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LAKE BUENA VISTA, Florida - Scientists at the Boyce Thompson Institute for
Plant Research at Cornell University have uncovered the genes that enable
plants to interact with beneficial soil dwelling fungi and to access
phosphate delivered to the roots by these fungi -- a first step, they say,
toward enhancing the beneficial relationship for crop plants , while
reducing fertilizer use and phosphate pollution in the environment, July
2004 by Brian Hyps .

Discovery of the phosphate-transport genes was announced today (July 28,
2004) by Maria Harrison, a senior scientist at the Ithaca, N.Y.-based
research institute, during the American Society of Plant Biologists' annual
meeting in Lake Buena Vista, Fla.

She said considerable work lies ahead before scientists learn to exploit the
genetic discovery and harness the potential of this naturally occurring,
symbiotic fungus-plant association, but that the payoff to growers and to
the environment could be substantial: more efficient plant growth with less
phosphorus-based fertilizer, and a subsequent reduction of phosphate runoff
in surface water.

"AM fungi are very efficient at helping plants absorb phosphorus from the
soil, and managing this symbiotic association is an essential part of
sustainable agriculture" Harrison explained in an interview before plant
biologists' meeting. "Phosphorus is a nutrient wherever it goes, and in our
lakes and rivers it often nourishes undesirable algae. Agriculture is a
major source of phosphate pollution, so anything we biologists can do to
improve phosphate uptake in crop plants will make agriculture more
sustainable and less harmful to the environment," she predicted. A thorough
understanding of how symbiotic fungi work with plants to assist the uptake
of phosphorous and other nutrients from the soil is an important goal in
plant biology with relevance to agriculture and ecology. Dr. Maria
Harrison?s identification of the phosphorous uptake protein in the plasma
membrane of the plant is an important step toward this goal. Now her
research group is focused on learning which genes in the plant play a role
in establishing the symbiotic relationship and of those that regulate the
transfer of phosphorous into the plant.

In addition to advancing our understanding of nutrient uptake by plants,
this work reveals the molecules behind the scenes of a fascinating example
of two species interacting to the benefit of both. Dr. Maria Harrison of the
Boyce Thompson Institute for Plant Research will present her work 2 p.m.
Wednesday, July 28 at the ASPB Annual Meeting. The meeting will be held at
Disney's Coronado Springs Resort & Convention Center in Lake Buena Vista
near Orlando. Dr. Harrison's research was funded by the National Science
Foundation Plant Genome Program and The Samuel Roberts Noble

Abstract In natural ecosystems, most vascular flowering plants live in
symbiosis with arbuscular mycorrhizal (AM) fungi. These mutually beneficial
associations develop in the roots, where the fungus colonizes the cortex to
obtain carbon from the plant. In addition to inhabiting the root, the fungus
establishes hyphal networks in the soil, via which phosphorus and other
mineral nutrients are transferred to the root. Thus the symbiosis has a
significant impact on plant mineral nutrition and consequently on plant
health. Fossil evidence suggests that plants have been associated with AM
fungi since they first colonized land and today, AM symbioses are formed by
almost all vascular flowering plant species. The symbiosis is a highly
compatible partnership, in which both symbionts differentiate to develop
specialized symbiotic interfaces (arbuscule-cortical cell) over which
phosphate is transported. The research in my lab focuses on the mechanisms
underlying development of the AM symbiosis and symbiotic phosphate
transport. A legume, Medicago truncatula, and an AM fungus, Glomus
versiforme are used for these analyses. To gain insight into the
transcriptional networks that are activated during development of the
symbiosis, ESTs were generated and transcript profiles were examined using
cDNA arrays. Of the genes showing elevated transcript levels, most appeared
to be responding to the AM fungus, rather than to the secondary effects of
increased phosphorus nutrition. The mycorrhiza-induced gene sets included a
significant proportion of putative signaling proteins, suggesting that novel
signaling pathways are activated in the symbiosis. Currently a 16K
oligonucleotide-based array is being used to survey transcript profiles in
M. truncatula mycorrhiza mutants, to further define the transcriptional
events that underlie development of the AM symbiosis. The M. truncatula EST
collections, available through [www.medicago.org] or
[www.tigr.org], contain
approximately 190,000 ESTs. Motif searching strategies enabled the
identification of a mycorrhiza-specific phosphate transporter, MtPT4 that is
expressed exclusively in mycorrhizal roots. The MtPT4 protein is located in
the peri-arbuscular membrane, where a function in symbiotic phosphate
transport in predicted. RNAi approaches are in progress to evaluate the
roles of MtPT4 and the other mycorrhiza-regulated genes in the symbiosis.

[www.eurekalert.org]

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