Quick look
Plants grow longer to cool off when faced with warm but not yet dangerous conditions, which can affect crop yields. New research led by an Iowa State University biologist could help fine-tune the response to a sweet spot that preserves both resilience and production.
AMES, Iowa - When they start to get too warm but before they're dangerously hot, most plants employ a similar playbook. They change their shape, a host of adaptations that includes growing longer stems and stalks to promote air circulation.
The protective reactions to stressful but nonlethal heat, called thermomorphogenesis, help plants endure challenging conditions, but the downside for crops is lower yields. Though it's a delicate balance, adjusting when a plant's cooling strategies kick in would be useful for developing crops that are resilient to warmer weather with minimal production loss.
"We want plants to be able respond to the warmth, but in a way that's not so responsive that they become frail," said Hongqing "Michelle" Guo, an assistant professor of genetics, development and cell biology at Iowa State University.
New research led by Guo could help plant scientists find a sweet spot that preserves both resilience and yield. The recent study in the Proceedings of the National Academy of Sciences identified a molecular mechanism for triggering the moderate-heat response, a crucial step toward fine-tuning how plants prioritize production and protection.
Uncovering a new connection
The new study builds on decades of research into phytochrome B (phyB), a plant protein that acts as a combination thermometer, light sensor and biological switch. When it is activated by absorbing sufficient light in favorable growing temperatures, phyB prevents plants from elongating. When an environment is too warm or dark for too long, phyB fades into a deactivated form and thermomorphogenesis begins.
Guo's lab focuses largely on another long-studied plant protein called Feronia, a workhorse receptor that spans cell membranes. Positioned both inside and outside of cells, Feronia acts as a command center for how a plant responds to its environment, detecting and decoding signals that drive a wide range of processes related to plant health and growth.
Working with Arabidopsis thaliana, a flowering plant often used in genetic research, Guo noticed specimens mutated to lack Feronia didn't react as intensely in settings warm enough to spur thermomorphogenesis. That implied a possible link to phyB, she said.
Looking for signs of a connection, researchers used a set of advanced whole-system analytical methods to compare natural and Feronia-free Arabidopsis. One of those methods was a phosphoproteomic analysis, which catalogs all the sites throughout a sample where adding a phosphate group could change a protein's function - a process called phosphorylation that toggles biological actions on and off. The comparison flagged two phyB amino acids as possible control switches for Feronia, Guo said.
More a dimmer than a switch
To investigate, the research team used gene editing to create two experimental types of Arabidopsis that swapped out the phyB amino acids of interest. In the "null" version, they were replaced with an amino acid that can't accept a phosphate group, preventing Feronia from acting on phyB. A "mimic" version was essentially the opposite, with replacements that imitated the effect of constantly being phosphorylated by Feronia.
The results matched what the researchers expected. At a little more than 80 degrees Fahrenheit, just outside the Arabidopsis comfort zone, the mimic plants grew taller than the natural variety while the null version had the most muted reaction. That shows that preventing Feronia from regulating phyB reduces its response to warmth, Guo said.
While thermomorphogenesis likely involves many phyB phosphorylation sites, seeing the impact from blocking just two of them suggests that inhibiting Feronia's role in the process could have crop development value, Guo said. The aim is to prevent an overreaction, not all reaction - more of a dimmer dial than a light switch.
"Using precise genome editing to manipulate these two sites, or even just one at a time, could impact phyB just enough to manage the response without affecting yield," she said.
What's next?
The study was funded in part by Guo's five-year, $1.8 million grant for promising early-career researchers from the National Institute of General Medical Sciences, a branch of the National Institutes of Health.
Her six collaborators included three Iowa State colleagues and three from the University of California, Riverside - including Meng Chen, an Iowa State doctoral graduate and UC-Riverside botany professor who died unexpectedly one day after paper was published.
"We'd really like to honor his memory," Guo said.
The next steps for Guo's research team could include conducting a similar experiment in a plant cultivated as a crop and exploring Feronia's newfound role in thermal sensing.
"We're doing a lot of research right now on this point, trying to figure out if Feronia can sense temperature independently," she said. "And even if Feronia itself isn't a heat sensor, there might be other sensors it regulates."
Research team
From Iowa State University
- Hongqing Guo
- Zhi Li
- Justin Walley
- Ping Wang
From University of California, Riverside
- Meng Chen
- Juan Du
- Jiangman He
