Transmission of the M2 double-stranded RNA inRhizoctonia solanianastomosis group 3 (AG-3)

Abstract

Horizontal transmission of the 3.57 kb M2 double-stranded RNA (dsRNA) between mycelia of somatically incompatible isolates of Rhizoctonia solani anastomosis group 3 (AG-3), an economically important pathogen of cultivated plants in the family Solanaceae, was investigated. Nine donor isolates of R. solani AG-3 containing the M2 dsRNA were paired on potato-dextrose agar with each of three different recipient isolates where the M2 dsRNA was absent. Reverse-transcription PCR (RT-PCR) was used to detect horizontal transmission of the M2 dsRNA via hyphal anastomosis from donor to recipient isolates by examining hyphal explants taken 3 cm from the hyphal interaction zone. PCR-RFLP genetic-based markers of two nuclear loci and one mitochondrial locus were used to confirm identity and transmission between donor and recipient isolates of R. solani AG-3. The frequency of transmission observed between 72 pairings of the eight donor and three recipient isolates was approximately 4% of the total pairings, and differences in the phenotype of the recipient isolates after acquisition of the M2 dsRNA via horizontal transmission were observed. To our knowledge this represents the first demonstration of transmission of dsRNA between genetically different individuals of R. solani confirmed with nuclear and mitochondrial markers. These results suggest that transmission can occur between somatically incompatible isolates of R. solani AG-3 but that maintenance of the dsRNA in the recipient isolates was not stable after repeated subculturing on nutrient medium.

Vertical Transmission of Fusarium circinatum Mitoviruses FcMV1 and FcMV2-2 via Microconidia

“…To date, both the genetic diversity and diversity of the VCGs of the Spanish population of F. circinatum have been found to be low and suitable for virus transmission, although this could change if the mating types reproduced sexually [54]. Although the classic hypothesis considers that the existence of the VCGs lowers the probability of movement of viruses between different species, there are some exceptions to this, and transmission of viruses between incompatible isolates or different species has been observed [13,48,[55][56][57][58]. This suggests that viruses can move from their fungal host to new hosts [42].…”

Mitovirus UGA(Trp) codon usage parallels that of host mitochondria

“…Published evidence for presence of Thanatephorus cucumeris mitovirus (TcMV) RNA in the cytosol as well as in mitochondria (Jian et al, 1997; Lakshman et al, 1998) is noteworthy, but perhaps not definitive because controls for proper separation of the different subcellular fractions were not analyzed in parallel. Published evidence for TcMV transfer from donor to recipient fungal strain by hyphal anastomosis without apparent co-transfer of donor mitochondria (Charlton and Cubeta, 2007; Jian et al, 1997) is also noteworthy, but perhaps again not definitive because the co-transfer of donor mitochondria allowing TcMV transmission by fusion with recipient mitochondria (Polashock et al, 1997) seems not to have been wholly ruled out. Whether TcMV or any other of the viruses with no UGA codons can indeed replicate in the cytosol of their respective hosts is clearly a subject that warrants further direct study.…”