Emerging Trends on Crosstalk of Jasmonates with Other Phytohormones under Plant Stress

Review Article

Ann Agric Crop Sci. 2023; 8(1): 1127.

Emerging Trends on Crosstalk of Jasmonates with Other Phytohormones under Plant Stress

Ghorbel M¹; Brini F²*

1Department of Biology, College of Sciences, University of Hail, Saudi Arabia

2Biotechnology and Plant Improvement Laboratory, Centre of Biotechnology of Sfax, Tunisia

*Corresponding author: Faiçal Brini, Biotechnology and Plant Improvement Laboratory, Centre of Biotechnology of Sfax, B.P ‘1177’, 3018 Sfax, Tunisia. Email: faical.brini@cbs.rnrt.tn

Received: March 13, 2023 Accepted: April 15, 2023 Published: April 22, 2023

Abstract

Plant hormones play crucial and basic roles in plant growth, developmental processes, and also in plant response to abiotic and biotic constraints. On the first time, plant hormones may allocate limited resources to the most serious stresses, on the second time, the crosstalk among multiple plant hormone signaling directs the balance between the plant growth and the plant defense. Various studies and investigations have reported the mechanism of crosstalk between Jasmonic Acid (JA) and other plant hormones in plant growth and stress responses. Based on these investigations, this chapter mainly reports the crosstalk between JA and other plant hormone signaling in regulating the balance between the plant growth and the defense response. The suppressor proteins JASMONATE ZIM DOMAIN PROTEIN (JAZ) and MYC2 as the key components in the crosstalk are also highlighted in the chapter. Eventually, we note that JA interacts with other hormone signaling pathways [such as Ethylene (ET), auxin, Gibberellic acid (GA), Abscisic Acid (ABA), Salicylic Acid (SA) and Brassinosteroids (BRs)] to regulate plant growth, abiotic stress tolerances, and defense resistance against pathogens.

Keywords: Jasmonic acid; Plant hormone; Environmental constraints; Defense response; Crosstalk

Introduction

During development and growth processes, plants are constantly battling against a challenging environment. These adverse environmental conditions are often categorized as: (i) Abiotic constraints, such like nutrient deficiency, Ultraviolet (UV) radiation, flood, drought, heavy metal toxicity and heat, cold and (ii) Biotic constraints, such as pathogen infection and animal herbivory [1]. Under multiple environmental constraints, the phytohormones allocate limited resources to respond to the most serious stress [2] and develop multiples signaling pathways [3,4] to govern the balance between the plant growth and the defense response [2]. Phytohormones are small endogenous signaling molecules, including Gibberellin (GA), Auxin (indole3-acetic acid, IAA), Cytokinin (CK), Brassinosteroids (BRs), Abscisic Acid (ABA), Ethylene (ET), Jasmonic Acid (JA), Salicylic Acid (SA), and Strigolactone (SL). In recent decades, JA anabolism has been widely studied and investigated in monocotyledons and dicotyledons. Indeed, in Arabidopsis, at least two pathways encode JA biosynthesis, namely, the a-linolenic acid (18:3) initial octadecane pathway and hexadecatrienoic acid (16:3) initial hexadecane pathway [5,6]. In those pathways, the 18:3 and 16:3 unsaturated fatty acids are converted to 12-oxo-phytodienoic acid (12-OPDA) and deoxymethylated vegetable dienic acid (dn-OPDA) in the chloroplast, respectively. Then, JA is formed from 12-OPDA and dn-OPDA through multiple β-oxidation in the peroxisome. Finally, different JA structures such as methyl Jasmonate (MeJA), JA–isoleucine (JA–Ile) and 12-hydroxyjasmonic acid (12-OH-JA) are formed from JA in the cytoplasm. Among these JAs, JA–Ile is the biological active form of JA in plants [7]. JA is widely distributed in plants as a natural plant growth regulator [5-8]. The importance of the crosstalk between JA and other phytohormones in regulating plant stress responses has attracted extensive attention [6-9]. In fact, through the crosstalk network, JAs often work in concert with other phytohormones, such as ABA, auxin, CK, ET, GA and SA, to balance between growth and defense-related processes, thereby conferring plants acclimation to the changing environments [10-12]. Studies in recent decades have remarkably expanded our knowledge on the molecular basis underlying JA biosynthesis, transportation, signal transduction and the crosstalk with other signaling pathways. The importance of JA in many developmental processes, including seedling development, lateral root formation, senescence, flower development, sex determination, and the circadian clock has also been elaborately discussed in several reviews [13-15]. In addition, extensive efforts have been made in elucidating the roles of JA in regulating plant responses to abiotic and biotic stress conditions, as well as the importance of the crosstalk between JA and other phytohormones in thoese regulations [11,16-20]. In this chapter, we focus on recent updates on JA anabolism and signal transduction, the crosstalk complexity between JA and other phytohormone signaling during plant development and stress responses, as well as the roles of the involved Transcription Factors (TFs) and other regulatory proteins.

JA Anabolism

To date, three JA anabolic pathways have been detected and identified in Arabidopsis: (1) the octadecane pathway with a-linolenic acid (a-LeA, 18:3) used as precursor, (2) the hexadecane pathway with hexadecatrienoic acid (16:3) used as precursor, and (3) the 12-Oxo-Phytodienoic Acid (OPDA) reductase 3 (OPR3)-independent pathway (Figure 1). All three pathways require multiple enzymatic reactions that take place sequentially in the chloroplast, the peroxisome and finally the cytosol [21]. Concerning the two first pathways, they start with the release of the polyunsaturated fatty acids a-LeA (18:3) and hexadecatrienoic acid (16:3) hydrolyzed from the membrane of chloroplast or plastid depending on the cell type. Through a sequential series of reactions catalyzed by 13-lipoxygenase (13-LOX), Allene Oxide Synthase (AOS) and Allene Oxide Cyclase (AOC), both the 18:3 and 16:3 are converted to OPDA and dnOPDA. Then, OPDA is transported from chloroplast into the peroxisome, where it gets reduced by OPR3 and subsequently shortened by three β-oxidation rounds, finally yielding JA[(+)-7-iso-JA] (Figure 1). dnOPDA is believed to follow the same pathway as OPDA to produce JA with one less β-oxidation round [22]. Upon release into the cytosol, JA is then metabolized into a variety of structures through different reactions, such as conjugation with amino acids, hydroxylation, carboxylation, and methylation, giving birth to a collection of JA derivatives with different biological activities [9,23,24]. Among them, the JA conjugation to the isoleucine by jasmonyl-isoleucine synthetase (JAR1) forms the most bioactive form of the hormone, i.e., (+)-7-iso-JA-Ile (JA-Ile) [25]. When transferred into the cell nucleus, the bioactive JA-Ile, through a “relief of repression” model, activates several key TFs, such as MYC2, for downstream JA-responsive gene expression [26-28]. The OPR3-independent pathway was recently identified by studying a total loss-of function OPR3 mutant, opr3-3 [29]. In the absence of OPR3 activity, OPDA can directly enter the β-oxidation pathway to form dnOPDA, which then gets converted into 4,5-didehydro-JA (4,5-ddh-JA) through two more rounds of β-oxidation. Lastly, 4,5-ddh-JA is reduced to JA by OPR2 in the cytosol (Figure 1). Nevertheless, the majority of JA biosynthesis still occurs through OPR3 [29].