Fungus covers fragments of its own cell wall to avoid plant defences

July 3, 2013
Fungi can make themselves invisible to the defence system of plants by producing a protein (blue & green) that encloses chunks of chitin, originating from the fungus cell wall (red).

Many fungi can make themselves invisible to the immune system of plants. Scientists from Wageningen University have discovered that the tomato fungus Cladosporium manages this by enclosing chunks of chitin originating from its own cell wall in a protein it specifically produces for this purpose. This prevents the tomato plant from sensing that it is being attacked by the fungus, which has free rein to infect the plant.

Back in 2010, scientists at Wageningen University, part of Wageningen UR, learned that the Cladosporium produces a compound– the so-called Ecp6 protein – which makes it invisible to the of plants. The immune systems of use special compounds to destroy invading micro-organisms such as fungi. For instance, the immune system uses chitinases, enzymes that can dissolve the cell walls of fungi, to combat . This process releases pieces of , that allow plants to sense the presence of an intruder, and to reinforce the immune response. The fungal Ecp6 protein binds to these chitin pieces. "The protein from the fungus seeks out these pieces of chitin and adheres to them," Professor Bart Thomma explains. "This hides the chitin particles from the tomato plant the same way that a stealth aircraft is invisible to radar. The immune system of the therefore no longer receives the signal to ramp up its activity, allowing the fungus to infect the plant without being noticed."

Andrea Sánchez-Vallet, a scientist in Bart Thomma's team, worked together with crystallographers at the University of Lübeck, Germany, to find out how exactly this process works. They already knew that plants can detect pathogens through immune receptors. Certain domains within these receptors, the so-called LysM domains, are able to bind to chunks of chitin from , generating the signal that an intruder came in.

Normally the receptor of the plant (blue & green) binds to chitin particles of the fungus' celwall (red), which enables the plant to recognise the fungus and to defend itself.

The Ecp6 protein of the fungus was found to also have such LysM domains. Moreover, the immune receptors of the plant and the Ecp6 protein of the fungus actually contain the same number of LysM domains. The two proteins are competitors in the 'capturing' of chitin particles. Given the equal number of binding sites, it seemed quite unlikely that the protein from the fungus would always win over the immune of the plant in the race to bind to the released chitin particles. So how do they do it?

"We discovered that the 3D structure of the Ecp6 protein allows two LysM domains from the fungal protein to work together to bind chitin on two sides," Thomma says. "The fungal protein literally latches onto the pieces of chitin in a sandwich construction. This way the bond is stronger and faster, and the plant can simply no longer reach the chitin particles, as they are quickly tucked away deep in the Ecp6 protein. Furthermore, the chitin was found to be bound so strongly to the Ecp6 protein that the plant gets no chance to liberate it, completely preventing the plant from perceiving it."

The scientists will publish their discovery in the scientific journal e-Life; the new open access journal for outstanding research in life sciences and biomedicine, founded by the Howard Hughes Medical Institute, the Max Planck Society, en the Wellcome Trust. The study was partly funded by a Young Visiting Scientist Stipend awarded by the Netherlands Genomics Initiative (NGI).

Explore further: Smart fungus disarms plant, animal and human immunity

More information:

Related Stories

Smart fungus disarms plant, animal and human immunity

August 20, 2010

Fungal and bacterial pathogens are well capable of infecting plants, animals and humans despite their immune systems. Fungi penetrate leafs, stalks and roots, or skin, intestines and lungs, to infect their hosts.

Great mystery of a plant defence pathway unravelled

June 3, 2013

( —Together with several partners, scientists from Wageningen UR (University & Research centre) have discovered that RLP-receptors located at the outside of plant cells and playing an important role in plant defence, ...

Plants recognise pathogenic and beneficial microorganisms

November 1, 2012

Plant roots are surrounded by thousands of bacteria and fungi living in the soil and on the root surface. To survive in this diverse environment, plants employ sophisticated detection systems to distinguish pathogenic microorganisms ...

Pharmaceuticals from crab shells

February 13, 2012

The pharmaceutical NANA is 50 times more expensive than gold. Now it can be produced from chitin - a very cheap natural resource. The process was made possible by genetically modifying mold fungi.

Tomato stands firm in face of fungus

May 9, 2008

Scientists at the University of Amsterdam have discovered how to keep one’s tomatoes from wilting – the answer lies at the molecular level. The story of how the plant beat the pathogen, and what it means for combating ...

Tomato gene may fend banana against formidable fungus

April 13, 2010

( -- Proteins from the fungus Cladosporium fulvum, which causes leaf blight in tomato plants, are very similar to the proteins of the fungus Mycosphaerella fijiensis, which causes the much-feared black Sigatoka ...

Recommended for you

Mammal long thought extinct in Australia resurfaces

December 15, 2017

A crest-tailed mulgara, a small carnivorous marsupial known only from fossilised bone fragments and presumed extinct in NSW for more than century, has been discovered in Sturt National Park north-west of Tibooburra.

Finding a lethal parasite's vulnerabilities

December 15, 2017

An estimated 100 million people around the world are infected with Strongyloides stercoralis, a parasitic nematode, yet it's likely that many don't know it. The infection can persist for years, usually only causing mild symptoms. ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.