Washington, DC
August 4, 2008
By Stacy Kish, CSREES Staff
Original article in PDF format
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Direct interaction
between the plant VIP1 protein and the bacterial
Virulence E2 protein component of the
Agrobacterium T-complex in the host cell nucleus
as detected by bimolecular fluorescent
complementation and laser scanning confocal
microscopy.
Credit: Vitaly Citovsky |
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Scientists are unlocking the process of how bacteria transfer
genetic material into the plant genome. This information may
lead to crop plants with improved resistance to pests and
disease.
With funding from USDA's
Cooperative State Research, Education, and Extension Service
(CSREES), a project team in New York systematically
investigates and uncovers fundamental biological principles
behind the action of Agrobacterium, which is known for its
ability to transfer DNA between itself and plants, making it an
important tool for genetic engineering.
Agrobacterium serves as both a genetic engineering tool for crop
production and an experimental system to study basic cellular
reactions in genetic transformation. It represents the only
known natural example of how genetic information can be
transferred between different kingdoms of life, in this case
from bacterium to plants. In nature, Agrobacterium promotes
uncontrolled growth of cells in the infected plants. In the
hands of scientists, it serves as a living nanomachine for
genetic transformation of plants in biotechnology industry and
research laboratories.
To genetically transform plants, Agrobacterium transports its
genetic material, in a form of a nucleic acid-protein complex
termed the T-complex, into the host cell nucleus. Once inside
the nucleus, the T-complex must reach the host chromosomes to
complete the integration into the genetic material of the host
cell. Agrobacterium employs a diverse number of biological
processes to genetically transform the host cell. This makes it
a unique model system to examine genetic material transport
between bacteria and eukaryotic cells, cells with internal
structures enclosed in membranes. It also works as a model for
the transport of genetic material into the cell nucleus.
Vitaly Citovsky and colleagues at the State University of New
York at Stony Brook, demonstrated that the plant protein VIP1
helps transfer the invading bacterial T-complex into the host
cell nucleus. Then, VIP1 targets the T-complex to the
integration site in the plant genome. The targeting process
occurs from the direct interaction of VIP1 with the host
nucleosomes, the protein-DNA structures that make up
chromosomes.
Having arrived to the host chromosome, the T-complex must lose
its coat of protein components to allow T-DNA integration. The
Citovsky team showed that this uncoating likely occurs when the
T-complex proteins begin to decompose; the research team
identified bacterial and plant factors that make this
decomposition possible. These experiments also revealed that
many of the cell functions involved in the genetic
transformation process are mimicked and/or augmented by
bacterial virulence proteins exported into the host cell.
"Besides this important contribution to our understanding of the
Agrobacterium-mediated genetic transformation of plant cells,
our work has practical implications for agriculture," Citovsky
said.
Using Agrobacterium, the studies discovered proteins essential
for the transformation process that may facilitate genetic
manipulation of crops that are currently difficult to transform.
On the other hand, this knowledge is also critical for
production of agronomically important plants resistant to
Agrobacterium, Citovsky said.
CSREES funded this research project through the National
Research Initiative's Developmental Processes of Crop Plants
program. Through federal funding and leadership for research,
education and extension programs, CSREES focuses on investing in
science and solving critical issues impacting people's daily
lives and the nation's future. For more information, visit
www.csrees.usda.gov.
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