Extreme Diversity of Mycoviruses Present in Single Strains of Rhizoctonia cerealis, the Pathogen of Wheat Sharp Eyespot.

Abstract

Rhizoctonia cerealis is the pathogen of wheat sharp eyespot, which occurs throughout temperate wheat-growing regions of the world. In this project, the genomes of viruses from four strains of R. cerealis were analyzed based on Illumina high-throughput transcriptome sequencing (RNA-Seq) data. After filtering out reads that mapped to the fungal genome, viral genomes were assembled. In total, 131 virus-like sequences containing complete open reading frames (ORFs), belonging to 117 viruses, were obtained. Based on phylogenetic analysis, some of them were identified as novel members of the families Curvulaviridae, Endornaviridae, Hypoviridae, Mitoviridae, Mymonaviridae, and Phenuiviridae, while others were unclassified viruses. Most of these viruses from R. cerealis were significantly different from the viruses already reported. We propose the establishment of a new family, Rhizoctobunyaviridae, and two new genera, Rhizoctobunyavirus and Iotahypovirus. We further clarified the distribution and coinfection of these viruses in the four strains. Surprisingly, 39 viral genomes of up to 12 genera were found in strain R1084. Strain R0942, containing the fewest viruses, also contained 21 viral genomes belonging to 10 genera. Based on the RNA-Seq data, we estimated the accumulation level of some viruses in host cells and found that the mitoviruses in R. cerealis generally have very high accumulation. In conclusion, in the culturable phytopathogenic fungus R. cerealis, we discovered a considerable diversity of mycoviruses and a series of novel viruses. This study expands our understanding of the mycoviral diversity in R. cerealis and provides a rich resource for the further use of mycoviruses to control wheat sharp eyespot. IMPORTANCE Rhizoctonia cerealis is a binucleate fungus that is widely distributed worldwide and can cause sharp eyespot disease in cereal crops. In this study, 131 virus-like sequences belonging to 117 viruses were obtained based on analysis of high-throughput RNA-Seq data from four strains of R. cerealis. Many of these viruses were novel members of various virus families, while others were unclassified viruses. As a result, a new family named Rhizoctobunyaviridae and two new genera, Rhizoctobunyavirus and Iotahypovirus, were proposed. Moreover, the discovery of multiple viruses coinfecting a single host and the high accumulation levels of mitoviruses have shed light on the complex interactions between different viruses in a single host. In conclusion, a significant diversity of mycoviruses was discovered in the culturable phytopathogenic fungus R. cerealis. This study expands our understanding of mycoviral diversity, and provides a valuable resource for the further utilization of mycoviruses to control wheat diseases.