EU-funded scientists sequence fungal disease genome

EU-funded researchers have sequenced the genome of a major fungal disease that affects various cereal crops including barley. Presented in the journal Science, the research could help bolster our understanding of the evolution of plants. The study was funded in part by the BIOEXPLOIT (‘Exploitation of natural plant biodiversity for the pesticide-free production of food’) project, which is backed with almost EUR 16 million under the ‘Food quality and safety’ Thematic area of the EU’s Sixth Framework Programme (FP6).

The researchers, led by Imperial College London (ICL) in the UK, say their study helps shed light on how parasites within the genome of the fungus facilitate a disease’s adaption and fight against a plant’s defences.

They add that new agricultural techniques can be developed, making it easier to keep infection at bay and sustain the health of cereal crops. Ensuring that plants stay free from disease is also a mega step towards securing food in our planet.

The team decoded the genome of Blumeria, which causes powdery mildew on barley. This mildew impacts many cereal crops, fruits and vegetables in northern Europe. Plants that fall victim to this mildew become covered in powdery white spots that spread all over the leaves and stems. So plants cannot produce crops, which in turn affects the overall agricultural output.

Farmers use several methods to stop the mildew from surfacing, namely fungicides, crop rotation and genetically resistant varieties. The problem, however, is that the fungi evolve much too fast for the techniques to work. The mildew evolves quickly because multiple parasites within the genome, so-called transposons, help it to conceal itself and act without setting any warning bells off. The host plant is ‘confused’ since the target molecules used by the plant to detect the onset of disease are altered.

According to the team, they found many large numbers of transposons within Blumeria. ‘It was a big surprise,’ says Dr Pietro D. Spanu from the Department of Life Sciences at ICL, the lead author of the study, ‘as a genome normally tries to keep its transposons under control. But in these genomes, one of the controls has been lifted. We think it might be an adaptive advantage for them to have these genomic parasites, as it allows the pathogens to respond more rapidly to the plant’s evolution and defeat the immune system.’

The results of this study will give scientists the boost they need to design new fungicides and resistance in food crops, particularly because they provide insight into how the mildew can adapt so quickly. ‘With this knowledge of the genome we can now rapidly identify which genes have mutated, and then can select plant varieties that are more resistant,’ Dr Spanu explains.

They could also monitor the spread and evolution of fungicide resistance in an emerging epidemic, according to the team. ‘We’ll be able to develop more efficient ways to monitor and understand the emergence of resistance, and ultimately to design more effective and durable control measures,’ Dr Spanu adds.

The researchers say mildew pathogens are a type of ‘obligate’ parasite, which means they cannot live freely in the soil and need their plant hosts to ensure their survival. This dependency forced the pathogens to figure out a way to disguise themselves and shoot down the plant’s defences.

‘We’ve now found this happening in lots of fungi and fungal-like organisms that are obligate pathogens,’ says Dr Spanu, adding that the costly genome inflation could therefore be a trade-off that makes these pathogens successful. ‘Non-obligate pathogens are not so dependent on their hosts, as they can live elsewhere, so they are less dependent on rapid evolution.’

Researchers from Germany and France contributed to this study.

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