Abstract
Ca2 +/calmodulin-dependent phosphatase calcineurin is one of the important regulators of intracellular calcium homeostasis and has been investigated extensively in Saccharomyces cerevisiae. However, only a few reports have explored the function of the Crz1 homolog in filamentous fungi, especially in Fusarium graminearum. In this study, we identified Fg01341 as a potential ortholog of yeast Crz1. Fg01341 could interact with calcineurin and initiate nuclear transport in a calcineurin-dependent manner. The ΔFg01341 mutant exhibited normal hyphal growth on basic medium and conidia formation, but sexual reproduction was partially blocked. Pathogenicity assays showed that the virulence of the ΔFg01341 mutant in flowering wheat heads and corn silks dramatically decreased and was thus consistent with the reduction in deoxynivalenol production. Unexpectedly, the sensitivity to osmotic stress of the deletion mutant and that of the wild-type strain did not present any differences. The deletion mutant showed higher sensitivity to tebuconazole than the wild-type strain. Results also showed that the transcription factor Fg01350 might be the calcineurin target and was independent of Crz1. Furthermore, ΔFg01350 showed defects in hyphal growth, sexual production, virulence, and deoxynivalenol production. Collectively, the results indicate that these two proteins functionally redundant and that the calcineurin–Crz1-independent pathway is particularly important in F. graminearum.
Highlights
Fusarium head blight (FHB), caused by the ascomycete fungus Fusarium graminearum, is a major disease in wheat worldwide, in the middle and lower reaches of the Yangtze River in China (Dubin et al, 1997; Goswami and Kistler, 2004)
The interaction between heat shock protein 90 (Hsp90) and calcineurin was first described in S. cerevisiae (Imai and Yahara, 2000), and studies have revealed that Crz1 partially modulates the tolerance to fluconazole in S. cerevisiae (Cowen et al, 2006) and echinocandin in C. albicans (Singh et al, 2009)
The wild-type (WT) F. graminearum strain (PH-1) and fungal transformants generated in this study were maintained on potato dextrose agar (PDA), complete medium (CM) and yeast extract glucose agar (YEG) at 25◦C for mycelial growth assays
Summary
Fusarium head blight (FHB), caused by the ascomycete fungus Fusarium graminearum, is a major disease in wheat worldwide, in the middle and lower reaches of the Yangtze River in China (Dubin et al, 1997; Goswami and Kistler, 2004). A number of previous studies on filamentous fungi have documented the importance of calcineurin in hyphal elongation, septum formation, and virulence in Aspergillus fumigatus (Steinbach et al, 2006; Ferreira et al, 2007), appressorium formation in Magnaporthe oryzae (Choi et al, 2009a), cell wall integrity and pathogenicity in Botrytis cinerea (Schumacher et al, 2008), and hyphal branching in Neurospora crassa (Kothe and Free, 1998). Ca2+ regulates downstream genes in a highly conserved manner through the mediation of a transcription factor calcineurin-responsive zinc finger, Crz (Choi et al, 2009b). Crz was first identified and best studied as a major calcineurin target in the yeast S. cerevisiae (Stathopoulos and Cyert, 1997). The study could increase the knowledge about the regulatory network of calcineurin in F. graminearum, and may provide novel insights for drug development
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