Plants, the climate crisis is destroying their immune systems

Plants, the climate crisis is destroying their immune systems


Of all the weeds, Arabidopsis thaliana is a rather fascinating specimen. On a spring day, it can be seen peeking out from the cracks of a parking lot, releasing a small riot of white flowers. However, the round leaves of this plant often have unwelcome guests: among them, a bacterium called Pseudomonas syringae. The bacterium is looking for an access route to the plant, usually the stomata through which the leaf absorbs water and carbon dioxide (CO 2), or through a crack. This is where things get interesting.

Typically, the first warning of invasion comes from receptors that tell plant cells to unleash their defenses. Among the most important is a hormone called salicylic acid, used to keep infections at bay, as well as from arabidopsis, also from many other plants, including major crops. But imagine that this spring day is unusually warm. After a few days of heat wave, you will notice that the leaves of the plant become more and more yellow and withered. His immune system doesn't seem to work anymore.

Restoring plant immunity

For much of the past decade, Duke University plant biologist Sheng-Yang He has been studying why the plant's immune system shuts down to work in the heat. This is a molecular mystery involving the unpacking of dozens of genes in an attempt to understand why plants can no longer produce important chemicals, such as salicylic acid, when temperatures rise a few degrees. It is the type of dysfunction that is predicted to become much more common for all types of plants as the climate changes and heat waves become more intense and frequent. In an article published in Nature, He's team describes how this immunity can be restored. There is no single way climate change will affect plants. In some cases, increased heat and CO 2 levels could speed up photosynthesis, causing plants to grow faster. In other cases, however, they may shrivel and die from overheating stress. The geography of climate change will also vary greatly, causing crippling drought in some places, while other ecosystems are doomed to drown. In general, such rapid change is not good for organisms that are unable to move quickly to new habitats, as animals do. And just as more diseases are predicted to spread among humans due to the widening range of pests and pathogens in an increasingly hot world, plants will also face new or more aggressive pestilences within the world. their native ecosystems or farmland. Recently a separate study published by researchers from the Chinese University of Hong Kong predicted that global harvests could decline by 20 percent by 2050 due to the effects of climate change.

But a surprising effect of heat is that changes also occur within the immune system of the plants themselves. Plants lack so-called adaptive immunity, like cells found in animals that learn from encountering a new microbial enemy and are ready to spring into action when they confront it again. But they have a whole arsenal of other defenses at their disposal. Any chemical response, such as the production of salicylic acid, depends on the action of many genes that translate various proteins into others. While these steps work well in a plant's usual environment, a hitch in the process caused by an external factor like heat can derail everything. "We are talking about millions of years of evolution - explains He, who is also a researcher at the Howard Hughes Medical Institute -. The last 150 years have drastically changed things, and man is responsible".

He grew up in a farming community in eastern China, where he remembers the smell of pesticides that lingered in the air during the growing season. In elementary school, he and other children formed a "pest control team" in the fields, which tore caterpillars from cotton plants. In the lab today, much of his job is to do just the opposite: inoculate plants with disease-causing bacteria. Its goal is to study the effects of increasing or decreasing the expression of specific plant genes, looking for changes that signal their role in immune responses.

The perfect guinea pig

Much of this work has been done on Arabidopsis thaliana, which due to its resistance is also known as "the laboratory mouse of plants". There are some elements that make this species a perfect guinea pig. One of these is that its genome is relatively short, one of the reasons that led it to be the first fully sequenced plant. Another is the unique way its code can be changed. For most plants, the process is painstaking. The new genetic material is introduced into a Petri dish, carried by bacteria that infiltrate the plant's cells. Once this is done, the modified cells must be grown and pushed to form new roots and stems. But arabidopsis offers a shortcut. Biologists only need to soak the plant's flowers in a solution full of gene-carrying bacteria and the messages will be taken directly to the seeds, which can simply be planted. In the field of botany, which has always been very slow, this method proceeds at the speed of light.

However, it took years to understand what all those genes that produce salicylic acid did under perfect greenhouse conditions. Only then could He's team begin tampering with the environment to see what goes wrong. Their goal was to find one or more genes that controlled any phase that blocked salicylic acid production when it gets too hot. It took ten years to find the answer. The researchers modified one gene after another, infecting plants and observing their effects. But whatever they did, the plants kept wilting from the disease: "You can't imagine how many failed experiments we ran," he says.

Eventually the lab found a winner. The Cbp60g gene appeared to act as a "master switch" for a number of steps involved in the production of salicylic acid. The process leading to genetic instructions and the production of a protein was hampered by an intermediate molecular step. The key was to get around it. The researchers found it was possible to do this by introducing a new piece of code that would have forced the plant to transcribe Cbp60g and restore the salicylic acid assembly line. There was also another apparent benefit: the modification also appeared to help restore lesser known disease resistance genes that were suppressed by heat.

Corrections and 'manipulations' The team began testing the gene modifications on food crops such as rapeseed, a close relative of arabidopsis. Beyond the genetic similarities, canola is a good plant to work on, He says, as it grows in cold climates where it is more likely to be affected by rising temperatures. So far the team has managed to reactivate the immune response in the laboratory, but has yet to perform field tests. Other potential candidates are wheat, soybeans, and potatoes.

Unsurprisingly, He's genetic correction can work in many plants, points out Marc Nishimura, a plant immunity expert at Colorado State University, who has no participated in the research. But it is only one of many climate-susceptible immune pathways that biologists must explore. And there are other variables besides heat waves that can affect plant immunity, such as rising humidity or sustained heat that lasts throughout the growing season. "It might not be the perfect solution for every plant, but it gives us a general idea of ​​what's wrong and how it can be fixed," adds Nishimura.

But for this to work, consumers will have to accept more genetic manipulations to their foods. The alternative, Nishimura explains, is greater crop losses and an increase in pesticides to remedy the problem. "As climate change accelerates we will be forced to learn things in the laboratory and move them to the field faster. I don't see how we can do this without accepting more genetically modified plants."

This article originally appeared on US.

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