Plant Defense Signaling and Responses Against Necrotrophic Fungal Pathogens Dinesh Pandey 1 • Subin Raj Cheri Kunnumal Rajendran 1,3 • Manu Gaur 1 • P. K. Sajeesh 2 • Anil Kumar 1 Received: 1 April 2015 / Accepted: 19 February 2016 Ó Springer Science+Business Media New York 2016 Abstract Fungal necrotrophic pathogens cause wide- spread crop losses and infect a variety of plants. The per- ception of these pathogens or their associated signals by specific receptors in plants triggers the mitogen-activated protein kinase (MAPK) cascades and activates hormone (jasmonates and ethylene)-dependent and hormone-inde- pendent signaling, which facilitates the mounting of a defense response against the invading necrotrophs. This response involves the activation of specific transcription factors that result in the production of antifungal proteins (plant defensins) or accumulation of defensive secondary metabolites (phytoalexins). The perception and communi- cation mechanisms triggered by pathogen-associated molecular patterns and the hormones are coordinated by the MAPK signaling cascades which integrate various aspects of the multi-layered plant defense response. This review focuses on compiling distinct and overlapping roles played by various components of the plant signaling machinery in recognizing and mounting a regulated defense response against necrotrophic fungal pathogens. Keywords Necrotrophic fungal pathogens Á Defense response signaling Á Camalexin Á Plant defensins Á MAPK cascades Introduction Plants live in an environment in which they have contin- uous exposure to various forms of biotic stresses such as insects and pathogens. They have evolved a multi-layered defense system to ward off the effect of different types of biotic stresses. Plants defend themselves against pathogens by constitutive and induced defense mechanisms. Consti- tutive mechanisms comprise thick protective coatings of cuticle bark or waxes, which prevent the access of patho- gens into the living cells and various secondary metabo- lites, phytoanticipins which deter pathogen growth. Inducible plant defense strategies have evolved based on pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI) where the pathogen-associated molecular patterns (MAMPs/PAMPs) are detected by pattern recog- nition receptors (PRRs) in the host which trigger Ca 2? and mitogen-activated protein (MAP) kinase signaling cascades and transcriptome reprogramming (Boller and Felix 2009), leading to defense responses such as oxidative burst, ethylene production, and plant cell wall modifications (Asai and others 2002). However, pathogens have evolved mechanisms to produce virulence factors or effectors, which suppress PTI to facilitate pathogenesis. As a counter measure, plants have acquired additional receptors, known as resistance (R) proteins, which recognize pathogen effectors to induce a response called effector-triggered immunity (ETI) which ultimately triggers HR cell death in plants (Liu and others 2007). In addition, plants also acti- vate induced systemic defense responses to restrict the & Dinesh Pandey dineshpandeymbge@gmail.com & Anil Kumar ak_gupta2k@rediffmail.com 1 Department of Molecular Biology and Genetic Engineering, College of Basic Sciences and Humanities, G.B. Pant University of Agriculture and Technology, Pantnagar, Uttarakhand, India 2 Department of Plant Pathology, College of Agriculture, G.B. Pant University of Agriculture and Technology, Pantnagar, Uttarakhand, India 3 Department of Environmental Sciences, Faculty of Agriculture, Dalhousie University, Truro, NS, Canada 123 J Plant Growth Regul DOI 10.1007/s00344-016-9600-7