title: CpBir1 is required for conidiation, virulence and anti-apoptotic effects and influences hypovirus transmission in Cryphonectria parasitica.
abstract: Inhibitors of apoptosis proteins (IAPs) are critically important in the regulation of unicellular yeast and metazoan apoptosis. All IAPs contain one to three baculovirus IAP repeat (BIR) domains, which are essential for the anti-apoptotic activity of the IAPs. A homolog of IAPs, CpBir1, which bears two BIR domains, was recently identified from the chestnut blight fungus Cryphonectria parasitica genome. CpIAP was deleted by gene replacement, and the phenotypes of ΔIAP were characterized. CpBir1 was significantly down-regulated by hypovirus infection but up-regulated by H(2)O(2). Similar to Saccharomyces cerevisiae Bir1p, the Cpbir1 mutant was sensitive to H(2)O(2), and constitutive overexpression of CpBir1 increased resistance to H(2)O(2). The Cpbir1 mutant also showed defects in aerial hyphal formation, colony growth, mycelial morphology, conidiogenesis, pigmentation, resistance to stress conditions and virulence. Genetic complementation with native Cpbir1 fully recovered all these defective phenotypes. The CpBir1-eGFP fusion protein was localized to the nucleus in juvenile cultures, while it was found in the cytoplasm in old cultures, suggesting that the localization pattern of CpBir1 may correlate with the process of anti-apoptosis. Increased accumulation of reactive oxygen species (ROS) in the Cpbir1 deletion mutant further supports the anti-apoptotic function of CpBir1. Among five selected vegetative compatible (vc) types of C. parasitica, Cpbir1 deletion was found to block virus from transferring between Cpbir1 mutants. However, hypovirus infected Cpbir1 mutants showed a similar ability to transmit virus to other virus-free isolates compared with the infected wild-type strain. In summary, Cpbir1 encodes an IAP CpBir1 that is down-regulated by hypovirus infection and required for conidiation, virulence and anti-apoptosis, as well as affects hypovirus transmission in chestnut blight fungus C. parasitica.
authors.affiliation: Key Laboratory of Monitoring and Management of Crop Diseases and Pest Insects, Ministry of Agriculture, Nanjing 210095, China.
authors.forename: Kun
authors.initials: K
authors.lastname: Gao
authors.forename: Qin
authors.initials: Q
authors.lastname: Xiong
authors.forename: Jing
authors.initials: J
authors.lastname: Xu
authors.forename: Kuijie
authors.initials: K
authors.lastname: Wang
authors.forename: Kerong
authors.initials: K
authors.lastname: Wang
mesh_terms: D051017:Apoptosis Regulatory Proteins / Q000235:genetics / Q000378:metabolism*; D001203:Ascomycota / Q000187:drug effects / Q000235:genetics* / Q000254:growth & development*; D002467:Cell Nucleus / Q000737:chemistry; D003593:Cytoplasm / Q000737:chemistry; D017353:Gene Deletion; D005816:Genetic Complementation Test; D006861:Hydrogen Peroxide / Q000633:toxicity; D012328:RNA Viruses / Q000254:growth & development; D017382:Reactive Oxygen Species / Q000032:analysis; D013172:Spores, Fungal / Q000235:genetics* / Q000254:growth & development*; D037521:Virulence Factors / Q000235:genetics / Q000378:metabolism*
chemical_list: D051017:Apoptosis Regulatory Proteins; D017382:Reactive Oxygen Species; D037521:Virulence Factors; D006861:Hydrogen Peroxide