Plants sense the presence of pathogens or pests through the recognition of evolutionarily conserved microbe- or herbivore-associated molecular patterns or specific pathogen effectors, as well as plant endogenous danger-associated molecular patterns. This sensory capacity is largely mediated through plasma membrane and cytosol-localized receptors which trigger complex downstream immune signaling cascades. As immune signaling outputs are often associated with a high fitness cost, precise regulation of this signaling is critical. Protease-mediated proteolysis represents an important form of pathway regulation in this context. Proteases have been widely implicated in plant–pathogen interactions, and their biochemical mechanisms and targets continue to be elucidated. During the plant and pathogen arms race, specific proteases are employed from both the plant and the pathogen sides to contribute to either defend or invade. Several pathogen effectors have been identified as proteases or protease inhibitors which act to functionally defend or camouflage the pathogens from plant proteases and immune receptors. In this review, we discuss known protease functions and protease-regulated signaling processes involved in both sides of plant–pathogen interactions.
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Cover Image
Cover Image
Cartoon illustration of the simultaneous binding of PAP (a competitive inhibitor of the physiological enzyme co-factor adeonosine 3′-phosphate 5′-phosphosulfate, PAPS) and a heptapeptide saccharide substrate (sticks), poised for sulfation (dashed line) in the active site of heparan sulfate 2-O-sulfotransferase (PDB ID: 4NDZ). The PAP(S)-binding site and the oligosaccharide-binding sites provide dual opportunities for the screening, identification and rational design of small molecule inhibitors of this enzyme, which include the highly sulfated polyanionic drug suramin and the promiscuous protein kinase inhibitor rottlerin. Rottlerin competes with the PAPS co-factor in sulfotransferases, opening the door for the discovery and optimisation of other kinase inhibitors that inhibit these classes of enzyme, including protein tyrosine sulfotransferases (TPSTs). For further details, see the article by Byrne et al. in this issue (pages 2417–2433) and its companion article on pages 2435–2455. Image kindly provided by Neil Berry and Patrick Eyers.
The cloak, dagger, and shield: proteases in plant–pathogen interactions
