MOLECULAR CHARACTERISATION OF AN EGYPTIAN ISOLATE OF NIGROSPORA ORYZAE NONSEGMENTED RNA VIRUS 1

Abstract

Mycoviruses are widely distributed among fungi, including plant-associated species. In this study, a Nigrospora oryzae isolate (NDC1) was isolated from Egypt and characterised based on morphology and molecular analysis, confirming its identity through ITS sequencing and phylogenetic analysis. Screening for mycoviruses revealed the presence of a ~3 kb dsRNA genome, which was sequenced using next-generation sequencing (NGS) and identified as an isolate of Nigrospora oryzae nonsegmented RNA virus 1 (NoNRV1-NDC1). The viral genome consists of 2858 nucleotides and contains two open reading frames (ORFs), with ORF2 encoding an RNA-dependent RNA polymerase (RdRp) that shares 98% identity with NoNRV1 isolates previously reported in China. Phylogenetic analysis clustered NoNRV1-NDC1 with closely related unclassified viruses, suggesting a common evolutionary origin. A conserved slippery sequence near the ORF1 stop codon indicates a potential -1 ribosomal frameshifting mechanism for RdRp expression. This study contributes to the expanding knowledge of fungal viromes and provides insights into the diversity of mycoviruses associated with N. oryzae. It also expands our understanding of NoNRV1 diversity, offers new insights into the genomic organisation of unclassified mycoviruses, and highlights mycoviruses' occurrence in N. oryzae from Egypt.