Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 8/28/2008
Publication Date: 3/1/2010
Citation: Weiland, J.J., Chung, K., Suttle, J.C. 2010. The Role of Cercosporin in the Virulence of Cercospora ssp. to Plant Hosts. In Lartey, R.T., Weiland, J.J., Panella, L., Crous, P.W., Windels, C.E., editors. Cercospora Leaf Spot of Sugar Beet and Related Species. St. Paul, MN: The American Phytopathological Society. p. 109-117.
Interpretive Summary: The fungus Cercospora beticola causes severe defoliation of sugar beet plants resulting in high crop losses. This destructive ability is partially mediated by a toxic compound, cercosporin, that is produced by the fungus during invasion of the plant. By removing only the ability to produce cercosporin, it was discovered that this compound plays an important, but not exclusive, role in causing leaf defoliation by this organism. By understanding the importance of compounds like cercosporin in the damage to crops by plant pathogens, crop protection strategies that target this toxic compound may be prioritized. Broader discussions on the nature of the production of toxins like cercosporin are presented as a conclusion to the chapter.
Technical Abstract: Phytotoxins classically have been divided into those that are host-specific, affecting distinct genotypes or species of plant hosts, or host non-specific. Host non-specific phytotoxins, with further investigation, can be found as generally toxic to living cells. For example, the trichothecene mycotoxins have well-known toxicities to animal cells and recently were found to be virulence factors in plant infection. The light-activated cercosporin toxin behaves similarly. Cercosporin production can be used to classify Cercospora species and has been the subject of elegant studies regarding toxin mode of action and resistance by Cercospora and other fungi to its damaging effects. Although the genes and enzymes involved in cercosporin production are only now being described, the regulation of cercosporin production by environmental cues has been known for decades. The following chapter begins with an overview of the effects of cercosporin on plant host tissue promoting pathogen invasion and on the regulation of cercosporin production by environmental stimuli. This is followed by a summary of recent data in which genes encoding proteins for cercosporin production and secretion and the regulation of this process have been cloned and characterized. The chapter concludes with speculation as to the origin of the ‘pathogenicity island’ encoding genes for cercosporin synthesis and secretion and for regulation of the gene cluster.