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Proc Natl Acad Sci U S A. 2012 Jun 19;109(25):10113-8. doi: 10.1073/pnas.1201628109. Epub 2012 Jun 4.

Tobacco calmodulin-like protein provides secondary defense by binding to and directing degradation of virus RNA silencing suppressors.

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  • 1Plant Breeding Science, Research Faculty of Agriculture, Hokkaido University, Sapporo, 060-8589, Japan.


RNA silencing (RNAi) induced by virus-derived double-stranded RNA (dsRNA), which is in a sense regarded as a pathogen-associated molecular pattern (PAMP) of viruses, is a general plant defense mechanism. To counteract this defense, plant viruses express RNA silencing suppressors (RSSs), many of which bind to dsRNA and attenuate RNAi. We showed that the tobacco calmodulin-like protein, rgs-CaM, counterattacked viral RSSs by binding to their dsRNA-binding domains and sequestering them from inhibiting RNAi. Autophagy-like protein degradation seemed to operate to degrade RSSs with the sacrifice of rgs-CaM. These RSSs could thus be regarded as secondary viral PAMPs. This study uncovered a unique defense system in which an rgs-CaM-mediated countermeasure against viral RSSs enhanced host antiviral RNAi in tobacco.

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