Solving a global wheat problem

Publication date
Friday, 20 Apr 2012

This particular fungus requires a dead or dying host: it needs to kill the host and then feed off the nutrients from the dying cells

Dr Peter Solomon from the Research School of Biology is studying a fungal disease that decimates $100 million worth of Australian wheat every year. With the global population set to boom (an extra 2.2 billion inhabitants are expected by 2050), the battle to beat crop disease is becoming urgent. Until recently, this fungal pathogen, Stagonospora nodorum, was considered pretty simplistic, but thanks to Solomon we now know some of the clever tricks it uses to manipulate its wheat host.

"This particular fungus requires a dead or dying host: it needs to kill the host and then feed off the nutrients from the dying cells," Solomon explains. Once the fungus has infiltrated the leaf, it deploys a battery of proteins known as ‘effectors’. These effectors trick the plant into killing off the infected appendage, providing the fungus with a nutritious, composted food source. There is, however, more to the story. The only way the invaders can trigger the plant’s death response is by interacting with a corresponding plant protein known as a ‘host susceptibility protein’. If the plant does not have this protein, disease does not occur.

This knowledge has led to important practical applications. Solomon now supplies commercial wheat breeders with purified effector protein to identify and exclude susceptible plants. "By infiltrating the effectors into their breeding lines, they can identify the lines that are susceptible to disease and remove them. It’s being seen as a very significant success," he says.

Intriguingly, these host susceptibility proteins seem to have no other function than to betray the plant by fraternising with the enemy. In an evolutionary sense, this is completely counterintuitive, says Solomon. The explanation may lie in the fact that other fungal wheat pathogens require their host to be alive.

"One way that plants have evolved resistance to pathogens that require a living host is to kill the infected area, depriving the pathogen of the [living] nutrients," according to Solomon. Hence, what are now considered susceptibility proteins may once have provided the plant with resistance to other fungi.

"Stagonospora nodorum has hijacked these proteins and said to the host ‘Well, here I am, go and kill yourself’. The host does, thinking ‘Ha, I’ve got you’ and the fungus thinks, ‘No, dead tissue is exactly what I want’," explains Solomon. "We’re working on this theory at the moment and evidence is starting to stack up that this might be the case."