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Eukaryotic Cell, August 2003, p. 798-808, Vol. 2, No. 4
1535-9778/03/$08.00+0     DOI: 10.1128/EC.2.4.798-808.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

Asexual Development Is Increased in Neurospora crassa cat-3-Null Mutant Strains

Shaday Michán, Fernando Lledías, and Wilhelm Hansberg^*

Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, México, D.F., México

Received 23 October 2002/ Accepted 29 May 2003

We use asexual development of Neurospora crassa as a model system with which to determine the causes of cell differentiation. Air exposure of a mycelial mat induces hyphal adhesion, and adherent hyphae grow aerial hyphae that, in turn, form conidia. Previous work indicated the development of a hyperoxidant state at the start of these morphogenetic transitions and a large increase in catalase activity during conidiation. Catalase 3 (CAT-3) increases at the end of exponential growth and is induced by different stress conditions. Here we analyzed the effects of cat-3-null strains on growth and asexual development. The lack of CAT-3 was not compensated by other catalases, even under oxidative stress conditions, and cat-3^RIP colonies were sensitive to H₂O₂, indicating that wild-type (Wt) resistance to external H₂O₂ was due to CAT-3. cat-3^RIP colonies grown in the dark produced high levels of carotenes as a consequence of oxidative stress. Light exacerbated oxidative stress and further increased carotene synthesis. In the cat-3^RIP mutant strain, increased aeration in liquid cultures led to increased hyphal adhesion and protein oxidation. Compared to the Wt, the cat-3^RIP mutant strain produced six times more aerial hyphae and conidia in air-exposed mycelial mats, as a result of longer and more densely packed aerial hyphae. Protein oxidation in colonies was threefold higher and showed more aerial hyphae and conidia in mutant strains than did the Wt. Results indicate that oxidative stress due to lack of CAT-3 induces carotene synthesis, hyphal adhesion, and more aerial hyphae and conidia.

Present address: Departamento de Biología Molecular de Plantas, Instituto de Biotecnología, Universidad Nacional Autónoma de México, 62250 Cuernavaca, Mor., México