Gall-forming plant pathogens produce high numbers of organism-specific effector proteins that help infiltrate the plant’s immune defenses. Image credit: Edel Pérez-López (CC BY 4.0)
Microbes can cause a variety of plant diseases and pose a major threat to global food production. To infect plants, many of these microbes release small proteins called effectors. Once inside the plant cell, the effectors can disarm the plant's immune defences and also reprogram its growth. In some cases, they trigger abnormal swellings called galls, which can seriously reduce harvests, such as the clubroot disease of canola, caused by the protist Plasmodiophora brassicae.
Effectors produced by gall-forming microbes remain poorly understood because these pathogens are hard to grow in the laboratory, and many of their proteins have no known function. Mukhopadhyay et al. provide new insights into how gall-forming microbes infect plants and how their effectors have evolved using artificial intelligence tools, such as AlphaFold. These tools can predict the three-dimensional structures of proteins, allowing researchers to look beyond gene sequences and uncover hidden patterns in protein shapes.
To explore the molecular strategies used by different gall-forming organisms to infect plants, the researchers studied the three-dimensional structure and properties of thousands of secreted proteins from fungi, protists and oomycetes.
The results showed that each group showed unique expansions – that is, unusually large numbers – of particular effector families. For example, the clubroot pathogen had expanded families of ankyrin-repeat proteins, a class of proteins characterized by repeating structural motifs that mediate protein-protein interactions. They also discovered clusters of proteins that shared similar shapes despite having little or no genetic similarity, highlighting that protein structure can be more conserved than genetic sequence. Notably, one ankyrin-repeat protein was found to interact with central components of plant immunity, suggesting a direct role in disabling host defenses. Together, these findings provide the first structural map of effectors in gall-forming microbes.
By understanding how effectors work, researchers can identify plant genes that confer stronger resistance to pathogens such as the clubroot microbe. While more experiments are needed to confirm the roles of effectors in plants, this structural resource already offers a powerful tool for scientists. It could help predict which microbial proteins are most likely to manipulate plant health and guide the development of durable crop protection strategies.
