A Conspiracy Theory: Cell Wall Proteins Facilitate Fungus Entry

Plant cells are bounded by a composite wall that serves as barrier against pathogen intrusion. The wall is composed of tightly linked molecules, making it tough and impenetrable to most pests. During fruit ripening, however, the cell wall disintegrates. This exposes the fruit to diseases caused by bacteria and fungi. Scientists have known for some time that two enzymes (proteins catalyzing chemical reactions), polygalacturonase and expansin, participate in ripening-related disassembly of plant cell walls.

To test if these proteins are also responsible for increased pathogen susceptibility in ripening fruit, researchers from the University of California Davis selected genetically modified (GM) tomato lines incapable of expressing the enzymes. The GM lines and a control group were inoculated with Botrytis cinerea (gray mold), a fungus that causes rotting in fruits and vegetables. The researchers found out that tomatoes modified to suppress the expression of only one of the enzymes were not any less susceptible to the fungus. However, lines incapable of expressing both the cell wall proteins produced fruits less vulnerable to gray mold infection, as if the enzymes conspire to allow the entry of fungal pathogens. The discovery may help minimize losses in harvested fruits during storage, handling, and distribution.

Read more at http://www.news.ucdavis.edu/search/news_detail.lasso?id=8507 . The abstract of the paper published by PNAS is available at http://www.pnas.org/cgi/content/abstract/105/3/859