Science - August 20, 2010

Intelligent mould cuts off defences

It's easy for moulds to infect plants and animals. The moulds discharge a protein that makes fragments of its own cell wall unrecognizable to the immune system. This reported Wageningen phytopathologists and their Japanese colleagues on 20 August in Science.

Moulds penetrate into the leaves, stems and roots of plants, and through the skin, intestines or lungs of animals. As a result, the hosts become sick. The moulds prepare for such an attack in advance. An example is the mould Cladosporium fulvum, the cause of leaf mould in tomatoes. Under normal circumstances, the tomato plant recognizes the mould quickly by the bits of chitin from the cell walls of the mould. The immune system of the tomato plant identifies the chitin bits as 'foreign' and immediately raises the alarm to curb infection.
Invisible
Yet, the mould can still penetrate into the plant by bringing up a secret weapon. This is now made clear under the leadership of Wageningen plant pathologist Bart Thomma. The mould produces the protein Ecp6 which attaches itself to the bits of chitin around the mould. This binding makes chitin invisible to the tomato plant. As a result, the immune system of the plant no longer gets the signals which activate the responses. Experiments carried out by the researchers showed that once the mould stops producing Ecp6, it becomes much less aggressive and has more difficulties in infecting tomato plants.
Health care
The research team encountered the protein Ecp6 when they were measuring signal substances in a tomato leaf. 'We were then struck by the high concentration of this protein', says Thomma. The Wageningers then contacted the Japanese group which discovered the receptor in plants for chitin earlier on.
Moulds in humans and animals have the protein Epc6 too, and they probably suppress the immune system of their hosts in this way. Therefore, this knowledge is not only important for disease control in agriculture, but also in human health care.
Receptor
Thomma will now search for receptors which can recognize the protein Ecp6. 'This protein can be found in almost all moulds. I hope that using such a receptor, we can find a sustainable resistance against mould diseases.' The alternative is to develop a pesticide which makes the protein harmless, so that hosts can recognize the chitin of harmful moulds and activate their immune systems.