New Insights Into the Roles of NADPH Oxidases in Sexual Development and Ascospore Germination in Sordaria macrospora

Abstract

NADPH oxidase (NOX)-derived reactive oxygen species (ROS) act as signaling determinants that induce different cellular processes. To characterize NOX function during fungal development, we utilized the genetically tractable ascomycete Sordaria macrospora. Genome sequencing of a sterile mutant led us to identify the NADPH oxidase encoding nox1 as a gene required for fruiting body formation, regular hyphal growth, and hyphal fusion. These phenotypes are shared by Δnor1, lacking the NOX regulator NOR1. Further phenotypic analyses revealed a high correlation between increased ROS production and hyphal fusion deficiencies in Δnox1 and other sterile mutants. A genome-wide transcriptional profiling analysis of mycelia and isolated protoperithecia from wild type and Δnox1 revealed that nox1 inactivation affects the expression of genes related to cytoskeleton remodeling, hyphal fusion, metabolism, and mitochondrial respiration. Genetic analysis of Δnox2, lacking the NADPH oxidase 2 gene, Δnor1, and transcription factor deletion mutant Δste12, revealed a strict melanin-dependent ascospore germination defect, indicating a common genetic pathway for these three genes. We report that gsa3, encoding a G-protein a-subunit, and sac1, encoding cAMP-generating adenylate cyclase, act in a separate pathway during the germination process. The finding that cAMP inhibits ascospore germination in a melanin-dependent manner supports a model in which cAMP inhibits NOX2 activity, thus suggesting a link between both pathways. Our results expand the current knowledge on the role of NOX enzymes in fungal development and provide a frame to define upstream and downstream components of the NOX signaling pathways in fungi. D URING sexual reproduction, filamentous fungi generate complex fruiting bodies that contain and protect meiosporangia. We used the ascomycetous model fungus Sordaria macrospora to identify genes directly involved in fruiting body development (Kück et al. 2009;Engh et al. 2010;Kück et al. 2009). Due to its homothallic life style, S. macrospora is able to complete the sexual life cycle without the mating of strains with opposite sex, and therefore, fruiting body-deficient mutants can be recognized directly without the need for crossing experiments. In earlier work, we generated sterile mutants showing a developmental block after formation of young fruiting bodies (protoperithecia), but being unable to generate mature perithecia, and referred to these mutants as pro. Recently, we have applied next-generation genome re-sequencing to identify the genes affected in some of these mutants . Based on this approach, we now have characterized mutant pro32 and show that it carries a mutation in the nox1 gene encoding NAPDH oxidase 1 (NOX1).NADPH oxidase (NOX) enzymes are transmembrane proteins that are highly conserved among eukaryotes and produce reactive oxygen species (ROS) through the oxidation of NADPH (Lambeth 2004;Kawahara and Lambeth 2007). ROS have long been recognized as damaging agents due to uncontrolled oxidizing re...

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