| Summary: | 碩士 === 國立臺灣大學 === 植物病蟲害學系 === 86 === The genome of dasheen mosaic virus (DsMV), belonging to the genus Potyvirus
, is a single-stranded, positive-sense RNA molecule of ca. 10 kb. DsMV is the
most important virus in aroid plants. Inoculation results indicated that
Philodendron selloum and Chenopodium amaranticolor can be used as a propagation
host and a local lesion host of DsMV, respectively. DsMV virions from a taro
isolate (DsMV-TW) and a calla lily isolate (DsMV-ZAN) were separately purified.
The average length of DsMV-TW virions is 813 nm. The estimated molecular
weights of the coat proteins of DsMV-TW and DsMV-ZAN, determined by Western
blot analysis were 44 and 43 kDa, respectively. Partial genome fragments of
DsMV-TW amplified by RT-PCR were cloned and sequenced. The region of 1,893
nucleotides contains a part of the NIb gene (630 nt), the complete coat
protein (CP) gene (990 nt), the 3'' non-coding region (248 nt) and a poly (A)
tail (25 nt). Comparison of amino acid sequence of the CP gene of DsMV-TW
with that of published DsMV isolates revealed that they all contain
deletion/insertion, tandem repeats and a proline-rich region at the N terminal
region of their CP genes, an unusual feature of DsMV compared to other
potyviruses.
A new potyvirus, distinct from DsMV in sequence, was cloned from a virus
infecting Dieffenbachia picta cv. Rudolph Roehrs and Zantedeschia sp. cv.
Black Magic, and tentatively named Zantedeschia mosaic virus (ZaMV). This is
the first sequence report for a potyvirus infecting aroid plants distinct from
DsMV. The sequence of the 3''-terminal 1,619 nucleotides of ZaMV-ZAN was
determined. This region contains a part of NIb gene (627 nt), the complete
CP gene (849 nt), the 3'' non-coding region (124 nt) and a poly (A) tail
(19 nt). Percent similarities of amino acid sequence between the CP gene of
ZaMV-ZAN and that of other viruses in Potyvirus is 59-73%. From the sequence
of ZaMV-ZAN, a putative cleavage site of the NIb and the CP (Q/S), the DAG
triplet and conserved amino acid motifs of the CP gene were found.
In addition, there were potyvirus-specific cytoplasmic inclusions found in
epidermal cells of ZaMV-infected calla lily. According to the above results,
ZaMV is a new virus species belonging to the genus Potyvirus.
In order to develop a detection system for DsMV and ZaMV, ELISA, RT-PCR
and dot-blot hybridization were chosen to detect these two viruses. The data
of ELISA did not clearly indicate the appearance of two viruses. This might
be due to the interference by the sticky materials of aroid plants. Although
RT-PCR gave high sensitivity of detection, the reactions were also affec
ted by the sticky materials of plant and viral mix infection. The meth
od of dot-blot hybridization could clearly detect the mix infection of DsMV
and ZaMV, its sensitivity was uq to 5 ng of total RNA, and its detection was
not affected by the materials of aroid plants. Therefore, dot-blot
hybridization with specific DNA probes is the best detection method for
detecting DsMV and ZaMV in aroid plants.
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