Ames, Iowa
September 4, 2008
There are numerous plant-parasitic
nematodes in the world, but only a handful are responsible for
the largest part of an estimated $157 billion in agricultural
damage globally every year. Nematodes are small worms that
burrow into plant roots and feed off living cells.
Now, Iowa State University
researchers have contributed to the release of the annotated
genome of one of the most destructive nematodes: Meloidogyne
incognita -- the southern root-knot nematode, as reported
recently in the journal
Nature Biotechnology.
Sequencing the genome is a critical step toward comprehensively
understanding how the organism works and may pave the way for
research on ways to fight the pest.
"This is considered to be one of, if not the most important
plant-parasitic nematode species across the world," said Thomas
Baum, professor and chair of plant pathology and head of Iowa
State University's contribution to the genome sequence project.
Root-knot nematodes are so important because they can be found
almost anywhere in the world on almost any plant, he said.
Nematodes are the most abundant animals on earth.
"Many of the nematodes that are really bad pathogens are very
specialized on which plant they attack," said Baum. "This
nematode has a huge host range. For us nematologists, it is very
interesting and challenging to study."
Because the pest is so widespread, many nematologists around the
world were eager to help with the project. The lead investigator
was Pierre Abad of the Insitut National de Recherche
Agronomiquea, a French research group, with help from
researchers in Belgium, Holland, Great Britain, Switzerland, and
Iowa State University and North Carolina State University in the
US.
"Because it is such a worldwide problem, people are eager to
contribute," Baum said. "Also, because it is the first
plant-parasitic nematode to have its sequence released, people
are very excited about it."
Chemical treatments for killing nematodes, called nematicides,
are dangerous to humans and other animals so they've been
restricted in use for decades. Technology for controlling
nematodes has advanced little in the past three decades.
Besides being a devastating crop pathogen, Meloidogyne incognita
has some remarkable biological adaptations that make it a
fascinating organism to study.
Baum said that the sex of the tiny worms, or better the lack
thereof is very intriguing. Only females reproduce and they do
so without having sex, so it remains a puzzle why males of the
species even exist. And since the females don't mate to
reproduce, the offspring should be genetically identical to the
mother -- like a clone - but they aren't. And as the offspring
matures into males or females, some start as females and then
change into males.
Baum's group included postdoctoral researcher Tarek Hewezi and
assistant scientist Tom Maier from Iowa State. The three worked
on a specific part of the genome and performed manual
annotations of genes. Professor Davis and postdoctoral research
associate, Noureddine Hamamouch, used the current known
parasitism genes to identify the full suite or predicted
parasitism genes in the root-knot nematode genome.
With this sequencing done, Baum thinks researchers can now try
to understand this nematode. He also cautions that finding ways
to control this pest will be a long process.
"For any effort in which you want to control the nematode, this
is a great resource," Baum said. "But having the genome is only
one of many steps in the right direction. Albeit, a very big
one!" |
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