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In Relations between Plants and Fungi, Phosphorous Plays a Key Role

BTIRecent research in Maria Harrison’s lab has exposed the vital importance of phosphorous transfer is in some relationships between plants and fungi. In a paper entitled “A Medicago truncatula phosphate transporter indispensable for the arbuscular mycorrhizal symbiosis”, published in the Proceedings of the National Academy of Sciences, Javot et al. revealed that a plant will terminate its association with certain fungi unless the fungi provide the plant with phosphorous.

These mutually beneficial associations, termed arbuscular mycorrhizal relationships, develop in the plants’ roots, where the fungi move into the inner cells of the root in order to access carbon, an element that the fungi depends on that it cannot produce itself. As the plant provides carbon to the fungus, the fungus transfers phosphorous from the soil to the plant.

While trying to identify genes that play a role in this symbiotic relationship, members of Dr. Harrison’s lab identified a protein, MtPT4, that they thought might be essential for the transfer of phosphorous. Using a technique known as RNA-interference, the Harrison lab “knocked out”; the function of this phosphate transporter and proved that MtPT4is not only needed for the transfer of phosphate to the plant, but that proper functioning of MtPT4 is critical for the relationship between the plant and fungus to be maintained.

Without proper MtPT4 functioning, the specialized structures that the fungus uses to transport phosphorous to the plant prematurely die and the fungus is no longer able to proliferate inside the plant’s root–the relationship between the plant and the fungus is terminated. As soon as the fungus, the invited houseguest, stops bringing presents, the plant ends the relationship and kicks the fungus out.

Over 80% of flowering plants form these arbuscular mycorrhizal relationships. Although plants do not require the phosphorous supplied by the fungi in order to survive, phosphorous is essential for plant growth, and many soils do not contain adequate levels of this nutrient. Phosphorous may be added to the soil as a fertilizer, but this often has detrimental impacts on the environment. Consequently, this symbiotic relationship and the resulting additional phosphate supplied via arbuscular mycorrhizal fungi may have a significant impact on plant development, influencing the structure of plant communities in ecosystems worldwide.

Javot, H., et al. 2007. http://intl.pnas.org/cgi/content/short/104/5/1720 A Medicago truncatula phosphate transporter indispensable for the arbuscular mycorrhizal symbiosis. Proceedings of the National Academy of Sciences of the United States. 104: 1720-1725.

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