Characterization of a hypovirulent Chrysovirus from Fusarium graminearum: processing of the viral proteins, replication and infection

• Applicant: Professor Dr. Wilhelm Schäfer
• Subject Area: Organismic Interactions, Chemical Ecology and Microbiomes of Plant Systems ; Plant Breeding and Plant Pathology
• Term: from 2013 to 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 237491017

The isolate Fusarium graminearum China 9 (Fg-ch9) is less virulent on wheat and maize as compared to infections of the wild type isolate Fusarium graminearum PH1 (Fg-PH1). This phenomenon of reduced virulence is known as hypovirulence and is characteristic of several filamentous phytopathogenic fungi. Hypovirulence is induced by mycoviruses from different genera. From Fg-ch9 35-40 nm isometric virus particles (V-ch9) were isolated. The sequence of the viral genome shares high similarity with the genome of Chrysoviruses (Chrysoviridae). Each of the five V-ch9 dsRNA segments, RNA 1 to RNA 5, encodes one open reading frame (ORF) resulting in proteins with molecular weights between 79 and 127 kDa. The 127 kDa ORF encodes the RNA-dependent RNA polymerase (RdRP) which is part of the particle. The proteins, translated from the ORF of RNA 2 and RNA 3, are processed and are part of the capsid. The protein translated from the ORF of RNA 5 contains several zinc-finger motifs and is able to suppress gene silencing. It is not part of the particle. The function and the kind of processing of the protein which is translated from the ORF of RNA 4 are completely unknown. The importance of mycoviruses has only recently been discovered, so that little information about the replication mechanism and interactions between fungus and virus is available. After cloning and sequencing of the genome of V-ch9 and first insights into processing and functions of some of the viral proteins, we want to investigate the replication cycle and processing of the viral proteins in more detail. On the basis of these results we hope to introduce more functions of the proteins. These functions have to be confirmed using a reverse genetics system in a next step. In principle, reverse genetics are applicable for dsRNA viruses. However, since the dsRNA virus genome is not infectious itself as it is for ssRNA viruses and needs a dsRNA protecting capsid as well as an RdRP; the establishment of such a system for dsRNA viruses is laborious. In addition, a simple infection system and a host with a stable virus replication are prerequisites and have to be found for the use of our Fg-ch9 isolate. Therefore, we intend to test an infection via anastomoses. Additionally, in order to obtain a host with stable virus infection we want to eliminate the virus from Fg-ch9 for re-infection and, in a second approach, want to modify the wild type Fg-PH1 to stabilize virus replication. An inoculation protocol and a suitable host are also prerequisites for the establishment of the reverse genetics system. Identifying the replication and functions of the viral proteins of V-ch9 we might, in future, be able to develop applications for the hypovirulence in Fusarium graminearum.

• DFG Programme: Research Grants
• Participating Person: Privatdozentin Dr. Cornelia Heinze