Just like humans, plants get sick. They can be infected by parasites as diverse as fungi, bacteria, viruses, nematode worms and insects.
Also like humans, plants have an immune system that helps them defend against disease.
Their first line of defence are disease resistance genes. Many of these genes encode immune receptors, which are proteins that detect parasites and kick-off the immune response.
Plant genomes may encode anywhere between 50 and 1000 immune receptors; some of which work solo as singletons, while others operate in pairs or as complex networks.
Understanding how immune receptor genes have evolved would give fundamental knowledge about how they work, which in turn would set the stage for researchers to be able to use them to protect agricultural crops from disease.
One driving force behind the evolution of many genes is gene duplication. Genes duplicate and afterwards the two copies can evolve in different ways. The original immune receptors are multi-tasking proteins that both detect parasites and trigger the immune response.
Following gene duplication, evolution has led to some immune receptors becoming dedicated to detection and losing the ability to trigger a defence response on their own.
Now, researchers at The Sainsbury Laboratory and the University of East Anglia have discovered a molecular signature – named the MADA motif – that defines the subset of immune receptors that can trigger the immune response in plants. This motif is made of just 21 amino acids (the building blocks of proteins) at one end of the receptor and, remarkably, a short fragment of the protein containing this motif is enough to trigger a defence response when produced in plants.
In contrast, the immune receptors that have specialised to only detect parasites have lost this molecular signature throughout evolution, presumably because they do not need it as they rely on their receptor partners to trigger defences instead.
Every year, billions of dollars’ worth of food is lost to plant diseases. These new findings will enable the research community to classify disease resistance genes into categories to help deduce the network architecture of the plant immune system.
A better understanding of this, and how networks of plant immune receptors evolve, should set the stage for breeding crop plants that are more able to resist diseases.
- The article: 'N-terminal motif in NLR immune receptors is functionally conserved across distantly related plant species', is in eLife