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

Abstract

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 H 2 O 2 , indicating that wild-type (Wt) resistance to external H 2 O 2 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.

Reactive Oxygen Species Affect Photomorphogenesis in Neurospora crassa

“…The intracellular concentration of ROS generated by light may have been enhanced by the loss of SOD resulting in a high level of carotenoid accumulation in the early light induction of carotenoid synthesis. Recently, in N. crassa, catalase-3-deficient mutant showed enhanced production of carotenoid synthesis in colonies under illumination (48). These results suggested that intracellular ROS affect light inducible carotenoid synthesis.…”

Involvement of OS-2 MAP kinase in regulation of the large-subunit catalases CAT-1 and CAT-3 in Neurospora crassa

“…This indicates that the hyphal CAT-3 activity was not related with their osmotic sensitivity of the os mutants. Although CAT-3 was detected in the cytosol, it could be secreted and bound to the cell walls (Michan et al, 2003). It is possible that the secreted CAT-3 would not bind to an abnormal cell wall, which os mutants might have, and hence would affect the level of the hyphal CAT-3 activity of these mutants.…”

“…Sensitivity to hydrogen peroxide of hyphal growth of os and cat mutants It is known that the cat-3 null mutant is sensitive to hydrogen peroxide (Michan et al, 2003). We previously reported that the os-2 mutants was more sensitive to oxidative stress than the wild-type strain .…”

“…CAT-3 activity increases during the exponential growth phase and is induced by various stress conditions such as exposure to hydrogen peroxide, methyl viologen (paraquat), cadmium, uric acid, nitrate and heat shock (Chary and Natvig, 1989;Michan et al, 2002). It has been reported that asexual development is enhanced in a cat-3 mutant strain (Michan et al, 2003). CAT-2 is a member of the catalase-peroxidase family and is possibly derived from a bacterial enzyme.…”

“…Both are protohemeor heme-containing enzymes, which convert hydrogen peroxide into oxygen and water (catalases) or reduce it to water (peroxidases). Multiple catalases are differentially regulated, and some catalases are involved in the development of filamentous fungi (Hansberg et al, 1993;Navarro et al, 1996;Kawasaki et al, 1997;Navarro and Aguirre 1998;Michan et al, 2002;Peraza and Hansberg, 2002;Michan et al, 2003). Neurospora crassa has four catalase genes-cat-1, cat-2, cat-3, and ctt-1/cat-4 (Galagan Edited by Hirokazu Inoue * Corresponding author.…”