Ritu Gill

Superoxide dismutase—mentor of abiotic stress tolerance in crop plants

Abiotic stresses impact growth, development, and productivity, and significantly limit the global agricultural productivity mainly by impairing cellular physiology/biochemistry via elevating reactive oxygen species (ROS) generation. If not metabolized, ROS (such as O2•−, OH•, H2O2, or 1O2) exceeds the status of antioxidants and cause damage to DNA, proteins, lipids, and other macromolecules, and finally cellular metabolism arrest. Plants are endowed with a family of enzymes called superoxide dismutases (SODs) that protects cells against potential consequences caused by cytotoxic O2•− by catalyzing its conversion to O2 and H2O2. Hence, SODs constitute the first line of defense against abiotic stress-accrued enhanced ROS and its reaction products. In the light of recent reports, the present effort: (a) overviews abiotic stresses, ROS, and their metabolism; (b) introduces and discusses SODs and their types, significance, and appraises abiotic stress-mediated modulation in plants; (c) analyzes major reports available on genetic engineering of SODs in plants; and finally, (d) highlights major aspects so far least studied in the current context. Literature appraised herein reflects clear information paucity in context with the molecular/genetic insights into the major functions (and underlying mechanisms) performed by SODs, and also with the regulation of SODs by post-translational modifications. If the previous aspects are considered in the future works, the outcome can be significant in sustainably improving plant abiotic stress tolerance and efficiently managing agricultural challenges under changing climatic conditions.

Metal/metalloid stress tolerance in plants: role of ascorbate, its redox couple, and associated enzymes

The enhanced generation of reactive oxygen species (ROS) under metal/metalloid stress is most common in plants, and the elevated ROS must be successfully metabolized in order to maintain plant growth, development, and productivity. Ascorbate (AsA) is a highly abundant metabolite and a water-soluble antioxidant, which besides positively influencing various aspects in plants acts also as an enigmatic component of plant defense armory. As a significant component of the ascorbate-glutathione (AsA-GSH) pathway, it performs multiple vital functions in plants including growth and development by either directly or indirectly metabolizing ROS and its products. Enzymes such as monodehydroascorbate reductase (MDHAR, EC 1.6.5.4) and dehydroascorbate reductase (DHAR, EC 1.8.5.1) maintain the reduced form of AsA pool besides metabolically controlling the ratio of AsA with its oxidized form (dehydroascorbate, DHA). Ascorbate peroxidase (APX, EC 1.11.1.11) utilizes the reduced AsA pool as the specific electron donor during ROS metabolism. Thus, AsA, its redox couple (AsA/DHA), and related enzymes (MDHAR, DHAR, and APX) cumulatively form an AsA redox system to efficiently protect plants particularly against potential anomalies caused by ROS and its products. Here we present a critical assessment of the recent research reports available on metal/metalloid-accrued modulation of reduced AsA pool, AsA/DHA redox couple and AsA-related major enzymes, and the cumulative significance of these antioxidant system components in plant metal/metalloid stress tolerance.

ATP-sulfurylase, sulfur-compounds, and plant stress tolerance

Sulfur (S) stands fourth in the list of major plant nutrients after N, P, and K. Sulfate (SO42-), a form of soil-S taken up by plant roots is metabolically inert. As the first committed step of S-assimilation, ATP-sulfurylase (ATP-S) catalyzes SO42--activation and yields activated high-energy compound adenosine-5′-phosphosulfate that is reduced to sulfide (S2-) and incorporated into cysteine (Cys). In turn, Cys acts as a precursor or donor of reduced S for a range of S-compounds such as methionine (Met), glutathione (GSH), homo-GSH (h-GSH), and phytochelatins (PCs). Among S-compounds, GSH, h-GSH, and PCs are known for their involvement in plant tolerance to varied abiotic stresses, Cys is a major component of GSH, h-GSH, and PCs; whereas, several key stress-metabolites such as ethylene, are controlled by Met through its first metabolite S-adenosylmethionine. With the major aim of briefly highlighting S-compound-mediated role of ATP-S in plant stress tolerance, this paper: (a) overviews ATP-S structure/chemistry and occurrence, (b) appraises recent literature available on ATP-S roles and regulations, and underlying mechanisms in plant abiotic and biotic stress tolerance, (c) summarizes ATP-S-intrinsic regulation by major S-compounds, and (d) highlights major open-questions in the present context. Future research in the current direction can be devised based on the discussion outcomes.

DNA damage and repair in plants under ultraviolet and ionizing radiations.

Being sessile, plants are continuously exposed to DNA-damaging agents present in the environment such as ultraviolet (UV) and ionizing radiations (IR). Sunlight acts as an energy source for photosynthetic plants; hence, avoidance of UV radiations (namely, UV-A, 315–400 nm; UV-B, 280–315 nm; and UV-C, <280 nm) is unpreventable. DNA in particular strongly absorbs UV-B; therefore, it is the most important target for UV-B induced damage. On the other hand, IR causes water radiolysis, which generates highly reactive hydroxyl radicals (OH•) and causes radiogenic damage to important cellular components. However, to maintain genomic integrity under UV/IR exposure, plants make use of several DNA repair mechanisms. In the light of recent breakthrough, the current minireview (a) introduces UV/IR and overviews UV/IR-mediated DNA damage products and (b) critically discusses the biochemistry and genetics of major pathways responsible for the repair of UV/IR-accrued DNA damage. The outcome of the discussion may be helpful in devising future research in the current context.

Plant adaptation to environmental change: significance of amino acids and their derivatives

SECTION I C INTRODUCTION 1. Environmental Change, and Plant Amino Acids and Their Derivatives - An Introduction SECTION II C AMINO ACIDS AND PEPTIDES, AND PLANT STRESS ADAPTATION 2. 5-Aminolevulinic Acid GBP5-ALA- A Multifunctional Amino Acid as A Plant Growth Stimulator and Stress Tolerance Factor 3. Cysteine - Jack of All Glutathione-based Plant Stress Defense Trades 4. Amino Acids and Drought Stress in Lotus: Use of Transcriptomics and Plastidic Glutamine Synthetase Mutants for New Insights in Proline Metabolism 5. Modulation of Proline - Implications in Plant Stress Tolerance and Development 6. Target Osmoprotectants for Abiotic Stress Tolerance in Crop Plants - Glycine Betaine and Proline SECTION III C AMINES AND BRASSINOSTEROIDS, AND PLANT STRESS ADAPTATION 7. Polyamines as Indicators and as Modulators in the Abiotic Stress in Plants 8. Polyamines in Stress Protection: Applications in Agriculture 9. Functional Role of Polyamines and Polyamine-Metabolizing Enzymes during Salinity, Drought and Cold stresses 10. Regulatory Role of Polyamines in Growth, Development and Abiotic Stress Tolerance in Plants 11. Polyamines - Involvement in Plant Stress Tolerance and Adaptation 12. Role of Polyamines in Plant-Pathogen Interactions 13. Role of Polyamines in Stress Management 14. Polyamines in Plant In Vitro Culture 15. Betaines and Related Osmoprotectants - Significance in Metabolic Engineering of Plant Stress Resistance 16. Brassinosteroids Role for Amino Acids, Peptides and Amines Modulation in Stressed Plants C A Review SECTION IV C APPRAISAL AND PERSPECTIVES 17. Plant Adaptation to Environmental Change and Significance of Amino Acids and Their Derivatives C Appraisal and Perspectives

Genetic engineering of crops: a ray of hope for enhanced food security.

Crop improvement has been a basic and essential chase since organized cultivation of crops began thousands of years ago. Abiotic stresses as a whole are regarded as the crucial factors restricting the plant species to reach their full genetic potential to deliver desired productivity. The changing global climatic conditions are making them worse and pointing toward food insecurity. Agriculture biotechnology or genetic engineering has allowed us to look into and understand the complex nature of abiotic stresses and measures to improve the crop productivity under adverse conditions. Various candidate genes have been identified and transformed in model plants as well as agriculturally important crop plants to develop abiotic stress-tolerant plants for crop improvement. The views presented here are an attempt toward realizing the potential of genetic engineering for improving crops to better tolerate abiotic stresses in the era of climate change, which is now essential for global food security. There is great urgency in speeding up crop improvement programs that can use modern biotechnological tools in addition to current breeding practices for providing enhanced food security.

Nanobiotechnology: Scope and Potential for Crop Improvement

The production level of foodgrains has become an issue of concern as it has shown a downward trend during the last decade. Since, there has been a drastic decrease in natural resources; it is through agriculture that we can visualize a self sustainable world. The growth in agriculture can be achieved only by increasing productivity through an effective use of modern technology as the land and water resources are limited. Nanobiotechnology provides the tool and technological platforms to advance agricultural productivity through genetic improvement of plants, delivery of genes and drug molecules, to specific sites at cellular levels. The interest is increasing with suitable techniques and sensors for precision in agriculture, natural resource management, early detection of pathogens and contaminants in food products and smart delivery systems for agrochemicals like fertilizers and pesticides. To achieve the goals of “nano-agriculture”, detailed investigation on the ability of nanoparticles to penetrate plant cell walls and work as smart treatment-delivery systems in plants, is needed. In this chapter, thorough studies and reliable information regarding the effects of nanomaterials on plant physiology and crop improvement at the organism level, are discussed.

Mechanism of Cadmium Toxicity and Tolerance in Crop Plants

Heavy metal pollution of arable soils is one of the major limiting factors affecting the plant growth and productivity worldwide. In particular, contamination of agricultural soils with cadmium (Cd) is one of the most serious agricultural problems in the world. Although Cd has no biological function in plants, it becomes easily available to the rooted plants. As soon as Cd enters the roots, it can reach the xylem through an apoplastic and/or symplastic pathway. Plants show a differing metal distribution and accumulation pattern among different plant parts. Once Cd enters the cells, it may disturb many physiological and metabolic processes in plants. Cd is a highly toxic nonessential element to plant growth and development and causes plant death even at low concentrations. It evokes a whole array of toxic effects, due to its long biological half-life and storage in plant vacuoles, interacts with carbon and nitrogen metabolism, interferes with sulphur assimilation and glutathione metabolism and decreases the absorption of nutritional elements, and causes oxidative damage. Plants are very well equipped with a wide array of defense mechanisms to cope with Cd accumulation and toxicity. The present chapter discusses the mechanisms of Cd toxicity and tolerance in crop plants.

Genome-Wide Collation of the Plasmodium falciparum WDR Protein Superfamily Reveals Malarial Parasite-Specific Features

Despite a significant drop in malaria deaths during the past decade, malaria continues to be one of the biggest health problems around the globe. WD40 repeats (WDRs) containing proteins comprise one of the largest and functionally diverse protein superfamily in eukaryotes, acting as scaffolds for assembling large protein complexes. In the present study, we report an extensive in silico analysis of the WDR gene family in human malaria parasite Plasmodium falciparum. Our genome-wide identification has revealed 80 putative WDR genes in P. falciparum (PfWDRs). Five distinct domain compositions were discovered in Plasmodium as compared to the human host. Notably, 31 PfWDRs were annotated/re-annotated on the basis of their orthologs in other species. Interestingly, most PfWDRs were larger as compared to their human homologs highlighting the presence of parasite-specific insertions. Fifteen PfWDRs appeared specific to the Plasmodium with no assigned orthologs. Expression profiling of PfWDRs revealed a mixture of linear and nonlinear relationships between transcriptome and proteome, and only nine PfWDRs were found to be stage-specific. Homology modeling identified conservation of major binding sites in PfCAF-1 and PfRACK. Protein-protein interaction network analyses suggested that PfWDRs are highly connected proteins with ~1928 potential interactions, supporting their role as hubs in cellular networks. The present study highlights the roles and relevance of the WDR family in P. falciparum, and identifies unique features that lay a foundation for further experimental dissection of PfWDRs.

Abiotic Stress Tolerance and Sustainable Agriculture: A Functional Genomics Perspective

Crop growth and productivity is being seriously constrained by a range of abiotic stress factors all over the globe. Literature revealed that abiotic stress factors [temperature extremes (heat and cold), water extremes (drought and flooding), salinity, sodicity, wounding, metal/metalloid toxicity, excess light, radiations, high speed wind, nutrient loss, and anaerobic conditions] are the key reason for declining the usual yield of major crop plants by more than 50 %, which causes significant economic losses every year. A number of genes and their products respond to abiotic stress factors at transcriptional and translational level; therefore, genetic engineering for abiotic stress resistance is an important goal for protecting/improving agricultural crop productivity. Adaptation of plants to various environmental insults is reliant upon the establishment of cascades of molecular networks involved in stress perception, signal transduction, and the expression of stress-specific genes and metabolites. Thus, engineering stress-responsive genes which can protect and/or preserve the function may be a potential target to enhance stress tolerance in plants. Genetic engineering and DNA markers have now emerged as important gear in crop improvement.