Biochemical mechanisms of signaling: Perspectives in plants under arsenic stress Ejazul Islam n,1 , Muhammad Tahir Khan 1 , Samra Irem 1 Soil & Environmental Biotechnology Division, National Institute for Biotechnology and Genetic Engineering (NIBGE), Faisalabad 38000, Pakistan article info Article history: Received 18 May 2014 Received in revised form 29 December 2014 Accepted 19 January 2015 Keywords: Arsenic toxicity Heavy metals Plants signaling Mitogen activated protein kinase abstract Plants are the ultimate food source for humans, either directly or indirectly. Being sessile in nature, they are exposed to various biotic and abiotic stresses because of changing climate that adversely effects their growth and development. Contamination of heavy metals is one of the major abiotic stresses because of anthropogenic as well as natural factors which lead to increased toxicity and accumulation in plants. Arsenic is a naturally occurring metalloid toxin present in the earth crust. Due to its presence in ter- restrial and aquatic environments, it effects the growth of plants. Plants can tolerate arsenic using several mechanisms like phytochelation, vacuole sequestration and activation of antioxidant defense systems. Several signaling mechanisms have evolved in plants that involve the use of proteins, calcium ions, hormones, reactive oxygen species and nitric oxide as signaling molecules to cope with arsenic toxicity. These mechanisms facilitate plants to survive under metal stress by activating their defense systems. The pathways by which these stress signals are perceived and responded is an unexplored area of research and there are lots of gaps still to be filled. A good understanding of these signaling pathways can help in raising the plants which can perform better in arsenic contaminated soil and water. In order to increase the survival of plants in contaminated areas there is a strong need to identify suitable gene targets that can be modified according to needs of the stakeholders using various biotechnological techniques. This review focuses on the signaling mechanisms of plants grown under arsenic stress and will give an insight of the different sensory systems in plants. Furthermore, it provides the knowledge about several path- ways that can be exploited to develop plant cultivars which are resistant to arsenic stress or can reduce its uptake to minimize the risk of arsenic toxicity through food chain thus ensuring food security. & 2015 Elsevier Inc. All rights reserved. Contents 1. Introduction ........................................................................................................ 127 2. Role of signal transduction in response to heavy metals in plants ............................................................. 128 3. Signaling pathways in plants in response to arsenic ........................................................................ 128 3.1. Protein signaling .............................................................................................. 128 3.1.1. TKL kinases, RLCKs, CRK and WAK ......................................................................... 128 3.1.2. Mitogen activated protein kinase (MAPK) ................................................................... 128 Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/ecoenv Ecotoxicology and Environmental Safety http://dx.doi.org/10.1016/j.ecoenv.2015.01.017 0147-6513/& 2015 Elsevier Inc. All rights reserved. Abbreviations: ; ABA, abscisic acid; APX, ascorbate peroxidase; CaM, calmodulin; CAT, catalase; CBL, calcineurin B-like protein; CDPK, calcium dependent protein kinase; CIPK, CBL-interacting protein kinase; CRK, CT10 regulator of kinase; EIN3, ethylene insensitive 3; ET, ethylene; G proteins, guanosine nucleotide-binding proteins; GR, glutathione reductase; GSH, glutathione; GST, glutathione S-transferase; JA, jasmonic acid; JAZ, jasmonate ZIM-domain; MAP, mitogen-activated protein; MAP4K, mitogen activated protein kinase kinase kinase kinase; MAPK, mitogen activated protein kinase; MAPKK, mitogen activated protein kinase kinase; MAPKKK, mitogen activated protein kinase kinase kinase; NADPH, nicotinamide adenine dinucleotide phosphate; NDP, nucleotide diphosphate; NO, nitric oxide; PCs, phytochelatins; PI3K, phosphoinositide 3-kinase; PP2C, protein phosphatase 2C; Prx, class III peroxidase; RLCKs, receptor like cytoplasmic kinases; ROS, reactive oxygen species; SH2 Phosphotyrosine, Src homology 2 domain phosphotyrosine; SIPK, salicylic acid (SA)-induced protein kinase; TDT, telurite-resistance/dicarboxylate transporter; TdT, terminal deoxynucleotidyl transferase; T–D–Y, threonine–aspartic acid–tyrosine; T–E–Y, threonine–glutamic acid–tyrosine; TFs, transcription factors; TKL, tyrosine kinase-like; WAK, wall-associated kinase; WRKY53, transcription factors which regulate leaf senescence; ZIM family proteins, zinc-finger protein which is expressed in inflorescence meristem n Corresponding author. Fax: þ92 41 2651472. E-mail address: ejazulislam75@yahoo.com (E. Islam). 1 All the three authors have explicitly equally contributed in writing this review article. Ecotoxicology and Environmental Safety 114 (2015) 126–133