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Wide spectrum and increasing use of nano-sized aluminum oxyhydroxide (boehmite, nBhm) particles have left a risk of their environmental exposure and possible toxic impacts. However, little is known about their toxicity. Current investigation was aimed to assess the toxic impacts of nBhm on Vigna radiata L., a model plant. Seedlings of V. radiata were exposed to 0 – 12 mM nBhm for ten days, and nBhm reduced the biomass production in a dose-dependent manner, with the greatest impacts under 12 mM nBhm causing 16% and 4% reduction in root and shoot dry weight (DW), respectively. Higher dose of nBhm damaged the cellular membrane stability and chlorophyll contents. The levels of major reactive oxygen species including superoxide radical, hydrogen peroxide and hydroxyl radical were increased by 2.65, 2.45 and 2.50 times more in leaves and 2.31, 2.55 and 5.71 times more in roots, respectively, in plants subjected to 12 mM nBhm treatment. Spectrophotometry and in-gel assays confirmed that the nBhm triggered antioxidative machinery with up-regulation of superoxide dismutase, catalase and peroxidase enzymes. Concurrent accumulation of non-enzymatic antioxidants was also recorded in the form of proline and ascorbic acid. The nBhm exposed plants showed higher nitric oxide production with 12 mM nBhm treatment causing 1.91- and 1.49-fold hike in nitric oxide content of leaves and roots, respectively. Interestingly, roots and leaves behaved contrastingly in terms of nitrate reductase activity in response to the nBhm treatment. The hierarchical clustering and principal component analysis revealed the closeness of the stress-indicating attributes towards higher nBhm concentrations. Collectively, nBhm exerted negative impacts on V. radiata in a dose-dependent manner, with higher toxicity at the concentration ≥ 8 mM, mediated through oxidative and nitrosative bursts.

Plants being sessile organisms are often exposed to various abiotic stress conditions, which greatly hamper the growth, yields as well as the quality of produce. Plants respond to abiotic stresses in an exceptionally complex and coordinated manner, involving the interactions and crosstalk with many metabolic-molecular pathways. One of the most common responses is generation of reactive chemical species including reactive oxygen species (ROS), reactive nitrogen species (RNS), reactive carbonyl species (RCS) and reactive sulfur species (RSS). ROS and RNS have long attracted attention from the plant researchers for both their damaging as well as protective effects. However, several reports are emerging to confirm similar roles played by the relatively newer 'reactive' members, the RCS and RSS. Plant reactive species are also hailed as vivacious signaling molecules that play regulatory roles in many plant metabolic procedures. Undeniably, these reactive species are involved in virtually all aspects of plant cell functions. Reactive species and the antioxidant machinery maintain a delicate but critical cellular redox-balance which gets disturbed under stress conditions, where their biosynthesis, transportation, scavenging and the overall metabolism gets decisive for plant survival. The current review aims to highlight and discuss the role of ROS, RNS, RCS, and RSS in plants especially under abiotic stresses, cross-talks between them, current approaches and technological advents for their characterization, and a perspective view on exploration/manipulation of the pathways and check-points involved in biosynthesis, transport and scavenging of these reactive species for engineering abiotic stress tolerant crop plants.

In an attempt to find an alternative and potent source of diosgenin, a steroidal saponin in great demand for its pharmaceutical importance, Helicteres isora suspension cultures were explored for diosgenin extraction. The effect of biotic elicitors on the biosynthesis of diosgenin, in suspension cultures of H. isora was studied. Bacterial as well as fungal elicitors such as Escherichia coli, Bacillus subtilis, Saccharomyces cerevisiae and Aspergillus niger were applied at varying concentrations to investigate their effects on diosgenin content. The HPLC based quantification of the treated samples proved that amongst the biotic elicitors, E. coli (1.5%) proved best with a 9.1-fold increase in diosgenin content over respective control cultures. Further, the scaling-up of the suspension culture to shake-flask and ultimately to bioreactor level were carried out for production of diosgenin. During all the scaling-up stages, diosgenin yield obtained was in the range between 7.91 and 8.64 mg l−1, where diosgenin content was increased with volume of the medium. The quantitative real-time PCR (qRT-PCR) analysis showed biotic elicitors induced the expression levels of regulatory genes in diosgenin biosynthetic pathway, the 3-hydroxy-3-methylglutaryl-CoA reductase (HMGR) and cycloartenol synthase (CAS), which can be positively correlated with elicited diosgenin contents in those cultures. The study holds significance as H. isora represents a cleaner and easy source of diosgenin where unlike other traditional sources, it is not admixed with other steroidal saponins, and the scaled-up levels of diosgenin achieved herein have the potential to be explored commercially.

MicroRNAs (miRNAs) are endogenous, tiny RNA molecules that sit at the heart of regulating gene expression in numerous developmental and signaling pathways. Recent investigations have revealed that abiotic stresses encourage non-typical expression patterns of several miRNAs, accordingly proposing miRNAs as potent and novel targets for enhancement plant tolerance against abiotic factors. The stress driven miRNA-response is dependent on types of miRNA, stress, tissues or organs as well as plant genotype. The stress responsive miRNAs act either as negative-regulatory entities by down regulating negative regulators for stress tolerance or as positive-regulatory entities approving amassing of positive regulators. The current scenario on miRNA-based research vastly focus on the identification and target prediction/validation of stress-responsive miRNAs along with their functional expression under stress conditions. It has predominately been accomplished with the advent of high throughput sequencing technologies coupled with online databases and tools. However, there is an urge of epigenomics, functional characterization, and expression-pattern studies to illuminate the communal regulatory pathways by miRNAs that trigger abiotic stress tolerance in major crops. The short tandem target mimic (STTM) and genome editing technologies can be exploited for efficient utilization of miRNAs for traits improvement. Beside the classical pathways, non canonical pathways and novel loci of miRNAs origin and their possible role in abiotic stress response need to be deciphered for their effective utilization. Through this review, we are presenting herein a current understanding about plant miRNAs, their biogenesis and involvement in stress-responses and modulation, various tools and databases used for prediction/identification of plant miRNAs and their targets. A perspective analysis on use of miRNAs as potent targets to engineer abiotic stress tolerance in plants has been presented with emphasis on recent developments, challenges and future perspectives.

Recent years have witnessed a gradual increase in the bioavailability and groundwater leaching of toxic heavy metals (HMs) in the environment, driven mainly by anthropogenic invasions. HMs, especially ranked as toxic/carcinogenic non-essential ones including Cadmium (Cd), Arsenic (As), Aluminium (Al), Mercury (Hg) and Lead (Pb) have emerged as the major soil, air and water contaminants affecting food production, quality and security worldwide. HMs affect plant growth and crop yield. Plants have developed intricate defense mechanisms for safeguarding themselves against the toxic effects imposed by HMs, including compartmentalization and sequestration in cell-organelles, inactivation by complex formation with the organic ligands and their exclusion using transporters, ion channels, transcription factors and signaling molecules, beside others. Omics approaches have generated significant resources and updates on the plant genome, transcriptome and metabolome plasticity against HM-induced stress stimuli. Omics technologies are pragmatic and seen as feasible approaches for characterizing the roles of genomes (genomics), coding (transcriptomics) and non-coding (miRNAomics) RNA transcripts, and metabolites (metabolomics) including metals (metallomics), which can ultimately be used for improving stress tolerance or generating resilience plant systems. This review aims to summarize the current understandings on the mechanistic insights of selected toxic (Cd, As, Al, Hg and Pb) HM-plant interactions, including their uptake, transport, toxicity and chelation/sequestration in cellular components, besides how plants respond and adapt to these stress factors. State-of-the-art in Omics approaches including genomics, transcriptomics, metabolomics, miRNAomics and metallomics for plant HM research have been presented. Present status, challenges and future prospects are also discussed.

Antibiotic resistance or microbial drug resistance is emerging as a serious threat to human healthcare globally, and the multidrug-resistant (MDR) strains are imposing major hurdles to the progression of drug discovery programs. Newer antibiotic-resistance mechanisms in microbes contribute to the inefficacy of the existing drugs along with the prolonged illness and escalating expenditures. The injudicious usage of the conventional and commonly available antibiotics in human health, hygiene, veterinary and agricultural practices is proving to be a major driver for evolution, persistence and spread of antibiotic-resistance at a frightening rate. The drying pipeline of new and potent antibiotics is adding to the severity. Therefore, novel and effective new drugs and innovative therapies to treat MDR infections are urgently needed. Apart from the different natural and synthetic drugs being tested, plant secondary metabolites or phytochemicals are proving efficient in combating the drug-resistant strains. Various phytochemicals from classes including alkaloids, phenols, coumarins, terpenes have been successfully demonstrated their inhibitory potential against the drug-resistant pathogens. Several phytochemicals have proved effective against the molecular determinants responsible for attaining the drug resistance in pathogens like membrane proteins, biofilms, efflux pumps and bacterial cell communications. However, translational success rate needs to be improved, but the trends are encouraging. This review highlights current knowledge and developments associated challenges and future prospects for the successful application of phytochemicals in combating antibiotic resistance and the resistant microbial pathogens.

Nitric oxide is a dynamic gaseous molecule involved in signalling, crosstalk with stress regulators, and plant abiotic-stress responses. It has great exploratory potentials for engineering abiotic stress tolerance in crops. Nitric oxide (NO), a redox-active gaseous signalling molecule, though present uniformly through the eukaryotes, maintain its specificity in plants with respect to its formation, signalling, and functions. Its cellular concentrations are decisive for its function, as a signalling molecule at lower concentrations, but triggers nitro-oxidative stress and cellular damage when produced at higher concentrations. Besides, it also acts as a potent stress alleviator. Discovered in animals as neurotransmitter, NO has come a long way to being a stress radical and growth regulator in plants. As a key redox molecule, it exhibits several key cellular and molecular interactions including with reactive chemical species, hydrogen sulphide, and calcium. Apart from being a signalling molecule, it is emerging as a key player involved in regulations of plant growth, development and plant-environment interactions. It is involved in crosstalk with stress regulators and is thus pivotal in these stress regulatory mechanisms. NO is getting an unprecedented attention from research community, being investigated and explored for its multifaceted roles in plant abiotic stress tolerance. Through this review, we intend to present the current knowledge and updates on NO biosynthesis and signalling, crosstalk with stress regulators, and how biotechnological manipulations of NO pathway are leading towards developing transgenic crop plants that can withstand environmental stresses and climate change. The targets of various stress responsive miRNA signalling have also been discussed besides giving an account of current approaches used to characterise and detect the NO.

Light constitutes one of the most important environmental factors for plant growth and development. It determines the photosynthetic rate and accumulate-assimilation besides its regulatory roles in plant growth and productivity. However, plants are frequently exposed to excess or inadequate light intensities and these fluctuations, collectively known as light stress, affect the agronomic traits in plants via inhibiting their physiological metabolic processes including photosynthesis, antioxidant machinery, and their abilities to fix atmospheric carbon and nitrogen. Within the photosynthetic machinery, photosystem II (PSII) and its reaction centers are particularly sensitive to these perturbations and have therefore been characterized as primary targets of light stress at physiological, biochemical, and molecular levels including microRNA (miRNA)-mediated post-transcriptional modifications. Through this review, we are presenting herein the current knowledge and recent updates on light stress and its significance for plant growth and crop yields, plant responses, and multilevel adaptation strategies to cope up with light stress including excess and low light. The review highlights and assesses the utilization of biotechnological tools for engineering light stress tolerance in major crops and model plants including omics and transgenic approaches and exploration of molecular markers and quantitative trait loci. The roles of miRNAs in regulation of light stress responses and adaptive mechanisms in plants have been discussed besides emphasizing on possible exploration of light-regulated miRNAs as potential targets for engineering light stress tolerance in crop plants.

Plant micro-RNAs (miRNAs) are a distinct class of non-coding, small regulatory RNA molecules emerging as key regulators of growth, development, and stress responses in plants. Therefore, plant miRNAs are looked upon as one of the most potent tools for crop improvement including generation of stress resilient crops. These small elements regulate the gene expression patterns at post-transcriptional as well as translational stages, and are proved to be concomitant with epigenetic regulations in plants during growth and developmental phases, and stress-mediated modulations/adaptations. Recent advancements in sequencing technologies have delivered the high-resolution clusters of sequence information from various organisms, making the miRNA characterization procedure more reliable, rapid, and promising. A typical miRNA investigation usually incorporates preparation of wide-range small RNA library and high-throughput sequencing, followed by the computational analysis of the obtained sequences using a variety of in silico tools. These in silico tools are proving vital in context of identification of miRNAs, their corresponding targets, and inclusive reports on metabolic networks incorporating the identified miRNAs. Current in silico progressions have made available a wide range of tools and databases for miRNA analysis. Therefore, diverse approaches can be seen amongst the researchers which might vary in terms of specificity of analysis, such as plant-, function-, target-specific analysis of miRNAs. Through this review, we discuss the recent developments and current understandings about the plant miRNAs and present the workflow of plant miRNAs including modern high-precision approaches for isolation, identification, target prediction and confirmation, miRNA-target network analysis, and functional characterization of plant miRNAs.

Plant sodium/hydrogen (Na+/H+) antiporters (NHXs) are key Na+ transporters, and play vital roles in plant growth, development and abiotic stress responses, in particular salinity stress. Present study was aimed at genome-wide identification, comprehensive in silico characterization and involvement of NHX antiporters in plant development and abiotic stress responses of Indica rice (Oryza sativa subsp. indica). Though there are reports of screening of NHXs from Japonica rice, such reports are lacking from the Indica counterparts. In the current investigation, genome-wide screening of O. sativa Indica subspecies revealed sixteen NHX orthologous, and these were confirmed to be Na+/H+ exchangers. The identified OsNHXs were distributed across nine chromosomes of O. sativa Indica. Probable sites of the OsNHXs were cell membranes or vacuoles, as suggested by their sub-cellular localization. The cis-regulatory elements of OsNHX promoters indicated their involvement in environmental stress responses. OsNHXs were predicted to be targets of 91 miRNA candidates belonging to 10 families. Three-dimensional OsNHX protein structures were also predicted using bioinformatics tools. In order to gain insights into the functional roles of the identified OsNHXs, digital gene expression analysis was carried out and the results revealed that the expression levels of OsNHXs varied amongst the growth and developmental phases and under salinity and drought stress conditions. These results hold significance in identifying potent NHX candidates from Indica rice, having key roles in Na+ transport and in maintaining cellular ionic homeostasis, and can be further explored as potent candidate genes for engineering salinity tolerance in rice and other crop plants.

Antibiotics, once considered the lifeline for treating bacterial infections, are under threat due to the emergence of threatening antimicrobial resistance (AMR). These drug-resistant microbes (or superbugs) are non-responsive to most of the commonly used antibiotics leaving us with few treatment options and escalating mortality-rates and treatment costs. The problem is further aggravated by the drying-pipeline of new and potent antibiotics effective particularly against the drug-resistant strains. Multidrug efflux pumps (EPs) are established as principal determinants of AMR, extruding multiple antibiotics out of the cell, mostly in non-specific manner and have therefore emerged as potent drug-targets for combating AMR. Plants being the reservoir of bioactive compounds can serve as a source of potent EP inhibitors (EPIs). The phyto-therapeutics with noteworthy drug-resistance-reversal or re-sensitizing activities may prove significant for reviving the otherwise fading antibiotics arsenal and making this combination-therapy effective. Contemporary attempts to potentiate the antibiotics with plant extracts and pure phytomolecules have gained momentum though with relatively less success against Gram-negative bacteria. Plant-based EPIs hold promise as potent drug-leads to combat the EPI-mediated AMR. This review presents an account of major bacterial multidrug EPs, their roles in imparting AMR, effective strategies for inhibiting drug EPs with phytomolecules, and current account of research on developing novel and potent plant-based EPIs for reversing their AMR characteristics. Recent developments including emergence of in silico tools, major success stories, challenges and future prospects are also discussed.

Polyamines (PAs) are small polycationic aliphatic amines and are ubiquitous in the plant kingdom. They play important roles in plant growth, development, and stress responses. Several research reports have established a correlation between their accumulation and salt stress tolerance in different plant species. Creditable research in the recent past has proved their vital roles in stress responses and adaptation strategies employed by plants, including scavenging of free radicals, neutralization of acids, and stabilization of cell membranes. They are able to bind several charged molecules including DNA, proteins, membrane phospholipids, and pectic polysaccharides, and have been credited with roles in protein phosphorylation and post-transcriptional modifications. They also play important roles in plant growth regulation, as well as acting as signaling molecules. Owing to their diverse functions in plant growth, development, and stress responses, they have emerged as potent targets for metabolic engineering to confer salt stress tolerance on manipulated plants. This chapter highlights their biosynthesis and transport, their exogenous applications to alleviate salt stress, and their metabolic engineering for developing salt-tolerant plants.

Over the past two decades, genetic engineering and related techniques have demonstrated striking progress in manipulation of the genes for induction of the desired characteristics into transgenic organisms. The regulatory mechanism of RNA interference (RNAi) has been studied in many higher organisms. The accuracy and precision of this phenomenon assures a great success rate in plant improvement. The RNAi provides us with an explicit methodology for down-regulation of genes of interest without hampering the expression of any other gene in the plant. The examination of different RNAi pathways, along with their components, including microRNAs and small interfering RNAs, have provided us with more than one way to achieve gene manipulation for mediated crop improvement. The phenomenon of RNAi has been studied in different abiotic environments; such as salinity, drought, extreme temperatures, heavy metals, and nutrition deprivation and radiation in various crops. RNAi-mediated crop manipulations have been reported that incorporate the utilization of vital stress-responsive elements with their subsequent mRNA and/or protein targets. Hence, collectively, RNAi technology has proven to be a promising tool for abiotic stress improvement in crops. This chapter focuses on the potential and successful application of RNAi technology for crop improvement in response to various abiotic stress factors.

Salinity is one of the most detrimental abiotic stress factors responsible for qualitative and quantitative deterioration in global crop production. By considering the inclusive food requirements, deciphering the complex salinity-mediated responses in plants is significant to develop salt-tolerant crops with higher yields. The recent advancements in analytical technologies have made possible to investigate and generate huge amount of data. Various tools have been successfully employed to check salt-induced alterations at genome, transcriptome, proteome, and metabolome levels of plants. Omics tools in combination with computational biological analysis have provided important information, which can be used to generate biological databases as well as in silico tools. Hence this combinatorial approach of omics-systems biology is currently considered as ultimate path in plant stress physiology analysis, which aims to improve agronomic characters. The present chapter is therefore focused on omics-mediated systems biology-based investigations targeting salinity responses in plants. This chapter also highlights precise computational tools and databases to analyze transcription factors, quantitative trait loci, and small RNAs. Collectively, the chapter illustrates the system biology approach as an essential and convenient tool in salinity studies.

Salinity is one of the most serious environmental factors limiting the global productivity and superior quality of the agricultural crops, thus jeopardizing the capability of agronomic production to withstand the ever-increasing human population. Hypersaline conditions show multiple effects on crops such as water stress, ionic imbalance and toxicity, nutrition deficiency, oxidative stress, metabolic alterations, osmotic stress, and genotoxicity, which collectively reduce growth, development, and survival rate of the stressed crops. As a consequence, declined photosynthetic electron transport takes place, leading to the generation of reactive oxygen species (ROS) such as singlet oxygen, superoxide radical, hydrogen peroxide, and hydroxyl radical, albeit various forms and in different cellular compartments. These ROS are considered as key components for oxidative injury to lipid membrane and other vital cellular macromolecules, including nucleic acids, pigments, and proteins, eventually provoking cell death. To counteract the deleterious effects, these stress-induced ROS need to be scavenged by antioxidant machinery activated by the cells. Reports have advocated the ROS influenced expression of number of genes and signal transduction pathways, which implies the cellular strategies to use ROS as stimuli and signals that trigger and regulate numerous stress-responsive genetic networks. Therefore, in contrast to their acknowledged role as destructive species, ROS also act as signaling molecules in the regulation of salinity-induced alterations. The present chapter focuses on the role of ROS as signaling molecules and inducers of gene expression under the influence of saline conditions. We discuss herein the process of salinity-induced ROS generation, types of ROS, cellular damage by ROS, role of ROS as signaling molecules, and recent evidences of differential expression of antioxidants under saline conditions.

Abiotic stresses like salinity, drought, heat, metal ions, radiation and oxidative stress, and especially their combinations, are major limiting factors for growth and productivity of the crops. Various molecular and biochemical processes governing the plant responses to abiotic stresses have often been investigated and hold the key for producing high-yielding and abiotic stress-tolerant crops. Plant responses to abiotic stresses are dynamic and intricate, and vary with type, level, and duration of the stress involved, as well as on the type of tissue under stress. However, one biochemical indicator common to all stresses is definite and controlled protein phosphorylation which is generally transmitted by highly complex protein kinase cascades. In recent years, using different biochemical as well as computational tools, many of such phosphoproteins are identified and characterized with respect to abiotic stresses. Subsequently, an upsurge has been witnessed in recent times for phosphoproteomics repositories or databases. The use of this crucial knowledge about such proteins and their phosphorylation sites is one of the promising ways for crop engineering against abiotic stress. Several reports have described abiotic stress-induced transcriptome, proteome and phosphoproteome changes in plants subjected to these stress factors. However, the investigations to assess precise phosphoproteomics deviations in response to environmental stresses and their implementation for crop improvement are limited. The present review summarizes and discusses the recent developments in deciphering abiotic stress induced changes in plant phosphoproteome besides development of phosphoproteomics tools and their repositories. A critical assessment of targeting phosphoproteins for crop improvement and phosphoproteomics mediated enhanced abiotic stress tolerance in transgenic plants has been presented.

The microRNAs (miRNAs) are small (20–24 nt) sized, non-coding, single stranded riboregulator RNAs abundant in higher organisms. Recent findings have established that plants assign miRNAs as critical post-transcriptional regulators of gene expression in sequence-specific manner to respond to numerous abiotic stresses they face during their growth cycle. These small RNAs regulate gene expression via translational inhibition. Usually, stress induced miRNAs downregulate their target mRNAs, whereas, their downregulation leads to accumulation and function of positive regulators. In the past decade, investigations were mainly aimed to identify plant miRNAs, responsive to individual or multiple environmental factors, profiling their expression patterns and recognizing their roles in stress responses and tolerance. Altered expressions of miRNAs implicated in plant growth and development have been reported in several plant species subjected to abiotic stress conditions such as drought, salinity, extreme temperatures, nutrient deprivation, and heavy metals. These findings indicate that miRNAs may hold the key as potential targets for genetic manipulations to engineer abiotic stress tolerance in crop plants. This review is aimed to provide recent updates on plant miRNAs, their biogenesis and functions, target prediction and identification, computational tools and databases available for plant miRNAs, and their roles in abiotic stress-responses and adaptive mechanisms in major crop plants. Besides, the recent case studies for overexpressing the selected miRNAs for miRNA-mediated enhanced abiotic stress tolerance of transgenic plants have been discussed.

Abiotic stresses including salinity, drought, extreme temperatures, and heavy metals are posing serious threats to agricultural yields as well as the quality of produce. This necessitates the production of cultivars capable to withstand the harsh environmental conditions without substantial yield losses. Owing to the complexity underlying stress tolerance traits, conventional breeding techniques have met with limited success and demand effective supplements to feed the growing food demands worldwide. This necessitates the development and deployment of novel and potent approaches, and engineering of phytohormone metabolism could be a method of choice to produce climate resilient crops with higher yields. Phytohormones are considered critical for regulating and coordinating plant growth and development; however, in recent years, they have received great attention for their multifunctional roles in plant responses to environmental stimuli. Creditable research has shown that phytohormones including the classical ones – auxins, cytokinins, ethylene, gibberellins, and newer members including brassinosteroids, jasmonates, and strigolactones – may prove to be potent targets for their metabolic engineering for producing abiotic stress-tolerant crop plants. This chapter presents short description of the roles of phytohormones in abiotic stress responses and tolerance followed by reviewing attempts made by the plant biotechnologists for engineering of phytohormone metabolism, signal, transport, and perception to develop abiotic stress-tolerant crop plants.