After plants are attacked by a pathogen, the researchers had previously found, they produce SA at the infection site to activate their defenses. Some of the SA is converted into methyl salicylate, which can be converted back into SA by SABP2.
Using plants in which SABP2 function was either normal, turned off or mutated in the infected leaves or the upper, uninfected leaves, Klessig's group showed that SABP2 must be active in the upper, uninfected leaves for systemic acquired resistance to develop properly. By contrast, SABP2 must be inactivated in the infected leaves by binding to SA.
"This inactivation allows methyl salicylate to build up," explained Klessig. "It then flows through the phloem (or food-conducting "tubes") to the uninfected tissue, where SABP2 converts it back into active SA, which can now turn on the plant's defenses."
Klessig said that it is unclear why plants send this hormone to uninfected tissue in an inactive form, which then must be activated by removal of the methyl group.
"This research also provides insight into how a hormone like SA can actively regulate its own structure -- and thereby determine its own activity -- by controlling the responsible enzyme," noted Park, the lead author of the paper.
|Contact: Blaine Friedlander|
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