Abstract

Peptide Elicitors in Defense Signaling against Biotic Stresses

Ramcharan Bhattacharya, Principal Scientist, National Research Centre On Plant Biotechnology

Plants, being sessile in nature, are continuously exposed to either environmental or biotic stresses. However, plants possess multi layered defense system to combat such threats. To combat biotic stresses, plants have several physical and chemical barriers which include trichomes, cuticular waxes, cross linking of cell wall, stomata, nutrient deprivation, plant defensins, antimicrobial proteins, secondary metabolites etc. Plant cells perceive the presence of pathogen or herbivore through a series of events and triggers specific induced defense responses to restrict the pathogen invasion.  Plants recognize the presence of pathogen or insect herbivores through interaction of microbe associated molecular patterns (MAMP; also known as pathogen associated molecular patterns, PAMP) and herbivore associated molecular patterns (HAMP) with membrane bound pattern recognition receptors (PPRs) to form a first line of basal defense against these threats. The induction of plant defense mechanism through MAMP-PPR interactions is commonly known as MAMP-triggered immunity (MTI). In triggering defense response, host-derived peptide elicitors are released at the primary site of injury and/or infection and play an important role in the signaling process. Significant progress has been achieved in identifying host-derived elicitors that activate the endogenous defense response against biotic stresses. These include reactive oxygen species (ROS), oligosaccharide fragments and small signal peptides. Among the several classes of endogenous elicitors that have been identified from higher plants, our interest limits to endogenous peptide elicitors and delineating the mechanisms of downstream signaling. Identification of these signal peptides, breadth of their occurrence across the plant kingdom, and the downstream signaling pathways involved in eliciting the defense response will be discussed.