Glutamate activates long-distance calcium-based defense system in PLANTS

Just like animals, plants also must respond within minutes to environmental stresses such as wounding, and plants do so –– with both local and system-wide reactions that prime nondamaged regions to mount defenses against the incoming adverse effect. For herbivory (something eating on a plant while it’s still alive!), production of the defense hormone jasmonic acid (JA) and accumulation of toxic, repellent, or digestibility-reducing compounds all aid in deterring future attacks. Hence, this is an example of gene-environment interactions. Reactive oxygen species (ROS), electrical signals, and changes in cytosolic calcium concentration ( [Ca2+]cyt ) are believed to form signaling-networks that support both local and systemic defense responses.

The electrical component is dependent on glutamate receptor–like (GLR) proteins, a family of cation-permeable ion channels (if you remember from high school chemistry, ‘cations’ are positive-charged ions) that function in plant processes ranging from pathogen defense to root growth. Authors [see attached article and editorial] asked how GLRs are triggered by wounding and how subsequent Ca2+-related signaling-events operate to mediate systemic defense. Multicellular organisms (both animals and plants) have developed mechanisms to communicate systemically “the occurrence, and location, of a wound” –– to help organisms escape or defend themselves from predators. Because plants are stationary and cannot escape herbivory, they must respond with chemical defenses to deter herbivores (plant-eating animals) and repair damaged tissue.

Authors [see attached] describe long-distance Ca2+-signaling in the model plant, Arabidopsis thaliana (in the mustard family) in response to caterpillar herbivory or mechanical wounding. Authors discovered long-distance calcium signals that require GLR channels for signal propagation. These channels are activated by extracellular glutamate –– which is a well-known neurotransmitter in mammals (including humans) and a more recently uncovered developmental signal in plants. In mammals, glutamate receptors are central to fast excitatory neurotransmission, which is an intriguing parallel to their role as long-distance signals in wounding and defense in plants. Authors found that glutamate is a wound signal in plants. Ion channels of the Arabidopsis thaliana GLUTAMATE RECEPTOR–LIKE family act as sensors that convert this signal into an increase in intracellular Ca2+ ion concentration that subsequently propagates to distant organs (roots, stems or leaves), where defense responses are then induced.


Science 14 Sept 2o18; 361: 1112–1115 [article] & pp 1068–1069 [editorial]

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