As sulfur becomes increasingly scarce in soils worldwide, scientists are studying how plants decide whether to invest limited resources in growth or defense.
New research points to a mechanism that helps plants reprogram their molecular machinery to carefully budget sulfur — a critical nutrient used for both functions.
Michigan State University researchers published a study in the Proceedings of the National Academy of Sciences detailing how this adaptive allocation strategy allows plants to allocate sulfur without dropping their defenses.
A molecular ‘dimmer switch’ — a protein called CDK8 — regulates the use of sulfur in plants’ defenses, allowing them to turn production of sulfur-containing defense compounds up or down, rather than strictly on or off.
“To stay healthy and resilient, plants deploy these costly chemical defense strategies,” co-author Hideki Takahashi, an associate professor of Biochemistry & Molecular Biology added.
This mechanism enables plants to switch to low-sulfur alternatives when possible and conserve sulfur for uses where it’s irreplaceable.
“This finding provides new insight into how plants balance immunity with nutrient availability and highlights a broader principle: biological systems actively allocate limited resources among competing needs,” explains Gregg Howe, a University Distinguished Professor in the MSU-DOE Plant Research Laboratory and the department of Biochemistry & Molecular Biology.
Stretching sulfur in short supply
CDK8 helps boost the activity of hormone-triggered genes responsible for plant defenses, helping plants produce a robust arsenal of defenses. In plants grown in sulfur-deficient soils, CDK8 shifted plants’ assembly line towards lower-sulfur alternatives. Production of defense compounds containing only one sulfur atom increased nearly eightfold, while production of those containing two or three times as much sulfur was reduced. It’s a cost-conscious strategy, the authors explain.
“There is no alternative to staples like amino acids — these irreplaceable biological building blocks require sulfur,” Takahashi explained.
When sulfur is limited, plants may become malnourished, resulting in slower growth and smaller sizes. But CDK8 can lessen these impacts by switching to defense strategies that free up sulfur for growth.
A subset of plants modified to have inactive CDK8 — effectively disconnecting the dimmer switch — were found to have lower levels of sulfur-based defense compounds and diminished resistance to pests and diseases. Not only does this demonstrate the role of CDK8 in promoting the production of defense compounds, but also that mutants without CDK8 are unable to properly reprogram their defense mechanisms when there’s a decrease in available sulfur, explained Howe.
Why are scientists studying sulfur?
How plants allocate sulfur is a time-sensitive question, as stores of plant-available sulfur — and the deposition which has historically replenished reserves — are in steep decline worldwide. In the United States, plant-available sulfur in soil has declined by up to 86 percent in the past two decades.
These findings provide scientists with clues about how more efficient, “budget-conscious” crops might be designed. Such plants could be engineered to be more disease resistant and less vulnerable when nutrient levels dip.
Next, Takahashi suggests, is to study how plants sense the nutrients around them: another stepping-stone to understanding how plants use environmental cues to make decisions.
This work was supported primarily by the U.S. Department of Energy Office of Science, Office of Basic Energy Sciences, award number DE-FG02-91ER20021, through the DOE Plant Research Laboratory at Michigan State University , with additional support from the Plant Resilience Institute and MSU AgBioResearch .
Proceedings of the National Academy of Sciences
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