A novel double-stranded RNA mycovirus isolated from Trichoderma harzianum

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RESEARCH

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A novel double-stranded RNA mycovirus isolated from Trichoderma harzianum Chenchen Liu†, Mei Li†, Estifanos Tsegaye Redda, Jie Mei, Jiantai Zhang, Beilei Wu* and Xiliang Jiang*

Abstract Background: Trichoderma spp. are used extensively in agriculture as biological control agents to prevent soil-borne plant diseases. In recent years, mycoviruses from fungi have attracted increasing attention due to their effects on their hosts, but Trichoderma mycoviruses have not been the subject of extensive study. We sought to discover novel mycoviruses from Trichoderma spp. and to determine the effects of the biocontrol function of Trichoderma spp. Methods: Mycoviruses were screened by dsRNA extraction and metagenomic analysis. RT-PCR, 5′ RACE, and 3′ RACE were used to obtain the genome sequence. MEGA software was used to classify the new mycovirus. The effects of the identified mycovirus on the biological properties of the host strain 525 were evaluated using cucumber plants and Fusarium oxysporum f. sp. cucumerinum. Results: A novel mycovirus, Trichoderma harzianum mycovirus 1 (ThMV1) (accession number MH155602), was discovered in Trichoderma harzianum strain 525, a soil-borne fungus collected from Inner Mongolia, China. The mycovirus exhibited a double-stranded RNA (dsRNA) genome with a complete genome sequence of 3160 base pairs and two open reading frames (ORFs) on the negative strand. Phylogenetic analysis indicated that it belongs to an unclassified family of dsRNA mycoviruses. The removal of ThMV1 from the host 525 strain reduced host biomass production and improved the biocontrol capability of the host for Fusarium oxysporum f. sp. cucumerinum. At same time, the presence of ThMV1 improved the growth of cucumber. Conclusion: ThMV1 is a new unclassified mycovirus found in T. harzianum. It not only affects the phenotype of the host strain but also reduces its biocontrol function, which sheds light on the interaction between the mycovirus and Trichoderma spp. Keywords: Mycovirus, Trichoderma harzianum, dsRNA, Trichoderma harzianum mycovirus 1

Background Mycoviruses are widespread viruses that infect filamentous fungi and yeasts, and most do not cause their hosts to exhibit obvious symptoms [1, 2]. The majority of mycoviruses exhibit a double-stranded RNA (dsRNA) genome, which is diagnostic. However, a few mycoviruses exhibit single-stranded RNA (ssRNA), doublestranded DNA (dsDNA), or single-stranded DNA (ssDNA) genomes [3]. Based on the mode of replication and the type of genome, the International Committee on Taxonomy of Viruses has divided all currently known mycoviruses into 16 families and an unclassified group. * Correspondence: [email protected]; [email protected] † Chenchen Liu and Mei Li contributed equally as first authors Institute of Plant Protection, Chinese Academy of Agricultural Sciences, No.2 West Yuanmingyuan Rd., Haidian District, Beijing 100193, People’s Republic of China

The 16 families include seven dsRNA virus families, five positive-sense ssRNA virus families, two rever