Characterization of a gene in the car cluster of Fusarium fujikuroi that codes for a protein of the carotenoid oxygenase family

Abstract

The ascomycete Fusarium fujikuroi produces carotenoids by means of the enzymes encoded by three car genes. The enzymes encoded by carRA and carB are responsible of the synthesis of beta-carotene and torulene, respectively, while the product encoded by carT cleaves torulene to produce the acidic xanthophyll neurosporaxanthin. carRA and carB are found in a cluster with a third gene, carO, which codes for an opsin-like protein. However, no information is available on the sequence or chromosomal location of carT, which has been identified only by mutant analysis. Transcription of the three clustered genes is stimulated by light and by mutations in a regulatory gene, leading to overproduction of carotenoids. We have now identified a fourth gene in the car cluster, called carX, which codes for a protein similar to known carotenoid-cleaving oxygenases. carX is transcribed divergently from carRA, and exhibits the same transcriptional pattern as carRA, carB and carO. Targeted deletion of carX resulted in a phenotype characterized by a significant increase in the overall carotenoid content. In the dark, the carX mutants accumulate at least five times more carotenoids than the wild type, and exhibit partial derepression of carRA and carB transcription. The mutants also show more intense pigmentation in the light, but the increase in the carotenoid content relative to the wild type is less than twofold. Under these conditions, the mutants also show a relative increase in the amounts of phytoene and cyclic carotenoids formed, suggesting that CarRA activity is enhanced.

Retinal Biosynthesis in Fungi: Characterization of the Carotenoid Oxygenase CarX fromFusarium fujikuroi

“…However, like in the case of NOP-1 from Neurospora (8), targeted deletion of carO did not lead to a detectable phenotype (26). In contrast to carO, the disruption of carX, which encodes a putative carotenoid oxygenase, resulted in a significant induction of carotenoid biosynthesis (40), indicating that the enzyme is involved in negative feedback regulation of the pathway and not in neurosporaxanthin formation, as presumed before. The car gene cluster resembles the recently described clusters from ␥-proteobacteria in that it harbors genes responsible for ␤-carotene formation and two genes encoding an opsin and a retinal-forming enzyme (29).…”

“…Sequence comparisons suggested that CarX is a member of the carotenoid oxygenase family (40). To investigate its ability to cleave carotenoids, we expressed CarX in lycopene-and ␤-caroteneaccumulating E. coli cells using the pBAD/TOPO expression system (Invitrogen, Paisley, United Kingdom).…”

“…The four genes exhibit the same transcriptional pattern, being expressed at low levels in the dark and induced by illumination to reach a maximum after 1 h of exposure. In addition, all four genes are deregulated in carotenoid-overproducing mutants (23,26,40).…”

The Oxygenase CAO-1 of Neurospora crassa Is a Resveratrol Cleavage Enzyme

“…Hence, we have investigated a possible relation of CAO-1 with carotenoid metabolism. The gene carX is strongly induced by light in F. fujikuroi (30). Since carotenoid biosynthesis in Neurospora mycelia is induced by light, we first investigated the effect of light on cao-1 regulation.…”

Role of the White Collar 1 Photoreceptor in Carotenogenesis, UV Resistance, Hydrophobicity, and Virulence of Fusarium oxysporum

“…The light induction of carotenogenesis was studied by extracting carotenes from mycelia grown for 7 days in the dark or under photoperiods and measuring them as described previously (31). The carotenoid levels in dark-grown mycelia of the ⌬wc1 mutant were similar to those of the wild-type or the ⌬wc1ϩwc1 strain.…”