New mechanism for nutrient uptake discovered
Uptake of a vital nutrient, nitrogen
Biologists at the Carnegie Institution's Department of Plant Biology have discovered a new way that plant cells govern nutrient regulation - neighboring pore-like structures at the cell's surface physically interact to control the uptake of a vital nutrient, nitrogen. It is the first time scientists have found that the interaction of neighboring molecules is essential to this regulation. Since plants, animals, bacteria, and fungi all share similar genes for this activity, the scientists believe that the same feature could occur across species. The discovery, published in the February 11th on-line edition of Nature, has widespread potential - from understanding human diseases, such as kidney function, to engineering better crops.
"Every cell in every organism has a system for bringing in nutrition and expelling waste," explained lead author Dominique Loquй. "Some are through pore-like protein structures called transporters, which reside at the surface of the cell's outer membrane. Each pore is capable of transporting nutrients individually, so we were really surprised to find that the pores simply can't act without stimulation from their neighbors."
In earlier research the Carnegie scientists, with colleagues, identified the genes responsible for initiating nitrogen uptake in plants. That identification has helped other researchers find the relatives of these genes in a variety of species from bacteria to humans. In this study, the scientists wanted to identify how ammonium transport is regulated.
Plants import nitrogen in the form of ammonium from the soil. The researchers found that the end portion, or so-called C-terminus, of the protein Arabidopsis ammonium transporter AtAMT1;1, located at the surface of the cell membrane, acts as a switch.
"The terminus is an arm-like feature that physically grabs a neighboring short-chain molecule, binds with it, and changes the shape of itself and its neighbor thereby activating all the pores in the complex," continued Loquй. "The pores can't function without this physical stimulation."
"The rapid chain-reaction among the different pores allows the system to shut down extremely fast and can even memorize previous exposures," noted co-author Wolf Frommer. "Imagine a large animal marking its territory. A sudden flow of ammonia could be toxic to the plant. If it weren't for a rapid-fire shutdown plants could die. The conservation of this feature in the related transporters in bacteria, fungi, plants, and animals suggests that an ancient organism, which was a precursor to all known organisms on Earth, had developed this feature because there was much more ammonia on the early Earth. The ubiquitous presence of this structure in all of the known ammonium transporters suggests that the regulation is still necessary today for all of these organisms