Satellite RNA
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in this chapter covers the symptoms modulation and diseases severity increases and decreases. and role of SiRNA in diseases severity reduction. and also covers the types of SRNA..
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Satellite RNA
- 1. Satellite RNA Course teacher : Dr. P. Renukadevi. Course associate : Dr. N. Indra Pat 602 - Plant Virology - (2+1) By RAMALINGAM.K 2015601610 TAMIL NADU AGRICULTURAL UNIVERSITY
- 2. Why we are concentrating on sat RNA ? It alters the symptoms . They do not encode their own RdRps & depends on helper virus and plant machineries. It provides additional information to study the replication of helper virus. It act as a Molecular Parasites. So that reduce the accumulation of their helper viral RNAs . They can accumulate to high levels in host plants and thus in some cases can be developed into high-level expression vectors for foreign genes. Kaper,j.M et al.. 1977: Mossop,d.W . et al .. 1979 :
- 3. Classification: Satellite RNA ssRNA Large satRNA satBaMV, TBRV satRNA, satGFLV, satArMV, Small linear satRNA PSV satRNA, TCV satRNA, CMV satRNA, TBSV satRNA. Small circular satRNA TobRV satRNA, SNMV satRNA , CYDV satRNA , dsRNA Saccharomyces cerevisiae M virus satellite, Trichomonas vaginalis T1 virus satellite NCBI, taxonomy ID :12877 https://en.wikipedia.org/wiki/Satellite_%28biology%29#Classification
- 4. PROTEIN FUCTIONS : TBRV satRNA are encode Mr 48,000 protein (419-424 AA) - in vivo - involved in replication. The P3 protein encoded by a GFLV-F13 satRNA (1,114 nt) - replication . satArMV - in planta - replication . The P20 protein encoded by BaMV satRNA is not essential for replication but is involved in the systemic movement of satBaMV RNA. Hans,f et.al..1993: Palani.pv et.al..2006,
- 5. Secondary structure : MARILYN J. ROOSSINCK et al.,1992 Sequence variation : A – CMV B – TCV C – TobRV D - LTSV
- 6. REPLICATION Helper virus specificity : SNMV does not support the replication of satellite RNA of LTSV, even though LTSV does support the replication of both satRNAs Host specificity : The small satellite RNA of ArMV replicates very efficiently in Chenopodium quinoa by contrast TBRV replicates poorly in C. quinoa but replicates very efficiently in Nicotiana clevelandii and Petunia hybrida . Enzymology : A membrane-bound RdRp complex was isolated from tobacco protoplasts inoculated with RNAs 1 and 2 of CMV; this complex was capable of synthesizing CMV and satellite ds RNAs in vitro . Davis, c et al .,1990 :Jones, A. T et al ., 1984
- 7. Symptom modulation : Interaction of SatRNA , Helper Virus , Host.., Symptom attenuation can attained by reduction in virus titer through competition for the replicase between the satellite and helper virus (Strain). changes in the nucleotides sequence of sat RNA are affect the pathogenicity in host specific manner. Example : (CMV sat RNA ) Chlorosis – 135-175 nt. Necrosis - 290-310 nt. Masuta c,et al..,1989: Sleat d. et al..,1990:
- 8. Exacerbated symptoms: The CP of TCV suppresses RNA silencing in N. benthamiana. TCV CP is a weak suppressor of RNA silencing when assembled into the intact virions but a strong suppressor when expressed freely in the cytosol. The satC associated with TCV can reduce the accumulation of virions, thereby increasing the level of free CP, which leads to the suppression of RNA silencing and subsequent exacerbation in symptom severity. Zhang F et al..,2003: Manfre A.J et al..2008
- 9. That siRNAs derived from a CMV satRNA can induce RNA silencing against the CMV helper virus. They showed that an abundant sat-siRNA, derived from the small region conserved between satRNA and 3′ UTRs of CMV, can target the homologous 3′ UTR sequence of CMV-inducing RDR6-dependent RNA silencing against CMV. Using a green florescent protein (GFP) sensor construct, they confirmed sat-siRNA-directed cleavage at the CMV 3′ UTR sequence. Thus, sat-siRNAs can have a direct role in reducing helper virus accumulation by directing cross silencing against the helper virus genome. Zhu et al. 2011 RNA silencing :
- 10. Supresses RNA silencing : To counter the defense system of host plants, RNA viruses usually encode proteins that function as suppressors of RNA silencing. The CP of TCV suppresses RNA silencing in N. benthamiana by obstructing the Dicer-like protein DCL2/DCL4 silencing pathway. Manfre A.J et al..2008
- 11. Practical application The application of mild strains of helper virus containing satellite RNA to field crops can protect plants to more virulent strains. Producing transgenic plants that express the sat RNA sequences. The development of satRNA-based vector systems for the expression of foreign genes in plants. satBaMV RNA has been used for the expression of individual TGBps in a complementary experiment for study of cell-to-cell movement of BaMV. Advantages of sat RNAs Ease of manipulation, High in vivo stability, High expression level Roossink M J et al.., 1997 : Montasser,M.S et al..,1991 :
Editor's Notes
- Subgroup 1 contains large satRNAs of about 0.7 to 1.5 kb that encode at least one nonstructural protein. Thus, satRNAs in this subgroup are usually referred to as messenger-type satRNAs. Arabis mosaic virus large satRNA (satArMV), Bamboo mosaic virus satRNA (satBaMV), Grapevine fanleaf virus satRNA (satGFLV), Tomato black ring virus (TBRV) satRNA
- It preferentially binds to 5’ and 3’ untranslated regions (UTRs) of satBaMV RNA [40] and interacts with the CP, a movement protein of its helper virus [triple gene block protein 1 (TGBp1)] and P20 itself [39]. its involvement in long-distance movement of satBaMV RNA
- (A) the linear B2 satRNA of CMV; (B) the linear RNA C of TCV; (C) the circular replication intermediate of the linear satellite RNA of TobRV; and (D) the circular satellite RNA of LTSV. A)., N and C indicate the necrosis- and chlorosis-inducing domains, B), M modulation of symptom expression. C), H can form a hammerhead ribozyme involved in self-cleavage of multimeric positive-sense TobRV satellite RNA transcripts); and P is the location of the sequences of negative-sense TobRV satellite RNA that form a paperclip ribozyme involved in self-cleavage reactions. Encapsidated TobRV satellite RNA is linear with contiguous 5' and 3' ends (arrow). In panel D, +H and -H refer to the locations of sequences that can form hammerhead ribozymes in the positive- and negative-sense LTSV satellite RNAs, respectively. The arrow indicates the position of residue 1, numbered randomly.
- attenuating the symptoms of its helper virus, does not attenuate the symptoms of the nonhelper viruses
- RNA silencing, also referred to as PTGS or RNA interference (RNAi), is a double-stranded, RNA-induced, sequence-specific RNA degradation process,
- TCV CP is a weak suppressor of RNA silencing when assembled into the intact virions but a strong suppressor when expressed freely in the cytosol. The satC associated with TCV can reduce the accumulation of virions, thereby increasing the level of free CP, which leads to the suppression of RNA silencing and subsequent exacerbation in symptom severity. First, they are simpler systems to use for cloning, sequencing, genetic modification, and regular maintenance. Second, most satRNAs are highly structured and thus significantly more resistant to degradation by nucleases in vivo finally, increase in level of proteins translated from the messenger-type RNAs of the satellites.