although the general expression pattern of the four genes is ide ntical, the maximum steady-state mRNA levels vary in different maize l ines. In situ hybridisation reveals the highest mRNA levels in the col eoptile, the first developed leaflets, the ground tissue of the nodula r complex, and in the cortex and pith of the region of cell division i n the root. The mapping of the maize CYPzm genes shows that, as in ani mals, P450 genes of the same family can be clustered. The presence of the CYPzm gene cluster in maize argues for generation of distinct plan t P450 gene families by gene duplication.