RNA editing of genomic neighbors controls antiviral response in fungi

Virus symptom expression involves complex interactions between viruses and their hosts, including antiviral defenses and counter-defenses, many of which are not well understood. This study utilizes Neurospora crassa as a model organism to investigate the role of RNA editing in the fungal antiviral response. We identify two adjacent genes in the genome: the A-to-I RNA-editing enzyme, OTT_1508-like deaminase (old), and its target, zinc fingers adjacent to old (zao). These genes regulate the transcriptional response to viral infection, with old modulating the expression of zao, which functions as a master transcription factor. This regulation contributes to asymptomatic infections by maintaining normal growth and development. However, in RNAi-deficient conditions, the overactivation of these genes leads to severe symptoms, akin to hypersensitive responses observed in plants. Additionally, homologs of zao-old are found as genomic neighbors in various filamentous ascomycetes, suggesting that this RNA-editing system may represent an evolutionarily conserved antiviral mechanism.