AnUstilago maydisGene Involved in H2O2 Detoxification Is Required for Virulence

Abstract

The fungus Ustilago maydis is a biotrophic pathogen of maize (Zea mays). In its genome we have identified an ortholog of YAP1 (for Yeast AP-1-like) from Saccharomyces cerevisae that regulates the oxidative stress response in this organism. yap1 mutants of U. maydis displayed higher sensitivity to H 2 O 2 than wild-type cells, and their virulence was significantly reduced. U. maydis yap1 could partially complement the H 2 O 2 sensitivity of a yap1 deletion mutant of S. cerevisiae, and a Yap1-green fluorescent protein fusion protein showed nuclear localization after H 2 O 2 treatment, suggesting that Yap1 in U. maydis functions as a redox sensor. Mutations in two Cys residues prevented accumulation in the nucleus, and the respective mutant strains showed the same virulence phenotype as Dyap1 mutants. Diamino benzidine staining revealed an accumulation of H 2 O 2 around yap1 mutant hyphae, which was absent in the wild type. Inhibition of the plant NADPH oxidase prevented this accumulation and restored virulence. During the infection, Yap1 showed nuclear localization after penetration up to 2 to 3 d after infection. Through array analysis, a large set of Yap1-regulated genes were identified and these included two peroxidase genes. Deletion mutants of these genes were attenuated in virulence. These results suggest that U. maydis is using its Yap1-controlled H 2 O 2 detoxification system for coping with early plant defense responses.

Reactive oxygen species and plant resistance to fungal pathogens

“…No accumulation of H 2 O 2 was observed around the tips of penetrating hyphae of the wild type fungus. Treating the host plant with DPI restores the virulence of the deletion mutant (Molina and Kahmann, 2007). These studies exemplify how detoxification of host-derived ROS is essential for fungal virulence and pathogenesis.…”

Unraveling the Tapestry of Networks Involving Reactive Oxygen Species in Plants

“…Three papers have brought to the fore the importance of ROS production and scavenging by the pathogen. Egan et al (2007) reported that the generation of ROS by the rice blast fungal NADPH oxidase is required for infection, whereas Molina and Kahmann (2007) documented that activation of ROS scavenging mechanisms by the fungal Ustilago maydis Yap1 gene is essential to overcome the plant defense mechanisms and allow infection. In addition, Mittapalli et al (2007) reported that the ROS scavenging mechanisms of the Hessian fly (Mayetiola destructor) could play an important function in the interaction with its wheat (Triticum aestivum) host.…”

TheO-Mannosyltransferase PMT4 Is Essential for Normal Appressorium Formation and Penetration inUstilago maydis

“…Due to their toxicity and importance in plant defense responses, ROS are essential for the progression of fungal infection (Wojtaszek, 1997;Apel and Hirt, 2004). U. maydis yap1, a gene involved in H 2 O 2 detoxification, is required for virulence, and the addition of diphenyleneiodonium (DPI), an inhibitor of the plant NADPH oxidase, restores the normal infectious growth in plant tissues (Molina and Kahmann, 2007). To determine whether the infection defect shown by Dpmt4 cells is somehow related to problems in H 2 O 2 detoxification, 0.5 mM DPI was added to the Dpmt4 cell culture during inoculation.…”

“…In the DPI treatment, DPI solved in DMSO was added at 0.5 mM directly to the U. maydis strains prior to inoculation. As a control, DMSO alone was added to the strains (Molina and Kahmann, 2007).…”