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Nuclear Import of Transcriptional Repressor in Jasmonate Signaling

Researchers examining how the hormone jasmonate works to protect plants and promote their growth have discovered how a transcriptional repressor of the jasmonate signaling pathway makes its way into the nucleus of the plant cell. The scientists hope that this recently published discovery will eventually help farmers experience better crop yields with less use of potentially harmful chemicals. “This is a small piece of a bigger picture, but it is a very important piece,” said Dr. Maeli Melotto, a University of Texas at Arlington (UT Arlington) assistant professor of biology. Dr. Melotto recently co-authored a paper that advances current understanding of plant defense mechanisms with her collaborator Dr. Sheng Yang and his team at Michigan State University’s Department of Energy Plant Research Laboratory (DOE-PRL). Dr. Yeng is a Howard Hughes Medical Institute-Gordon and Betty Moore Foundation investigator. The collaborative paper was published in the December 4, 2012 issue of PNAS. Jasmonate signaling has been a target of intense research because of its important role in maintaining the balance between plant growth and defense. In healthy plants, jasmonates play a role in reproductive development and growth responses. But, when stressors such as herbivorous insects, pathogen attack, or drought come into play, jasmonate signaling shifts to defense-related cellular processes. The team from UT Arlington and Michigan State focused on the role of jasmonate signaling repressors referred to as JAZ. Specifically, the scientists looked at how JAZ interacts with a major transcription factor called MYC2 and a protein called COI1, which is a receptor necessary for jasmonate signaling. The researchers discovered that a physical interaction between the repressors and the MYC2 persisted inside the plant cell nucleus, preventing jasmonate-associated gene transcription. “This tight repression of transcription factors may be important because activation of jasmonate signaling, although important for plant defense against pathogens and insects, is energy-consuming and could lead to growth inhibition – a widely known phenomenon called growth-defense tradeoff,” said Dr. He, the Michigan State plant biologist. “In other words, plants have developed a mechanism to tightly repress presumably energy-consuming, jasmonate-mediated defense responses until it becomes necessary, such as upon pathogen and insect attacks.” Dr. Melotto said that understanding jasmonate signaling at the molecular level is also vital because some plant pathogens, such as Pseudomonas syringae, have developed ways to mimic the hormone’s action in the cell. This gives them the ability to aggressively colonize plants without activating natural defense mechanisms, she said. Dr. Melotto, who is currently receiving NIH funding to examine plant defenses, said the next step in her jasmonate research is to determine which domain of the JAZ protein is responsible for plant innate immunity. “This is one way to have sustainable agriculture,” Dr. Melotto said of the research. “By increasing genetic resistance we could reduce the use of pesticides, decrease crop production costs, and promote environmentally friendly farming practices.” The image depicts methyl jasmonate. [Press release] [PNAS abstract]