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.

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 Foundation.

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 http://www.medicago.org/ or http://www.tigr.org/tigr-scripts/tgi/T_index.cgi?species=medicago, 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.

The American Society of Plant Biologists, founded in 1924, is a non-profit society of nearly 6,000 plant scientists from the United States and 60 other nations.  The Society's annual meeting here at Disney's Coronado Springs Resort & Convention Center near Orlando, Florida attracted more than 1,200 scientists in attendance.  ASPB publishes two of the most frequently cited plant science journals in the world:  The Plant Cell and Plant Physiology.