PDE1 Encodes a P-Type ATPase Involved in Appressorium-Mediated Plant Infection by the Rice Blast Fungus Magnaporthe grisea

Abstract

Plant infection by the rice blast fungus Magnaporthe grisea is brought about by the action of specialized infection cells called appressoria. These infection cells generate enormous turgor pressure, which is translated into an invasive force that allows a narrow penetration hypha to breach the plant cuticle. The Magnaporthe pde1 mutant was identified previously by restriction enzyme-mediated DNA integration mutagenesis and is impaired in its ability to elaborate penetration hyphae. Here we report that the pde1 mutation is the result of an insertion into the promoter of a P-type ATPase-encoding gene. Targeted gene disruption confirmed the role of PDE1 in penetration hypha development and pathogenicity but highlighted potential differences in PDE1 regulation in different Magnaporthe strains. The predicted PDE1 gene product was most similar to members of the aminophospholipid translocase group of P-type ATPases and was shown to be a functional homolog of the yeast ATPase gene ATC8 . Spatial expression studies showed that PDE1 is expressed in germinating conidia and developing appressoria. These findings implicate the action of aminophospholipid translocases in the development of penetration hyphae and the proliferation of the fungus beyond colonization of the first epidermal cell. INTRODUCTIONOne of the principal reasons why pathogenic fungi are so successful at causing plant disease is their ability to penetrate the plant cuticle directly, often using specialized infection cells called appressoria (Mendgen et al., 1996). A wide variety of fungal pathogens form appressoria, and the development of these cells involves a complex morphogenetic program that results in rapid differentiation of a highly specialized structure (Dean, 1997). The rice blast fungus Magnaporthe grisea is an important pathogen of cultivated rice and has emerged as an experimental model for the study of plant infection processes (for reviews, see Howard and Valent, 1996;Hamer and Talbot, 1998). Magnaporthe develops dome-shaped appressoria, which form at the ends of germ tubes soon after spore germination on the leaf surface. Appressoria attach strongly to the leaf and then generate enormous turgor pressure (up to 8 MPa), which is used to rupture the plant cuticle (Howard et al., 1991). The turgor inside appressoria is generated by a rapid increase in intracellular glycerol levels, which is maintained by a specialized cell wall layer containing melanin (Howard and Ferrari, 1989;de Jong et al., 1997). If melanin biosynthesis is blocked, either by chemical intervention or mutation, then Magnaporthe is unable to penetrate the plant surface and cannot cause disease (Chida and Sisler, 1987;Chumley and Valent, 1990).How such enormous cellular turgor is translated into the substantial invasive force necessary to breach the plant cell wall is not clear, but it appears to involve polarization of the cytoskeleton to the point of infection and localized cell wall modification Howard, 1990, 1992;Bechinger et al., 1999). A narrow penetration hypha forms at t...

Four conserved intramolecular disulphide linkages are required for secretion and cell wall localization of a hydrophobin during fungal morphogenesis

“…Light microscopy was carried out using a Zeiss Askioskop. Low temperature scanning electron microscopy was carried out as described by Balhadère and Talbot (2001). Conidial surface replicas were prepared by freeze fracture, freeze etch, in a Balzer 301 evaporator (Balzer Pfeiffer GmbH, Germany) and shadowed with carbon and platinum at 45∞C .…”

Sequence analysis and expression pattern ofMGTA1gene in rice blast pathogenMagnaporthe grisea

“…As a model fungal pathogen, its pre-penetration processes, including conidium dissemination, adhesion (Hamer et al, 1988) and germination, appressorium differentiation (Howard et al, 1991) and maturation (Howard and Ferrari, 1989), penetration peg differentiation (Bourett and Howard, 1990;, had been reported. Several chemical and physical factors activating these processes have been found and many genes related to these processes have been cloned and characterized (Balhadere and Talbot, 2001;Talbot et al, 1993;Xu and Hamer, 1996). The post-penetration processes of M. grisea, including infection hyphae differentiation and colonization, are far less known (Balhadere and Talbot, 2001).…”

“…Several chemical and physical factors activating these processes have been found and many genes related to these processes have been cloned and characterized (Balhadere and Talbot, 2001;Talbot et al, 1993;Xu and Hamer, 1996). The post-penetration processes of M. grisea, including infection hyphae differentiation and colonization, are far less known (Balhadere and Talbot, 2001). Our work focuses on genes involved in such processes.…”

Parallels in Fungal Pathogenesis on Plant and Animal Hosts

“…VOL. 5,2006 MINIREVIEW 1945 (22). A homolog is present in the saprophytic fungus N. crassa, and there are hypothetical protein homologs in the animalpathogenic fungus Coccidioides immitis and in the multihost pathogen Chaetomium globosum.…”

“…For instance, some plantpathogenic fungi produce invasive hyphae and/or infection structures such as appressoria, which sequester high concentrations of glycerol, producing high turgor pressure and thus allowing the fungus to puncture the leaf and gain entry (81). Appressorial formation involves a range of molecules and signals, including tetraspanins, P-type ATPases, and cyclophilins in M. grisea (5,85,86). Tetraspanins are integral membrane proteins involved in a variety of cellular functions such as differentiation and adhesion in animal cells and are necessary for virulence in plant-pathogenic fungi such as B. cinerea and M. grisea due to their role in the formation of the penetration pegs which emerge from appressoria and enter the host tissue and facilitate endocytosis as a means of penetrating the host cells.…”