An international team of researchers led by scientists at the Virginia Bioinformatics Institute at Virginia Tech have uncovered how important chemical pathways involving plant hormones help plants respond to stress.
The discovery of the unique signaling mechanism was recently published in the Proceedings of the National Academy of Sciences and involves jasmonates, which are hormones that plants use to defend themselves from wounding, insects, disease, damage from ultraviolet rays, and a variety of other threats. Jasmonates also help fruits ripen, stimulate and inhibit root growth, and cause seeds to germinate.
But scientists don’t know how all the pieces fit, because many jasmonate precursors and derivatives are at work.
The research highlights the important role of a protein called CYP20-3 found in chloroplasts, which are structures in plant cells that contain chlorphyll and carry out photosynthesis. CYP20-3 is a well-known target for immunosuppressive drugs and has been associated with various forms of cancer in humans.
Researchers discovered CYP20-3 acts as a sensor for increased levels of a fatty acid called oxylipin OPDA, which is induced during stress. Working with the well-known laboratory plant, Arabidopsis, researchers studied how the physical interaction of the compounds enabled other proteins respond to stress in an effort to restore cellular balance.
"This discovery sheds further light on how plants perceive and respond to stress," said Christopher Lawrence, an associate professor of biological sciences with the College of Science at the institute and senior author of the study. "Moreover, it shows a new mechanism of how a plant hormone-like molecule called an oxylipin transmits a signal by facilitating several proteins to join together and form a biosynthetic complex that affects cellular redox. This has broad implications beyond plants because changes in redox states have long been associated with stressful conditions leading to inflammation and various disease states in many organisms, including humans, that also have oxylipin like molecules."
The Virginia Tech-based study also involved researchers from the University of California-Berkeley, the University of California-Davis, and the Ohio State University, in addition to international collaborators in Germany and Sweden.
"This study establishes, beyond explaining the molecular mechanisms of OPDA signaling in plants, the significance of hormone binding-effector proteins such as CYP20-3 in signaling, and validates a biochemical tool we have developed to identify hormone effectors," said Sang-Wook Park, the first author of the study and a fungal biotechnology specialist at the Virginia Bioinformatics Institute. "It is highly likely that diverse types of proteins can function as effectors, serving as non-classical receptors and subsequently transducers of hormone-based signals. This is a somewhat new paradigm in plant biology and may prove to be a useful way to look at hormone signaling in other organisms, including humans."
In a companion commentary about the study, Stanislav Kopriva of the John Innes Center for excellence in plant science and microbiology in the United Kingdom, said, "The detailed dissection of OPDA signaling by Park et al., forms a benchmark for characterizations of other retrograde-signaling pathways in plants. The results of Park et al., thus, provide the mechanistic explanation for this observation and place OPDA onto the growing list of phytohormones for which the receptor has been identified."