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The role of necrotrophic effectors in the ability of Botrytis and Monilinia species to infect host plants

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Protein study targets fungal-resistant fruit crops

Identifying the proteins that play a key role in fruit spoilage could be critical to breeding fungal-resistant crops, eliminating the need for pesticides.

Food and Natural Resources

Botrytis cinerea and Monilinia fructicola are two fungal species that cause post-harvest rot and spoilage of agricultural products. Botrytis is best known for destroying strawberries before consumers can enjoy them, and also spoils grapes, kiwifruit, tomatoes, peppers and lettuce. Monilinia causes rot in stone fruit, such as peaches, nectarines, cherries, apricots and almonds. The global economic damage caused by Botrytis and Monilinia is estimated to be well over EUR 2 billion a year. The agricultural sector has increasingly been looking for alternatives to chemical fungicides to tackle these pests. This is in part due to environmental concerns, and also because fungal resistance means that chemical sprays are increasingly ineffective. “Breeding crops to be fungi-resistant is an option, but is a challenge because infection depends on many genetic and environmental factors,” explains the EU’s NECROFUNGI project coordinator Jan van Kan, assistant professor at Wageningen University’s Laboratory of Phytopathology in the Netherlands. “The ripening of fruit also affects their susceptibility to infection, and properties can change rapidly during infection tests. This means it is very difficult to obtain reproducible infection results.”

Targeting fungal proteins

The NECROFUNGI project sought to address these challenges by focusing on the biological function of proteins. Both Botrytis and Monilinia produce and excrete proteins during infection, which help the fungi to attack the host plant. “We knew that if we could identify the proteins that play a role in infections, we could exploit these proteins for breeding purposes,” says van Kan. “Our working hypothesis was that plant responses to pure protein would be more predictive, making it easier to breed fungal-resistant plants.” The research was undertaken with the support of the Marie Skłodowska-Curie Actions programme. This enabled Spanish researcher Laura Vilanova Torren, a specialist in postharvest fruit-pathogen interactions, to work with van Kan at Wageningen.

Pesticide-free harvests

After successfully sequencing the genome of Monilinia fructicola (the genome of Botrytis was already sequenced), proteins excreted by fungi were identified. These were then produced in the lab using a yeast. “The rapid assembly and accurate annotation of the Monilinia genome sequence were crucial for our success,” adds van Kan. “Furthermore, we were able to develop an infection assay in the laboratory for Monilinia on detached peach leaves. This yielded reproducible infections, better than could have been achieved in the orchard.” Van Kan notes that working with seasonal crops like peach and apricot remains a challenge, given that leaves or fruits are available for experiments only 3 to 4 months a year. Nonetheless, the successes of NECROFUNGI can now be built upon, not only at Wageningen but also at the research centre IRTA Lleida in Spain. Following project completion, Vilanova secured a position at the institute, where she will continue her work on Monilinia. Her aim is to generate further biological insights and deliver fungal proteins that can support resistance breeding in peach, apricot and nectarine. “Projects with similar approaches are ongoing at Wageningen University for other Botrytis species, one infecting onion and the other infecting lily,” notes van Kan. Ultimately, van Kan hopes that the biological knowledge delivered through the NECROFUNGI project will help breeding companies on the pathway towards developing plants resistant to fungal infection. “This objective will require several years if not decades to accomplish,” he says. “But it is one of the few strategies we have for reducing pesticides to control postharvest diseases that have been around for decades in the case of Monilinia, and millennia when it comes to Botrytis.”

Keywords

NECROFUNGI, fruit, crop, fungal, Botrytis, Monilinia, pesticides, fungicides, harvest, agricultural, proteins, biological

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