NOW that its genome has been sequenced, the pest that ruins a third of
Brazil鈥檚 oranges each year could be facing its nemesis, announced Andrew Simpson
from the Ludwig Institute for Cancer Research in S茫o Paulo, Brazil. Armed
with the genome sequence of the bacterium Xyella fastidiosa鈥攖he first
plant pest genome to be completely sequenced鈥擲impson and his colleagues
are confident they鈥檒l find ways to combat it.
The bacterium causes the devastating disease citrus variegated chlorosis,
which affects 80 per cent of the orange trees around S茫o Paulo鈥攖he
world鈥檚 premier orange juice producing region. 鈥淭he oranges are very small and
hard, and simply don鈥檛 grow,鈥� says Simpson. 鈥淭he bacteria block up the xylem,
the channel which transports sap from the roots to the periphery of the plant,
and this means the oranges have no juice.鈥� At present, farmers use insecticide
to kill the leafhoppers that spread the bacterium.
Already, Simpson and his colleagues have used the genome to look
for chinks in the bacterium鈥檚 armour. For example, they鈥檝e found that it relies
on proteins called adhesins to colonise the plant. 鈥淭hey are all involved with
helping the bacterium establish itself by clinging to surfaces in the host,鈥� he
says.
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Simpson鈥檚 team and other researchers around the world have also
discovered 67 genes that enable the bacterium to scavenge and hoard iron. 鈥淚t
looks like it鈥檚 dependent on iron for survival,鈥� says Simpson. He adds that it
might be possible to genetically alter orange trees to resist the disease.
Details of the sequencing effort also appeared in last week鈥檚
Nature (vol 406, p 151).
