Phytohormone signaling and crosstalk in regulating drought stress response in plants.

Phytohormones are ubiquitously involved in plant biological processes and regulate cellular signaling pertaining to unheralded environmental cues, such as salinity, drought, extreme temperature and nutrient deprivation. The association of phytohormones to nearly all the fundamental biological processes epitomizes the phytohormone syndicate as a candidate target for consideration during engineering stress endurance in agronomically important crops. The drought stress response is essentially driven by phytohormones and their intricate network of crosstalk, which leads to transcriptional reprogramming. This review is focused on the pivotal role of phytohormones in water deficit responses, including their manipulation for mitigating the effect of the stressor. We have also discussed the inherent complexity of existing crosstalk accrued among them during the progression of drought stress, which instigates the tolerance response. Therefore, in this review, we have highlighted the role and regulatory aspects of various phytohormones, namely abscisic acid, auxin, gibberellic acid, cytokinin, brassinosteroid, jasmonic acid, salicylic acid, ethylene and strigolactone, with emphasis on drought stress tolerance.

Cloning, expression and functional validation of drought inducible ascorbate peroxidase (Ec-apx1) from Eleusine coracana.

Eleusine coracana (finger millet) is a stress-hardy but under-utilized cereal crop that possesses an efficient antioxidant defense system. The plant is capable of enduring long durations of water deficit stress. Experiments were conducted to clone a potent stress responsive isoform of ascorbate peroxidase and validate its role under drought stress. Reverse transcriptase PCR was used to obtain the partial cDNA of apx1 gene, from a meticulously screened drought tolerant genotype of E. coracana (PR202). Using RACE strategy, the full length apx1 cDNA was cloned and sequenced. The cDNA length of the E. coracana apx1 (Ec-apx1) gene is 1,047 bp with a 750 bp ORF, encoding a 250 amino acid protein having a molecular weight of 28.5 kDa. The identity of the amino acid sequence, deduced from the cDNA, with the APX family homologs was about 74-97 %. The full-length apx1 ORF was sub-cloned in a prokaryotic expression vector pET23b. The recombinant fusion protein, Ec-apx1, had high expression level in BL21 strain of E. coli and exhibited APX enzyme activity. The structure-function relationship of the protein was deduced by modelling a three-dimensional structure of Ec-apx1, on the basis of comparative homology using SWISS-MODEL. Real time PCR analysis of Ec-apx1 expression at mRNA level showed that the transcript increased under drought stress, with maximum levels attained 5-days after imposition of stress. Our results suggest that Ec-apx1 has a distinct pattern of expression and plays a pivotal role in drought stress tolerance. Therefore, the cloned isoform of ascorbate peroxidase can be used for developing stress tolerant genotypes of important crops, through transgenic approach.

Identification of Eight High Yielding Strains via Morpho-Molecular Characterization of Thirty-Three Wild Strains of Calocybe indica.

Calocybe indica, generally referred as milky mushroom, is one of the edible mushroom species suitable for cultivation in the tropical and sub-tropical regions of the world. However, lack of potential high yielding strains has limited its wider adaptability. To overcome this limitation, in this study, the germplasms of C. indica from different geographical regions of India were characterized based on their morphological, molecular and agronomical attributes. Internal transcribed spacers (ITS1 and ITS4)-based PCR amplification, sequencing and nucleotide analysis confirmed the identity of all the studied strains as C. indica. Further, evaluation of these strains for morphological and yield parameters led to the identification of eight high yielding strains in comparison to the control (DMRO-302). Moreover, genetic diversity analysis of these thirty-three strains was performed using ten sequence-related amplified polymorphism (SRAP) markers/combinations. The Unweighted Pair-group Method with Arithmetic Averages (UPGMA)-based phylogenetic analysis categorized the thirty-three strains along with the control into three clusters. Cluster I possesses the maximum number of strains. Among the high yielding strains, high antioxidant activity and phenol content was recorded in DMRO-54, while maximum protein content was observed in DMRO-202 and DMRO-299 as compared with the control strain. The outcome of this study will help the mushroom breeders and growers in commercializing C. indica.

Responses to drought induced oxidative stress in five finger millet varieties differing in their geographical distribution.

The study presents the impact of drought stress on five finger millet varieties (PR202, VL146, VL315, PES400 and VR708), representing contrasting areas of Indian sub-continent. Drought stress induced increase in the activity of superoxide dismutase, ascorbate peroxidase and glutathione reductase was higher in PR202 and VL315, while the activity was lower in the varieties PES400 and VR708. Ascorbate peroxidase : superoxide dismutase ratio, which is a crucial factor in alleviating drought stress, was higher in varieties PR202 and VL315, whilst the varieties PES400 and VR708 exhibited a lower ratio under stress. The variety PES400 recorded maximum stress induced damage, as indicated by higher accumulation of malondialdehyde and hydrogen peroxide; whereas the variety PR202 recorded least stress induced cytotoxic damage. The results clearly indicate that better drought tolerance of the variety PR202 is positively related to the capacity of its antioxidant system to scavenge reactive oxygen species, resulting in a reduced incidence of oxidative damage. Ascorbate peroxidase : superoxide dismutase ratio is found to be a critical factor governing the stress tolerance potential of different varieties. Therefore, varieties PR202 and VL315 were found to be tolerant while PES400 was susceptible to drought stress.

Nanofomulation of zinc oxide and chitosan zinc sustain oxidative stress and alter secondary metabolite profile in tobacco.

Advancement in nanotechnology has improved ways for large-scale production and characterization of nanoparticles of physiologically important metals. The current study explores the impact of Zinc Oxide Nanoparticles (ZnO-NP) and Chitosan-Zinc oxide nano-bioformulation (CH-ZnO) in tissue culture raised callus of Nicotiana benthamiana. Results indicated augmented biomass in CH-ZnO treated callus, while a reduced biomass was observed in ZnO-NP treated callus, at all the concentrations tested. Higher chlorophyll and carotenoid content were recorded in callus treated with 800 ppm CH-ZnO as compared to ZnO-NP treated callus. A higher accumulation of proline was observed in CH-ZnO treated callus when compared to ZnO-NP treatment, which was significantly higher at 50, 200 and 400 ppm CH-ZnO treatment. A maximum reduction in malondialdehyde (MDA) content was recorded at 800 ppm, for both the nano-formulations tested. Likewise, a significant reduction in the H2O2 levels was observed in all the treatments, while the callus treated with 400 ppm ZnO-NP and 800 ppm CH-ZnO recorded the highest reduction. Phenylalanine Ammonia-Lyase (PAL), activity increased significantly in callus treated with 400 ppm concentration for both ZnO-NP and CH-ZnO with respect to control. An increased level of tannin and nicotine were recorded in callus supplemented with 50, 200 and 400 ppm CH-ZnO. Notably, a significant decline of 94 and 52% in tannin content and 25 and 50% in nicotine content was recorded in the callus treated with 800 ppm CH-ZnO and ZnO-NP, respectively. The findings of this study suggest that an optimized dosage of these nano-bioformulations could be utilized to regulate the nicotine content and stress tolerance level.

Molecular cloning, in-silico characterization and functional validation of monodehydroascorbate reductase gene in Eleusine coracana.

Ascorbic acid is a ubiquitous water soluble antioxidant that plays a critical role in plant growth and environmental stress tolerance. It acts as a free radical scavenger as well as a source of reducing power for several cellular processes. Because of its pivotal role in regulating plant growth under optimal as well as sub-optimal conditions, it becomes obligatory for plants to maintain a pool of reduced ascorbic acid. Several cellular processes help in maintaining the reduced ascorbic acid pool, by regulating its synthesis and regeneration processes. Current study demonstrates that monodehydroascorbate reductase is an important enzyme responsible for maintaining the reduced ascorbate pool, by optimizing the recycling of oxidized ascorbate. Cloning and functional characterization of this important stress inducible gene is of great significance for its imperative use in plant stress management. Therefore, we have cloned and functionally validated the role of monodehydroascorbate reductase gene (mdar) from a drought tolerant variety of Eleusine coracana. The cloned Ecmdar gene comprises of 1437bp CDS, encoding a 478 amino acid long polypeptide. The active site analysis showed presence of conserved Tyr348 residue, facilitating the catalytic activity in electron transfer mechanism. qPCR expression profiling of Ecmdar under stress indicated that it is an early responsive gene. The analysis of Ecmdar overexpressing Arabidopsis transgenic lines suggests that monodehydroascorbate reductase acts as a key stress regulator by modulating the activity of antioxidant enzymes to strengthen the ROS scavenging ability and maintains ROS homeostasis. Thus, it is evident that Ecmdar is an important gene for cellular homeostasis and its over-expression could be successfully used to strengthen stress tolerance in crop plants.

Reactive Oxygen Species Generation-Scavenging and Signaling during Plant-Arbuscular Mycorrhizal and Piriformospora indica Interaction under Stress Condition.

A defined balance between the generation and scavenging of reactive oxygen species (ROS) is essential to utilize ROS as an adaptive defense response of plants under biotic and abiotic stress conditions. Moreover, ROS are not only a major determinant of stress response but also act as signaling molecule that regulates various cellular processes including plant-microbe interaction. In particular, rhizosphere constitutes the biologically dynamic zone for plant-microbe interactions which forms a mutual link leading to reciprocal signaling in both the partners. Among plant-microbe interactions, symbiotic associations of arbuscular mycorrhizal fungi (AMF) and arbuscular mycorrhizal-like fungus especially Piriformospora indica with plants are well known to improve plant growth by alleviating the stress-impacts and consequently enhance the plant fitness. AMF and P. indica colonization mainly enhances ROS-metabolism, maintains ROS-homeostasis, and thereby averts higher ROS-level accrued inhibition in plant cellular processes and plant growth and survival under stressful environments. This article summarizes the major outcomes of the recent reports on the ROS-generation, scavenging and signaling in biotic-abiotic stressed plants with AMF and P. indica colonization. Overall, a detailed exploration of ROS-signature kinetics during plant-AMF/P. indica interaction can help in designing innovative strategies for improving plant health and productivity under stress conditions.

The circadian clock and defence signalling in plants.

The circadian clock is the internal time-keeping machinery in higher organisms. Cross-talk between the circadian clock and a diverse range of physiological processes in plants, including stress acclimatization, hormone signalling, photomorphogenesis and defence signalling, is currently being explored. Recent studies on circadian clock genes and genes involved in defence signalling have indicated a possible reciprocal interaction between the two. It has been proposed that the circadian clock shapes the outcome of plant-pathogen interactions. In this review, we highlight the studies carried out so far on two model plant pathogens, namely Pseudomonas syringae and Hyaloperonospora arabidopsidis, and the involvement of the circadian clock in gating effector-triggered immunity and pathogen-associated molecular pattern-triggered immunity. We focus on how the circadian clock gates the expression of various stress-related transcripts in a prolific manner to enhance plant fitness. An understanding of this dynamic relationship between clock and stress will open up new avenues in the understanding of endogenous mechanisms of defence signalling in plants.

Silver nanoparticle-mediated enhancement in growth and antioxidant status of Brassica juncea.

Metal nanoparticles can potentially be used as tools for engineering biological redox reactions. Present study underlines the effect of silver metal nanoparticles (at 0, 25, 50, 100, 200 and 400 ppm) on the growth and antioxidant status of 7-day-old Brassica juncea seedlings. Fresh weight, root and shoot length, and vigor index of seedlings is positively affected by silver nanoparticle treatment. It induced a 326 % increase in root length and 133 % increase in vigor index of the treated seedlings. Improved photosynthetic quantum efficiency and higher chlorophyll contents were recorded in leaves of treated seedlings, as compared to the control seedlings. Levels of malondialdehyde and hydrogen peroxide decreased in the treated seedlings. Nanoparticle treatment induced the activities of specific antioxidant enzymes, resulting in reduced reactive oxygen species levels. Decrease in proline content confirmed the improvement in antioxidant status of the treated seedlings. The observed stimulatory affects of silver nanoparticles are found to be dose dependent, with 50 ppm treatment being optimum for eliciting growth response. Present findings, for the first time indicate that silver nanoparticles promote the growth of B. juncea seedlings by modulating their antioxidant status.