Polyamines: Natural and engineered abiotic and biotic stress tolerance in plants

Methylglyoxal (MG) is a key signaling molecule resulting from glycolysis and other metabolic pathways. During abiotic stress, MG levels accumulate to toxic levels in affected cells. However, MG is routinely detoxified through the action of DJ1/PARK7/Hsp31 proteins that are highly conserved across kingdoms and mutations in such genes are associated with neurodegenerative diseases. Here, we report for the first time that, similar to abiotic stresses, MG levels increase during biotic stresses in plants, likely contributing to enhanced susceptibility to a wide range of stresses. We show that overexpression of yeast Heat shock protein 31 (Hsp31), a DJ-1 homolog with robust MG detoxifying capabilities, confers dual biotic and abiotic stress tolerance in model plant Nicotiana tabacum. Strikingly, overexpression of Hsp31 in tobacco imparts robust stress tolerance against diverse biotic stress inducers such as viruses, bacteria and fungi, in addition to tolerance against a range of abiotic stress inducers. During stress, Hsp31 was targeted to mitochondria and induced expression of key stress-related genes. These results indicate that Hsp31 is a novel attractive tool to engineer plants against both biotic and abiotic stresses.

Chapter 2 - WRKY transcription factors for biotic and abiotic stress tolerance in plants

Seed priming is a state-of-the-art, low-cost, and environment-friendly strategy to improve seed germination, seed vigor, abiotic and biotic stress tolerance, and the yield of field and horticultural crops. Seed priming involves imbibing the seeds in a priming solution under a desired set of environmental conditions for a period followed by drying before the radicle protrusion. Several seed priming approaches including hydropriming, osmopriming, bio-priming, hormonal priming, nutrient priming, nanoparticle priming, and electropriming can be effectively employed under different environmental conditions to improve crop growth and stress resilience. Seed priming is known to trigger enzymatic, hormonal, physiological, transcriptomic, metabolomic, and proteomic regulations in seed embryos during seed germination and plant growth, which leads to faster and synchronized seed germination and higher abiotic and biotic stress tolerance in crop plants. Furthermore, seed priming can induce cross-tolerance between abiotic and biotic stressors and induce stress memory for higher resilience of the next generation to environmental stresses. The present review paper discusses the applications of seed priming in biotic and abiotic stress tolerance and the underlying abiotic and biotic stress tolerance physiological, biochemical, and molecular mechanisms of seed priming. Furthermore, we discuss the current challenges/bottlenecks in the widespread application of seed priming in crop production.

Abiotic and biotic stresses negatively influence survival, biomass production and crop yield. Being multigenic as well as a quantitative trait, it is a challenge to understand the molecular basis of abiotic stress tolerance and to manipulate it as compared to biotic stresses. Lately, some transcription factor(s) that regulate the expression of several genes related to stress have been discovered. One such class of the transcription factors is DREB/CBF that binds to drought responsive cis-acting elements. DREBs belong to ERF family of transcription factors consisting of two subclasses, i.e. DREB1/CBF and DREB2 that are induced by cold and dehydration, respectively. The DREBs are apparently involved in biotic stress signaling pathway. It has been possible to engineer stress tolerance in transgenic plants by manipulating the expression of DREBs. This opens an excellent opportunity to develop stress tolerant crops in future. This review intends to focus on the structure, role of DREBs in plant stress signaling and the present status of their deployment in developing stress tolerant transgenic plants.

Chapter 11 - CRISPR/Cas-mediated genome editing for improved stress tolerance in plants

Plants are constantly challenged by various abiotic stresses that negatively affect growth and productivity worldwide. During the course of their evolution, plants have developed sophisticated mechanisms to recognize external signals allowing them to respond appropriately to environmental conditions, although the degree of adjustability or tolerance to specific stresses differs from species to species. Overproduction of reactive oxygen species (ROS; hydrogen peroxide, H2O2; superoxide, ; hydroxyl radical, OH⋅ and singlet oxygen, 1O2) is enhanced under abiotic and/or biotic stresses, which can cause oxidative damage to plant macromolecules and cell structures, leading to inhibition of plant growth and development, or to death. Among the various ROS, freely diffusible and relatively long-lived H2O2 acts as a central player in stress signal transduction pathways. These pathways can then activate multiple acclamatory responses that reinforce resistance to various abiotic and biotic stressors. To utilize H2O2 as a signaling molecule, non-toxic levels must be maintained in a delicate balancing act between H2O2 production and scavenging. Several recent studies have demonstrated that the H2O2-priming can enhance abiotic stress tolerance by modulating ROS detoxification and by regulating multiple stress-responsive pathways and gene expression. Despite the importance of the H2O2-priming, little is known about how this process improves the tolerance of plants to stress. Understanding the mechanisms of H2O2-priming-induced abiotic stress tolerance will be valuable for identifying biotechnological strategies to improve abiotic stress tolerance in crop plants. This review is an overview of our current knowledge of the possible mechanisms associated with H2O2-induced abiotic oxidative stress tolerance in plants, with special reference to antioxidant metabolism.

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.

In plants, stress is one of the major constraints affecting plant growth and yield, leading to a decrease in crop productivity. The stress can be abiotic or biotic stress, or both can affect crops. Biotic stress involves crop damage caused by living organisms, including insects, parasites, bacteria, fungi, and viruses, and affects crop yield. Abiotic stresses such as drought, salinity, heat, water logging, mineral toxicity and frost limit crop productivity. The development of in vitro drought- and salt-tolerant crops, such as vegetables, cereals, fruits and other commercial plants, has contributed to food production. Worldwide, wheat and rice are the major crops and are affected by biotic and abiotic stresses. Conventional breeding techniques and several agronomic methods have been applied for the management of newly developed stresses. Moreover, most of the implemented methods were found to be less successful and undesirable for use in field trials or in greenhouses. Recently, the tissue culture method has proven to be a more powerful and cost-effective approach for the development of stress tolerance in plants. The in vitro plant tissue culture method requires less time and space, and experimental trials are performed under controlled environmental conditions, with high potential for the development of various stress-tolerant crop plants. This method allows a good understanding of the biochemistry and physiology of plants cultured under environmental stress in vitro. The tissue culture technique allows the development of various stress-tolerant crops in the laboratory and has improved tolerance to both abiotic and biotic stresses and improved yield. Therefore, in vitro plant tissue culture methods provide new opportunities for developing stress tolerance in crop plants for environmental sustainability.

Abiotic and biotic stresses are major environmental factors reducing crop productivity and causing losses worth billions of dollars annually. Understanding the mechanisms of biotic and abiotic stress using physiological, biochemical and advanced molecular biology-based techniques will help in developing crop cultivars resistant to abiotic and biotic stresses. Over the past two decades, it has been established that calcium (Ca2+) is an essential macronutrient and plays a vital role in plant tolerance against biotic and abiotic stresses. Addition of Ca2+ fertilizers to the growth medium or its application as seed priming and as a foliar spray has already been shown to enhance stress tolerance in plants. Besides some fundamental roles of Ca2+ in plant growth and development, it has been recognized as a principal secondary-messenger molecule regulating diverse physiological processes in plants in a stressful environment. Biotic and abiotic stresses enhance the cytosolic Ca2+, which then binds with Ca2+ sensor proteins such as Ca calmodulin (CaM), Ca-dependent protein kinases (CDPKs), calcineurin B-like proteins (CBLs), CBL interacting protein kinase (CIPKs) and mediates downstream responses for stress tolerance. Activation of downstream responses for inducing stress tolerance in plants depends on changes in cytosolic Ca2+ concentration, which depends on duration and amplitude. However, increase in cytosolic Ca2+ concentration for a longer duration causes the production of toxic compounds which damage proteins and membrane lipids. To maintain ion homeostasis, plants efficiently export Ca2+ outside the cell or to the cellular organelles via ATP-dependent cation exchangers. Here we reviewed the recent updates on the physiological roles of Ca2+ in plant development and stress tolerance. Moreover, uptake and interaction with other mineral nutrients have also been discussed. In addition, the emerging role of Ca2+ signaling in mediating stress tolerance, which needs further research, is also reviewed. Finally, we discussed at length up to what extent Ca2+ fertilization or exogenous application mitigate the adverse effects of abiotic stresses.

Climate change and extreme environmental conditions are recognized as the most challenging threats to agricultural systems, leading to significant limitations in crop production and yield worldwide. It is a big concern to increase or maintain crop productivity under changing climate conditions to cater for increasing food demand. Among abiotic stresses, salinity, drought and extreme heat are the most common stresses. Abiotic stresses contribute to reducing crop plant production by 50% or more. Like the effects of abiotic stress, constant exposure to biotic stresses—which include pathogen infections and pest and insect attacks—contribute to a major drop in crop productivity and wastage of crops. There is also constant pressure from extreme weather conditions due to climate change and the incidence of biotic stresses. There is a great need to develop biotic and abiotic stress resilience in crops to mitigate the adverse effects of stresses. Such resilience can be achieved through development and adoption of eco-friendly approaches in agricultural systems for crop sustainability and food security. The focus on plant–microbe interactions has attracted more attention in recent years for inducing plant resistance and defence against abiotic and biotic stresses. Plant growth–promoting rhizobacteria facilitate abiotic stress resilience in plants by several strategies through activation of plant growth regulators (which include ethylene, auxin (indole-3-acetic acid)), activity of enzymes such as 1-aminocyclopropane-1-carboxylate (ACC)–deaminase and production of bacterial products such as exopolysaccharide. Diverse plant–microbe interactions in the rhizosphere also help to regulate plant defence pathways under adverse conditions through induction of systematic resistance or systemic acquired resistance. Moreover, other strategies such as microbial antagonism through production of several compounds such as antibiotics, siderophores, bacteriocins and secondary metabolites further boost disease resistance in plants.

Silicon-mediated abiotic and biotic stress mitigation in plants: Underlying mechanisms and potential for stress resilient agriculture

Advances in the chemistry of the coorination compounds: Proceedings of the Sixth International Conference on Coordination Chemistry, Detroit, August 27–September 1, 1961: Edited by Stanley Kirschner, Wayne State University, Detroit, Michigan. The Macmillan Company, New York, New York, 1961. xii + 682 pp. Price $15.00

With the advancement of biotechnological tools and techniques such as next generation sequencing, RNAomics, epigenomics, gene silencing, plant, microbe transformation, proteomics and metabolomics, the understanding of metabolic pathways and their manipulation for the desired characters became feasible. Metabolic engineering has been successful in the production of golden rice, bioprocess for artemisinin production, flavonoids in plant and microbes as well as generated biotic and abiotic stress tolerance in several crop plants. In view of the significance of metabolic engineering, this article includes recent techniques developed and their use in manipulation of glyoxalase metabolism for multiple abiotic stress tolerance in plants. The importance of engineering of flavonoids pathway for high value antioxidants production as well as improving the biotic and abiotic stress tolerance has been documented. Importance and success of metabolic engineering has been realized by its promising hope for sustainable technologies of bioactives production for mankind’s health as well as in the generation of improved crop varieties.

Chapter 5 - Microbe-mediated biotic and abiotic stress tolerance in crop plants

BackgroundProtein disulfide isomerase (PDI) and PDI-like proteins contain thioredoxin domains that catalyze protein disulfide bond, inhibit aggregation of misfolded proteins, and function in isomerization during protein folding in endoplasmic reticulum and responses during abiotic stresses.Chinese cabbage is widely recognized as an economically important, nutritious vegetable, but its yield is severely hampered by various biotic and abiotic stresses. Because of, it is prime need to identify those genes whose are responsible for biotic and abiotic stress tolerance. PDI family genes are among of them.ResultsWe have identified 32 PDI genes from the Br135K microarray dataset, NCBI and BRAD database, and in silico characterized their sequences. Expression profiling of those genes was performed using cDNA of plant samples imposed to abiotic stresses; cold, salt, drought and ABA (Abscisic Acid) and biotic stress; Fusarium oxysporum f. sp. conglutinans infection. The Chinese cabbage PDI genes were clustered in eleven groups in phylogeny. Among them, 15 PDI genes were ubiquitously expressed in various organs, while 24 PDI genes were up-regulated under salt and drought stress. By contrast, cold and ABA stress responsive gene number were ten and nine, respectively. In case of F. oxysporum f. sp. conglutinans infection 14 BrPDI genes were highly up-regulated. Interestingly, BrPDI1–1 gene was identified as putative candidate against abiotic (salt and drought) and biotic stresses, BrPDI5–2 gene for ABA stress, and BrPDI1–4, 6–1 and 9–2 were putative candidate genes for both cold and chilling injury stresses.ConclusionsOur findings help to elucidate the involvement of PDI genes in stress responses, and they lay the foundation for functional genomics in future studies and molecular breeding of Brassica rapa crops. The stress-responsive PDI genes could be potential resources for molecular breeding of Brassica crops resistant to biotic and abiotic stresses.