A team of scientists from The Australian National University (ANU) has discovered how a powerful "weapon" used by many fungal pathogens enables them to cause disease in major food crops such as rice and corn. Published in Science, this breakthrough may offer new strategies to safeguard global food security.
The researchers found that a diverse group of plant fungal pathogens relies on an enzyme, NUDIX hydrolase, to infect their hosts. First author Dr. Carl McCombe, who conducted the experiments during his PhD at ANU, teamed up with collaborators at ANSTO to use the Macromolecular Crystallography beamline at the Australian Synchrotron, to reveal the enzyme's structure in detail.
"Understanding what the enzyme looks like gave us critical insights into how it used by pathogens to attack plants," said Dr McCombe. "We discovered that it specifically targets and breaks down a key signaling molecule called PP-INP, which helps plant cells monitor their phosphate levels."
Phosphate is a vital nutrient for plants and humans, acting as a building block for DNA, cell membranes, and molecules that store and transfer energy. When phosphate is scarce, plants typically form beneficial partnerships with microbes to boost their phosphate supply.
However, as Associate Professor Simon Williams, who led the ANU research team, explained, "To establish these beneficial associations, plants appear to lower their immune defenses. Disease-causing fungi exploit this process by hijacking the phosphate-sensing pathway, which is crucial for their ability to cause infection."
The large-scale study was conducted through crucial collaborations with researchers from RWTH Aachen University in Germany and Louisiana State University in the United States, highlighting the global importance of these findings.
"Much of our work focused on the pathogenic fungus Magnaporthe oryzae, which causes rice blast disease," said Associate Professor Williams. "Rice is a staple food for over half of the world's population, and crop losses from this disease could feed around 60 million people. We also showed that fungi in the Colletotrichum genus, which infect crops like melons, corn, and chickpeas, use the same enzymatic weapon."
"By revealing how these fungal pathogens use NUDIX hydrolases to manipulate phosphate signaling, we now have a roadmap to develop new disease management strategies," Dr. McCombe added.
"This could involve engineering the plant immune system to detect the weapon or block its function-effectively turbocharging the plant's response to these pathogens, helping support our farmers to secure our global food supplies."
Beamline scientist Dr Daniel Eriksson has a long standing collaboration with the ANU team, which included a previous paper also in Science in 2014 on the Structural basis for assembly and function of a heterodimeric plant immune receptor.
"Many are unaware that plants have an immune system. The relationship between plants and pathogens is an ancient struggle. We're now looking at a system that has been evolving over a very long time and we have been trying to piece together what is going on here. The mechanism is not a new thing. It's just that we are starting to finally understand how it works," explained Dr Eriksson.
"We're talking about form and function which on the molecular scale is basically the same thing. So, understanding what something looks like at atomic resolution tells you something about how it functions."
A suite of instruments at the Australian Synchrotron, the MX beamlines, allow scientists across Australasia to determine the fine structure of molecules using a technique called crystallography.
"Developing these instruments as well as training researchers in the handling and measurement of challenging samples is part of the service," he added,
Dr Carl McCombe was the recipient of an Australian Institute of Nuclear Science and Engineering (AINSE) Postgraduate Research Award..
