ISOLATION, SEQUENCE, AND CHARACTERIZATION OF THE CERCOSPORA-NICOTIANAE PHYTOENE DEHYDROGENASE GENE

We have cloned and sequenced the Cercospora nicotianae gene for the carotenoid biosynthetic enzyme phytoene dehydrogenase. Analysis of the derived amino acid sequence revealed it has greater than 50% identity with its counterpart in Neurospora crassa and approximately 30% identity with prokaryotic phytoene dehydrogenases and is related, but more distantly, to phytoene dehydrogenases from plants and cyanobacteria. Our analysis confirms that phytoene dehydrogenase proteins fall into two groups: those from plants and cyanobacteria and those from eukaryotic and noncyanobacter prokaryotic microbes. Southern analysis indicated that the C. nicotianae phytoene dehydrogenase gene is present in a single copy. Extraction of beta-carotene, the sole carotenoid accumulated by C. nicotianae, showed that both light and dark-grown cultures synthesize carotenoids, but higher levels accumulate in the light. Northern (RNA) analysis of poly(A)(+) RNA, however, showed no differential accumulation of phytoene dehydrogenase mRNA between light- and dark-grown fungal cultures.