Plant Defences against Fungal Attack: Biochemistry

Abstract

A wide variety of biochemical constituents, including small molecules, peptides and sugar polymers, contribute to the interactions between plant and fungal or oomycete pathogens. Molecules of microbe or plant origin are critical for the pathogen recognition and further triggering of plant defence responses. Moreover, defence molecules of a broad range of biological activity are produced by plants either before fungal attack (preformed) or in response to infection (induced). During the course of their host adaptation, fungal pathogens developed sophisticated molecular tools to overcome plant biochemical weapons. These tools include enzymes able to metabolise plant bioactive molecules as well as own toxins interfering with plant defence reactions. Contribution of various biochemical components to different stages of plant–pathogen interactions has been supported by genetic tools available for model organisms.

Key Concepts:

  • Small molecules, peptides and biopolymers are critical players in plant–fungus interactions.

  • Recognition in plant–microbe interactions is mediated by biochemical motifs associated with a wide range of pathogens.

  • Cell wall polymers constitute a physical barrier protecting protoplast from attacking fungi.

  • Secretion of small molecules at the sites of attempted fungal penetration is critical for pre‐invasive defence.

  • Particular constitutive and inducible secondary metabolites can terminate fungal development.

  • Detoxification of plant antibiotics contributes to fungal virulence.

Keywords: cell wall; fungal pathogens; hypersensitive response (HR); microbe‐associated molecular patterns (MAMPs); pathogenesis‐related (PR) proteins; plant immunity; phytoalexins; secondary metabolites; signal transduction; toxins

Figure 1.

Structures of secondary metabolites with roles in plant–microbe interactions discussed in the text.

Figure 2.

Hypersensitive response: early plant responses to fungal invasion include changes in cell wall structure. Cytoskeletal rearrangements may be involved in deposition of cell wall materials. Defence genes are activated, including those that result in the production of phytoalexins and degradative enzymes. The host cell undergoes programmed cell death. Hydrolytic enzymes such as β‐1,3‐glucanases (PR‐2s) and chitinases (PR‐3s) are released into the plant intercellular spaces and can degrade fungal cell walls. Signal molecules are also released that trigger defence gene expression in adjacent cells. Redrawn from the work of M Hazzard with permission from Medical Arts & Photography, Chandler Medical Center, University of Kentucky (1999).

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Further Reading

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Funnell, Deanna L, Schardl, Christopher L, and Bednarek, Paweł(May 2010) Plant Defences against Fungal Attack: Biochemistry. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0001323.pub2]