Dehydrins as key protector of plant abiotic tolerance: an update

Chapter 3 - Transcription Factors and Environmental Stresses in Plants

Abiotic stress affects the growth and development of crops tremendously, worldwide. To avoid adverse environmental effects, plants have evolved various efficient mechanisms to respond and adapt to harsh environmental factors. Stress conditions are associated with coordinated changes in gene expressions at a transcriptional level. Dehydrins have been extensively studied as protectors in plant cells, owing to their vital roles in sustaining the integrity of membranes and lactate dehydrogenase (LDH). Dehydrins are highly hydrophilic and thermostable intrinsically disordered proteins (IDPs), with at least one Lys-rich K-segment. Many dehydrins are induced by multiple stress factors, such as drought, salt, extreme temperatures, etc. This article reviews the role of dehydrins under abiotic stress, regulatory networks of dehydrin genes, and the physiological functions of dehydrins. Advances in our understanding of dehydrin structures, gene regulation and their close relationships with abiotic stresses demonstrates their remarkable ability to enhance stress tolerance in plants.

Transcription factors (TFs) are master regulators of abiotic stress responses in plants. This review focuses on TFs from seven major TF families, known to play functional roles in response to abiotic stresses, including drought, high salinity, high osmolarity, temperature extremes and the phytohormone ABA. Although ectopic expression of several TFs has improved abiotic stress tolerance in plants, fine-tuning of TF expression and protein levels remains a challenge to avoid crop yield loss. To further our understanding of TFs in abiotic stress responses, emerging gene regulatory networks based on TFs and their direct targets genes are presented. These revealed components shared between ABA-dependent and independent signaling as well as abiotic and biotic stress signaling. Protein structure analysis suggested that TFs hubs of large interactomes have extended regions with protein intrinsic disorder (ID), referring to their lack of fixed tertiary structures. ID is now an emerging topic in plant science. Furthermore, the importance of the ubiquitin-proteasome protein degradation systems and modification by sumoylation is also apparent from the interactomes. Therefore; TF interaction partners such as E3 ubiquitin ligases and TF regions with ID represent future targets for engineering improved abiotic stress tolerance in crops.

Being sessile organisms, plants are frequently exposed to various environmental stresses that cause several physiological disorders and even death. Oxidative stress is one of the common consequences of abiotic stress in plants, which is caused by excess generation of reactive oxygen species (ROS). Sometimes ROS production exceeds the capacity of antioxidant defense systems, which leads to oxidative stress. In line with ROS, plants also produce a high amount of methylglyoxal (MG), which is an α-oxoaldehyde compound, highly reactive, cytotoxic, and produced via different enzymatic and non-enzymatic reactions. This MG can impair cells or cell components and can even destroy DNA or cause mutation. Under stress conditions, MG concentration in plants can be increased 2- to 6-fold compared with normal conditions depending on the plant species. However, plants have a system developed to detoxify this MG consisting of two major enzymes: glyoxalase I (Gly I) and glyoxalase II (Gly II), and hence known as the glyoxalase system. Recently, a novel glyoxalase enzyme, named glyoxalase III (Gly III), has been detected in plants, providing a shorter pathway for MG detoxification, which is also a signpost in the research of abiotic stress tolerance. Glutathione (GSH) acts as a co-factor for this system. Therefore, this system not only detoxifies MG but also plays a role in maintaining GSH homeostasis and subsequent ROS detoxification. Upregulation of both Gly I and Gly II as well as their overexpression in plant species showed enhanced tolerance to various abiotic stresses including salinity, drought, metal toxicity, and extreme temperature. In the past few decades, a considerable amount of reports have indicated that both antioxidant defense and glyoxalase systems have strong interactions in conferring abiotic stress tolerance in plants through the detoxification of ROS and MG. In this review, we will focus on the mechanisms of these interactions and the coordinated action of these systems towards stress tolerance.

Diverse abiotic stresses constitute one of the major factors which adversely affect the normal plant growth and development which results worldwide in decreased agricultural productivity. At present, utilization of new molecular tools to achieve improved stress tolerance and increased crop productivity is highly desirable. Abiotic stress in plants induces expression of a wide range of genes like transcription factors, defense related genes and so on, and the products of these genes are important in combating stress conditions. Helicases are one such category of proteins that play a key role in maintaining the genomic integrity of the cell by participating in nucleic acid mediated processes such as recombination, replication, and repair of DNA as well as the unwinding of misfolded RNA structures that are formed during stress conditions. The DEAD box helicases are a subgroup of helicases which contain the amino acids Asp-Glu-Ala-Asp (DEAD) and are involved in the above molecular functions that mediate adaptation to stress. Overexpression of DEAD box helicases is known to provide stress tolerance in various plants and thus their use in developing stress tolerant plants is gaining importance. The plausible physiological mechanisms of helicases in bestowing abiotic stress tolerance of plants include ROS scavenging, enhanced photosynthesis, ion homeostasis and regulation of various stress responsive genes. In this review, the characteristics of plant DEAD box helicases and the stress conditions under which they express are discussed. We have provided a detailed description on the transgenic plants overexpressing DEAD box helicases with an emphasis on their stress tolerance abilities.

Chapter 20 - Proteomics in relation to abiotic stress tolerance in plants

Production sites of reactive oxygen species (ROS) in organelles from plant cells.- What do the mitochondrial antioxidant and redox systems have to say under salinity, drought and extreme temperature?.- ROS as key players of abiotic stress responses in plants.- Redox regulation and antioxidant defence during abiotic stress: What have we learned from Arabidopsis and its relatives?.- ROS signaling: Relevance with site of production and metabolism of ROS.- Heavy metal-induced oxidative stress in plants: Response of the antioxidative system.- Arsenic and chromium induced oxidative stress in metal accumulator and non-accumulator plants and detoxification mechanisms.- Phytochelatin and oxidative stress under heavy metal stress tolerance in plants.- General roles of phytochelatins and other peptides in plant defense mechanisms against oxidative stress/primary and secondary damages induced by heavy metals.- Role of polyphenols as antioxidants in native species from Argentina under drought and salinization.- Reactive oxygen species and plant disease resistance.- Modulation of the ascorbate-glutathione cycle antioxidant capacity by post-translational modifications mediated by nitric oxide in abiotic stress situations.- ROS-RNS-phytohormones network in root response strategy.- Relationship between changes in contents of nitric oxide and amino acid particularly proline in plants under abiotic stress.- Transgenic plants and antioxidative defense: Present and future?.

Global climate change has caused severe abiotic and biotic stresses, affecting plant growth and food security. The mechanical understanding of plant stress responses is critical for achieving sustainable agriculture. Intrinsically disordered proteins (IDPs) are a group of proteins without unique three-dimensional structures. The environmental sensitivity and structural flexibility of IDPs contribute to the growth and developmental plasticity for sessile plants to deal with environmental challenges. This article discusses the roles of various disordered proteins in plant stress tolerance and resistance, describes the current mechanistic insights into unstructured proteins such as the disorder-to-order transition for adopting secondary structures to interact with specific partners (i.e., cellular membranes, membrane proteins, metal ions, and DNA), and elucidates the roles of liquid-liquid phase separation driven by protein disorder in stress responses. By comparing IDP studies in animal systems, this article provides conceptual principles of plant protein disorder in stress adaptation, reveals the current research gaps, and advises on the future research direction. The highlighting of relevant unanswered questions in plant protein disorder research aims to encourage more studies on these emerging topics to understand the mechanisms of action behind their stress resistance phenotypes.

Extremes of temperatures, drought and salinity cause widespread crop losses throughout the world and impose severe limitations on the amount of land that can be used for agricultural purposes. Hence, there is an urgent need to develop crops that perform better under such abiotic stress conditions. Here, we discuss intriguing, recent evidence that circadian clock contributes to plants’ ability to tolerate different types of environmental stress, and to acclimate to them. The clock controls expression of a large fraction of abiotic stress-responsive genes, as well as biosynthesis and signaling downstream of stress response hormones. Conversely, abiotic stress results in altered expression and differential splicing of the clock genes, leading to altered oscillations of downstream stress-response pathways. We propose a range of mechanisms by which this intimate coupling between the circadian clock and environmental stress-response pathways may contribute to plant growth and survival under abiotic stress.

Exogenous application of different plant growth regulators is a well-recognized strategy to alleviate stress-induced adverse effects on different crop plants by regulating a variety of physiobiochemical processes such as photosynthesis, chlorophyll biosynthesis, nutrient uptake, antioxidant metabolism, and protein synthesis, which are directly or indirectly involved in the mechanism of stress tolerance. Of various environmental factors, salinity, drought, and extreme temperature (low or high) considerably diminish plant growth and yield by modulating endogenous levels as well as signaling pathways of plant hormones. Of various plant hormones/regulators, a potential plant growth regulator, 5-aminolevulinic acid (ALA), is known to be effective in counteracting the injurious effects of various abiotic stresses in plants. Until now the mechanisms behind ALA regulation of growth under stress have not been fully elucidated. It is also not yet clear how far growth and yield in different crops can be promoted by exogenous application of ALA and whether this ALA-induced growth and yield promotion is cost-effective. Thus, in this review we discuss at length the effects of ALA in regulating growth and development in plants under a variety of abiotic stress conditions, including salinity, drought, and temperature stress. Furthermore, advances in the functional and regulatory interactions of this plant growth regulator with plant stress tolerance, as well as the effective mode of exogenous application of ALA in inducing stress tolerance in plants are also comprehensively discussed in this review. In the future, overaccumulation of ALA in plants through manipulation of gene(s) could enhance plant stress tolerance. Thus, genetic manipulation of plants with the goal of attaining increased synthesis/accumulation of ALA and hence improved stress tolerance under stress conditions is an important area for research.

Plant growth and productivity is restricted by a multitude of abiotic stresses. These stresses negatively affect physiological and metabolic pathways, leading to the production of many harmful substances like ROS, lipid peroxides and aldehydes. This study was conducted to investigate the role of Arabidopsis ALDH3I1 gene in multiple abiotic stress tolerance. Transgenic tobacco plants were generated that overexpress the ALDH3I1 gene driven by the CaMV35S promoter and evaluated under different abiotic stresses, namely salt, drought, cold and oxidative stress. Tolerance to stress was evaluated based on responses of various growth and physiological traits under stress condition. Transgenic plants displayed elevated ALDH3I1 transcript levels compared to WT plants. The constitutive ectopic expression of ALDH3I1 conferred increased tolerance to salt, drought, cold and oxidative stresses in transgenic plants, along with improved plant growth. Transgenic plants overexpressing ALDH3I1 had higher chlorophyll content, photosynthesis rate and proline, and less accumulation of ROS and malondialdehyde compared to the WT, which contributed to stress tolerance in transgenic plants. Our results further revealed that ALDH3I1 had a positive effect on CO2 assimilation rate in plants under abiotic stress conditions. Overall, this study revealed that ALDH3I1 positively regulates abiotic stress tolerance in plants, and has future implications in producing transgenic cereal and horticultural plants tolerant to abiotic stresses.

Plants require extrinsic factors like air, water, light, nutrition, etc. for the regulation of their growth and development. Similarly, phytohormones are equally important for plants as intrinsic factors. Phytohormones are active molecules vital for various aspects in growth and development starting from embryogenesis, plant-pathogen defense and organ size regulation to reproductive development. These hormones also play an active role in mediating defense response against biotic and abiotic stresses in plants. According to estimates, a substantial loss in agricultural yields leading to concerns on food security worldwide has been reported due to abiotic stresses like salinity, extreme temperatures, drought, etc. To cope up with harsh stress conditions, plants develop certain altered growth patterns and physiological processes. Among various groups of phytohormones produced by plants, those which are based on isoprenoid origin are quite important in safeguarding plants against environmental stress. Brassinosteroids are one of the novel groups of plant hormones of isoprenoid origin. Due to its remarkable growth supporting property, these are regarded as phytohormones with pleiotropic effects. They dominate miscellaneous physiological activities such as growth, development, rhizogenesis, seed germination, senescence and most importantly abiotic stress tolerance in plants. In general, when a plant perceives a signal produced by stress, then it triggers a cascade mechanism of signal transduction with plant growth regulators, acting as alphatransducers.

Chapter 5 - Metabolomics-Guided Elucidation of Abiotic Stress Tolerance Mechanisms in Plants

Chapter 9 - Rhizospheric Microbial Diversity: An Important Component for Abiotic Stress Management in Crop Plants Toward Sustainable Agriculture

Silicon (Si): Review and future prospects on the action mechanisms in alleviating biotic and abiotic stresses in plants