"Plants are unlike humans in that they can’t escape environmental stresses or bad conditions. If the temperature gets too cold or hot, we move inside. Plants have roots and are unable to relocate. They deal with heat, drought, cold, pathogens, herbivores, and mechanical stresses. The process of their survival through all of that is amazing- and it’s thanks in large part to the functionality of stomata."

In addition to regulating the rate of gas exchange, stomata also help manage hydration levels in plants through the process of transpiration. When stomata are open, water vapor from photosynthesis is released. However, when stomata are closed, transpiration is greatly reduced.

Dr. Chen explained that if the rate of transpiration is too high on hot days, plants can become dehydrated. Some desert plants have learned to counteract this issue by permanently functioning on a nocturnal cycle to escape the high heat.

"[Most plants’ stomata] open during the day when the sun is out. The plants can photosynthesize, grow, and repair themselves. On the other hand, desert plants have learned over the course of their evolution that if they do this in their hot climates, they will lose water too fast and die. To prevent this, they open their stomata at night when the temperature is cooler and close them during the day to prevent water loss."

Desert plants with this nocturnal stomata cycle are up to ten times more effective at conserving water than common agricultural crops like tomatoes and wheat. If the Chen Lab is able to unlock what makes these plants different on a molecular level, crops that typically need significant amounts of water could be modified to have more effective stomata movement and water use.

"Over 70% of the fresh water used each year goes to support agriculture. If we could understand that beautifully complex mechanism of stomata function, we would know what molecular switches are flipped to allow this nocturnal cycle to occur. We can potentially move these mechanisms over to crops. We can make them more drought resistant and ultimately conserve our precious freshwater resources."

As quality agricultural land and freshwater resources are being consumed, other resources will need to be utilized to keep up with global crop demands. Semi-arid environments, growing in numbers due to climate change, could be accessed if crops were made to be more drought-tolerant. Dr. Chen is hopeful that his lab’s research will help unlock the molecular communication of plants with their stomata and encourage agricultural growth in new areas.

"This is what has inspired our lab. By researching one part of this complex mechanism, we hope to understand how stomata function and how to control them for the good of our agricultural future."

Active Adaption of the Stomata in the Common Ice Plant

A model organism used to spearhead the Chen Lab’s research into understanding and controlling stomatal movement is Mesembryanthemum crystallinum, the common ice plant.

Ice plants are perfect models for stomatal movement being affected by environmental factors. When living in good conditions, these plants behave as one would expect. Their stomata open during the day to allow photosynthesis and gaseous exchange to occur and close at night. When this variety of plant experiences stress, such as drought conditions, high salinity, or high levels of carbon dioxide in the air, it does something unusual: it actively adapts.

"They can sense the environment and react accordingly. They know they need to change their behavior to improve their chances of survival. Similar to people with jetlag, ice plants take about three days to make the decision to shift to a nighttime stomata cycle like desert plants use. That dramatic change over the course of those three days is what my lab is most interested in right now."

In order to understand what is occurring, it is necessary to go down to a genetic level. Technology such as mass spectrometry allows for the profiling of the presence and change of molecules in ice plants during this three-day transitionary period. It also allows researchers to see which molecular pathways are turned on or off, potentially revealing which genes are the primary regulators of this unique survival trait.

"Discovering on a molecular level what changes is of the utmost importance to our research. We have already identified several transcription factors within the ice plant genome that are responsible for this change. Now we want to know what happens during those three days that triggers this adaptation."

Once the molecular regulators are characterized, the genetics of common crops could be altered to include it. Dr. Chen explained that once activated, these new pathways could positively impact food security and boost crop resilience to drought and high temperatures.

"Just think about the next generation. Climate change will affect crop productivity, not just in this country, but all over the world. Food insecurity is a major problem in many places, and it will continue to get worse unless we do something."

Dr. Chen explained that scientists in the United States should be cautious not to narrowly focus on just their country’s affairs and that COVID-19 is a notable example of this circumstance.

"The United States has an excess of vaccines, but other countries don’t have enough. This results in viral mutations in heavily unvaccinated areas that can then spread to the rest of the world. Their problems become all of our problems. We should look beyond ourselves, beyond just our country, in order to benefit the greater good."

Plant-Pathogen Interactions and the Stomatal Disease Triangle

Bacterial pathogens cannot excrete enzymes to chemically degrade their host plants. Instead, bacteria must find a physical pathway directly into the plant, often occurring through its stomata. When bacteria attempt to enter, guard cells can sense the attempted infiltration. They react by closing and blocking the bacteria out.

However, over many years of evolution, certain bacteria like Pseudomonas syringae pv. tomato have developed a unique method to trick guard cells into opening the stomatal pores for them. Dr. Chen explained that the bacteria secrete a chemical very similar to plant hormones, causing the stomata to reopen. This infiltration is known as a stomatal disease, and once inside, they can multiply in intercellular space and damage the plant.

Dr. Chen’s research aims to understand how the environment plays a role in this type of bacterial infection and how to improve stomatal immunity without disturbing other important molecular pathways within the plant.

P. syringae pv. tomato causes dark spots to cover fruit and leaves, spreading quickly to nearby plants. This strain of bacteria is part of the larger Pseudomonas genus, most of which can negatively affect a variety of crops in similar ways.

For most researchers, removing external factors from an experiment clarifies relationships between variables. In the Chen Lab, they are adding these environmental factors back into the equation to get more directly applicable results.

"Traditionally, bacteria are applied to plants in a lab or growth chamber and the plants’ reactions are studied. This is not a whole picture of how infections occur in real life," Dr. Chen stated, noting that environmental impacts are often not considered in this scenario. "An outdoor farm is not a homogenous environment. The temperature, humidity, and other factors are always changing."

Dr. Chen described this interplay between guard cells, pathogens, and environmental factors as the Stomatal Disease Triangle, a holistic take on plant disease research. By adding these external factors back into the equation, the Chen Lab can better understand what and how environmental changes affect the tomato plant and cause different molecular pathways to activate or deactivate within it.

"We want to make our growth conditions as close to the outside environment as possible that plants are actually experiencing. We don’t want to measure just one factor in a sterile, consistent lab environment. We want to know if and how this bacterial infection changes if the plant is experiencing drought or high humidity conditions. It’s a more holistic approach that bridges research labs to the agricultural fields."

Research Collaboration and Dr. Chen’s Students

Dr. Chen stated that some of the biggest sources of pride in his career are being a teacher and helping his fellow researchers achieve their academic goals. As the director of the UF ICBR Proteomics and Mass Spectrometry Facility, he takes great care to assist others with their research problems in medicine, biology, and beyond.

"I find great satisfaction in collaborating with others, especially in regards to utilizing tools like mass spectrometry and other methods of measuring molecules. I’ve trained my whole life for this and want to share that knowledge with others."

With all of his various successes in mind, Dr. Chen is most proud of his students and their growth as researchers and people. He expressed that had he not received his doctorate and become a scientist, he would have been very content being a high school biology teacher.

"After [my students] move on from my classes and lab, they move on to a great career, a great life. My student’s success is my success. They make me really proud."

"We really need to teach our next generation good critical thinking skills. It is so important for the general public to understand. Not only for the sake of applied science in everyday life, but also to appreciate the basic science that we do in our lab and other labs."

Dr. Chen hopes to lay a strong foundation for a big impact in his research fields, noting that while not all projects have major breakthroughs, he is sure some will.

"I hope to really contribute to the future of agriculture. It takes time, you know, maybe one generation, maybe multiple generations, but we are making progress. Through our lab's fundamental research, we are definitely making a difference and increasing our knowledge base for the good of the world’s future." ∎