Course teacher :
Dr. P. Renukadevi.
Course associate :
Dr. N. Indra
Pat 602 - Plant Virology - (2+1)
TAMIL NADU AGRICULTURAL UNIVERSITY
Why we are concentrating on sat RNA ?
It alters the symptoms .
They do not encode their own RdRps & depends on helper virus and
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
Kaper,j.M et al.. 1977: Mossop,d.W . et al .. 1979 :
Classification: Satellite RNA
PSV satRNA, TCV
satRNA, CMV satRNA,
TobRV satRNA, SNMV
satRNA , CYDV
cerevisiae M virus
vaginalis T1 virus
NCBI, taxonomy ID :12877
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) -
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
Hans,f et.al..1993: Palani.pv et.al..2006,
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
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
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
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:
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
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
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
Zhu et al. 2011
RNA silencing :
Supresses RNA silencing :
To counter the defense
system of host plants, RNA
viruses usually encode
proteins that function as
suppressors of RNA
The CP of TCV suppresses
RNA silencing in N.
benthamiana by obstructing
the Dicer-like protein
Manfre A.J et al..2008
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
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 :