Washington, DC
January 8, 2008
By Stacy Kish
Cyst nematodes are menacing, microscopic roundworms that infect
and feed on the root cells of many important agricultural crops.
One species of cyst nematode, Heterodera glycines, feeds
on soybean crops, resulting in up to $1 billion in crop loss in
the United States each year. Recent research, funded by USDA's
Cooperative State Research,
Education, and Extension Service (CSREES), is uncovering the
mechanisms used by this nematode to weaken the plant's defense
system.
Recent work by scientists at the University of Missouri (UM) and
Iowa State University (ISU) is featured on the cover of the
March issue of the journal Molecular Plant-Microbe Interactions.
The results from their studies may lead to more effective
management tools to combat the agricultural pest and protect
this vital U.S. crop.
Nematodes have developed a highly evolved relationship with the
host plant. During the juvenile stage, cyst nematodes penetrate
the roots of the soybean plant and travel to the vascular
tissue. Here the juvenile nematode stops to feed. During the
feeding process, the nematode injects secretions that modify the
root cells, creating specialized feeding cells, called syncytia,
which provide nutrients to the nematode necessary for growth and
development, as well as maintains the host-parasite
relationship. In essence, the plant cell is reprogrammed by
these secretions to support the feeding nematode rather than
support and benefit the plant. Without a functioning syncytium,
the nematode will die.
Lead scientist Melissa Mitchum and colleagues at the UM and ISU
examined the molecular mechanisms that lead to the development
of the syncytia cells. The scientists examined 35,611 soybean
genes and obtained the first comprehensive gene expression
profile of the developing syncytium during very early stages of
the plant-nematode interaction. Their work shows that within two
days after syncytium formation over 1,765 soybean genes changed
expression.
This team found that genes for proteins involved in plant cell
wall formation are compromised by interplay between plant
hormones, called phytohormones. In addition, a decrease in the
production of jasmonic acid may suppress the plant defense
response, which allows the nematode to survive and thrive.
The results from this study provide the most comprehensive
picture of gene expression changes within developing syncytia to
date. These findings may provide scientists the key to decipher
which genes play essential roles in the induction, formation,
and function of the syncytium for the survival and growth of
cyst nematodes. Future work in this area may lead to new
management techniques through the use of biotechnology to better
control these important agricultural pests.
Current nematode management strategies focus on reduction and
control of pest population levels below the damage thresholds.
Field eradication of this pest is rarely a feasible option. Crop
rotation using non-host crops (e.g., corn) or planting nematode
resistant soybean varieties are the most efficient management
strategies to date. Chemicals, like nematicides, are available,
but rarely have the necessary long-term effect on nematode
populations and are not cost-effective for the grower.
Cyst nematode-induced damage is difficult to diagnose, because
the symptoms are nondescript and are often contributed to other
factors, such as compaction, nutrient deficiencies, drought
stress, herbicide injury, or other plant diseases.
The USDA's Cooperative State Research, Education, and Extension
Service (CSREES) funded this research project through the NRI
Functional Genomics of Arthropods and Nematodes program. CSREES
advances knowledge for agriculture, the environment, human
health and well-being, and communities by supporting research,
education and extension programs in the Land-Grant University
System and other partner organizations. For more information,
visit www.csrees.usda.gov. |
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