Researchers from Virginia Tech have identified the mechanism several important microbial pathogens use to infect plants and cause devastating diseases. The study, published in the July 23, 2010, issue of Cell, also provides insights into how some microbes cause diseases in humans and animals.
The identified mechanism is used by fungi and oomycetes (microbes related to algae), including the kind of fungi that are causing wheat rust epidemics in Africa and Asia, and by oomycete pathogens that caused the Irish potato famine of the 19th century and continue to cause crop losses for producers today.
“Our findings suggest broad, new strategies for combating the most damaging diseases of the world’s major crop foods, including wheat, rice, maize and potatoes, as well as several nasty human diseases,” said Brett Tyler of Virginia Tech’s Virginia Bioinformatics Institute and leader of the study.
The study, which was funded by USDA’s National Institute of Food and Agriculture (NIFA) and the National Science Foundation, shows that once a fungus or an oomycete comes into contact with a host, it may initiate an infection by secreting special proteins, called effectors, that have the ability to enter and reprogram the host’s cells. Each of these effectors consists of a long chain of amino acids designed to disable a host cell’s immune system. But a small stretch of the amino acid chain, which contains four particular amino acids, binds to a specific type of lipid; this lipid is a fat-like molecule that is part of the membrane surrounding the host cell.
When the identified four amino acids in the effector’s protein chain binds to the lipid on the host cell’s membrane, it acts like a key that opens a locked door, unlocking the membrane to the invading effector. Once unlocked, the cell extends itself to engulf and absorb the effector.
Previously, scientists were only aware of how effectors of bacteria were able to enter plant cells, which they did through a needle-like structure produced by the bacteria that punctured the host cell’s membrane . The Tyler Team made two surprising discoveries: 1) the existence of the binding lipid (called PI3P) on host cell surfaces and 2) the ability of the microbial effectors to use the binding lipid to invade host cells. Also surprising were:
- The novelty and simplicity of the mechanism used by fungi and oomycetes to insert their effectors into host cells.
- The discovery that fungi and oomycetes use the same binding mechanism to introduce effectors into plant cells, even though these two classes of microbes are evolutionarily distinct from one another.
- The presence of an abundance of the binding lipids on the surfaces of plant cells as well as animal cells, including some human cells. This discovery suggests that fungal and oomycete effectors might also enter animal and human cells through the same newly-discovered method they use in plants. Thus this phenomenon may, in fact, be an attack mechanism common to fungal and oomycete diseases of plants, animals and humans.
This research demonstrated the possibility that fungal and oomycete effectors could be blocked from entering the host cells by preventing them from attaching to binding lipids. Further research will be needed to exploit this information to develop therapies for fighting diseases caused by fungi and oomycetes.
Through federal funding and leadership for research, education and extension programs, NIFA focuses on investing in science and solving critical issues impacting people's daily lives and the nation’s future. For more information, visit www.nifa.usda.gov.
