Ustilago maydis accumulates β-carotene at levels determined by a retinal-forming carotenoid oxygenase

Alejandro F. Estrada, Thomas Brefort, Carina Mengel, Violeta Díaz-Sánchez, Adrian Alder, Salim Al-Babili, Javier Avalos*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

31 Scopus citations

Abstract

The basidiomycete Ustilago maydis, the causative agent of corn smut disease, has emerged as a model organism for dimorphism and fungal phytopathogenicity. In this work, we line out the key conserved enzymes for β-carotene biosynthesis encoded by the U. maydis genome and show that this biotrophic fungus accumulates β-carotene. The amount of this pigment depended on culture pH and aeration but was not affected by light and was not increased by oxidative stress. Moreover, we identified the U. maydis gene, cco1, encoding a putative β-carotene cleavage oxygenase. Heterologous overexpression and in vitro analyses of purified enzyme demonstrated that Cco1 catalyzes the symmetrical cleavage of β-carotene to yield two molecules of retinal. Analyses of β-carotene and retinal contents in U. maydis cco1 deletion and over-expression strains confirmed the enzymatic function of Cco1, and revealed that Cco1 determines the β-carotene content. Our data indicate that carotenoid biosynthesis in U. maydis is carried out to provide retinal rather than to deliver protective pigments. The U. maydis genome also encodes three potential opsins, a family of photoactive proteins that use retinal as chromophore. Two opsin genes showed different light-regulated expression patterns, suggesting specialized roles in photobiology, while no mRNA was detected for the third opsin gene in the same experiments. However, deletion of the cco1 gene, which should abolish function of all the retinal-dependent opsins, did not affect growth, morphology or pathogenicity, suggesting that retinal and opsin proteins play no relevant role in U. maydis under the tested conditions.

Original languageEnglish (US)
Pages (from-to)803-813
Number of pages11
JournalFungal Genetics and Biology
Volume46
Issue number10
DOIs
StatePublished - Oct 1 2009

Keywords

  • Apocarotenoids
  • Carotenogenesis
  • Carotenoid cleavage oxygenase
  • Light regulation
  • Opsins

ASJC Scopus subject areas

  • Microbiology
  • Genetics

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