Researchers are working on isolating plant
molecules which naturally defend against
fungal disease.
Image: iStockphoto

With fungus and mould still very significant bogeymen, success in combating their handiwork could make an extremely valuable contribution to the quality and economics of the world’s food supply and health care.

Two La Trobe University scientists, Marilyn Anderson and Kim Plummer, are working towards that objective, leading a range of broadly-based research – as well as tackling the problem at the sharp end, by targeting some very specific molecules to protect plants against fungal disease.

Work on a protein discovered in Professor Anderson’s laboratory has the potential to control a broad-spectrum of fungal pathogens and is already well advanced, as the researchers explained nationally on a recent edition of the ABC radio flagship science program The Science Show.

While many biochemists check their results in a test tube or under a microscope, Professor Anderson and her colleague Dr Robyn Heath at the University of Melbourne have been able to survey their results from an aircraft.

‘As a spin-off from our work we have formed a biotechnology company called Hexima,’ she told Science Show presenter Robyn Williams. ‘We’ve had three years of field trials with transgenic cotton. I shouldn’t say that we were surprised, but we were; we could see an effect.

‘It’s the first time we’ve ever done an experiment where we could look at results from the air, and we saw protection. We’re still working on it, but we’re very encouraged.

‘Hexima has also started a new project in collaboration with Pioneer DuPont to try to make corn more fungal resistant, and that’s a very valuable crop worldwide,’ she said.

Professor Anderson said her work with Dr Plummer, a highly trained fungal plant pathologist, involves naturally occurring plant molecules that protect plants against fungal disease. They are derived from flowers which use them to protect against infection in order to produce seeds for the next generation.

‘We found flowers were very rich in natural antibiotics, went ahead to try and isolate these molecules – and discovered one that was really very effective.’

Using Dr Plummer’s expertise in how plants interact with fungus, Professor Anderson’s lab is trying to understand how these molecules work and exactly how they kill fungus.

Examining different mechanisms

Says Dr Plummer: ‘The majority of the fungi that have been looked at so far have been found to be killed by this molecule, and we’re examining various different mechanisms to dissect the interaction leading to this result.

‘One of Marilyn’s students, Nicole van der Weerden, has done some nice work in looking at biochemically treating fungi to work out what the molecules from the plant bind to on the fungal surface.’

‘And we’ve had other students working on being able to biochemically treat and look at different layers of where the protein might bind.’

As part of an ARC Discovery grant project, Dr Plummer and postdoctoral researcher, La Trobe graduate Dr Peter Dracatos, are assisting Professor Anderson’s group by modifying the genetics of the particular fungus.

‘We aim to get at the genes involved with the structures that the plant proteins attack, and then try and dissect how those proteins are getting in and how the whole thing works.’ But Professor Anderson’s efforts are not restricted to this anti-fungal molecule.

‘We’re also looking at other naturally occurring plant molecules that are toxic to fungi, and trying to find ones that work by different mechanisms. The ultimate aim is to use combinations of molecules so that if a fungus becomes resistant to one, it will still be aff ected by another.

Plant pathogens, including fungi, as Robyn Williams pointed out, have changed the course of history. Take the Irish potato famine; and they’re still a threat to countless crops, from wine making to third-world food staples. However, Professor Anderson said it was hard to quantify losses.

‘These vary from year to year. In good seasons maybe twenty per cent of the crop. Other years you might lose the entire crop, and that’s especially devastating.

‘That’s especially true for small crops where there hasn’t been the same amount of research into developing the ideal chemical, or organic crops only dependent on copper which doesn’t always hold the fungus.’

Some fungi, says Dr Plummer, require a host, and many have developed survival structures so that they can live in the soil for 15 or more years. Often they are the most difficult to control. Another major issue is how specific they are in terms of the plants that they will infect.

‘One of the pathogens that I work with, sclerotinia, produces resting structures that survive in the soil for many years, and it can infect just about every broad-leafed crop species that we grow.

‘Many broad-leafed fruit and vegetables and crops such as canola are susceptible to sclerotinia, so because this one species of fungus can attack many different hosts and devastate many diff erent crop species, it’s quite hard to understand how it works. Therefore any kind of control useful for one crop could have many different applications for other crops as well. Another pathogen I work on only infects apples.’