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food of the gods?
04-01-2010, 11:47 PM,
food of the gods?
Fungi can transfer chromosomes
Wednesday, 31 March 2010

by Julianna Kadar
Cosmos Online

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Credit: iStockphoto

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SYDNEY: Some species of crop-destroying fungi, in the genus Fusarium, can transfer two of their four chromosomes into other harmless fungi, transforming them into destructive pathogens.

The Fusarium genus of fungi contains over 20 species and is responsible for billions of dollars in damage to crops such as wheat, corn, bananas and tomatoes in Australia and around the world.

"By discovering more about the aggressive nature of these pathogens we can develop ways to protect our agricultural products," said plant pathologist Kemal Kazan, from the CSIRO Institute in Brisbane, one of the authors on the study published in Nature.

"Holy Grail" of plant pathology research

One species of Fusarium graminearum, which is harmful to wheat and barley, and effects both the malting and brewing industries. Other crops such as bananas, tomatoes and cotton are under risk from Fusarium oxysporum.

Some species of Fusarium are harmless or non-pathogenic and cannot overtake agricultural crops, explained Kazan, but these fungi are at risk of becoming counterparts if they come into contact with one another.

"Understanding how fungi are able to adapt and define themselves to be plant pathogens is considered the Holy Grail of this research," said Brett Summerell, director of conservation and horticultural research at Botanic Gardens Trust in Sydney, who did not take part in the study.

Evolving nature of the pathogenic fungi

"It is possible, that in the absence of certain types of food they undergo types of evolutionary changes to expand their host range," said Kazan.

The international consortium that Kazan was a part of wanted to know why the different pathogens are specialised in different plant species. "We thought one way of answering questions is to sequence genomes of different Fusarium species," he said.

The researchers compared the genomic sequences and were able to deduce that horizontal gene transfer took place, which has only been seen on rare occasions in some eukaryotes.

However, such a large transfer of the genome that is meant to target a certain host has never been recorded before.

The chromosome transfer was observed by putting non-pathogenic and pathogenic tomato-attacking strain in a plate. Through this process researchers could deduce that pathogenic fungi could transfer lineage to non-pathogenic fungi.

They could prove that the non-pathogenic strain became pathogenic because when released upon tomato plants, the originally non-pathogenic fungi started causing disease, Kazan explained.

A bigger problem for plant industries

"These findings will probably open up some opportunities for the development of technology within plants which enhances their ability to fight the diseases," said Summerell.

However, with this new knowledge, the non-pathogenic fungi are revealed to be a larger threat because of their adaptive nature.

"If these fungi pick up the strain they can create a bigger problem for plant industries," said Kazan. The originally non-pathogenic fungi could be better adapted to some environments and will be even more difficult to kill if they become pathogenic.

A new, more virulent strain

Through the increase in virulence of the new strain, a more incessant fungus could emerge which presents more problems because of its ability to survive longer.

"Some fungi can survive for 10 to 15 years in soil and are transmittable through irrigation soil, making them quite persistent and problematic pathogens," said Kazan.

Consequently, even through understanding the methods that the Fusarium uses, it is not easy to devise a strategy to inhibit it. If the plants are changed to become more resistant to the fungi, the pathogen will undergo changes to stay there and compete.

"It is an evolutionary arms race between plants and pathogens and minimising the damage is the main idea," said Kazan.

Summerell believes the next step is looking to see if the same process occurs in other strains of Fusarium oxysporum or if it is just unique to this strain of Fusarium. "It would be interesting to know the actual process of how genes get from one fungus to another fungus," he said.

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