BRIEF REPORT
De novo emergence of a novel satellite RNA of cucumber mosaic
virus following serial passages of the virus derived from RNA
transcripts
M. R. Hajimorad Æ S. A. Ghabrial Æ
M. J. Roossinck
Received: 17 September 2008 / Accepted: 12 November 2008 / Published online: 10 December 2008
Ó Springer-Verlag 2008
Abstract Satellite RNA (satRNA) is often associated
with cucumber mosaic virus (CMV); however, its origin
remains unexplained and a subject for speculation. We
passaged progeny of molecularly cloned CMV-Fny and
CMV-LS in Nicotiana tabacum cv. Ky 14 under green-
house conditions. A satRNA emerged after at least eight
successive transfers of CMV-Fny, but no satRNA was
recovered after eleven serial transfers of CMV-LS under
the same conditions. The sequences of the newly emerged
satRNA were determined, and an infectious cDNA clone
was synthesized. Comparison of the sequences of the
newly emerged satRNA with those of known CMV satR-
NAs showed that it is unique. This observation raises
interesting questions regarding the enigmatic nature of the
origin of CMV satRNAs.
Virions of cucumber mosaic virus (CMV) isolates may
contain small linear RNA molecules known as satellite
RNA (satRNA) [9]. Despite isolation and characterization
of a number of satRNA strains of CMV, the origin of
satRNAs remains unexplained and subject to much spec-
ulation [5, 14, 17]. One hypothesis is that many CMV
strains contain subliminal levels of satRNAs that begin to
replicate and become evident under laboratory conditions
[14]. This notion is supported by the observations that
serial passages of naturally occurring strains of CMV under
greenhouse conditions occasionally result in ‘‘spontane-
ous’’ emergence of satRNAs and that 20 serial passages of
RNA transcripts of CMV-Fny under growth chamber
conditions did not generate a satRNA [6, 7, 10, 14]. Nev-
ertheless, in one study, non-mutant forms of a satRNA of
turnip crinkle virus emerged in plants inoculated with a
mixture of RNA transcripts derived from molecularly
cloned virus and mutant forms of the satRNA [4], sug-
gesting that the source of information for generation of
satRNAs is not only the inoculum. In this communication,
we present sequences of a novel CMV satRNA that
‘‘spontaneously’’ emerged in tobacco following serial
transfer of the progeny of molecularly cloned CMV-Fny
under greenhouse conditions.
RNA transcripts of CMV-Fny and CMV-LS [15, 16, 21]
were generated in vitro by using bacteriophage SP6 or T7
polymerase (Ambion, Austin, TX, USA) and were inocu-
lated onto carborundum-dusted tobacco (Nicotiana
tabacum cv. Xanthi nc). Virions were purified from sys-
temically infected leaves [3]. The virions of each of the two
viruses were inoculated onto burley tobacco (N. tabacum
cv. Ky 14), which is an easy tobacco genotype to grow and
maintain under greenhouse conditions. Subsequently, the
inoculated plants were maintained in an insect-proof
greenhouse at 25/22°C day/night with a 16 h photoperiod.
This was considered the first passage of the virus. For each
of the two viruses, two infected plants were selected
14 days post-inoculation (dpi), and infectious sap from
The nucleotide sequence data reported in this article have been
deposited in the GenBank under accession number DQ975201.
M. R. Hajimorad (&)
Department of Entomology and Plant Pathology,
The University of Tennessee, Knoxville, TN 37996, USA
e-mail: mrh@utk.edu
S. A. Ghabrial
Department of Plant Pathology, University of Kentucky,
Lexington, KY 40546, USA
M. J. Roossinck
Plant Biology Division, The Samuel Roberts Noble Foundation,
Ardmore, OK 73402, USA
123
Arch Virol (2009) 154:137–140
DOI 10.1007/s00705-008-0280-x