Reported in Nov. 12th Nature, Findings Suggests Brain Signaling Systems Evolved From Mechanism That Existed Before Divergence of Plants and Animals
NYU plant molecular biologist Gloria Coruzzi and collaborators have discovered evidence that plants have a signaling mechanism that is similar to one in the human brain. This discovery suggests that signaling between cells by excitatory amino acids may have evolved from a mechanism that existed before the divergence of plants and animals. It also helps explain why plants make neuroactive compounds that act on receptors in the brains of humans and other animals.
Coruzzi's NYU team and collaborator Hon-Ming Lam of the Chinese University of Hong Kong report their findings in the November 12th issue of Nature in a scientific correspondence entitled "Glutamate receptor genes in plants." For a copy of the article, contact Lauren Funkhouser at Nature at (202) 737-2355.
Examining the DNA of Arabidopsis (a common lab plant), Coruzzi's lab found genes that encode for glutamate receptors (iGluRs), which are known to be involved in cell signaling in the human brain. In the brain, glutamate receptors are activated by the amino acid glutamate. This lock-and-key relationship is the linchpin of one of the brain's cell-to-cell communication and activation systems.
Based on their findings, the NYU researchers have concluded that glutamate also acts as a chemical messenger in plants. They found that it is involved in communicating the presence of light and regulating light-dependent processes such as stem growth and chlorophyll synthesis. Furthermore, they found that Arabidopsis cannot respond properly to light when glutamate receptors are inhibited*.
Prior to this discovery, glutamate receptors were thought to be a specialized signaling system that first evolved in the brains of animals and was exclusive to them.
Coruzzi said, "Our research suggests that the glutamate receptor and other similar signaling systems, which were first described in animal brains, are actually ancestral methods of simple cell-to-cell communication, common to plants and animals alike."
Coruzzi's discovery may also explain why certain plants manufacture compounds that activate glutamate receptors in the brains of animals. Likewise, the research suggests a possible explanation for why plants make other neuroactive compounds: nicotine, caffeine and cocaine, for example. Coruzzi suggests that these compounds' primary function in plants may be to activate a variety of still undiscovered cell-to-cell signaling systems.
This would contradict the most widely held hypothesis, that psychoactive substances made by plants are primarily defense mechanisms against herbivory. Coruzzi argues that the primary function of these compounds in plants may be to regulate signal transduction and that their role as a plant defense against herbivory is a secondary function that evolved in some plant species under selective pressure.
Finally, Coruzzi's research suggests that Arabidopsis might be useful as a screen for new drugs. Researchers on animal brains have suggested a relationship between glutamate receptor malfunction and dementias including Alzheimer's disease. By growing Arabidopsis in the presence of a given candidate drug, researchers could quickly screen for the drug's effect on glutamate receptors.
Coruzzi's research was funded by NIH's National Institute of General Medical Sciences.
Contacts:
Josh Plaut, NYU, (212) 998-6797
Alison Davis, NIGMS, (301) 496-7301
Journal
Nature