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United Kingdom
March 2008
John Innes Centre scientists
have found that plants may cluster the genes needed to make
defence chemicals. Their findings may provide a way to discover
new natural plant products of use as drugs, herbicides or crop
protectants. Using a gene cluster that makes an antifungal
compound in oats as a template, they uncovered a previously
unknown gene cluster making a related compound in a very
different species, and now want to extend the search to other
plants.
Anne Osbourn and colleagues previously found that the genes
needed to make an antifungal compound in oats, called avenacin,
were next to each other in the genome. One of a group of
chemicals known as triterpenes, avenacin is produced exclusively
by oats and protects the roots against a wide spectrum of fungal
diseases. Gene clusters are common in bacteria and fungi but
extremely rare in plants. Maize has a gene cluster for a
defence-related compound, and another possible cluster has been
reported in rice.
Could other plant gene clusters exist, and how do they arise? To
investigate this, the researchers used the ‘signature’ of the
avenacin genes to scan the genome of the model plant
Arabidopsis. Publishing in the journal Science, they identified
a gene cluster for a new pathway that makes and modifies a
triterpene called thalianol, which has not been found in plants
before. The thalianol gene cluster consists of four genes next
to each other in the Arabidopsis genome. The first gene,
responsible for making thalianol, is from the same family as the
gene for the first step of the avenacin pathway in oats. The
next three genes in the thalianol cluster are responsible for
making sequential modifications to thalianol. Having
successfully discovered one gene cluster, the researchers now
plan to look for other gene clusters that may produce novel
natural products of value for crop protection or as medicines,
and investigate how and why these clusters evolve.
Although the oat, maize, rice and this new Arabidopsis gene
clusters make related products, they have been assembled
independently of each other as a result of relatively recent
evolutionary events. This suggests that plant species are able
to show remarkable plasticity in their genomes to assemble these
gene clusters. Understanding the evolutionary driving forces
behind their assembly will give insights into why some plant
product pathways are maintained in these clusters whilst others
are not, and this may have implications for our understanding of
plant metabolism.
Clustering genes together lets plants easily inherit an entire
pathway. The thalianol gene cluster is one of the most conserved
areas of the genome, suggesting that this beneficial combination
of genes has recently and rapidly spread throughout the
population. Breaking up a gene cluster can have severe
consequences. When the avenacin pathway is blocked then
unfinished intermediates accumulate that can have a toxic effect
on the roots, making them deformed and ineffective.
Intermediates which affect plant growth also accumulate when the
thalianol synthesis pathway is blocked. If these intermediates
accumulate in parts of the plant where the thalianol pathway is
usually not present then they cause severe stunting of growth.
Dr Ben Field, who contributed to the research, said "This
suggests that gene clusters, as well as keeping beneficial
combinations of genes together, may prevent toxic side-effects
by strictly controlling where and when the pathway is switched
on."
Reference
This paper will be published online by the journal Science, at
the Science Expressweb site, on Thursday, 20 April, 2008. See
http://www.sciencexpress.org and also
http://www.aaas.org. Science
and Science Express are published by the AAAS, the science
society, the world's largest general scientific organization
Metabolic diversification – Independent assembly of operon-like
gene clusters in different plants.
Ben Field and Anne Osbourn
DOI: 10.1126/science.1154990
The John Innes Centre, Norwich, UK is an independent,
world-leading research centre in plant and microbial sciences
with over 800 staff. JIC carries out high quality fundamental,
strategic and applied research to understand how plants and
microbes work at the molecular, cellular and genetic levels. The
JIC also trains scientists and students, collaborates with many
other research laboratories and communicates its science to
end-users and the general public. The JIC is grant-aided by the
Biotechnology and Biological Sciences Research Council.
http://www.jic.ac.uk
The Biotechnology and Biological Sciences Research Council
(BBSRC) is the UK funding agency for research in the life
sciences. Sponsored by Government, BBSRC annually invests around
£380 million in a wide range of research that makes a
significant contribution to the quality of life for UK citizens
and supports a number of important industrial stakeholders
including the agriculture, food, chemical, healthcare and
pharmaceutical sectors.
http://www.bbsrc.ac.uk |
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