Deciphering fungal genomes of white and gray mold rot

All results have been published in the online edition of PloS Genetics.

White and gray mold rot are two diseases that affect agricultural plants (sunflower, onion, grapevine, tomato, colza, etc.) both during cultivation and after harvesting. They are caused by microscopic fungi, respectively Sclerotinia sclerotiorum and Botrytis cinerea. The two very closely related species quickly kill plant cells during infection, facilitating colonization of dead tissues; they are known as necrotrophic pathogens.

Both in France and around the world, white and gray mold rot has resulted in considerable economic losses and significant production costs related to the application of fungicidal treatments. New regulations also require finding alternatives to the use of chemicals. In this context, improved understanding of the strategies these fungi use to infect plants is essential.

To compare S. sclerotiorum and B. cinerea and better understand the strategies used in pathogenesis, sequencing of their genomes, which are highly similar, was completed by Genoscope (CEA, France) and the Broad Institute (USA) with the help of a consortium of international laboratories led by INRA. Analysis of their genes shows that they have an impressive arsenal of enzymes with which they can easily decompose the pectin on which they live. This characteristic is related to the fact that they develop essentially on the aerial parts and fruit of plants that are rich in pectin (colza, grapevine, strawberry). Most genes associated with the infection are similar in the two species, including those involved in plant cell wall degradation.

There are also significant differences. There are twice as many secondary metabolism genes, i.e., those involved in the production of bioactive molecules (toxins, signaling components and antibiotics), in B. cinerea as there are in S. sclerotiorum. This diversity may lead to various infectious mechanisms (necrosis-inducing toxins in Botrytis). The two species also differ in their mode of sexual reproduction, S. sclerotiorum is self-fertile (homothallism) while B. cinerea requires a sexual partner of the opposite type (heterothallism). This is explained by some major differences observed in the sequence and organization of genes involved in this process. In practice, these differences in reproduction have an important impact on epidemiology and the methods that may be developed to control these two fungi.

Analysis of the genomes provides valuable information about how S. sclerotiorum and B. cinerea evolved. They also lay the foundations for functional analyses that may explain the necrotrophic nature of the fungi and their distinctive reproductive characteristics, both of which contribute to their ability to infect plants. In the future, further study of the molecular mechanisms involved in the necrotrophic nature of the fungi should lead to the development of new, integrated methods for sustainable management of the diseases.