Isolation and characterization of two tightly linked catalase genes from castor bean that are differentially regulated.

Two catalase genes, cat1 and cat2, have been isolated from the castor bean genome. They were located in the same direction on a chromosome at a distance of 2.4 kb, cat1 being on the downstream side of cat2. The two genes contained introns at the same positions except that one of the 7 introns in cat1 is missing in cat2 and the corresponding introns differed in size and sequence between the two genes. The translated regions of the two genes had the same number of nucleotides and exhibited 81.3% nucleotide sequence identity. In addition to introns, the nucleotide sequences of the 5'- and 3'-flanking regions are highly divergent between the two genes. In etiolated seedlings, cat1 mRNA was present abundantly in endosperms and cotyledons and only in a small amount in roots. The cat1 mRNA could not be detected in hypocotyls. By contrast, cat2 mRNA is most abundant in hypocotyls and roots, while endosperms and cotyledons contained only low levels of cat2 mRNA. Although neither cat1 nor cat2 mRNA could be detected in dry seeds, both mRNAs showed temporal accumulation in the endosperm in response to germination. These results suggest that expression of two tightly linked catalase genes of castor bean, cat1 and cat2, are differentially regulated during development.