www.tjprc.org editor@tjprc.org HYPERSENSITIVE RESPONSE: “A PLAYER IN PLANT DEFENSE” ARPITA MISHRA & NEHA TIWARI IILM-College of Engineering and Technology, Greater Noida, India ABSTRACT Plants have developed sophisticated mechanisms to protect themselves from various diseases. Besides preformed physical and chemical barrier that hinders infection, a wide range of defence responses are induced only after pathogen attack. These responses include translocation of Ca 2+ and protons across the plasma membrane into the cytosol, hypersensitive response, protein phosphorylation/ dephosphorylation, activation of enzymes that generate ROS such as NADPH-oxidase and peroxidase, accumulation of NO and SA and expression of defense related genes. Hypersensitive response is one of the immediate defence mechanisms of plant against pathogen infection. It is a form of programmed cell death (PCD) that helps in restricting the pathogen growth. Present review includes the role of hypersensitive response in defense, molecular marker of hypersensitive response and the components of major signalling pathways that play an important role in defence. This review will give us an insight on hypersensitive response (HR) of plants with respect to the physiological, biochemical and molecular determinants in different plant species. KEYWORDS: Hypersensitive Respo nse, Map Kinase, SAR, Plant Defence and HSR203J Received: May 29, 2017; Accepted: Jun 20, 2017; Published: Jun 29, 2017; Paper Id.: IJBTRAUG20171 INTRODUCTIONS Plants are a source of food and shelter by a wide range of microorganisms including viruses, bacteria, nematodes and insects. Many of these microbes act as pathogens that impair plant growth and development. However, plants have developed diverse strategies to defend themselves. They respond to infection using two- branched innate immune system. The first branch uses trans-membrane pattern recognition receptors (PRR) that responds to slowly evolving microbial or pathogen-associated molecular pattern (PAMP) such as flagellin or chitin, a component of fungal cell walls (Jones and Dangl, 2006). During interaction with virulent parasites, PRRs confer weak immune responses that attenuates pathogen growth and contribute to basal defence. Reduced PAMP- mediated defence probably results from successful host defence suppression by pathogen effectors. The second branch acts largely through protein products encoded by most Resistance genes (R genes) (Jones and Dangl, 2006). Resistance (R) proteins represents mainly intracellular, immune receptor class having the capacity to directly or indirectly detect isolate-specific pathogen effectors, encoded by avirulence (avr) genes. Recognition requires the presence of matching avr and R genes in the two species and is thought to be mediated by ligand receptor binding (Glazebrook, 1999). Efforts have been made to elucidate plant-pathogen interaction leading to the identification and cloning of several avr and R genes (Keen and Staskawicz, 1998; Dangl, 1995). In conclusion, the multi-component response of plants to pathogens in host and non-host resistance appears to be activated by ligand receptor interactions, in which avr gene products and PAMPs serve as ligands for plasma membrane located or cytosolic receptors (Odjakova and Hadjiivanova, 2001). Receptor mediated recognition initiates cellular and systemic signaling processes that activate Original Article International Journal of Bio-Technology and Research (IJBTR) ISSN (P):2249-6858; ISSN (E):2249-796X Vol. 7, Issue 4, Aug 2017, 1-20 © TJPRC Pvt. Ltd.