A Magnaporthe grisea Cyclophilin Acts as a Virulence Determinant during Plant Infection

Abstract

Cyclophilins are peptidyl prolyl cis-trans isomerases that are highly conserved throughout eukaryotes and that are best known for being the cellular target of the immunosuppressive drug cyclosporin A (CsA). The activity of CsA is caused by the drug forming a complex with cyclophilin A and inhibiting the calmodulin-dependent phosphoprotein phosphatase calcineurin. We have investigated the role of CYP1 , a cyclophilin-encoding gene in the phytopathogenic fungus Magnaporthe grisea , which is the causal agent of rice blast disease. CYP1 putatively encodes a mitochondrial and cytosolic form of cyclophilin, and targeted gene replacement has shown that CYP1 acts as a virulence determinant in rice blast. Cyp1 mutants show reduced virulence and are impaired in associated functions, such as penetration peg formation and appressorium turgor generation. CYP1 cyclophilin also is the cellular target for CsA in Magnaporthe, and CsA was found to inhibit appressorium development and hyphal growth in a CYP1 -dependent manner. These data implicate cyclophilins as virulence factors in phytopathogenic fungi and also provide evidence that calcineurin signaling is required for infection structure formation by Magnaporthe. INTRODUCTIONRice blast is the most serious disease of cultivated rice and causes serious recurrent epidemics throughout the ricegrowing regions of the world (Baker et al., 1997). The disease is caused by the ascomycete fungus Magnaporthe grisea , which produces specialized infection structures called appressoria to penetrate the leaves and stems of rice plants, allowing the fungus entry to the underlying tissue (for reviews, see Howard and Valent, 1996; Hamer and Talbot, 1998). Plant infection by appressoria is accomplished by the generation of enormous turgor pressure, which is translated into mechanical force to breach the plant cuticle (Howard et al., 1991). Once in the plant, the fungus develops bulbous secondary hyphae and quickly colonizes the host tissue (Bourett and Howard, 1990; Heath et al., 1990; Talbot et al., 1993). Damage to the rice crop results from either leaf blast, which kills or debilitates seedlings, or neck and panicle blast, which destroy the rice grain during the seed-setting stage (Ou, 1985). The economic cost of rice blast is significant, both in direct losses to the rice harvest and in the costs of control measures such as rice breeding programs, fungicide applications, and the development of new antifungal chemicals (Baker et al., 1997).Developing novel mechanisms to control rice blast will require detailed understanding of both the disease and the developmental biology of Magnaporthe. Considerable progress has been made in identifying the genes required for elaboration of appressoria because the fungus is tractable to molecular genetics (Talbot, 1995; Howard and Valent, 1996), but far less is known about the later stages of plant infection and how the growth of the fungus within rice tissue is regulated. Appressorium formation on the rice leaf surface requires a cAMP signaling pathway...

The putative flavin carrier family FlcA-C is important forAspergillus fumigatusvirulence

“…7 Cyclosporin A, an immunosuppressant, reduces calcineurin activity and causes morphological changes and growth reduction in A. nidulans, A. oryzae, Magnaporthe oryzae and Neurospora crassa. [8][9][10][11][12] Calcineurin activates the transcription factor Crz1 (Calcineurin Responsive Zinc Finger 1) transcription factor by dephosphorylating it when there in an increase cytosolic calcium and permitting its translocation to the nuclei. 1,13 Crz1 has a C 2 H 2 zinc finger motif responsible for the binding to a CDRE (calcineurindependent response element) sequence in the promoter regions of the Crz1-regulated genes.…”

The Tig1 Histone Deacetylase Complex Regulates Infectious Growth in the Rice Blast Fungus Magnaporthe oryzae

“…The putative CPR1 ortholog, CYP1, was not included in this study because it is known to be involved in plant infection in M. oryzae (Viaud et al, 2002). The snt1, set3, hos4, hos2, and hst1 deletion mutants (Table 1) were identified by PCR and confirmed by DNA gel blot analysis (see Supplemental Figure 5 online).…”

Comparison of gene expression in trap cells and vegetative hyphae of the nematophagous fungus Monacrosporium haptotylum

“…In Ma. grisea, cyclophilin1 mutants showed reduced virulence and were impaired in penetration peg formation and generation of appressorium turgor pressure (Viaud et al, 2002). In B. graminis, a putative metallothionein gene was identified as having high transcriptional levels in both conidia and appressoria (Thomas et al, 2002).…”