Plant virus-derived small interfering RNAs originate predominantly from highly structured single-stranded viral RNAs.
RNA silencing is conserved in a broad range of eukaryotes and includes the phenomena of RNA interference in animals and posttranscriptional gene silencing (PTGS) in plants. In plants, PTGS acts as an antiviral system; a successful virus infection requires suppression or evasion of the induced silencing response. Small interfering RNAs (siRNAs) accumulate in plants infected with positive-strand RNA viruses and provide specificity to this RNA-mediated defense. We present here the results of a survey of virus-specific siRNAs characterized by a sequence analysis of siRNAs from plants infected with Cymbidium ringspot tombusvirus (CymRSV). CymRSV siRNA sequences have a nonrandom distribution along the length of the viral genome, suggesting that there are hot spots for virus-derived siRNA generation. CymRSV siRNAs bound to the CymRSV p19 suppressor protein have the same asymmetry in strand polarity as the sequenced siRNAs and are imperfect double-stranded RNA duplexes. Moreover, an analysis of siRNAs derived from two other nonrelated positive-strand RNA viruses showed that they displayed the same asymmetry as CymRSV siRNAs. Finally, we show that Tobacco mosaic virus (TMV) carrying a short inverted repeat of the phytoene desaturase (PDS) gene triggered more accumulation of PDS siRNAs than the corresponding antisense PDS sequence. Taken together, these results suggest that virus-derived siRNAs originate predominantly by direct DICER cleavage of imperfect duplexes in the most folded regions of the positive strand of the viral RNA.
Molnár
Attila
A
Agricultural Biotechnology Center, Plant Biology Institute, P. O. Box 411, H-2101 Gödöllö, Hungary.
Csorba
Tibor
T
Lakatos
Lóránt
L
Várallyay
Eva
E
Lacomme
Christophe
C
Burgyán
József
J
D020868:Gene Silencing; D010088:Oxidoreductases / Q000235:genetics / Q000378:metabolism; D010935:Plant Diseases / Q000821:virology; D018515:Plant Leaves / Q000821:virology; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism*; D012367:RNA, Viral / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D043244:Ribonuclease III / Q000378:metabolism; D014026:Nicotiana / Q000821:virology; D014027:Tobacco Mosaic Virus / Q000235:genetics / Q000378:metabolism; D019183:Tombusviridae / Q000235:genetics / Q000378:metabolism
D034741:RNA, Small Interfering; D012367:RNA, Viral; D010088:Oxidoreductases; C022398:phytoene dehydrogenase; D043244:Ribonuclease III