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How do horticultural crops defend themselves against fungal pathogens?


by Nanjing Agricultural University The Academy of Science
Recently, scientists from the Chinese Academy of Sciences summarized recent research progress on defense responses of horticultural crops to fungal pathogens and novel strategies to regulate the induction of plant resistance, as well as problems, challenges, and future research directions.

Phytochemicals with antimicrobial effects are important components of defense systems in plants. Among such phytochemicals, phytoalexins are induced by external factors, whereas phytoanticipins occur naturally or increase after induction. Antimicrobial phytochemicals are classified according to their chemical structures and are primarily phenolics, flavonoids, coumarins, lignins, terpenoids, alkaloids, glucosinolates, and stilbenes. Phenolics and flavonoids are secondary metabolites that constitute one of the most common and extensive groups of phytochemicals. These compounds inhibit pathogens by inducing membrane lipid peroxidation, which disrupts fungal cell membrane permeability and mitochondrial function. Similarly, terpenoids inhibit fungal growth and also induce disease resistance. The other phytochemicals also exhibit strong and stable broad-spectrum antifungal activity, suggesting that they could be developed as alternatives to chemical fungicides.

When fungal pathogens penetrate physical barriers by modifying or degrading host cell walls, pattern recognition receptors (PRRs) may recognize conserved damage-associated molecular patterns (DAMPs) from plants or pathogen-associated molecular patterns (PAMPs) from pathogens and activate pattern-triggered immunity (PTI). Fungal pathogens can secrete effectors or virulence factors, which may be recognized by nucleotide-binding and leucine-rich repeat (NB-LRR or NLR) proteins and other plant resistance (R) proteins. Such recognition may result in further effector-triggered immunity (ETI), which is postulated to be an accelerated and amplified PTI response. A varied number of NB-LRR genes exhibit special evolutionary patterns among plant species. To date, only a few NB-LRR genes have been confirmed to function in response to fungal pathogens. Further in-depth exploration of potential NB-LRRs and their mechanisms of action may substantially enrich our arsenal to counterstrike against fungal pathogens.

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