Ames, Iowa
May 27, 2008
In an international collaboration,
researchers in Allen Miller's lab in the Department of Plant
Pathology at Iowa State
University have shown that a tiny gene exists in all members
of the largest family of plant viruses. Without this gene, the
virus is harmless. The discovery was published recently in the
Proceedings of the National Academy of Sciences.
The work was based on a prediction made in the lab of John
Atkins of University College Cork, in Cork, Ireland. Atkins is a
world-renowned expert in the field of "recoding" - genetic
decoding events that don't follow the normal rules. A researcher
in Atkins' lab, Andrew Firth, turned to computers to discover
tiny genes hidden in the sequences of viruses.
Firth set his program to work crunching through the genome
sequences of the largest and most devastating family of plant
viruses - potyviruses. The computer output soon revealed what
appeared to be a new gene that overlaps with a much larger and
well-known gene in these viruses. At this stage the possible
gene was identified simply as a stretch of nucleotide bases in
the viral RNA uninterrupted by a "stop" signal and hence known
as an open reading frame or ORF. Firth said he thought this was
a "pretty interesting potyvirus ORF" so he called it by the
acronym pipo and the name stuck.
This is where Iowa State entered the picture. Firth and
molecular biology graduate student Betty Chung, also of Atkins'
lab, temporarily joined the lab of Allen Miller, who is an
expert on plant virus recoding, to obtain the necessary
materials and expertise needed to investigate plant viruses.
This Irish-Iowa State team used a potyvirus called Turnip mosaic
virus (TuMV) that had been engineered to express a protein that
turns infected plant parts fluorescent green. It was brought to
Iowa State previously by Steve Whitham, associate professor of
plant pathology.
TuMV infects not just turnips, but many important vegetable
crops. The researchers altered the sequence of the virus genome
so the protein synthesis machinery of the plant cell could not
make any protein from the predicted pipo minigene, while all the
well-known large genes it overlaps with still could be
translated normally.
These small mutations "killed" the virus. The normal virus
infected plants, causing them to become stunted and glow green
under UV light before ultimately dying. The plants inoculated
with the mutant virus were healthy and did not glow green
because the virus was unable to multiply without the pipo gene.
These results indicated this team of scientists discovered a key
gene essential to this diverse family of plant pathogens.
The mysteries now confronting Miller and Atkins' team are to
figure out how the pipo protein is expressed from the viral
genome, and what it actually does during virus infection. To
answer these questions, Miller and Atkins recently were awarded
a nearly $400,000 competitive grant from the USDA National
Research Initiative.
The team will use these funds to explore what kind of "recoding"
event allows translation of the pipo gene, and to determine the
process in the virus life cycle in which it is involved.
This research is important to agriculture because 30 percent of
all plant viruses are in the potyvirus family. These include the
potato virus Y, a new strain of which has tormented potato
growers in Europe and North America in recent years, Wheat
streak mosaic virus which threatens wheat production in Nebraska
and elsewhere, and soybean mosaic virus in Iowa which discolors
the beans, reducing their market value. Major fruits such as
plum and other stone fruits and vegetables such as lettuce and
pepper also often are devastated by potyviruses. |
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