Virus-mediated or transgenic suppression of a G-protein alpha subunit and attenuation of fungal virulence.

Abstract

Strains of the chestnut blight fungus Cryphonectria parasitica harboring RNA viruses of the genus Hypovirus exhibit significantly reduced levels of virulence (called hypovirulence). The accumulation of a heterotrimeric GTP-binding protein (G protein) a subunit of the G1 class was found to be reduced in hypovirus-containing C. parasitica strains. Transgenic cosuppression, a phenomenon frequently observed in transgenic plants, reduced the accumulation of this cr subunit in virus-free fungal strains. Significantly, the resulting transgenic fungal strains were also hypovirulent. These results indicate a crucial role for G-protein-linked signal transduction in fungal pathogenesis and suggest a molecular basis for virus-mediated attenuation of fungal virulence.Strains of the chestnut blight fungus Cryphonectria parasitica stably infected with members of the genus Hypovirus exhibit reduced levels of virulence (called hypovirulence) (1, 2). Since these viral elements are transmissible to vegetatively compatible fungal strains through fused hyphae (anastomoses), application of an appropriate hypovirulent strain can result in conversion of a recipient virulent strain providing the basis for biological control (1, 3). The development of an infectious cDNA copy of a hypovirus RNA (2) has further enhanced the potential for effective biological control by leading to the construction of engineered hypovirulent fungal strains that exhibit modes of hypovirus transmission not observed for natural hypovirulent strains (4). It is also possible to modify hypovirus genetic information in the context of the infectious viral cDNA to generate hypovirulent strains altered in specific phenotypic traits (5). Chen et at (6) recently demonstrated that transfection-mediated introduction of infectious hypovirus RNA transcripts into several other fungal pathogens not previously shown to harbor hypoviruses also results in profound phenotypic changes including hypovirulence, thus broadening the potential application of virus-mediated hypovirulence to other fungal pathogens.It is now well established that hypovirus infection modifies the gene expression profile of the fungal host (7-13). Such alterations presumably cause the array of phenotypic changes observed in hypovirulent strains, including virulence attenuation. Thus, an understanding of the mechanisms involved in virus-mediated alteration of host gene expression is likely to provide insights into fungal virulence. Several recent studies have shown that hypovirus infection suppresses expression of the gene lac-1, encoding the enzyme laccase, at the level of transcriptional promoter activity and that the mechanism involves perturbation of signal transduction pathways that normally govern lac-1 transcription in virus-free strains (10, 11). Although a role for laccase in fungal infection remains to be demonstrated, it is tempting, by way of extrapolation, to speculate that hypovirus-mediated attenuation of fungal vir-The publication costs of this article were defrayed in part by page ch...

Characterization of the ERK homologue CpMK2 from the chestnut blight fungus Cryphonectria parasitica

“…However, the cpmk2 phenotypes of changes in growth pattern related to culture conditions (liquid vs solid media) and a complete lack of conidiation are unusual. Similar phenotypes have been observed previously in strains with mutations in genes related to G-proteins (Choi et al, 1995;Segers & Nuss, 2003). The G-proteincoupled MAPK cascade that responds to mating pheromones in S. cerevisiae is a good example of G-proteins activating a downstream MAPK pathway.…”

“…Mutations related to reduced conidiation, pigmentation and vegetative growth have been reported in several studies of C. parasitica signal-pathway-related genes (Zhang et al, 1993;Choi et al, 1995;Kim et al, 2002). However, the cpmk2 phenotypes of changes in growth pattern related to culture conditions (liquid vs solid media) and a complete lack of conidiation are unusual.…”

“…studies have demonstrated the implementation of a signal transduction pathway during viral symptom development. Genes modulated during this process encode components of various signal transduction pathways, including heterotrimeric G-proteins, a putative regulator of these G-proteins (Choi et al, 1995;Kasahara & Nuss, 1997;Kasahara et al, 2000), a novel kinase (Kim et al, 2002) and many others that are under investigation (Dawe & Nuss, 2001). Recently, we have demonstrated the hypoviral regulation of components of a mitogen-activated protein kinase (MAPK) signalling pathway in C. parasitica (Park et al, 2004).…”

Signal Transduction Cascades Regulating Fungal Development and Virulence

“…The double-stranded RNA viruses HAV1 and CHV1-713, which attenuate virulence, have also provided a unique tool with which to examine virulence mechanisms in this organism (214). G proteins involved in signal transduction have been identified (49,88,127,128,292). C. parasitica G proteins regulate growth and virulence in C. parasitica.…”

G protein and MAPK signaling pathways control the ability of <i>Cochliobolus heterostrophus</i> to exploit different carbon sources

“…To date, only a few studies have examined the influence of the G protein or MAPK signaling on extracellular enzyme secretion. Wang and Nuss [29] first reported that the induction of CHB-1, a cellobiohydrolase gene from Cryphonectria parasitica, is mediated through a G-protein α subunit linked signal transduction pathway shown earlier to be required for fungal pathogenesis [43]. In saprophytic and pathogenic fungi, it is known that extracellular glycan hydrolases are induced by their substrate and repressed by glucose at the level of gene expression (reviewed by a Extracellular CMCase enzymatic activity was measured for liquid cultures grown on 1% CMC and 0.1% maltose containing minimal medium.…”