Perception and transduction of damage-associated molecular patterns (DAMPs) in plant immunity

Gruppo di Ricerca: 
Giulia De Lorenzo, Felice Cervone, Simone Ferrari, Benedetta Mattei Technical staff: Gianni Salvi, Daniela Pontiggia RTD and post-docs: Francesca Sicilia, Francesco Spinelli, Lorenzo Mariotti, Daniel V. Savatin P.h.D. students: Federico Andreani, Giovanna

In an environment full of harmful microbes, an efficient sensing of danger and a rapid mounting of
defence responses are crucial for the survival of plants as well as of animals. Protective
mechanisms, collectively referred to as innate immunity, include the perception of conserved
pathogen- or microbe-associated molecular patterns (PAMPs or MAMPs) by germline-encoded
pattern recognition receptors (PRRs) [1]. In plants, the activation upon PAMP recognition of a
complex array of defence responses that eventually terminates microbial infection [2] has been
indicated as PAMP-triggered immunity (PTI) [3]. Successful pathogens need to suppress PTI to
express their full virulence potential, and do so by using effectors or toxins leading to the so-called
effector-triggered susceptibility (ETS). Many plants then evolve the ability to sense specific
pathogen effectors through the so-called resistance (R)-proteins and mount a second level of
defence called effector-triggered immunity (ETI) [3]. ETI leads to a defence response that is
stronger than PTI and normally accompanied by a form of programmed cell death called
hypersensitive response. Like in animals, plant immunity also relies on the ability to sense invading
microbes by means of endogenous molecular patterns that are present only when the tissue is
infected or damaged (damage-associated molecular patterns or DAMPs); also the discrimination
between self and altered self leads to the activation of the immune system.
An important class of DAMPs is represented by oligogalacturonides (OGs), fragments released
from the homogalacturonan of the plant extracellular matrix upon wounding or by the action of
microbial endopolygalacturonases (PGs), which instead behave as MAMPs [4]. The formation of
OGs may be favoured by the interaction of fungal PGs with specific LRR recognition proteins
present in the apoplast (Polygalacturonase-inhibiting Proteins or PGIPs) [5]. Both at the structural
and the functional level, OGs are reminiscent of the hyaluronan fragments of the animal
extracellular matrix, a well-known class of DAMPs involved in wound response and healing [6].
OGs induce a complex response that largely overlaps the typical response activated by MAMPs
and induce protection against the necrotrophic fungus Botrytis cinerea. Our group has made the
substantial contribution of identifying the long-awaited receptor of these signal molecules. Using an
innovative approach in the plant field based on the construction of chimeric receptors, the wallassociated
kinase 1 (WAK1) was demonstrated to function in perception and transduction of the
OG signal [4, 7]. The WAK family in Arabidopsis includes five tightly clustered genes (WAK1–
WAK5). WAKs display an ectodomain containing a pectin/OG binding-site and several EGF-like
repeats; so far, lethality and redundancy have hampered the study of WAKs by genetic
approaches. Current work aims at investigating the biological significance of the interaction
between WAKs and OGs and at elucidating the role of WAKs in alerting cells of pathogen attack
and mechanical damage. Furthermore, novel chimeric receptors derived from WAKs and other
PRRs are being constructed to engineer resistance to pathogens in crop plants.
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[2] Boller T, Felix G (2009). A renaissance of elicitors: perception of microbe-associated molecular patterns and danger
signals by pattern-recognition receptors. Annu. Rev. Plant Biol. 60, 379-406.
[3] Jones JD, Dangl JL (2006). The plant immune system. Nature 444, 323-329
[4] De Lorenzo G, Brutus A, Savatin DV, Sicilia F & Cervone F. (2011) Engineering plant resistance by constructing
chimeric receptors that recognize damage-associated molecular patterns (DAMPs). FEBS Letters 585, 1521-1528
[5] De Lorenzo G, Ferrari S (2002). Polygalacturonase-inhibiting proteins in defense against phytopathogenic fungi. Curr.
Opin. Plant Biol. 5, 295-299.
[6] Jiang D, Liang J, Noble PW (2007). Hyaluronan in tissue injury and repair. Annu. Rev. Cell Dev. Biol. 23, 435-461.
[7] Brutus A, Sicilia F, Macone A, Cervone F, De Lorenzo G (2010). A domain swap approach reveals a role of the plant
wall-associated kinase 1 (WAK1) as a receptor of oligogalacturonides. Proc. Natl. Acad. Sci. USA .107, 9452-9457.

Anno del Convegno: 
2011

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