The ubiquitin–proteasome complex comprises suppressor of kinetochore protein 1 (SKP1)–cullin–F-box (SCF). Within the Jas domain, the minimal amino acid sequence that can bind the coronatine or JA-Ile is termed the JAZ degron, the bipartite structure of which contains a loop and an amphipathic alpha-helix that binds to coronatine or JA-Ile and coronatine insensitive 1 (COI1), respectively. Among the 13 JAZ proteins of Arabidopsis, JAZ5, JAZ6, JAZ7, JAZ8, and JAZ13 contain an additional EAR motif that can interact directly with TPL in the absence of NINJA. The JAZ proteins interact with the TFs via the ZIM domain, interacting with NINJA (which contains an ethylene-responsive element binding factor-associated amphiphilic repression (EAR) motif) and recruiting TPL to form the JAZ–NINJA–TPL repressor complex. The various domains present in the JAZ proteins facilitate their protein-protein interactions. To date, 13 JAZ proteins have been identified in Arabidopsis, most of which have two conserved domains: the central domain known as the ZIM domain, and the C-terminal JA-associated (Jas) domain. Biosynthesis and Metabolism of Jasmonic Acid during Abiotic Stress Consequently, plants activate various anti-stress mechanisms to acclimate or adapt to the various stresses. These stress-sensing mechanisms can activate downstream signal transduction pathways individually or in combination. Some of the mechanisms used by plants to sense the abiotic stresses are as follows : (i) Physical sensing, involving mechanical effects of the stress on the plant or cell structure, such as contraction of the plasma membrane from the cell wall during drought stress (ii) biophysical sensing, involving changes of the protein structure or enzymatic activity, such as the inhibition of different enzymes during heat stress (iii) metabolic sensing, involving the detection of by-product accumulation due to the uncoupling of electron transfer or enzymatic reactions, such ROS accumulation due to high light intensity (iv) biochemical sensing, involving the presence of specialized proteins to sense a particular stress, such as calcium channels that can alter the Ca 2+ homeostasis and sense changes in the temperature and (v) epigenetic sensing, involving modifications of the DNA or RNA structure without altering the genetic sequences, such as the changes in chromatin that occur during temperature stress. Any of these alterations could be a signal to the plant that a change in environmental conditions has occurred and that it is the optimum time to respond by either activating the stress-response pathways or altering existing ones. Abiotic Stress-Sensing Mechanisms in PlantsĪbiotic stresses alter the physiological processes in plants by affecting gene expression, RNA or protein stability, the coupling of reactions, ion transport, or other cellular functions. In this review, we focus on the biosynthesis and signaling of JA, cis-jasmone, MeJA, and JA-Ile in response to abiotic stresses because of the high bioactivity of these compounds. As signaling molecules, JAs regulate the expression of numerous genes in response to abiotic stresses (e.g., salt, drought, heavy metals, micronutrient toxicity, low temperature, etc.) and promote specific protective mechanisms ( Figure 1). JAs modulate many crucial processes in plant growth and development, such as vegetative growth, cell cycle regulation, anthocyanin biosynthesis, stamen and trichome development, fruit ripening, senescence, rubisco biosynthesis inhibition, stomatal opening, nitrogen and phosphorus uptake, and glucose transport.
The JAs are ubiquitous in higher plant species, where their levels are high in the reproductive tissues and flowers, but very low in the mature leaves and roots. In this review, we discuss the biosynthesis and signal transduction pathways of the JAs and the roles of these molecules in the plant responses to abiotic stresses. Besides these, jasmonates are involved in several developmental and physiological processes throughout the plant life.
As cellular hubs for integrating informational cues from the environment, jasmonates play significant roles in alleviating salt stress, drought stress, heavy metal toxicity, micronutrient toxicity, freezing stress, ozone stress, CO 2 stress, and light stress. As the major immunity hormone, jasmonates participate in numerous signal transduction pathways, including those of gene networks, regulatory proteins, signaling intermediates, and proteins, enzymes, and molecules that act to protect cells from the toxic effects of abiotic stresses. In response to stress, jasmonates (jasmonic acid, its precursors and derivatives), a class of polyunsaturated fatty acid-derived phytohormones, play crucial roles in several biotic and abiotic stresses. Plants as immovable organisms sense the stressors in their environment and respond to them by means of dedicated stress response pathways.
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