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Updated: Sep 4, 2026

Reverse Genetics to Engineer Positive-Sense RNA Virus Variants
Published on: June 9, 2022
A newly established reverse genetic system for a circular RNA virus reveals new requirements for infection and its
Yi Guo1, Marco Forgia1,2, Nadia Serale2
1Institute for Sustainable Plant Protection, National Research Council of Italy, Strada delle Cacce 73, 10135, Torino, Italy.
Abstract:
Ambiviruses are fungal-infecting circular RNA viruses that uniquely combine viroid-like and viral features, yet the function of their conserved ORF-B protein and their effects on hosts remain unknown, hindered by the lack of a reverse genetics system. Here, we constructed the first infectious cDNA clone of an ambivirus, Fusarium graminearum ambivirus 1 (FgAV1), using a head-to-tail dimer placed downstream of a fungal promoter. FgAV1 was horizontally transmitted via hyphal anastomosis to virus-free Fusarium graminearum strains. Notably, a reverse-oriented dimer construct was also infectious and transmissible. Targeted mutagenesis revealed that both ORF-A- and ORF-B-encoded proteins and the presence of embedded ribozymes are indispensable for ambivirus replication. Our results further demonstrate that FgAV1 infection triggers a fungal RNAi response, extending the antiviral role of host sRNAs to circular RNA viruses. Furthermore, FgAV1 infection suppressed fungal growth and significantly reduced the virulence of F. graminearum on wheat. These findings provide novel insights into ambivirus replication and their potential in fungal pathogen biocontrol.
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