Characterization of catalase transcripts and their differential expression in maize.

In maize, the three unlinked catalase (EC 1.11.1.6) structural genes (Cat1, Cat2 and Cat3) are differentially expressed temporally, spatially and in response to environmental signals in the developing seedling. In order to understand more fully the molecular mechanisms involved in catalase gene expression, full-length cDNA clones representing the maize Cat1, Cat2 and Cat3 transcripts were isolated and characterized. DNA sequence analysis confirmed that each cDNA encodes a unique catalase protein. Gene-specific probes for the three maize catalase cDNAs were isolated and used to probe blots of poly(A)+ RNA isolated from various maize tissues. Cat1 mRNA was found in scutella, milky endosperm of immature kernels, leaves and epicotyls. The Cat2 mRNA was present primarily in post-germinative scutella, with lower levels in leaves and epicotyls. Cat3 mRNA was detected primarily in epicotyls and, to a lesser extent, in leaves and scutella. The gene-specific probes hybridized with maize genomic DNA blots in simple, but unique patterns, indicating that there is one, or a very few copies of each catalase gene. The coding region of the Cat3 cDNA comprised 66% G + C, which led to a strong codon usage bias in this gene. This codon bias was also seen with the Cat2 transcripts, but not with those for Cat1. A high degree of similarity was found between the maize catalase nucleic acid and deduced amino-acid sequences and those of sweet potato and rat liver catalase.