Dr. Michael Marletta
Could a simple spray be developed to block a pathogen from entering the leaves of rice plants, thereby preventing blast disease – one of the world’s most devastating cereal diseases – from destroying between 10 and 35 percent of the world’s rice harvest every year?
That’s the goal of Dr. Michael Marletta, a ‘73 SUNY Fredonia graduate and Professor of Chemistry and Molecular and Cell Biology at the University of California, Berkeley, who’s leading a team of biochemists and chemists in that mission. They identified a fungus that secretes an enzyme that punches holes in the outer layer of rice leaves, so once inside, the fungus grows rapidly and inevitably kills every plant that it touches.
How the enzyme works to help the fungus invade plants was described in great detail in a paper by Dr. Marletta and his associates that was recently published in the journal Proceedings of the National Academy of Sciences. Marletta, the Choh Hao and Annie Li Chair in Molecular Biology of Diseases at UC Berkeley, reasoned that because the enzyme is secreted onto the surface of the rice leaves, perhaps a simple spray could effectively destroy the enzyme’s ability to digest the wall of the plant.
It’s estimated that an additional 60 million people could be fed if this fungus could be knocked out, Marletta noted. “This enzyme is a unique target. Our hope here is that we’ll screen to find some unique chemicals and spin out a company to develop inhibitors for this enzyme,” he said.
Marletta’s team is targeting a family of enzymes called polysaccharide monooxygenases (PMOs) that he and his UC Berkeley colleagues discovered more than 10 years ago. Polysaccharides are sugar polymers that include starch as well as the tough fibers that make plants sturdy, including cellulose. PMO enzymes break cellulose into smaller pieces, making the polysaccharide susceptible to other enzymes, such as cellulases, and speeding up the breakdown of plant fibers. The PMO in the rice blast fungus that Marletta discovered has a specialized function that is to make a very specific cut in the polysaccharide that makes up the rice leaf.
The major function of most PMOs is to degrade polysaccharides to provide a nutrient source for the fungus. The rice blast PMO has evolved the specialized function noted above. Similar PMOs in fungi that attack grapes, tomatoes, lettuce and other major crops were found, so the new findings of their research may have a broad application against plant fungal diseases.
The use of small molecular inhibitors is not confined just to rice, Marletta said, but could be widely used against a variety of different crop pathogens. In fact, Marletta uses the words “pretty exciting” to describe the future in terms of drug development for plant pathogens.
There is an urgent need for more sustainable control measures for rice blast disease in South Asia and sub-Saharan Africa. The study of PMOs in plant infection may lead to developing new chemistries that could be applied at lower dosage rates than existing fungicides, thus reducing their impact on the environment.
Marletta is a member of the Berkeley branch of the California Institute for Quantitative Biosciences. The research was funded by the National Science Foundation and the National Institutes of Health. Marletta is a current member and former Chair of the Fredonia College Foundation Board of Directors and a recipient of the Fredonia Alumni Association’s Outstanding Achievement Award.
