Researchers at the University of Washington have found that defence mechanisms that plants use to protect themselves from pests like caterpillars arise from a single gene that has evolved over the years. They have found that some plants, such as soybeans, have lost this protective gene over time which results to crop failure. However, genetically reinducing this gene might help.
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How do plants defend themselves?
The health status and defence system of plants depend on the immune system it inherits from their parent plants. Here, inheriting refers to getting specific types of pattern-recognition receptors that can identify pathogens or pests and trigger a suitable immune response.
“Inheriting the right types of pattern recognition receptors can allow plants to recognize threats and cope with diseases and pests,” said Simon Snoeck, lead study author. “Although we know many pest-derived molecules which activate immune responses in plants, our knowledge of how plants evolved the ability to sense new threats is limited.”
The team tried to find the evolutionary events that helped plants to respond to common pests like caterpillars. They already knew that some legume species, such as black-eyed peas and mung beans, can uniquely respond to secretions or peptides released by caterpillars as they munch through the leaves. So they studied the genomes or DNA of these plants to know if a common pattern recognition receptor Inceptin Receptor (INR), had evolved over millions of years or still possessed the ability to recognize caterpillars. They found a 28-million-year-old single gene responds well to the caterpillar peptides. However, in the descendants of the old plant species in which the gene was first evolved, some species couldn’t respond to the peptides and lost the gene.
How could a 28-million-year-old gene recognize new peptides?
As evolution is happening fast, it was curious to know how a 28-million-year-old gene could recognize new peptides from today’s pathogens. Therefore, the researchers used a modern technique called ancestral sequence reconstruction. They combined information from the upgraded versions of genes to predict the ancestral gene’s sequence. This ancestral gene was able to respond to caterpillar peptides. However, its older mutated version couldn’t respond. The combination of genetic history and computer models highlighting how ancestral and current receptors may differ provide evidence of how receptors evolved. It proposes that there was an insertion of a new gene into the ancestral plant genome more than 32 million years ago, followed by the continuous evolution of different forms of new receptors. One of these forms acquired a tendency to respond to caterpillar peptides and is now shared in multiple descendants of legume species.
“We have identified the emergence and secondary loss of a key immunity trait over plant evolution,” said Adam Steinbrenner, said study’s co-author. “In the future, we hope to learn more about genome-level processes that generate new receptor diversity and identify as-yet unknown immune receptors within plant groups. As increasing genomic data becomes available, such approaches will identify ‘missing’ receptors that are useful traits to reintroduce into plants to help protect crops.”
The research was published in the journal eLife.