Researchers identify gene that regulates how plants respond to stress
Maybe you go for a leisurely walk, curl up with a good book, lift weights or reach for some comfort food when you're not feeling well or have had a particularly stressful day. Although there are myriad ways that we all outwardly cope with stressors, one thing is constant: At the cellular level, the stress response is universal across both the animal and plant kingdoms.
Sure, plants may not have a bad day because they failed a test, got a speeding ticket or had a fight with a friend, but the struggle is still real. Plants face biotic stresses from bacterial, fungal, and viral pathogens and abiotic stresses from extreme temperatures, drought or flood, excessive salinity and alterations in exposure to the sun.
Plant cells, like human and animal cells, rely on a complex system of genes and their expression and regulation to mount an appropriate defense or immune response against an external stressor. In a recently published study in Frontiers in Plant Science, researchers from the University of Delaware and Syracuse University have identified a single gene that modulates responses against both biotic and abiotic stress.
"SDA1 is actually a very small gene, but it's critical because it controls both biotic and abiotic responses simultaneously within the plant," said Aditya Dutta, assistant professor in the Department of Animal and Food Sciences. "Reactive oxygen species, or ROS, are critically important in a plant's immune response and they're produced in normal physiological processes. ROS levels increase in response to a stressor and a defense process is launched. Through its remediation of ROS, SDA1 acts as a master regulator. It's a gene that regulates other genes, affecting both the biotic and abiotic response, and making the plant hardier on both fronts."
Dutta began this research during his doctoral work at Syracuse University studying gene expression arrays that tracked gene expression after plant exposure to more than 20 different stressors. One thing that jumped out to him was that SDA1 was induced in almost every instance. Initially, Dutta said he thought that SDA1 might just be a passenger gene or one that doesn't control any particular process.
"But then I started looking into it more and what I saw was that SDA1 was actually interacting with salicylic acid-mediated processes. This is the same hormone that controls a large portion of the biotic response. In fact, salicylic acid is so important in the plant world that it's often sprayed on commercial plants so that they can use it to naturally boost their immune response," said Dutta. "What I found was that not only does SDA1 interact with salicylic acid, but if you remove SDA1 it affects the amount of salicylic acid that a plant can hold. If it can't hold that much salicylic acid, it basically reduces the plant's ability to fight off infection."
Dutta and his fellow researchers also found that SDA1 affected responses to abiotic stressors. For instance, SDA1 impacts the amount of root growth in response to drought. Without appropriate root growth, a plant cannot survive.
Recognizing that SDA1 was a critically important but previously uncategorized gene, the research team looked for genes or proteins with similar functions. Finding no such similarities, they took a closer look at the entire gene sequence to pinpoint what makes this protein so unique. In doing so, they identified a seven amino acid-domain. "When we started looking at this domain, our initial hunch was that it was probably important because it was conserved; but then we went back and we mutated each amino acid, one at a time, to see which ones were important," said Dutta. "We found that you need the entire domain. There is functional relevance for these seven amino acids as this domain is what controls the response against both biotic and abiotic stress."
Most importantly, the team found that this seven amino acid-domain is present in a majority of plants that have been sequenced over time, including commercial crops. This could be a critical discovery as we face increasing pressures caused by climate change.
"Over time, we have started cultivating crops that are super-efficient for the environment that we are in, but things are changing. Temperatures are going up, soil salinity is changing, and more land needs to be irrigated to get the kind of production that you would normally get," said Dutta. "Things that were not a factor even five to 10 years ago are now really important not only for the U.S. market but throughout the world."
Because the SDA1 gene and it's seven amino acid-domain is naturally occurring, scientists could identify cultivars and select for strains of crops that express this gene at high levels. This is different from genetically modified crops as it would not require changing the genes, but simply selecting and propagating the plants that express SDA1 in ways that make them more resistant to stress.
Can we produce hardier crops? Can we make them drought resistant? Can we make them more resistant to bacterial pathogens? With more research forthcoming, Dutta said he believes many of these answers lie with SDA1.
Searching for clues
Dutta, now a poultry researcher in the College of Agriculture and Natural Resources at UD, has experience examining different living models to understand cellular stress, from bacteria to plants and chickens. In addition to enhancing farm productivity, his current work may identify and define drivers of cancers in human reproductive organs.
"Ovarian cancer is not a top-10 cancer for women in terms of incidence or rate of occurrence, but is a top-five cancer in terms of the number of deaths," Dutta said. "One of the problems we face with ovarian cancer is detection. It's not that we can't treat it, but by the time the patient gets to the doctor it's typically in an advanced stage."
Dutta said he started working with chickens to study reproductive health because they develop spontaneous ovarian cancer in the laboratory unlike other animal models, providing insights potentially of benefit to both poultry and humans.
Oxidative stress is one of the biggest contributors to cancer onset. By understanding oxidative stress across both the plant and animal kingdoms, Dutta hopes to be able to make more generalizations across fields and apply gene regulation knowledge to different phenomena.
"This goes back to the idea of One Health and the idea that whatever you learn in one sphere can be applied elsewhere," Dutta said. "A lot of the basic principles stay the same, we're just looking at it in different physiological environments and how it relates to different disease outputs. In every instance, we're learning how cells respond to oxidative stress, and how critical this response is in ensuring good outcomes for both poultry and humans alike."
More information: Aditya Dutta et al. Arabidopsis SMALL DEFENSE-ASSOCIATED PROTEIN 1 Modulates Pathogen Defense and Tolerance to Oxidative Stress, Frontiers in Plant Science (2020). DOI: 10.3389/fpls.2020.00703
Provided by University of Delaware