The disease known as Mushroom Virus X ( MVX) causes serious management and economic problems for growers of Agaricus bisporus and the associated Phase 3 compost industry. Research has provided evidence that this disease is caused by a number of double-stranded RNA (ds-RNA) viruses. This hypothesis has been strengthened with the findings that a number of transcripts found at high exprssion levels in MVXdiseased mushrooms are not of A. bisporus origin but hybridise to the ds-RNAs. The small amount of sequence information currently available on these viruses is limiting the understanding of the biology, epidemiology and transmission of these infective agents. Two genomic technologies ( Next Generation Sequencing and whole genome microarrays) are being employed to fully characterise the viruses and to understand the host responses and mechanism of symptom development. Diagnostic quantitative-PCR tests developed from the existing sequences has shown that viral transcript level increases approximately 100-fold in the compost during the 17 day period between spawn-run and cropping. This explains the observation that a small amount of infection early in the crop can lead to high levels of disease. Much lower viral transcript levels and therefore activity were observed in the casing material than compost. The microarray analyses have identified transcripts differentially expressed between MVX infected and non-infected samples. Agaricus mycelium in casing had 6. 5％ of genes up-regulated and 11. 9％ down-regulated upon infection while mycelium growing in compost had 18. 7％ of genes up-regulated and 19. 1％ downregulated during infection. Surprisingly small numbers of genes were identified as up-regulated in either fruitbodies or mycelium growing on laboratory culture. This suggests an interaction between viral action and tissue type/differentiation. Although the infected fruitbodies exhibited symptoms of brown colouration the transcriptomic data reveals that two of the tyrosinase genes were massively down-regulated in infected fruitbodies. The Next Generation Sequencing of the ds-RNAs is currently underway which will enable the viruses to be described and add understanding to the biology and epidemiology of the disease.
Agaricus bisporus Disease Genomics Transcriptiomics Mushroom Virus X Tyrosinase Epidemiology Double-Stranded RNA Viruses Mycovirus Next Generation Sequencing (NGS) Microarray
Gregory L. Deakin Edward Dobbs Julie M. Bennett Julian Green Ian M. Jones Helen M. Grogan Kerry S. Burton
East Mailing Research, Kent, UK ME19 6BJ School of Biological Sciences, University of Reading,Readin East Mailing Research, Kent, UK ME19 6BJ School of Life Science, University of Warwick, Coventry, UK School of Biological Sciences, University of Reading,Reading, UK School of Life Science, University of Warwick, Coventry, UK Teagasc, Kinsealy, Dublin 17, Ireland