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Background Metal homeostasis is critical for plant growth, development and adaptation to environmental stresses and largely governed by a variety of metal transporters. The plant ZIP ( Z n-regulated transporter, I ron-regulated transporter-like P rotein) family proteins belong to the integral membrane transporters responsible for uptake and allocation of essential and non-essential metals. However, whether the ZIP family members mediate metal efflux and its regulatory mechanism remains unknown. Results In this report, we provided evidence that OsZIP1 is a metal-detoxified transporter through preventing excess Zn, Cu and Cd accumulation in rice. OsZIP1 is abundantly expressed in roots throughout the life span and sufficiently induced by excess Zn, Cu and Cd but not by Mn and Fe at transcriptional and translational levels. Expression of OsZIP-GFP fusion in rice protoplasts and tobacco leaves shows that OsZIP1 resides in the endoplasmic reticulum (ER) and plasma membrane (PM). The yeast ( Saccharomyces cerevisiae ) complementation test shows that expression of OsZIP1 reduced Zn accumulation. Transgenic rice overexpressing OsZIP1 grew better under excess metal stress but accumulated less of the metals in plants. In contrast, both oszip1 mutant and RNA interference (RNAi) lines accumulated more metal in roots and contributed to metal sensitive phenotypes. These results suggest OsZIP1 is able to function as a metal exporter in rice when Zn, Cu and Cd are excess in environment. We further identified the DNA methylation of histone H3K9me2 of OsZIP1 and found that OsZIP1 locus, whose transcribed regions imbed a 242 bp sequence, is demethylated, suggesting that epigenetic modification is likely associated with OsZIP1 function under Cd stress. Conclusion OsZIP1 is a transporter that is required for detoxification of excess Zn, Cu and Cd in rice.

Background Being sessile organisms, plants are often exposed to a wide array of abiotic and biotic stresses. Abiotic stress conditions include drought, heat, cold and salinity, whereas biotic stress arises mainly from bacteria, fungi, viruses, nematodes and insects. To adapt to such adverse situations, plants have evolved well-developed mechanisms that help to perceive the stress signal and enable optimal growth response. Phytohormones play critical roles in helping the plants to adapt to adverse environmental conditions. The elaborate hormone signaling networks and their ability to crosstalk make them ideal candidates for mediating defense responses. Results Recent research findings have helped to clarify the elaborate signaling networks and the sophisticated crosstalk occurring among the different hormone signaling pathways. In this review, we summarize the roles of the major plant hormones in regulating abiotic and biotic stress responses with special focus on the significance of crosstalk between different hormones in generating a sophisticated and efficient stress response. We divided the discussion into the roles of ABA, salicylic acid, jasmonates and ethylene separately at the start of the review. Subsequently, we have discussed the crosstalk among them, followed by crosstalk with growth promoting hormones (gibberellins, auxins and cytokinins). These have been illustrated with examples drawn from selected abiotic and biotic stress responses. The discussion on seed dormancy and germination serves to illustrate the fine balance that can be enforced by the two key hormones ABA and GA in regulating plant responses to environmental signals. Conclusions The intricate web of crosstalk among the often redundant multitudes of signaling intermediates is just beginning to be understood. Future research employing genome-scale systems biology approaches to solve problems of such magnitude will undoubtedly lead to a better understanding of plant development. Therefore, discovering additional crosstalk mechanisms among various hormones in coordinating growth under stress will be an important theme in the field of abiotic stress research. Such efforts will help to reveal important points of genetic control that can be useful to engineer stress tolerant crops.

Background Sesame is an important oil crop due to its high oil, antioxidant, and protein content. Drought stress is a major abiotic stress that affects sesame production as well as the quality of sesame seed. To reveal the adaptive mechanism of sesame in response to water deficient conditions, transcriptomic and metabolomics were applied in drought-tolerant (DT) and drought-susceptible (DS) sesame genotypes. Results Transcriptomic analysis reveals a set of core drought-responsive genes (684 up-regulated and 1346 down-regulated) in sesame that was robustly differently expressed in both genotypes. Most enriched drought-responsive genes are mainly involved in protein processing in endoplasmic reticulum, plant hormone signal transduction photosynthesis, lipid metabolism, and amino acid metabolism. Drought-susceptible genotype was more disturbed by drought stress at both transcriptional and metabolic levels, since more drought-responsive genes/metabolites were identified in DS. Drought-responsive genes associated with stress response, amino acid metabolism, and reactive oxygen species scavenging were more enriched or activated in DT. According to the partial least-squares discriminate analysis, the most important metabolites which were accumulated under drought stress in both genotypes includes ABA, amino acids, and organic acids. Especially, higher levels of ABA, proline, arginine, lysine, aromatic and branched chain amino acids, GABA, saccharopine, 2-aminoadipate, and allantoin were found in DT under stress condition. Combination of transcriptomic and metabolomic analysis highlights the important role of amino acid metabolism (especially saccharopine pathway) and ABA metabolism and signaling pathway for drought tolerance in sesame. Conclusion The results of the present study provide valuable information for better understanding the molecular mechanism underlying drought tolerance of sesame, and also provide useful clues for the genetic improvement of drought tolerance in sesame.

Background Bioactive compounds, vitamins, phenolic acids, flavonoids of A. tricolor are the sources of natural antioxidant that had a great importance for the food industry as these detoxify ROS in the human body. These natural antioxidants protect human from many diseases such as cancer, arthritis, emphysema, retinopathy, neuro-degenerative cardiovascular diseases, atherosclerosis and cataracts. Moreover, previous literature has shown that drought stress elevated bioactive compounds, vitamins, phenolics, flavonoids and antioxidant activity in many leafy vegetables. Hence, we study the nutritional and bioactive compounds, phenolic acids, flavonoids and antioxidant capacity of amaranth under drought stress for evaluation of the significant contribution of these compounds in the human diet. Results The genotype VA3 was assessed at four drought stress levels that significantly affected nutritional and bioactive compounds, phenolic acids, flavonoids and antioxidant capacity. Protein, ash, energy, dietary fiber, Ca, K, Cu, S, Mg, Mn, Mo, Na, B content, total carotenoids, TFC, vitamin C, TPC, TAC (DPPH), betacarotene, TAC (ABTS + ), sixteen phenolic acids and flavonoids were remarkably increased with the severity of drought stress. At moderate and severe drought stress conditions, the increments of all these components were more preponderant. Trans -cinnamic acid was newly identified phenolic acid in A. tricolor . Salicylic acid, vanilic acid, gallic acid, chlorogenic acid, Trans -cinnamic acid, rutin, isoquercetin, m -coumaric acid and p -hydroxybenzoic acid were the most abundant phenolic compounds in this genotype. Conclusions In A. tricolor, drought stress enhanced the quantitative and qualitative improvement of nutritional and bioactive compounds, phenolic acids, flavonoids and antioxidants. Hence, farmers of semi-arid and dry areas of the world could be able to grow amaranth as a substitute crop.

Background Heavy metal toxicity has become a major threat to sustainable crop production worldwide. Thus, considerable interest has been placed on deciphering the mechanisms that allow plants to combat heavy metal stress. Strategies to deal with heavy metals are largely focused on detoxification, transport and/or sequestration. The P 1B subfamily of the H eavy M etal-transporting P-type A TPases (HMAs) was shown to play a crucial role in the uptake and translocation of heavy metals in plants. Here, we report the locus-specific expression changes in the rice HMA genes together with several low-copy cellular genes and transposable elements upon the heavy metal treatment and monitored the transgenerational inheritance of the altered expression states. We reveal that plants cope with heavy metal stress by making heritable changes in gene expression and further determined gene-specific responses to heavy metal stress. Results We found most HMA genes were upregulated in response to heavy metal stress, and furthermore found evidence of transgenerational memory via changes in gene regulation even after the removal of heavy metals. To explore whether DNA methylation was also altered in response to the heavy metal stress, we selected a Tos17 retrotransposon for bisulfite sequencing and studied its methylation state across three generations. We found the DNA methylation state of Tos17 was altered in response to the heavy metal stress and showed transgenerational inheritance. Conclusions Collectively, the present study elucidates heritable changes in gene expression and DNA methylation in rice upon exposure to heavy metal stress and discusses implications of this knowledge in breeding for heavy metal tolerant crops.

Background Abiotic stresses due to environmental factors could adversely affect the growth and development of crops. Among the abiotic stresses, drought and heat stress are two critical threats to crop growth and sustainable agriculture worldwide. Considering global climate change, incidence of combined drought and heat stress is likely to increase. The aim of this study was to shed light on plant growth performance and leaf physiology of three tomatoes cultivars (‘Arvento’, ‘LA1994’ and ‘LA2093’) under control, drought, heat and combined stress. Results Shoot fresh and dry weight, leaf area and relative water content of all cultivars significantly decreased under drought and combined stress as compared to control. The net photosynthesis and starch content were significantly lower under drought and combined stress than control in the three cultivars. Stomata and pore length of the three cultivars significantly decreased under drought and combined stress as compared to control. The tomato ‘Arvento’ was more affected by heat stress than ‘LA1994’ and ‘LA2093’ due to significant decreases in shoot dry weight, chlorophyll a and carotenoid content, starch content and NPQ (non-photochemical quenching) only in ‘Arvento’ under heat treatment. By comparison, the two heat-tolerant tomatoes were more affected by drought stress compared to ‘Arvento’ as shown by small stomatal and pore area, decreased sucrose content, Φ PSII (quantum yield of photosystem II), ETR (electron transport rate) and q L (fraction of open PSII centers) in ‘LA1994’ and ‘LA2093’. The three cultivars showed similar response when subjected to the combination of drought and heat stress as shown by most physiological parameters, even though only ‘LA1994’ and ‘LA2093’ showed decreased F v /F m (maximum potential quantum efficiency of photosystem II), Φ PSII , ETR and q L under combined stress. Conclusions The cultivars differing in heat sensitivity did not show difference in the combined stress sensitivity, indicating that selection for tomatoes with combined stress tolerance might not be correlated with the single stress tolerance. In this study, drought stress had a predominant effect on tomato over heat stress, which explained why simultaneous application of heat and drought revealed similar physiological responses to the drought stress. These results will uncover the difference and linkage between the physiological response of tomatoes to drought, heat and combined stress and be important for the selection and breeding of tolerant tomato cultivars under single and combine stress.

Background NAC (NAM, ATAF and CUC) transcriptional factors constitute a large family with more than 150 members in rice and several members of this family have been demonstrated to play crucial roles in rice abiotic stress response. In the present study, we report the function of a novel stress-responsive NAC gene, ONAC066 , in rice drought and oxidative stress tolerance. Results ONAC066 was localized in nuclei of cells when transiently expressed in Nicotiana benthamiana and is a transcription activator with the binding ability to NAC recognition sequence (NACRS) and AtJUB1 binding site (JBS). Expression of ONAC066 was significantly induced by PEG, NaCl, H 2 O 2 and abscisic acid (ABA). Overexpression of ONAC066 in transgenic rice improved drought and oxidative stress tolerance and increased ABA sensitivity, accompanied with decreased rate of water loss, increased contents of proline and soluble sugars, decreased accumulation of reactive oxygen species (ROS) and upregulated expression of stress-related genes under drought stress condition. By contrast, RNAi-mediated suppression of ONAC066 attenuated drought and oxidative stress tolerance and decreased ABA sensitivity, accompanied with increased rate of water loss, decreased contents of proline and soluble sugars, elevated accumulation of ROS and downregulated expression of stress-related genes under drought stress condition. Furthermore, yeast one hybrid and chromatin immunoprecipitation-PCR analyses revealed that ONAC066 bound directly to a JBS-like cis -elements in OsDREB2A promoter and activated the transcription of OsDREB2A . Conclusion ONAC066 is a nucleus-localized transcription activator that can respond to multiple abiotic stress factors. Functional analyses using overexpression and RNAi-mediated suppression transgenic lines demonstrate that ONAC066 is a positive regulator of drought and oxidative stress tolerance in rice.

Background High temperature is a major environmental stress that limits plant growth and agriculture productivity. Mitogen-activated protein kinases (MAPKs) are highly conserved serine and threonine protein kinases that participate in response to diverse environmental stresses in plants. A total of 16 putative SlMAPK genes are identified in tomato, and SlMAPK3 is one of the most extensively studied SlMAPKs . However, the role of SlMAPK3 in response to heat stress is not clearly understood in tomato plants. In this study, we performed functional analysis of SlMAPK3 for its possible role in response to heat stress. Results qRT-PCR analyses revealed that SlMAPK3 relative expression was depressed by heat stress. Here, wild-type (WT) tomato plants and CRISPR/Cas9-mediated slmapk3 mutant lines (L8 and L13) were used to investigate the function of SlMAPK3 in response to heat stress. Compared with WT plants, slmapk3 mutants exhibited less severe wilting and less membrane damage, showed lower reactive oxygen species (ROS) contents, and presented higher both activities and transcript levels of antioxidant enzymes, as well as elevated expressions of genes encoding heat stress transcription factors ( HSFs ) and heat shock proteins ( HSPs ). Conclusions CRISPR/Cas9-mediated slmapk3 mutants exhibited more tolerance to heat stress than WT plants, suggesting that SlMAPK3 was a negative regulator of thermotolerance. Moreover, antioxidant enzymes and HSPs / HSFs genes expression were involved in SlMAPK3 -mediated heat stress response in tomato plants.

Background High temperature is a major abiotic stress that limits wheat ( Triticum aestivum L.) productivity. Variation in levels of a wide range of lipids, including stress-related molecular species, oxidative damage, cellular organization and ultrastructural changes were analyzed to provide an integrated view of the factors that underlie decreased photosynthetic rate under high temperature stress. Wheat plants of cultivar Chinese Spring were grown at optimum temperatures (25/15 °C, maximum/minimum) until the onset of the booting stage. Thereafter, plants were exposed to high temperature (35/25 °C) for 16 d. Results Compared with optimum temperature, a lower photosynthetic rate was observed at high temperature which is an interplay between thylakoid membrane damage, thylakoid membrane lipid composition, oxidative damage of cell organelle, and stomatal and non-stomatal limitations. Triacylglycerol levels were higher under high temperature stress. Polar lipid fatty acyl unsaturation was lower at high temperature, while triacylglycerol unsaturation was the same at high temperature and optimum temperature. The changes in lipid species indicates increases in activities of desaturating, oxidizing, glycosylating and acylating enzymes under high temperature stress. Cumulative effect of high temperature stress led to generation of reactive oxygen species, cell organelle and membrane damage, and reduced antioxidant enzyme activity, and imbalance between reactive oxygen species and antioxidant defense system. Conclusions Taken together with recent findings demonstrating that reactive oxygen species are formed from and are removed by thylakoid lipids, the data suggest that reactive oxygen species production, reactive oxygen species removal, and changes in lipid metabolism contribute to decreased photosynthetic rate under high temperature stress.

Background Salinity is one of the damaging abiotic stress factor. Proper management techniques have been proposed to considerably lower the intensity of salinity on crop growth and productivity. Therefore experiments were conducted to assess the role of improved nitrogen (N) supplementation on the growth and salinity stress tolerance in wheat by analyzing the antioxidants, osmolytes and secondary metabolites. Results Salinity (100 mM NaCl) stress imparted deleterious effects on the chlorophyll and carotenoid synthesis as well as the photosynthetic efficiency. N supplementation resulted in increased photosynthetic rate, stomatal conductance and internal CO 2 concentration with effects being much obvious in seedlings treated with higher N dose. Under non-saline conditions at both N levels, protease and lipoxygenase activity reduced significantly reflecting in reduced oxidative damage. Such effects were accompanied by reduced generation of toxic radicals like hydrogen peroxide and superoxide, and lipid peroxidation in N supplemented seedlings. Antioxidant defence system was up-regulated under saline and non-saline growth conditions due to N supplementation leading to protection of major cellular processes like photosynthesis, membrane structure and function, and mineral assimilation. Increased osmolyte and secondary metabolite accumulation, and redox components in N supplemented plants regulated the ROS metabolism and NaCl tolerance by further strengthening the antioxidant mechanisms. Conclusions Findings of present study suggest that N availability regulated the salinity tolerance by reducing Na uptake and strengthening the key tolerance mechanisms.