M. Carmen Cañizares,1
Eduardo R. Bejarano,2
David M. Bisaro,4
Jesús Navas-Castillo,1 and
1Instituto de Hortofruticultura Subtropical y Mediterránea ‘La Mayora’, Universidad de Málaga-Consejo Superior de Investigaciones Científicas (IHSM-UMA-CSIC), Estación Experimental ‘La Mayora', 29750 Algarrobo-Costa, Málaga, Spain; 2IHSM-UMA-CSIC, Departamento de Biología Celular, Genética y Fisiología, Universidad de Málaga, Campus Teatinos, 29071 Málaga, Spain; 3Centro de Investigaciones Biológicas, Departamento de Biología de Plantas, Ramiro de Maeztu 9, 28040 Madrid, Spain; 4Department of Molecular Genetics, Center for Applied Plant Sciences, and Center for RNA Biology, The Ohio State University, Columbus 43210, U.S.A.
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Accepted 14 May 2013.
In plants, post-transcriptional gene silencing (PTGS) is a sequence-specific mechanism of RNA degradation induced by double-stranded RNA (dsRNA), which is processed into small interfering RNAs (siRNAs). siRNAs are methylated and, thereby, stabilized by the activity of the S-adenosylmethionine-dependent RNA methyltransferase HEN1. PTGS is amplified by host-encoded RNA-dependent RNA polymerases (RDR), which generate dsRNA that is processed into secondary siRNAs. To counteract this RNA silencing-mediated response of the host, plant viruses express proteins with silencing suppression activity. Here, we report that the coat protein (CP) of crinivirus (family Closteroviridae, genus Crinivirus) Tomato chlorosis virus, a known suppressor of silencing, interacts with S-adenosylhomocysteine hydrolase (SAHH), a plant protein essential for sustaining the methyl cycle and S-adenosylmethionine-dependent methyltransferase activity. Our results show that, by contributing to an increased accumulation of secondary siRNAs generated by the action of RDR6, SAHH enhances local RNA silencing. Although downregulation of SAHH prevents local silencing, it enhances the spread of systemic silencing. Our results also show that SAHH is important in the suppression of local RNA silencing not only by the crinivirus Tomato chlorosis virus CP but also by the multifunctional helper component-proteinase of the potyvirus Potato virus Y.
© 2013 The American Phytopathological Society