Send Orders for Reprints to reprints@benthamscience.ae 450 Current Protein and Peptide Science, 2015, 16, 450-461 Crosstalk among Jasmonate, Salicylate and Ethylene Signaling Pathways in Plant Disease and Immune Responses You-Xin Yang 1,2,# , Golam J. Ahammed 2,# , Caijun Wu 1 , Shu-ying Fan 1,* and Yan-Hong Zhou 2,* 1 Department of Horticulture, College of Agronomy, Jiangxi Agricultural University, Nanchang, 330045, P.R. China; 2 Department of Horticulture, Zhe- jiang University, Zijingang Campus, 866 Yuhangtang Road, Hangzhou, 310058, P.R. China Abstract: Phytohormone crosstalk is crucial for plant defenses against pathogens and insects in which salicylic acid (SA), jasmonic acid (JA), and ethylene (ET) play key roles. These low molecular mass signals critically trigger and modulate plant resistance against biotrophic as well as necrotrophic pathogens through a complex signaling network that even involves participation of other hormones. Crosstalk among SA, JA and ET is mediated by different molecular players, considered as integral part of these cross- communicating signal transduction pathways. Recent progress has revealed that the positive versus negative interac- tions among those pathways ultimately enable a plant to fine-tune its defense against specific aggressors. On the other hand, pathogens have evolved strategies to manipulate the signaling network to their favour in order to intensify viru- lence on host plant. Here we review recent advances and current knowledge on the role of classical primary defense hormones SA, JA and ET as well as their synergistic and antagonistic interaction in plant disease and immune re- sponses. Crosstalk with other hormones such as abscisic acid, auxin, brassinosteroids, cytokinins and melatonin is also discussed mainly in plant disease resistance. In addition to our keen focus on hormonal crosstalk, this review also highlights potential implication of positive and negative regulatory interactions for developing an efficient disease management strategy through manipulation of hormone signaling in plant. Keywords: Crosstalk, ethylene, jasmonic acid, plant resistance, salicylic acid. 1. INTRODUCTION In their natural habitats, plants are continuously chal- lenged by a wide range of biotic enemies such as bacteria, viruses, fungi, nematodes and insect herbivores. Such natu- ral enemies have different virulence and infection strategies that not only determine the yield but also affect the survival of plants. Each of these attackers exploits highly specialized features to establish a forced parasitic and/or deadly rela- tionship with its host plant. Upon infection and infestation by those microbial pathogens and insects, plants rapidly activate sophisticated defense mechanisms in order to pro- tect themselves from foreign threats [1, 2]. The plant innate immune system is dependent on its capacity to recognize the invaders using membrane proteins such as receptor-like kinases, known as surface pattern-recognition receptors (PRRs) of relatively conserved molecules of the patho- gen/microbe-associated molecular patterns (PAMPs), result- ing in pattern-triggered immunity (PTI) to prevent pathogen colonization. *Address correspondence to these authors at the Department of Horticulture, College of Agronomy, Jiangxi Agricultural University, Nanchang 330045, P.R. China; Tel/Fax: 0086-791-83813185; E-mail: fansy12@126.com and Department of Horticulture, Zhejiang University, Zijingang Campus, 866 Yuhangtang Road, Hangzhou, 310058, P.R. China; Tel/Fax: 0086-571-88982276; E-mail address: yanhongzhou@zju.edu.cn # These authors contributed equally to this work. Successful pathogens deliver virulence molecules called ef- fector proteins that suppress PTI. Plants have evolved resis- tance (R) genes that encode cytoplasmic receptors to recog- nize specific pathogen effectors and activate effector- triggered immunity (ETI), and are usually accompanied with hypersensitive responses (HR) and eventually programmed cell death (PCD) to restrict biotrophic cellular pathogens, viruses and insects [3, 4]. Through evolutionary experience, plants have evolved sophisticated mechanisms to sense biotic aggressors and to deploy proper responses accordingly. Downstream of ETI or PTI activation, the activation of complex phytohormones signaling networks is vital resistance player that stimulates plant immune signaling network [5, 6]. Numerous studies demonstrate that plant hormones are small signal molecules synthesized in low concentrations. Among them, salicylic acid (SA), jasmonate (JA), and ethylene (ET) are the critical major defense players in the regulation of signaling networks of basal resistance against multiple pathogens [7, 8]. The SA signaling positively induces plant defense against biotrophic pathogens that feed and reproduce on living host cells, whereas the JA/ET pathways are required for resistance pre- dominantly against necrotrophic pathogens and herbivores insects which derive nutrients from living host cells, commonly through specialized feeding structures [2, 9, 10]. It has been verified that SA is a key regulator of pathogen- 1875-5550/15 $58.00+.00 © 2015 Bentham Science Publishers