Metabolism and aging in the filamentous fungus Podospora anserina.

In Podospora anserina, lifespan is under the control of environmental and genetic factors. Both suggest an important impact of metabolism on lifespan and aging. Environmental changes of temperature, of the carbon source in the growth medium, or the addition of specific inhibitors to the growth medium are some of the investigated factors. Genetic approaches underscore the significance of metabolism. In particular, the mitochondrial electron transport plays a major role. As a by-product of a cytochrome oxidase (COX) dependent energy transduction, reactive oxygen species (ROS) are generated and lead to damage of cellular biomolecules. Damaged mitochondria, compromised at complex IV (COX) of the respiratory chain, signal to the nucleus and induce a nuclear gene, PaAox, encoding an alternative oxidase (AOX). This pathway resembles the retrograde response that, at least in yeast, is induced by dysfunctional mitochondria. ROS generation is lowered when electrons are transferred via an alternative pathway utilizing the AOX. As a consequence, lifespan of the corresponding strains is increased. Cellular copper levels were found to play a significant role not only in the generation of ROS but also have an impact on the cytoplasmic and the mitochondrial superoxide dismutase (SOD). In addition, copper is involved in the control of mitochondrial DNA rearrangements and affects the ability of the system to remodel damaged mitochondria. All these different components and pathways are part of the complex molecular network involved in lifespan control of this aging model.

Characterization of a Ustilago maydis gene specifically induced during the biotrophic phase: evidence for negative as well as positive regulation.

The phytopathogenic basidiomycete Ustilago maydis requires its host plant, maize, for completion of its sexual cycle. To investigate the molecular events during infection, we used differential display to identify plant-induced U. maydis genes. We describe the U. maydis gene mig1 (for "maize-induced gene"), which is not expressed during yeast-like growth of the fungus, is weakly expressed during filamentous growth in axenic culture, but is extensively upregulated during plant infection. mig1 encodes a small, highly charged protein of unknown function which contains a functional N-terminal secretion sequence and is not essential for pathogenic development. Adjacent to mig1 is a second gene (mdu1) related to mig1, which appears to result from a gene duplication. mig1 gene expression during the infection cycle was assessed by fusing the promoter to eGFP. Expression of mig1 was absent in hyphae growing on the leaf surface but was detected after penetration and remained high during subsequent proliferation of the fungus until teliospore formation. Successive deletions as well as certain internal deletions in the mig1 promoter conferred elevated levels of reporter gene expression during growth in axenic culture, indicative of negative regulation. During fungal growth in planta, sequence elements between positions -148 and -519 in the mig1 promoter were specifically required for high levels of induction, illustrating additional positive control. We discuss the potential applications of mig1 for the identification of inducing compounds and the respective regulatory genes.