TY - JOUR
T1 - Suppression of RNAi by dsRNA-degrading RNaseIII enzymes of viruses in animals and plants
AU - Weinheimer, Isabel
AU - Jiu, Yaming
AU - Rajamäki, Minna-Liisa
AU - Matilainen, Olli
AU - Kallijärvi, Jukka
AU - Cuellar, Wilmer J.
AU - Lu, Rui
AU - Saarma, Mart
AU - Holmberg, Carina I.
AU - Jäntti, Jussi
AU - Valkonen, Jari P.T.
PY - 2015
Y1 - 2015
N2 - Certain RNA and DNA viruses that infect plants, insects,
fish or poikilothermic animals encode Class 1 RNaseIII
endoribonuclease-like proteins. dsRNA-specific
endoribonuclease activity of the RNaseIII of rock bream
iridovirus infecting fish and Sweet potato chlorotic
stunt crinivirus (SPCSV) infecting plants has been shown.
Suppression of the host antiviral RNA interference (RNAi)
pathway has been documented with the RNaseIII of SPCSV
and Heliothis virescens ascovirus infecting insects.
Suppression of RNAi by the viral RNaseIIIs in non-host
organisms of different kingdoms is not known. Here we
expressed PPR3, the RNaseIII of Pike-perch iridovirus, in
the non-hosts Nicotiana benthamiana (plant) and
Caenorhabditis elegans (nematode) and found that it
cleaves double-stranded small interfering RNA (ds-siRNA)
molecules that are pivotal in the host RNA interference
(RNAi) pathway and thereby suppresses RNAi in non-host
tissues. In N. benthamiana, PPR3 enhanced accumulation of
Tobacco rattle tobravirus RNA1 replicon lacking the 16K
RNAi suppressor. Furthermore, PPR3 suppressed
single-stranded RNA (ssRNA)-mediated RNAi and rescued
replication of Flock House virus RNA1 replicon lacking
the B2 RNAi suppressor in C. elegans. Suppression of RNAi
was debilitated with the catalytically compromised mutant
PPR3-Ala. However, the RNaseIII (CSR3) produced by SPCSV,
which cleaves ds-siRNA and counteracts antiviral RNAi in
plants, failed to suppress ssRNA-mediated RNAi in C.
elegans. In leaves of N. benthamiana, PPR3 suppressed
RNAi induced by ssRNA and dsRNA and reversed silencing;
CSR3, however, suppressed only RNAi induced by ssRNA and
was unable to reverse silencing. Neither PPR3 nor CSR3
suppressed antisense-mediated RNAi in Drosophila
melanogaster. These results show that the RNaseIII
enzymes of RNA and DNA viruses suppress RNAi, which
requires catalytic activities of RNaseIII. In contrast to
other viral silencing suppression proteins, the RNaseIII
enzymes are homologous in unrelated RNA and DNA viruses
and can be detected in viral genomes using gene modeling
and protein structure prediction programs.
AB - Certain RNA and DNA viruses that infect plants, insects,
fish or poikilothermic animals encode Class 1 RNaseIII
endoribonuclease-like proteins. dsRNA-specific
endoribonuclease activity of the RNaseIII of rock bream
iridovirus infecting fish and Sweet potato chlorotic
stunt crinivirus (SPCSV) infecting plants has been shown.
Suppression of the host antiviral RNA interference (RNAi)
pathway has been documented with the RNaseIII of SPCSV
and Heliothis virescens ascovirus infecting insects.
Suppression of RNAi by the viral RNaseIIIs in non-host
organisms of different kingdoms is not known. Here we
expressed PPR3, the RNaseIII of Pike-perch iridovirus, in
the non-hosts Nicotiana benthamiana (plant) and
Caenorhabditis elegans (nematode) and found that it
cleaves double-stranded small interfering RNA (ds-siRNA)
molecules that are pivotal in the host RNA interference
(RNAi) pathway and thereby suppresses RNAi in non-host
tissues. In N. benthamiana, PPR3 enhanced accumulation of
Tobacco rattle tobravirus RNA1 replicon lacking the 16K
RNAi suppressor. Furthermore, PPR3 suppressed
single-stranded RNA (ssRNA)-mediated RNAi and rescued
replication of Flock House virus RNA1 replicon lacking
the B2 RNAi suppressor in C. elegans. Suppression of RNAi
was debilitated with the catalytically compromised mutant
PPR3-Ala. However, the RNaseIII (CSR3) produced by SPCSV,
which cleaves ds-siRNA and counteracts antiviral RNAi in
plants, failed to suppress ssRNA-mediated RNAi in C.
elegans. In leaves of N. benthamiana, PPR3 suppressed
RNAi induced by ssRNA and dsRNA and reversed silencing;
CSR3, however, suppressed only RNAi induced by ssRNA and
was unable to reverse silencing. Neither PPR3 nor CSR3
suppressed antisense-mediated RNAi in Drosophila
melanogaster. These results show that the RNaseIII
enzymes of RNA and DNA viruses suppress RNAi, which
requires catalytic activities of RNaseIII. In contrast to
other viral silencing suppression proteins, the RNaseIII
enzymes are homologous in unrelated RNA and DNA viruses
and can be detected in viral genomes using gene modeling
and protein structure prediction programs.
U2 - 10.1371/journal.ppat.1004711
DO - 10.1371/journal.ppat.1004711
M3 - Article
SN - 1553-7366
VL - 11
JO - PLoS Pathogens
JF - PLoS Pathogens
IS - 3
ER -