Stress Tolerance Response Research Articles

Low Temperature Antioxidant Activity QTL Associate with Genomic Regions Involved in Physiological Cold Stress Tolerance Responses in Rice (Oryza sativa L.).

Boosting cold stress tolerance in crop plants can minimize stress-mediated yield losses. Asian rice (Oryza sativa L.), one of the most consumed cereal crops, originated from subtropical regions and is generally sensitive to low temperature environments. Within the two subspecies of rice, JAPONICA, and INDICA, the cold tolerance potential of its accessions is highly variable and depends on their genetic background. Yet, cold stress tolerance response mechanisms are complex and not well understood. This study utilized 370 accessions from the Rice Diversity Panel 1 (RDP1) to investigate and correlate four cold stress tolerance response phenotypes: membrane damage, seedling survivability, and catalase and anthocyanin antioxidative activity. Most JAPONICA accessions, and admixed accessions within JAPONICA, had lower membrane damage, higher antioxidative activity, and overall, higher seedling survivability compared to INDICA accessions. Genome-wide association study (GWAS) mapping was done using the four traits to find novel quantitative trait loci (QTL), and to validate and fine-map previously identified QTL. A total of 20 QTL associated to two or more traits were uncovered by our study. Gene Ontology (GO) term enrichment analyses satisfying four layers of filtering retrieved three potential pathways: signal transduction, maintenance of plasma membrane and cell wall integrity, and nucleic acids metabolism as general mechanisms of cold stress tolerance responses involving antioxidant activity.

Genome sequencing of turmeric provides evolutionary insights into its medicinal properties

Curcuma longa, or turmeric, is traditionally known for its immense medicinal properties and has diverse therapeutic applications. However, the absence of a reference genome sequence is a limiting factor in understanding the genomic basis of the origin of its medicinal properties. In this study, we present the draft genome sequence of C. longa, belonging to Zingiberaceae plant family, constructed using 10x Genomics linked reads and Oxford Nanopore long reads. For comprehensive gene set prediction and for insights into its gene expression, transcriptome sequencing of leaf tissue was also performed. The draft genome assembly had a size of 1.02 Gbp with ~70% repetitive sequences, and contained 50,401 coding gene sequences. The phylogenetic position of C. longa was resolved through a comprehensive genome-wide analysis including 16 other plant species. Using 5,388 orthogroups, the comparative evolutionary analysis performed across 17 species including C. longa revealed evolution in genes associated with secondary metabolism, plant phytohormones signaling, and various biotic and abiotic stress tolerance responses. These mechanisms are crucial for perennial and rhizomatous plants such as C. longa for defense and environmental stress tolerance via production of secondary metabolites, which are associated with the wide range of medicinal properties in C. longa.

Species stress tolerance and community competitive effects drive differences in species composition between calcareous and siliceous plant communities

Abstract Both chemical and physical properties of soils have been used for two centuries for explaining differences in species composition and diversity between plant communities from calcareous and siliceous soils. Here, we examine the prediction from the ‘physical hypothesis’, which proposes that species from siliceous soils are absent from calcareous soils because of high drought stress, while species from calcareous soils are absent from siliceous soils because of high competition due to higher water availability. This hypothesis therefore predicts a trade‐off between stress tolerance and competitive response that allows calcareous and siliceous species to dominate their respective communities. There has been no attempt to experimentally assess these predictions. We cross‐transplanted with and without neighbours using a removal experiment, two dominant species from calcareous soils (Bromus erectus and Brachypodium sylvaticum) and two species from siliceous soils (Pseudarrhenatherum longifolium and Deschampsia flexuosa) in herbaceous communities from the two soils types. We repeated the experiment 4 years, taking advantage of inter‐annual climatic variability to test the interplay between year quality (dry vs. wet years) and soil types on survival responses with and without neighbours. We quantified species stress tolerances, their competitive responses and the competitive effect of the two community types. In the absence of neighbours, species from siliceous soils had much lower survival than species from calcareous soils during dry years, in particular on calcareous soils. It indicates a lower stress tolerance of siliceous species and a higher level of stress occurring on calcareous soils. Competition strongly reduced the survival of calcareous but not siliceous species, indicating a greater competitive response of the latter and competition was more important on siliceous soils than on calcareous soils during wet years. However, we found that species stress tolerances were more important than competitive effect of neighbours in driving differences in species composition. Synthesis. The contrasting responses found for dominant species from calcareous and siliceous soils support the trade‐off between stress tolerance and competitive response proposed by the physical hypothesis. Our results bring additional evidence that differences in water availability and stress between the two soil types are driving species responses to bedrock types.

Antiaging and Antioxidant Bioactivities of Asteraceae Plant Fractions on the Cellular Functions of the Yeast Schizosaccharomyces pombe.

Research on antioxidants has been gaining worldwide attention because of their essential applications for medicinal purposes. In this study, we conducted bioprospecting of six Asteraceae plants as the source of antiaging and antioxidant agents. Water and chloroform fractions from Ageratum conyzoides L., Dichrocephala integrifolia (L.f.) Kuntze, Galinsoga parviflora (Cav.), Mikania micrantha Kunth, Sphagneticola trilobata (L.) Pruski, and Synedrella nodiflora L. were collected and assayed for their in vitro antioxidant activities and potential antiaging properties using the yeast Schizosaccharomyces pombe as the model organism. Based on the in vitro assay, the water fractions of S. trilobata showed a strong antioxidant activity. Interestingly, all treatment solutions promoted the stress tolerance phenotype of S. pombe to strong H2O2-induced oxidative stress conditions. Moreover, compared with the treatments without plant extract/fraction, all extract and fraction treatments, except the chloroform fractions of A. conyzoides, promoted yeast cell longevity. Strong induction of mitochondria activity was found following the treatments with the extracts and fractions of S. nodiflora, D. integrifolia, and M. micrantha and likely mimicked the calorie restriction-induced lifespan. Interestingly, S. nodiflora water fractions significantly upregulated the mRNA transcripts of the Pap1-mediated core environmental stress response, namely, ctt1 gene in S. pombe. These data indicated that the fractions of Asteraceae plants had potential antioxidant and antiaging activities through various cellular modulations. S. nodiflora water fraction has been shown to have antioxidant and antiaging activities in S. pombe, by modulating stress tolerance response, inducing mitochondrial activity, and increasing the ctt1 gene expression. Compounds analysis identified that S. nodiflora water fraction contained some primarily compounds including oxyphyllacinol, valine, and sugiol.

Strain diversity of plant-associated Lactiplantibacillus plantarum.

SummaryLactiplantibacillus plantarum (formerly Lactobacillus plantarum) is a lactic acid bacteria species found on plants that is essential for many plant food fermentations. In this study, we investigated the intraspecific phenotypic and genetic diversity of 13 L. plantarum strains isolated from different plant foods, including fermented olives and tomatoes, cactus fruit, teff injera, wheat boza and wheat sourdough starter. We found that strains from the same or similar plant food types frequently exhibited similar carbohydrate metabolism and stress tolerance responses. The isolates from acidic, brine‐containing ferments (olives and tomatoes) were more resistant to MRS adjusted to pH 3.5 or containing 4% w/v NaCl, than those recovered from grain fermentations. Strains from fermented olives grew robustly on raffinose as the sole carbon source and were better able to grow in the presence of ethanol (8% v/v or sequential exposure of 8% (v/v) and then 12% (v/v) ethanol) than most isolates from other plant types and the reference strain NCIMB8826R. Cell free culture supernatants from the olive‐associated strains were also more effective at inhibiting growth of an olive spoilage strain of Saccharomyces cerevisiae. Multi‐locus sequence typing and comparative genomics indicated that isolates from the same source tended to be genetically related. However, despite these similarities, other traits were highly variable between strains from the same plant source, including the capacity for biofilm formation and survival at pH 2 or 50°C. Genomic comparisons were unable to resolve strain differences, with the exception of the most phenotypically impaired and robust isolates, highlighting the importance of utilizing phenotypic studies to investigate differences between strains of L. plantarum. The findings show that L. plantarum is adapted for growth on specific plants or plant food types, but that intraspecific variation may be important for ecological fitness and strain coexistence within individual habitats.

Streptococcus mutans Lacking sufCDSUB Is Viable, but Displays Major Defects in Growth, Stress Tolerance Responses and Biofilm Formation.

Streptococcus mutans appears to possess a sole iron-sulfur (Fe-S) cluster biosynthesis system encoded by the sufCDSUB cluster. This study was designed to examine the role of sufCDSUB in S. mutans physiology. Allelic exchange mutants deficient of the whole sufCDSUB cluster and in individual genes were constructed. Compared to the wild-type, UA159, the sufCDSUB-deficient mutant, Δsuf::kanr, had a significantly reduced growth rate, especially in medium with the absence of isoleucine, leucine or glutamate/glutamine, amino acids that require Fe-S clusters for biosynthesis and when grown with medium adjusted to pH 6.0 and under oxidative and nitrosative stress conditions. Relative to UA159, Δsuf::kanr had major defects in stress tolerance responses with reduced survival rate of > 2-logs following incubation at low pH environment or after hydrogen peroxide challenge. When compared to UA159, Δsuf::kanr tended to form aggregates in broth medium and accumulated significantly less biofilm. As shown by luciferase reporter fusion assays, the expression of sufCDSUB was elevated by > 5.4-fold when the reporter strain was transferred from iron sufficient medium to iron-limiting medium. Oxidative stress induced by methyl viologen increased sufCDSUB expression by > 2-fold, and incubation in a low pH environment led to reduction of sufCDSUB expression by > 7-fold. These results suggest that lacking of SufCDSUB in S. mutans causes major defects in various cellular processes of the deficient mutant, including growth, stress tolerance responses and biofilm formation. In addition, the viability of the deficient mutant also suggests that SUF, the sole Fe-S cluster machinery identified is non-essential in S. mutans, which is not known in any other bacterium lacking the NIF and/or ISC system. However, how the bacterium compensates the Fe-S deficiency and if any novel Fe-S assembly systems exist in this bacterium await further investigation.

Diversity of Marine Macro-Algicolous Endophytic Fungi and Cytotoxic Potential of Biscogniauxia petrensis Metabolites Against Cancer Cell Lines.

Hypersaline environments are known to support diverse fungal species from various orders. The production of secondary metabolites is one of the strategies that fungi adopt to thrive under such extreme environments, bringing up the stress tolerance response. Some such unique secondary metabolites also exhibit clinical significance. The increasing prevalence of drug resistance in cancer therapy demands further exploration of these novel bioactive compounds as cancer therapeutics. In the present study, a total of 31 endophytic fungi harboring inside red, green, and brown marine algae have been isolated and identified. The maximum likelihood analysis and diversity indices of fungal endophytes revealed the phylogenetic relationship and species richness. The genus Aspergillus was found to be the dominating fungus, followed by Cladosporium spp. All the isolated endophytic fungal extracts were tested for their cytotoxicity against HeLa and A431 cancer cell lines. Nine isolates were further analyzed for their cytotoxic activity from the culture filtrate and mycelia extract. Among these isolates, Biscogniauxia petrensis showed potential cytotoxicity with CC50 values of 18.04 and 24.85 μg/ml against HeLa and A431 cells, respectively. Furthermore, the media and solvent extraction optimization revealed the highest cytotoxic active compounds in ethyl acetate extract from the potato dextrose yeast extract broth medium. The compound-induced cell death via apoptosis was 50–60 and 45% when assayed using propidium iodide-live/dead and loss of mitochondrial membrane potential assay, respectively, in HeLa cells. Four bioactive fractions (bioassay-based) were obtained and analyzed using chromatography and spectroscopy. This study reports, for the first time, the cytotoxic activity of an endophytic fungal community that was isolated from marine macro-algae in the Rameswaram coastal region of Tamil Nadu, India. In addition, B. petrensis is a prominent apoptotic agent, which can be used in pharmaceutical applications as a therapeutic.

Impact of Mycorrhization on Phosphorus Utilization Efficiency of Acacia gummifera and Retama monosperma under Salt Stress

The impact of salt stress on the growth and phosphorus utilization efficiency (PUE) of two leguminous species: Retama monosperma and Acacia gummifera was studied. The effectiveness of arbuscular mycorrhizal fungi (AMF) to mitigate salt stress was furthermore assessed. Growth, N and P tissue concentrations, mycorrhizal root colonization frequency and intensity, and P utilization efficiency (PUE) in the absence or presence of AMF were evaluated under no salt (0 mM L−1) and three salt (NaCl) concentrations of (25, 50 and 100 mM L−1) using a natural sterilized soil. A significant difference in mycorrhizal colonization intensity, root-to-shoot ratio, P uptake, PUE, and N uptake was observed between the legume species. Salt stress inhibited the shoot and root growth, and reduced P and N uptake by the legume species. Mycorrhizal inoculation aided to mitigate the effects of salt stress with an average increase of shoot and root growth responses by 35% and 32% in the inoculated than in the non-inoculated A. gummifera treatments. The average shoot and root growth responses were 37% and 45% higher in the inoculated compared to the non-inoculated treatments of R. monosperma. Average mycorrhizal shoot and root P uptake responses were 66% and 68% under A. gummifera, and 40% and 95% under R. monosperma, respectively. Mycorrhizal inoculated treatments consistently maintained lower PUE in the roots. The results provide insights for further investigations on the AMF conferred mechanisms to salt stress tolerance response by A. gummifera and R. monosperma, to enable the development of effective technologies for sustainable afforestation and reforestation programs in the Atlantic coast of Morocco.

Rab11‐FIP1 Deficient Mice Develops Spontaneous Inflammation and Show DSS Susceptibility in the Colon

Background and Aims A small GTPase, Rab11a regulates vesicle trafficking and cell polarity in epithelial cells through interacting with Rab11 family-interacting proteins (Rab11-FIPs). Intestine-specific Rab11a knockout mice demonstrate epithelial hyperplasia, dysplasia, and immune cell infiltration, implicating that Rab11a-mediated protein trafficking is important to maintain mucosal homeostasis. Nevertheless, the specific phenotype for loss of Rab11a-binding protein family members, FIPs, had not been fully characterized. We hypothesize that the deficiency of Rab11-FIP1, also known as RCP, affects mucosal integrity in the intestine. Methods Global Rab11-FIP1 knockout (KO) mice were generated by deletion of the exon 2. The immunoreactivity for Rab11-FIP1 antibody in the intestinal epithelial cells was lost in Rab11-FIP1 KO mouse tissues. Pathology of intestinal tissues were analyzed by immunostaining of intestinal sections and RNA-sequencing of isolated colonic epithelial cells. Low concentration of sodium dextran sulfate (DSS, 2%) was added into drinking water for 5 days and colitis score was compared between Rab11-FIP1 KO and heterozygous littermates. Results Birth rate and body weight gain were normal in the Rab11-FIP1 KO mouse line and no gross phenotype was found by the age of 8 weeks. At the age of 8–12 weeks, some Rab11-FIP1 KO mice spontaneously developed rectal prolapse along with chronic inflammation. The morphology and frequency of trefoil factor (TFF)3+ goblet cells in the colon were altered by Rab11-FIP1 loss. The number of lymphoid patches and neutrophil infiltration, which was quantified by Ly6B.2+ cell numbers, in the colon were significantly increased by Rab11-FIP1 loss before the development of rectal prolapse compared to wild type and Rab11-FIP1 heterozygous mice. The frequency of CD3+ intraepithelial lymphocytes and F4/80+ macrophages in colonic lamina propria were also higher in Rab11-FIP1 KO mice. The crypt height and the ratio of Ki67+ proliferating cells were significantly higher in Rab11-FIP1 KO colon. After DSS treatment followed by a 24-hour-recovery period, Rab11-FIP1 KO mice showed greater body weight loss and more severe colonic mucosal damage than in heterozygous littermates. mRNA signatures indicated that Rab11-FIP1 deletion downregulates genes that mediate stress tolerance response, such as Hsp members, Reg4, Nox1, and Ces1g. Genes that mediate the response to infection, including Pla2g2a, Duox2, Abca13, reg3g, Pecam1, and Optn, were significantly upregulated in Rab11-FIP1 KO colon, consistent with spontaneous neutrophil infiltration. Conclusion Loss of Rab11-FIP1 increases spontaneous and DSS-induced inflammatory response, suggesting a decrease in cytoprotection mechanisms in the colon.

Environmental Stress Tolerance and Antioxidant Response of Palisada perforata (Rhodophyta) from a Tropical Reef1.

In this study, we analyzed the antioxidant activity and total phenolic content of the intertidal seaweed Palisada perforata collected from different reef microhabitats (sheltered site, tide pool, plateau, and exposed site) along the coast of Pernambuco (Brazil). Both parameters were compared with the same parameters of this species grown in the laboratory under two experiments simulating temperature, salinity, and desiccation conditions found in the reef. After both experiments (temperature x salinity and desiccation), the algal photosynthetic performance was measured through chlorophyll fluorescence parameters using a pulse-amplitude modulation fluorometer to test their stress response. Palisada perforata likely underwent stress by desiccation due to tidal fluctuations rather than to temperature or salinity changes. This conclusion agrees with our observations of the plateau site´s specimens, which were exposed to both air and UV radiation during low tides and exhibited higher antioxidant activity to avoid oxidative damage. However, despite the environmental stress, the antioxidant activity remained low, suggesting that photoinhibition is a crucial protection mechanism against oxidative damage.

CRISPR-Cas technology based genome editing for modification of salinity stress tolerance responses in rice (Oryza sativa L.).

Clustered regularly interspaced short palindromic repeats (CRISPR)-CRISPR associated protein (Cas) technology is an effective tool for site-specific genome editing, used to precisely induce mutagenesis in different plant species including rice. Salinity is one of the most stressful environmental constraints affecting agricultural productivity worldwide. As plant adaptation to salinity stress is under polygenic control therefore, 51 rice genes have been identified that play crucial role in response to salinity. This review offers an exclusive overview of genes identified in rice genome for salinity stress tolerance. This will provide an idea to produce rice varieties with enhanced salt tolerance using the potentially efficient CRISPR-Cas technology. Several undesirable off-target effects of CRISPR-Cas technology and their possible solutions have also been highlighted.

Yeasts Isolated from Traditional Brem Bali Show Stress Tolerance Phenotype against Fermentation-Related Stresses

The search for microbes, primarily yeasts with unique characters such as the tolerance against fermentation-related-stresses, is gaining significant interest nowadays. Traditionally made alcoholic beverages can be used as sources for such yeasts, given that during fermentation and storage, microbes may develop stress tolerance responses leading to naturally stress-tolerant yeast strains. In this study, we used an alcoholic beverage, that is, Brem Bali, as the source of potential yeast isolates. We isolated nine yeast isolates from two traditional Brem Bali products. All isolates showed tolerance against high glucose stress (40–50%) and sensitivity against high-temperature stress (37–50 °C). Notably, isolate BT5 showed tolerance phenotype against ethanol stress (up to 12.5%). Notably, the ethanol stress tolerance phenotype shown by isolate BT5 was unlikely correlated to the ability of the isolates in combating other stresses. Based on the internal transcribed spacer sequence, isolates BT2, BT5, and BT6 shared high similarity with Wickerhamomyces anomalus (98%). Further approaches may be needed to clarify the identity of these isolates. Based on our study, isolate BT5 bears potential as a fermentation agent based on its ability to combat high glucose and ethanol stresses.

Nutritional manipulation to combat heat stress in poultry - A comprehensive review.

Global warming and climate change adversely affect livestock and poultry production sectors under tropical and subtropical conditions. Heat stress is amongst the most significant stressors influencing poultry productivity in hot climate regions, causing substantial economic losses in poultry industry. These economic losses are speculated to increase in the coming years with the rise of global temperature. Moreover, modern poultry strains are more susceptible to high ambient temperature. Heat stress has negative effects on physiological response, growth performance and laying performance, which appeared in the form of reducing feed consumption, body weight gain, egg production, feed efficiency, meat quality, egg quality and immune response. Numerous practical procedures were used to ameliorate the negative impacts of increased temperature; among them the dietary manipulation, which gains a great concern in different regions around the world. These nutritional manipulations are feed additives (natural antioxidants, minerals, electrolytes, phytobiotics, probiotics, fat, and protein), feed restriction, feed form, drinking cold water and others. However, in the large scale of poultry industry, only a few of these strategies are commonly used. The current review article deliberates the different practical applications of useful nutritional manipulations to mitigate the heat load in poultry. The documented information will be useful to poultry producers to improve the general health status and productivity of heat-stressed birds via enhancing stress tolerance, oxidative status and immune response, and thereby provide recommendations to minimize production losses due to heat stress in particular under the growing global warming crisis.

Differential gene expression reveals candidate genes for osmotic stress response in faba bean (Vicia faba L.) involved in different molecular pathways

Drought and salinity are the most important environmental constraints affecting faba bean (Vicia faba L.) development and crop yield in Tunisia and other Mediterranean countries. Through using different strategies, associating in silico analysis of gene expression and qRT-PCR, this study aims at identifying key genes of faba bean molecular pathways potentially involved in salt and drought response. The impact of these stresses on several physiological and biochemical parameters were investigated in two genotypes (Bachar and Giza 3). To uncover abiotic stress-related genes and better understand the mechanisms of salt and drought stress tolerance in faba bean, a total of 25 faba bean genes were identified through in silico analysis. These genes were associated with important cellular processes such as transcription regulation, signal transport, kinases, phytohormonal signaling, and defense/stress responses. Most of the studied candidates were expressed at various levels in different organs including leaves, roots, flowers, stems, cotyledons, and seeds suggesting a potential role in the growth and development of faba bean plants. Furthermore, qRT-PCR was used to study gene expression profiles in leaves and roots of Bachar and Giza 3 plants under salt and drought stresses, and ABA treatment. The results showed that selected transcripts were differentially expressed under various treatments in both genotypes suggesting their important roles in abiotic stress tolerance responses. The osmotic-responsive genes identified in this study may be considered as potential candidates with a further application as stress selection markers for the creation of faba bean stress-tolerant varieties in various breeding programs.

A Multi-OMICs Approach Sheds Light on the Higher Yield Phenotype and Enhanced Abiotic Stress Tolerance in Tobacco Lines Expressing the Carrot lycopene β-cyclase1 Gene.

Recently, we published a set of tobacco lines expressing the Daucus carota (carrot) DcLCYB1 gene with accelerated development, increased carotenoid content, photosynthetic efficiency, and yield. Because of this development, DcLCYB1 expression might be of general interest in crop species as a strategy to accelerate development and increase biomass production under field conditions. However, to follow this path, a better understanding of the molecular basis of this phenotype is essential. Here, we combine OMICs (RNAseq, proteomics, and metabolomics) approaches to advance our understanding of the broader effect of LCYB expression on the tobacco transcriptome and metabolism. Upon DcLCYB1 expression, the tobacco transcriptome (~2,000 genes), proteome (~700 proteins), and metabolome (26 metabolites) showed a high number of changes in the genes involved in metabolic processes related to cell wall, lipids, glycolysis, and secondary metabolism. Gene and protein networks revealed clusters of interacting genes and proteins mainly involved in ribosome and RNA metabolism and translation. In addition, abiotic stress-related genes and proteins were mainly upregulated in the transgenic lines. This was well in line with an enhanced stress (high light, salt, and H2O2) tolerance response in all the transgenic lines compared with the wild type. Altogether, our results show an extended and coordinated response beyond the chloroplast (nucleus and cytosol) at the transcriptome, proteome, and metabolome levels, supporting enhanced plant growth under normal and stress conditions. This final evidence completes the set of benefits conferred by the expression of the DcLCYB1 gene, making it a very promising bioengineering tool to generate super crops.

Repression of the TreR transcriptional regulator in Streptococcus mutans by the global regulator, CcpA

Streptococcus mutans, the etiologic agent of dental caries in humans, is considered a dominating force in the oral microbiome due to its highly-evolved propensity for survival. The oral pathogen encodes an elaborate array of regulatory elements, including the carbon catabolite-responsive regulator, CcpA, a global regulator key in the control of sugar metabolism and in stress tolerance response mechanisms. The recently characterized trehalose utilization operon, integral for the catabolism of the disaccharide trehalose, is controlled by a local regulator, TreR, which has been implicated in a number of cellular functions outside of trehalose catabolism. Electrophoretic mobility shift assays demonstrated that CcpA bound a putative cre site in the treR promoter. Loss of ccpA resulted in elevated expression of treR in cultures of the organism grown in glucose or trehalose, indicating that CcpA not only acts as a repressor of trehalose catabolism genes, but also the local regulator. The loss of both CcpA and TreR in S. mutans resulted in an impaired growth rate and fitness response, supporting the hypothesis that these regulators are involved in carbon catabolism control and in induction of components of the organism's stress response.

Transcription factors as key molecular target to strengthen the drought stress tolerance in plants.

Amid apprehension of global climate change, crop plants are inevitably confronted with a myriad of abiotic stress factors during their growth that inflicts a serious threat to their development and overall productivity. These abiotic stresses comprise extreme temperature, pH, high saline soil, and drought stress. Among different abiotic stresses, drought is considered the most calamitous stressor with its serious impact on the crops' yield stability. The development of climate-resilient crops that withstands reduced water availability is a major focus of the scientific fraternity to ensure the food security of the sharply increasing population. Numerous studies aim to recognize the key regulators of molecular and biochemical processes associated with drought stress tolerance response. A few potential candidates are now considered as promising targets for crop improvement. Transcription factors act as a key regulatory switch controlling the gene expression of diverse biological processes and, eventually, the metabolic processes. Understanding the role and regulation of the transcription factors will facilitate the crop improvement strategies intending to develop and deliver agronomically-superior crops. Therefore, in this review, we have emphasized the molecular avenues of the transcription factors that can be exploited to engineer drought tolerance potential in crop plants. We have discussed the molecular role of several transcription factors, such as basic leucine zipper (bZIP), dehydration responsive element binding (DREB), DNA binding with one finger (DOF), heat shock factor (HSF), MYB, NAC, TEOSINTE BRANCHED1/CYCLOIDEA/PCF (TCP), and WRKY. We have also highlighted candidate transcription factors that can be used for the development of drought-tolerant crops.

Cell Membrane Stability and Relative Cell Injury in Response to Heat Stress during Early and Late Seedling Stages of Diverse Carrot (Daucus carota L.) Germplasm

Heat waves occur with more regularity and they adversely affect the yield of cool season crops including carrot (Daucus carota L.). Heat stress influences various biochemical and physiological processes including cell membrane permeability. Ion leakage and increase in cell permeability are indicators of cell membrane stability and have been used to evaluate the stress tolerance response in numerous crops and inform plant breeders for improving heat tolerance. No study has been published about the effects of heat stress on cell membrane stability and relative cell injury of carrot. Therefore, the present study was designed to estimate these stress indicators in response to heat stress at the early and late seedling developmental stages of 215 diverse accessions of wild and cultivated carrot germplasm. The article identifies the relationship between early and late stages of seedling tolerance across carrot genotypes and identifies heat-tolerant genotypes for further genetic analysis. Significant genetic variation among these stress indicators was identified with cell membrane stability and relative cell injury ranging from 6.3% to 97.3% and 2.8% to 76.6% at the early seedling stage, respectively; whereas cell membrane stability and relative cell injury ranged from 2.0% to 94.0% and 2.5% to 78.5%, respectively, at the late seedling stage under heat stress. Broad-sense heritability ranged from 0.64 to 0.91 for traits of interest under study, which indicates a relatively strong contribution of genetic factors in phenotypic variation among accessions. Heat tolerance varied widely among both wild and cultivated accessions, but the incidence of tolerance was higher in cultivated carrots than in wild carrots. The cultivated carrot accessions PI 326009 (Uzbekistan), PI 451754 (Netherlands), L2450 (USA), and PI 502654 (Pakistan) were identified as the most heat-tolerant accessions with highest cell membrane stability. This is the first evaluation of cell membrane stability and relative cell injury in response to heat stress during carrot development.

Multiple Cold Tolerance Trait Phenotyping Reveals Shared Quantitative Trait Loci in Oryza sativa

BackgroundDeveloping chilling tolerant accessions of domesticated Asian rice is a potential source of significant crop improvement. The uniquely chilling sensitive nature of the tropically originating Oryza sativa make it the most important cereal crop that can gain significantly from improved tolerance to low temperatures. However, mechanisms underlying this complex trait are not fully understood. Oryza sativa has two subspecies with different levels of chilling tolerance, JAPONICA and INDICA, providing an ideal tool to investigate mechanistic differences in the chilling stress tolerance responses within this important crop species.ResultsThe Rice Diversity Panel 1 (RDP1) was used to investigate a core set of Oryza sativa accessions. The tools available for this panel allowed for a comprehensive analysis of two chilling tolerance traits at multiple temperatures across a 354-cultivar subset of the RDP1. Chilling tolerance trait values were distributed as mostly subpopulation specific clusters of Tolerant, Intermediate, and Sensitive accessions. Genome-wide association study (GWAS) mapping approaches using all 354 accessions yielded a total of 245 quantitative trait loci (QTL), containing 178 unique QTL covering 25% of the rice genome, while 40 QTL were identified by multiple traits. QTL mappings using subsets of rice accession clusters yielded another 255 QTL, for a total of 500 QTL. The genes within these multiple trait QTL were analyzed for Gene Ontology (GO) term and potential pathway enrichments. Terms related to “carbohydrate biosynthesis”, “carbohydrate transmembrane transport”, “small molecule protein modification”, and “plasma membrane” were enriched from this list. Filtering was done to identify more likely candidate pathways involved in conferring chilling tolerance, resulting in enrichment of terms related to “Golgi apparatus”, “stress response”, “transmembrane transport”, and “signal transduction”.ConclusionsTaken together, these GO term clusters revealed a likely involvement of Golgi-mediated subcellular and extracellular vesicle and intracellular carbohydrate transport as a general cold stress tolerance response mechanism to achieve cell and metabolic homeostasis under chilling stress.

Significance of Individual Domains of ClpL: A Novel Chaperone from Streptococcus mutans.

ClpL is a member of the HSP100 family of AAA+ chaperones that is widely present in Gram-positive but surprisingly absent in Gram-negative bacteria. ClpL is involved in various cellular processes, including stress tolerance response, long-term survival, virulence, and antibiotic resistance. ClpL is poorly characterized, and its molecular mechanisms of chaperone activity are largely unclear. Here, we biochemically characterized the ClpL protein from Streptococcus mutans, a dental pathogen, to understand its biological functions. ClpL harbors five domains: N-domain, two nucleotide binding domains (NBD-1 and NBD-2), M-domain, and C-domain. NBD-1 and NBD-2 contain distinct Walker A and B motifs for ATP binding and hydrolysis, respectively. We found that ClpL predominantly exists as a trimer in solution; however, upon ATP binding, it rapidly forms a hexameric structure. To study structure-function activity, we constructed several substitution and deletion mutants. We found that mutations in the Walker A and B motifs interfered with ATP hydrolysis and oligomerization. Similarly, deletions of N-, M-, and C-domains abolished both ATPase activity and oligomerization. Because we previously found that ClpL acts as a chaperone, we analyzed the chaperone activity. Surprisingly, we found that the NBD-2 mutants did not display any chaperone activity, indicating that ATP binding and hydrolysis by NBD-2 are essential for the chaperone. However, NBD-1 mutants showed chaperone activities, but the activities were variable depending on the nature of the mutations. Our results indicate that unlike other HSP100 family chaperones, ClpL is a novel chaperone that does not require any additional secondary chaperones for its activity.