Characterization of the promoter region of an Arabidopsis gene for 9-cis-epoxycarotenoid dioxygenase involved in dehydration-inducible transcription

Nanoparticles as a Tool for Alleviating Plant Stress: Mechanisms, Implications, and Challenges

Plants, being sessile, are continuously exposed to varietal environmental stressors, which consequently induce various bio-physiological changes in plants that hinder their growth and development. Oxidative stress is one of the undesirable consequences in plants triggered due to imbalance in their antioxidant defense system. Biochemical studies suggest that nanoparticles are known to affect the antioxidant system, photosynthesis, and DNA expression in plants. In addition, they are known to boost the capacity of antioxidant systems, thereby contributing to the tolerance of plants to oxidative stress. This review study attempts to present the overview of the role of nanoparticles in plant growth and development, especially emphasizing their role as antioxidants. Furthermore, the review delves into the intricate connections between nanoparticles and plant signaling pathways, highlighting their influence on gene expression and stress-responsive mechanisms. Finally, the implications of nanoparticle-assisted antioxidant strategies in sustainable agriculture, considering their potential to enhance crop yield, stress tolerance, and overall plant resilience, are discussed.

The Effect of External Treatment of Arabidopsis thaliana with Plant-Derived Stilbene Compounds on Plant Resistance to Abiotic Stresses

Stilbenes are a group of plant phenolic secondary metabolites, with trans-resveratrol (3,5,4'-trihydroxy-trans-stilbene) being recognized as the most prominent and studied member. Stilbenes have a great potential for use in agriculture and medicine, as they have significant activities against plant pathogens and have valuable beneficial effects on human health. In this study, we analyzed the effects of direct application of stilbenes, stilbene precursor, and stilbene-rich extract solutions to the plant foliar surface for increasing the resistance of Arabidopsis thaliana to various abiotic stresses (heat, cold, drought, and soil salinity). Exogenous treatment of A. thaliana with stilbenes (trans-resveratrol, piceid, and spruce bark extract) and phenolic precursor (p-coumaric acid or CA) during germination resulted in considerable growth retardation of A. thaliana plants: a strong delay in the root and stem length of 1-week-old seedlings (in 1.3-4.5 fold) and rosette diameter of 1-month-old plants (in 1.2-1.8 fold), while the 2-month-old treated plants were not significantly different in size from the control. Plant treatments with stilbenes and CA increased the resistance of A. thaliana to heat and, to a lesser extent, to soil salinity (only t-resveratrol and spruce extract) to drought (only CA), while cold resistance was not affected. Plant treatments with stilbenes and CA resulted in a significant increase in plant resistance and survival rates under heat, with plants showing 1.5-2.3 times higher survival rates compared to untreated plants. Thus, exogenous stilbenes and a CA are able to improve plant survival under certain abiotic stresses via specific activation of the genes involved in the biosynthesis of auxins, gibberellins, abscisic acid, and some stress-related genes. The present work provides new insights into the application of stilbenes to improve plant stress tolerance.

Characteristics analysis of Early Responsive to Dehydration genes in Arabidopsis thaliana (AtERD)

Early Responsive to Dehydration (ERD) genes are rapidly induced in response to various biotic and abiotic stresses, such as bacteria, drought, light, temperature and high salt in Arabidopsis thaliana. Sixteen ERD of Arabidopsis thaliana (AtERD) genes have been previously identified. The lengths of the coding region of the genes are 504-2838 bp. They encode 137-745 amino acids. In this study, the AtERD genes structure and promoter are analyzed through bioinformatics, and a overall function is summarized and a systematic signal pathway involving AtERD genes is mapped. AtERD9, AtERD11 and AtERD13 have the GST domain. AtERD10 and AtERD14 have the Dehyd domain. The promoters regions contain 32 light responsive elements, 23 ABA responsive elements, 5 drought responsive elements, 5 meristem expression related elements and 132 core promoter elements. The study provides a theoretical guidance for subsequent studies of AtERD genes.

Physiological and transcriptional regulation in Taxodium hybrid 'Zhongshanshan' leaves in acclimation to prolonged partial submergence

MAIN CONCLUSION

Taxodium 703 leaves activate fermentation, amino acids metabolism and ROS detoxification, and reduce TCA cycle and ABA biosynthesis in acclimation to prolonged partial submergence stress. Taxodium hybrid 'Zhongshanshan 703' (T. mucronatum × T. distichum; Taxodium 703) is a highly flooding-tolerant woody plant. To investigate the physiological and transcriptional regulatory mechanisms underlying its leaves in acclimation to long-term flooding, we exposed cuttings of Taxodium 703 to either non-flooding (control) or partial submergence for 2 months. The leaf tissues above (AL) and below (BL) flooding-water were separately harvested. Partial submergence decreased concentrations of chlorophyll (a + b) and dehydroascorbate (DHA) and lactate dehydrogenase (LDH) activity in AL, and reduced biomass, concentrations of succinic acid, fumaric acid and malic acid, and transcript levels of genes involved in tricarboxylic acid (TCA) cycle in BL. Under partial submergence, concentrations of starch, malondialdehyde and abscisic acid (ABA) decreased, and also mRNA levels of nine-cis-epoxycarotenoid dioxygenases that are involved in ABA biosynthesis in AL and BL of Taxodium 703. Partial submergence increased O2- content in AL, and improved concentrations of pyruvate and soluble sugars and activities of LDH and peroxidase in BL. In addition, partial submergence increased concentrations of ethanol, lactate, alanine, γ-aminobutyric acid, total amino acids and ascorbic acid (ASA), and ASA/DHA, activities of alcohol dehydrogenases (ADH) and ascorbate peroxidase, as well as transcript levels of ADH1A, ADH1B and genes involved in alanine biosynthesis and starch degradation in AL and BL of Taxodium 703. Overall, these results suggest that Taxodium 703 leaves activate fermentation, amino acids metabolism and reactive oxygen species detoxification, and maintain a steady supply of sugars, and reduce TCA cycle and ABA biosynthesis in acclimation to prolonged partial submergence stress.

Characterization of wheat Wrab18 gene promoter and expression analysis under abiotic stress

BACKGROUND

Promoters play key roles in plant gene expression in complex and varied natural environments. The type and amount of cis-acting elements in the promoter sequence tend to indicate the response of genes to induction factors. WRAB18 is a group III member of the late embryogenesis abundant (LEA) protein family that performs multiple functions in plant stress physiology. To elucidate the particularly biological effects of WRAB18 on stress, exploration of its promoter sequence is necessary.

METHODS AND RESULTS

In this study, the full-length and promoter sequences of Wrab18 were isolated from the Zhengyin 1 cultivar of Triticum aestivum. The gene sequences and cis-acting elements in the promoter were analyzed using the Plant Promoter Database and bioinformatics methods. The results showed that Wrab18 possessed one intron with 100 bp, the promoter sequence contained various stress-related cis-acting elements, and the functionality of the promoter was checked using green fluorescent protein (GFP) marker protein expression by transient assay in Nicotiana benthamiana. Furthermore, based on promoter prediction analysis, quantitative real-time fluorescent PCR results confirmed the response of gene expression levels to stress factors.

CONCLUSIONS

In summary, the promoter sequence of Wrab18 plays a role in plant stress responses, contains multiple cis-acting elements, and provides insights into the role of WRAB18 in plant resilience to stress. This study has guiding significance for further studies of gene function and mechanism of action, and lays a theoretical foundation for improving wheat quality.

Overexpression of 9-cis-Epoxycarotenoid Dioxygenase Gene, IbNCED1, Negatively Regulates Plant Height in Transgenic Sweet Potato

Plant height is one of the key agronomic traits for improving the yield of sweet potato. Phytohormones, especially gibberellins (GAs), are crucial to regulate plant height. The enzyme 9-cis-epoxycarotenoid dioxygenase (NCED) is the key enzyme for abscisic acid (ABA) biosynthesis signalling in higher plants. However, its role in regulating plant height has not been reported to date. Here, we cloned a new NCED gene, IbNCED1, from the sweet potato cultivar Jishu26. This gene encoded the 587-amino acid polypeptide containing an NCED superfamily domain. The expression level of IbNCED1 was highest in the stem and the old tissues in the in vitro-grown and field-grown Jishu26, respectively. The expression of IbNCED1 was induced by ABA and GA3. Overexpression of IbNCED1 promoted the accumulation of ABA and inhibited the content of active GA3 and plant height and affected the expression levels of genes involved in the GA metabolic pathway. Exogenous application of GA3 could rescue the dwarf phenotype. In conclusion, we suggest that IbNCED1 regulates plant height and development by controlling the ABA and GA signalling pathways in transgenic sweet potato.

Characterization of a Stress-Enhanced Promoter from the Grass Halophyte, Spartina alterniflora L

Stress-inducible promoters are vital for the desirable expression of genes, especially transcription factors, which could otherwise compromise growth and development when constitutively overexpressed in plants. Here, we report on the characterization of the promoter region of a stress-responsive gene SaAsr1 from monocot halophyte cordgrass (Spartina alterniflora). Several cis-acting elements, such as ABRE (ABA-responsive element), DRE-CRT (dehydration responsive-element/C-Repeat), LTRE (low temperature-responsive element), ERE (ethylene-responsive element), LRE (light-responsive element), etc. contributed at varying degrees to salt-, drought- and ABA-enhanced expression of gusA reporter gene in Arabidopsis thaliana under the full-length promoter, pAsr11875 and its deletion derivatives with an assortment of cis-regulatory motifs. The smallest promoter, pAsr1491, with three cis-acting elements (a CCAAT box-heat responsive, an LRE, and a copper responsive element) conferred drought-enhanced expression of gusA; pAsr1755 (with an ABRE and a DRE) presented the highest expression in ABA and drought; and pAsr1994 with seven ABREs and two DREs conferred optimal induction of gusA, especially under drought and ABA. Arabidopsis transgenics expressing a known abiotic stress-responsive gene, SaADF2 (actin depolymerization factor 2), under both pAsr11875 and p35S promoters outperformed the wild type (WT) with enhanced drought and salt tolerance contributed by higher relative water content and membrane stability with no significant difference between pAsr11875:SaADF2 or p35S:SaADF2 lines. However, pAsr11875:SaADF2 lines produced healthy plants with robust shoot systems under salt stress and control compared to slightly stunted growth of the p35S:SaADF2 plants. This reestablished the evidence that transgene expression under a stress-inducible promoter is a better strategy for the genetic manipulation of crops.

Glucose-6-P/phosphate translocator2 mediates the phosphoglucose-isomerase1-independent response to microbial volatiles

In Arabidopsis (Arabidopsis thaliana), the plastidial isoform of phosphoglucose isomerase (PGI1) mediates photosynthesis, metabolism, and development, probably due to its involvement in the synthesis of isoprenoid-derived signals in vascular tissues. Microbial volatile compounds (VCs) with molecular masses of <45 Da promote photosynthesis, growth, and starch overaccumulation in leaves through PGI1-independent mechanisms. Exposure to these compounds in leaves enhances the levels of GLUCOSE-6-PHOSPHATE/PHOSPHATE TRANSLOCATOR2 (GPT2) transcripts. We hypothesized that the PGI1-independent response to microbial volatile emissions involves GPT2 action. To test this hypothesis, we characterized the responses of wild-type (WT), GPT2-null gpt2-1, PGI1-null pgi1-2, and pgi1-2gpt2-1 plants to small fungal VCs. In addition, we characterized the responses of pgi1-2gpt2-1 plants expressing GPT2 under the control of a vascular tissue- and root tip-specific promoter to small fungal VCs. Fungal VCs promoted increases in growth, starch content, and photosynthesis in WT and gpt2-1 plants. These changes were substantially weaker in VC-exposed pgi1-2gpt2-1 plants but reverted to WT levels with vascular and root tip-specific GPT2 expression. Proteomic analyses did not detect enhanced levels of GPT2 protein in VC-exposed leaves and showed that knocking out GPT2 reduced the expression of photosynthesis-related proteins in pgi1-2 plants. Histochemical analyses of GUS activity in plants expressing GPT2-GUS under the control of the GPT2 promoter showed that GPT2 is mainly expressed in root tips and vascular tissues around hydathodes. Overall, the data indicated that the PGI1-independent response to microbial VCs involves resetting of the photosynthesis-related proteome in leaves through long-distance GPT2 action.

Impression of foliar-applied folic acid on coriander (Coriandrum sativum L.) to regulate aerial growth, biochemical activity, and essential oil profiling under drought stress

Drought is one of the major environmental limitations in the crop production sector that has a great impact on food security worldwide. Coriander (Coriandrum sativum L.) is an herbaceous angiosperm of culinary significance and highly susceptible to rootzone dryness. Elucidating the drought-induced physio-chemical changes and the foliar-applied folic acid (FA; vitamin B9)-mediated stress tolerance mechanism of coriander has been found as a research hotspot under the progressing water scarcity challenges for agriculture. The significance of folic acid in ameliorating biochemical activities for the improved vegetative growth and performance of coriander under the mild stress (MS75), severe stress (SS50), and unstressed (US100) conditions was examined in this study during two consecutive seasons. The results revealed that the plants treated with 50 mM FA showed the highest plant fresh biomass, leaf fresh biomass, and shoot fresh biomass from bolting stage to seed filling stage under mild drought stress. In addition, total soluble sugars, total flavonoids content, and chlorophyll content showed significant results by the foliar application of FA, while total phenolic content showed non-significant results under MS75 and SS50. It was found that 50 mM of FA upregulated the activity of catalase, superoxide dismutase, and ascorbate peroxidase enzymes in MS75 and SS50 plants compared with untreated FA plants. Thus, FA treatment improved the overall biological yield and economic yield regardless of water deficit conditions. FA-accompanied plants showed a decline in drought susceptibility index, while it improved the drought tolerance efficiency, indicating this variety to become stress tolerant. The optimum harvest index, essential oil (EO) percentage, and oil yield were found in MS75 followed by SS50 in FA-supplemented plants. The gas chromatography-mass spectrometry analysis revealed a higher abundance of linalool as the major chemical constituent of EO, followed by α-terpeniol, terpinene, and p-Cymene in FA-treated SS50 plants. FA can be chosen as a shotgun tactic to improve drought tolerance in coriander by delimiting the drastic changes due to drought stress.

The threshold between life and death in Cistus albidus L. seedlings: mechanisms underlying drought tolerance and resilience

Drought can lead to important shifts in population dynamics if it occurs during seedling establishment. With the aim of elucidating the underlying mechanisms of drought tolerance and resilience, here we monitored the survival of seedlings of the Mediterranean shrub Cistus albidus L. throughout a year growing in the natural Park of the Montserrat Mountains (Spain) and, additionally, we studied the response to severe drought and subsequent recovery after rewatering of seedlings grown in growth chambers. To find possible mechanisms explaining how seedlings respond to drought, growth and survival together with physiological-related parameters such as chlorophyll contents, vitamin E and stress-related phytohormones were measured. We found that survival decreased by 30% at the end of summer and that the main proxy of seedling survival was total chlorophyll. This proxy was further confirmed in the growth chambers, where we found that seedlings that recovered from drought had higher levels of total chlorophyll compared with the seedlings that did not recover. Furthermore, modulation of vitamin E and jasmonates contents appeared to be crucial in the drought response of C. albidus seedlings. We propose a prediction model of survival that includes total chlorophyll height, leaf mass area and maximum photosystem II efficiency with chlorophyll contents being a good long-term predictor of C. albidus seedling survival under severe stress, which, in turn, could help to better foresee population fluctuations in the field.

Melatonin and Phytomelatonin: Chemistry, Biosynthesis, Metabolism, Distribution and Bioactivity in Plants and Animals-An Overview

Melatonin is a ubiquitous indolamine, largely investigated for its key role in the regulation of several physiological processes in both animals and plants. In the last century, it was reported that this molecule may be produced in high concentrations by several species belonging to the plant kingdom and stored in specialized tissues. In this review, the main information related to the chemistry of melatonin and its metabolism has been summarized. Furthermore, the biosynthetic pathway characteristics of animal and plant cells have been compared, and the main differences between the two systems highlighted. Additionally, in order to investigate the distribution of this indolamine in the plant kingdom, distribution cluster analysis was performed using a database composed by 47 previously published articles reporting the content of melatonin in different plant families, species and tissues. Finally, the potential pharmacological and biostimulant benefits derived from the administration of exogenous melatonin on animals or plants via the intake of dietary supplements or the application of biostimulant formulation have been largely discussed.

Regulation of carotenoid degradation and production of apocarotenoids in natural and engineered organisms

Carotenoids are important precursors of a wide range of apocarotenoids with their functions including: hormones, pigments, retinoids, volatiles, and signals, which can be used in the food, flavors, fragrances, cosmetics, and pharmaceutical industries. This article focuses on the formation of these multifaceted apocarotenoids and their diverse biological roles in all living systems. Carotenoid degradation pathways include: enzymatic oxidation by specific carotenoid cleavage oxygenases (CCOs) or nonspecific enzymes such as lipoxygenases and peroxidases and non-enzymatic oxidation by reactive oxygen species. Recent advances in the regulation of carotenoid cleavage genes and the biotechnological production of multiple apocarotenoids are also covered. It is suggested that different developmental stages and environmental stresses can influence both the expression of carotenoid cleavage genes and the formation of apocarotenoids at multiple levels of regulation including: transcriptional, transcription factors, posttranscriptional, posttranslational, and epigenetic modification. Regarding the biotechnological production of apocarotenoids especially: crocins, retinoids, and ionones, enzymatic biocatalysis and metabolically engineered microorganisms have been a promising alternative route. New substrates, carotenoid cleavage enzymes, biosynthetic pathways for apocarotenoids, and new biological functions of apocarotenoids will be discussed with the improvement of our understanding of apocarotenoid biology, biochemistry, function, and formation from different organisms.

Transcriptomics of Biostimulation of Plants Under Abiotic Stress

Plant biostimulants are compounds, living microorganisms, or their constituent parts that alter plant development programs. The impact of biostimulants is manifested in several ways: via morphological, physiological, biochemical, epigenomic, proteomic, and transcriptomic changes. For each of these, a response and alteration occur, and these alterations in turn improve metabolic and adaptive performance in the environment. Many studies have been conducted on the effects of different biotic and abiotic stimulants on plants, including many crop species. However, as far as we know, there are no reviews available that describe the impact of biostimulants for a specific field such as transcriptomics, which is the objective of this review. For the commercial registration process of products for agricultural use, it is necessary to distinguish the specific impact of biostimulants from that of other legal categories of products used in agriculture, such as fertilizers and plant hormones. For the chemical or biological classification of biostimulants, the classification is seen as a complex issue, given the great diversity of compounds and organisms that cause biostimulation. However, with an approach focused on the impact on a particular field such as transcriptomics, it is perhaps possible to obtain a criterion that allows biostimulants to be grouped considering their effects on living systems, as well as the overlap of the impact on metabolism, physiology, and morphology occurring between fertilizers, hormones, and biostimulants.

Melatonin-Induced Water Stress Tolerance in Plants: Recent Advances

Water stress (drought and waterlogging) is severe abiotic stress to plant growth and development. Melatonin, a bioactive plant hormone, has been widely tested in drought situations in diverse plant species, while few studies on the role of melatonin in waterlogging stress conditions have been published. In the current review, we analyze the biostimulatory functions of melatonin on plants under both drought and waterlogging stresses. Melatonin controls the levels of reactive oxygen and nitrogen species and positively changes the molecular defense to improve plant tolerance against water stress. Moreover, the crosstalk of melatonin and other phytohormones is a key element of plant survival under drought stress, while this relationship needs further investigation under waterlogging stress. In this review, we draw the complete story of water stress on both sides-drought and waterlogging-through discussing the previous critical studies under both conditions. Moreover, we suggest several research directions, especially for waterlogging, which remains a big and vague piece of the melatonin and water stress puzzle.

Melatonin-Induced Water Stress Tolerance in Plants: Recent Advances

Water stress (drought and waterlogging) is severe abiotic stress to plant growth and development. Melatonin, a bioactive plant hormone, has been widely tested in drought situations in diverse plant species, while few studies on the role of melatonin in waterlogging stress conditions have been published. In the current review, we analyze the biostimulatory functions of melatonin on plants under both drought and waterlogging stresses. Melatonin controls the levels of reactive oxygen and nitrogen species and positively changes the molecular defense to improve plant tolerance against water stress. Moreover, the crosstalk of melatonin and other phytohormones is a key element of plant survival under drought stress, while this relationship needs further investigation under waterlogging stress. In this review, we draw the complete story of water stress on both sides-drought and waterlogging-through discussing the previous critical studies under both conditions. Moreover, we suggest several research directions, especially for waterlogging, which remains a big and vague piece of the melatonin and water stress puzzle.

Identification of drought tolerant mechanisms in a drought-tolerant maize mutant based on physiological, biochemical and transcriptomic analyses

BACKGROUND

Frequently occurring drought stress negatively affects the production of maize worldwide. Numerous efforts have been made to develop drought-tolerant maize lines and to explore drought tolerant mechanisms in maize. However, there is a lack of comparative studies on transcriptomic changes between drought-tolerant and control maize lines.

RESULTS

In the present study, we have developed a drought-tolerant maize mutant (C7-2t) by irradiating the seeds of maize inbred line ChangC7-2 (C7-2) with ⁶⁰Co-γ. Compared to its wild type C7-2, C7-2t exhibited a significantly delayed wilting and higher drought tolerance under both the controlled and field conditions, indicating its high water-holding ability. Transcriptomic profiling was performed to identify differentially expressed genes (DEGs) between C7-2 and C7-2t during drought. As a result, a total of 4552 DEGs were implied in drought tolerance of C7-2 and C7-2t. In particular, the expression of photosynthesis-related genes in C7-2 was inhibited, whereas these genes in C7-2t were almost unaffected under drought. Moreover, a specific set of the DEGs were involved in phenylpropanoid biosynthesis and taurine (hypotaurine) metabolism in C7-2t; these DEGs were enriched in cell components associated with membrane systems and cell wall biosynthesis.

CONCLUSIONS

The drought tolerance of C7-2t was largely due to its high water-holding ability, stable photosynthesis (for supporting osmoregulation) and strengthened biosynthesis of cell walls under drought conditions.

Metabolite/phytohormone-gene regulatory networks in soybean organs under dehydration conditions revealed by integration analysis

Metabolites, phytohormones, and genes involved in dehydration responses/tolerance have been predicted in several plants. However, metabolite/phytohormone-gene regulatory networks in soybean organs under dehydration conditions remain unclear. Here, we analyzed the organ specificity of metabolites, phytohormones, and gene transcripts and revealed the characteristics of their regulatory networks in dehydration-treated soybeans. Our metabolite/phytohormone analysis revealed the accumulation of raffinose, trehalose, and cis-zeatin (cZ) specifically in dehydration-treated roots. In dehydration-treated soybeans, raffinose, and trehalose might have additional roles not directly involved in protecting the photosynthetic apparatus; cZ might contribute to root elongation for water uptake from the moisture region in soil. Our integration analysis of metabolites-genes indicated that galactinol, raffinose, and trehalose levels were correlated with transcript levels for key enzymes (galactinol synthase, raffinose synthase, trehalose 6-phosphate synthase, trehalose 6-phosphate phosphatase) at the level of individual plants but not at the organ level under dehydration. Genes encoding these key enzymes were expressed in mainly the aerial parts of dehydration-treated soybeans. These results suggested that raffinose and trehalose are transported from aerial plant parts to the roots in dehydration-treated soybeans. Our integration analysis of phytohormones-genes indicated that cZ and abscisic acid (ABA) levels were correlated with transcript levels for key enzymes (cytokinin nucleoside 5'-monophosphate phosphoribohydrolase, cytokinin oxidases/dehydrogenases, 9-cis-epoxycarotenoid dioxygenase) at the level of individual plants but not at the organ level under dehydration conditions. Therefore, processes such as ABA and cZ transport, among others, are important for the organ specificity of ABA and cZ production under dehydration conditions.

Overexpression of AtNCED3 gene improved drought tolerance in soybean in greenhouse and field conditions

Water deficit is an important climatic problem that can impair agriculture yield and economy. Genetically modified soybean plants containing the AtNCED3 gene were obtained aiming drought-tolerance improvement. The NCED3 gene encodes a 9-cis-epoxycarotenoid dioxygenase (NCED, EC 1.13.11.51), an important enzyme in abscisic acid biosynthesis. ABA activates the expression of drought-responsive genes, in water-deficit conditions, targeting defense mechanisms and enabling plants to survive under low water availability. Results from greenhouse experiments showed that the transgene AtNCED3 and the endogenous genes GmAREB1, GmPP2C, GmSnRK2 and GmAAO3 presented higher expression under water deficit (WD) in the event 2Ha11 than in WT-plants. No significant correlation was observed between the plant materials and WD conditions for growth parameters; however, gas exchange measurements decreased in the GM event, which also showed 80% higher intrinsic water use when compared to WT plants. In crop season 2015/16, event 2Ha11 showed higher total number of pods, higher number of pods with seeds and yield than WT plants. ABA concentration was also higher in GM plants under WD. These results obtained in field screenings suggest that AtNCED3 soybean plants might outperform under drought, reducing economic and yield losses, thus being a good candidate line to be incorporated in the soybean-breeding program to develop drought-tolerant cultivars.

Melatonin regulates the functional components of photosynthesis, antioxidant system, gene expression, and metabolic pathways to induce drought resistance in grafted Carya cathayensis plants

The Chinese hickory (Carya cathayensis) is an economically important tree species popular for its nuts. However, the tree requires a long time to reach the nut-producing phase. To overcome this problem, grafting is widely used to reduce the time from the vegetative to the reproductive phase. This tree species also faces many environmental challenges due to climate change; drought is an important factor affecting growth and development. Here, we designed an experiment to assess the protective efficiency of melatonin in grafted Chinese hickory plants under drought stress. The results revealed that exogenously applied melatonin successfully recovered the growth of grafted Chinese hickory plants and improved photosynthetic efficiency. Exogenously applied melatonin also boosted the antioxidative defense system of the plants under drought stress, resulting in enhanced reactive oxygen species (ROS) scavenging. The accumulation of compatible solutes such as total soluble sugars and proline was also triggered by melatonin. Moreover, the analyses using metabolomics revealed that drought-stressed plants treated with melatonin regulated key metabolic pathways such as phenylpropanoid, chlorophyll and carotenoid biosynthesis, carbon fixation, and sugar metabolism. To further validate the physiological, biochemical, and metabolomic factors, we studied the molecular mechanisms by analyzing the expression of key genes involved in chlorophyll metabolism (chlorophyllase, CHLASE), antioxidative defense (superoxide dismutase, SOD; catalase, CAT; ascorbate peroxidase, APX; peroxidase, POD), and phenylalanine ammonia-lyase (PAL). Exogenously applied melatonin significantly regulated the transcript levels of key genes involved in the biological processes mentioned above. Melatonin also showed crosstalk with other hormones (zeatin, gibberellin A14, 24-epibrassinolide, jasmonic acid, and abscisic acid) to regulate the physiological processes. The results of this study show that melatonin regulates biological processes at the metabolic and molecular levels to resist drought stress.

Identification and characterization of the GmRD26 soybean promoter in response to abiotic stresses: potential tool for biotechnological application

BACKGROUND

Drought is one of the most harmful abiotic stresses for plants, leading to reduced productivity of several economically important crops and, consequently, considerable losses in the agricultural sector. When plants are exposed to stressful conditions, such as drought and high salinity, they modulate the expression of genes that lead to developmental, biochemical, and physiological changes, which help to overcome the deleterious effects of adverse circumstances. Thus, the search for new specific gene promoter sequences has proved to be a powerful biotechnological strategy to control the expression of key genes involved in water deprivation or multiple stress responses.

RESULTS

This study aimed to identify and characterize the GmRD26 promoter (pGmRD26), which is involved in the regulation of plant responses to drought stress. The expression profile of the GmRD26 gene was investigated by qRT-PCR under normal and stress conditions in Williams 82, BR16 and Embrapa48 soybean-cultivars. Our data confirm that GmRD26 is induced under water deficit with different induction folds between analyzed cultivars, which display different genetic background and physiological behaviour under drought. The characterization of the GmRD26 promoter was performed under simulated stress conditions with abscisic acid (ABA), polyethylene glycol (PEG) and drought (air dry) on A. thaliana plants containing the complete construct of pGmRD26::GUS (2.054 bp) and two promoter modules, pGmRD26A::GUS (909 pb) and pGmRD26B::GUS (435 bp), controlling the expression of the β-glucuronidase (uidA) gene. Analysis of GUS activity has demonstrated that pGmRD26 and pGmRD26A induce strong reporter gene expression, as the pAtRD29 positive control promoter under ABA and PEG treatment.

CONCLUSIONS

The full-length promoter pGmRD26 and the pGmRD26A module provides an improved uidA transcription capacity when compared with the other promoter module, especially in response to polyethylene glycol and drought treatments. These data indicate that pGmRD26A may become a promising biotechnological asset with potential use in the development of modified drought-tolerant plants or other plants designed for stress responses.

The specific MYB binding sites bound by TaMYB in the GAPCp2/3 promoters are involved in the drought stress response in wheat

BACKGROUND

Drought stress is one of the major abiotic stresses that affects plant growth and productivity. The GAPCp genes play important roles in drought stress tolerance in multiple species. The aim of this experiment was to identify the core cis-regulatory elements that may respond to drought stress in the GAPCp2 and GAPCp3 promoter sequences.

RESULTS

In this study, the promoters of GAPCp2 and GAPCp3 were cloned. The promoter activities were significantly improved under abiotic stress via regulation of Rluc reporter gene expression, while promoter sequence analysis indicated that these fragments were not almost identical. In transgenic Arabidopsis with the expression of the GUS reporter gene under the control of one of these promoters, the activities of GUS were strong in almost all tissues except the seeds, and the activities were induced after abiotic stress. The yeast one-hybrid system and EMSA demonstrated that TaMYB bound TaGAPCp2P/3P. By analyzing different 5' deletion mutants of these promoters, it was determined that TaGAPCp2P (- 1312~ - 528) and TaGAPCp3P (- 2049~ - 610), including the MYB binding site, contained enhancer elements that increased gene expression levels under drought stress. We used an effector and a reporter to co-transform tobacco and found that TaMYB interacted with the specific MYB binding sites of TaGAPCp2P (- 1197~ - 635) and TaGAPCp3P (- 1456~ - 1144 and - 718~ - 610) in plant cells. Then, the Y1H system and EMSA assay demonstrated that these MYB binding sites in TaGAPCp2P (- 1135 and - 985) and TaGAPCp3P (- 1414 and - 665) were the target cis-elements of TaMYB. The deletion of the specific MYB binding sites in the promoter fragments significantly restrained the drought response, and these results confirmed that these MYB binding sites (AACTAAA/C) play vital roles in improving the transcription levels under drought stress. The results of qRT-PCR in wheat protoplasts transiently overexpressing TaMYB indicated that the expression of TaGAPCp2/3 induced by abiotic stress was upregulated by TaMYB.

CONCLUSION

The MYB binding sites (AACTAAA/C) in TaGAPCp2P/3P were identified as the key cis-elements for responding to drought stress and were bound by the transcription factor TaMYB.

Melatonin Mediated Regulation of Drought Stress: Physiological and Molecular Aspects

Drought stress adversely effects physiological and biochemical processes of plants, leading to a reduction in plant productivity. Plants try to protect themselves via activation of their internal defense system, but severe drought causes dysfunction of this defense system. The imbalance between generation and scavenging of reactive oxygen species (ROS) leads to oxidative stress. Melatonin, a multifunctional molecule, has the potential to protect plants from the adverse effects of drought stress by enhancing the ROS scavenging efficiency. It helps in protection of photosynthetic apparatus and reduction of drought induced oxidative stress. Melatonin regulates plant processes at a molecular level, which results in providing better resistance against drought stress. In this review, the authors have discussed various physiological and molecular aspects regulated by melatonin in plants under drought conditions, along with their underlying mechanisms.

Genome-wide cis-regulatory signatures for modulation of agronomic traits as exemplified by drought yield index (DYI) in chickpea

Developing functional molecular tags from the cis-regulatory sequence components of genes is vital for their deployment in efficient genetic dissection of complex quantitative traits in crop plants including chickpea. The current study identified 431,194 conserved non-coding SNP (CNSNP) from the cis-regulatory element regions of genes which were annotated on a chickpea genome. These genome-wide CNSNP marker resources are made publicly accessible through a user-friendly web-database ( http://www.cnsnpcicarbase.com ). The CNSNP-based quantitative trait loci (QTL) and expression QTL (eQTL) mapping and genome-wide association study (GWAS) were further integrated with global gene expression landscapes, molecular haplotyping, and DNA-protein interaction study in the association panel and recombinant inbred lines (RIL) mapping population to decode complex genetic architecture of one of the vital seed yield trait under drought stress, drought yield index (DYI), in chickpea. This delineated two constituted natural haplotypes and alleles from a histone H3 protein-coding gene and its transcriptional regulator NAC transcription factor (TF) harboring the major QTLs and trans-acting eQTL governing DYI in chickpea. The effect of CNSNPs in TF-binding cis-element of a histone H3 gene in altering the binding affinity and transcriptional activity of NAC TF based on chromatin immunoprecipitation-quantitative PCR (ChIP-qPCR) assay was evident. The CNSNP-led promising molecular tags scanned will essentially have functional significance to decode transcriptional gene regulatory function and thus can drive translational genomic analysis in chickpea.

Omeprazole alleviates water stress in peppermint and modulates the expression of menthol biosynthesis genes

Water stress is a worldwide agricultural challenge that limits crop growth and quality. Chemical compounds that promote tolerance to water stress, such as omeprazole showed recently promising results. The present study investigates the effect of weekly drenching applications of 0, 10, 50, 100, or 200 μM omeprazole on Mentha piperita (peppermint) subjected to water stress by watering at 100%, 70%, and 50% of container substrate capacity for 7 weeks in an experiment that spanned two seasons. Peppermint that received higher doses of omeprazole showed increased plant height, leaf number, leaf area, and dry weight under normal and water stress conditions. The amounts of chlorophyll and proline in the leaves as well as gas exchange increased in omeprazole-treated plants relative to the control plants. Omeprazole treatment also resulted in increased activity of the enzymes catalase and ascorbate peroxidase, reduced accumulation of the reactive oxygen species hydrogen peroxide, increase in the essential oil ratio, and improvement in essential oil composition. Omeprazole-treated plants showed higher ratios of menthol and menthone composition relative to the control plants. The changes in essential oil composition were associated with increased expression of genes associated with the menthol biosynthesis pathway. These findings indicate that omeprazole can ameliorate water stress in peppermint by increasing vegetative and root growth; increasing chlorophyll amount, photosynthetic rate, and gas exchange; reducing water loss by boosting leaf water potential and relative water content; increasing proline content; and modulating the gene expression of secondary metabolites.

ABA-Induced Vegetative Diaspore Formation in Physcomitrella patens

The phytohormone abscisic acid (ABA) is a pivotal regulator of gene expression in response to various environmental stresses such as desiccation, salt and cold causing major changes in plant development and physiology. Here we show that in the moss Physcomitrella patens exogenous application of ABA triggers the formation of vegetative diaspores (brachycytes or brood cells) that enable plant survival in unfavorable environmental conditions. Such diaspores are round-shaped cells characterized by the loss of the central vacuole, due to an increased starch and lipid storage preparing these cells for growth upon suitable environmental conditions. To gain insights into the gene regulation underlying these developmental and physiological changes, we analyzed early transcriptome changes after 30, 60, and 180 min of ABA application and identified 1,030 differentially expressed genes. Among these, several groups can be linked to specific morphological and physiological changes during diaspore formation, such as genes involved in cell wall modifications. Furthermore, almost all members of ABA-dependent signaling and regulation were transcriptionally induced. Network analysis of transcription-associated genes revealed a large overlap of our study with ABA-dependent regulation in response to dehydration, cold stress, and UV-B light, indicating a fundamental function of ABA in diverse stress responses in moss. We also studied the evolutionary conservation of ABA-dependent regulation between moss and the seed plant Arabidopsis thaliana pointing to an early evolution of ABA-mediated stress adaptation during the conquest of the terrestrial habitat by plants.

The Research on the Osmotic Stress Gene Mining Model Based on the Arabidopsis Genome

In the field of the bioinformatics, during osmotic stress response genes mining processing, it is also very crucial to verify experimental data obtained in the course of complex experiments by using the computer. Aim of this paper is taking Arabidopsis thaliana as the experimental crop, designing technology roadmap, taking advantage of the skills of function and programming, then designing algorithms. After using the program to predict the transcription start point, the promoter sequence is extracted and simplified. In addition, different alignment methods are classified. Then, comparing the promoter sequence with the cis-element and using the formula for further processing. Finally, get the probability P value, which provide further help to experts and scholars on the basis of probability values to determine the correlation between the osmotic stress. The experimental data source of chromosomal sequences is received from Genbank database files, and cis-element sequence that associated with osmotic stress is collected from TRANSFAC and TRRD database. From this, the authors not only used the Arabidopsis promoter as the experimental data, but also use a variety of eukaryotic promoters include promoters GhNHX1 rice, cotton OsNHX1 promoter, as a comparison. Wherein the data obtained in the biological laboratory, which in the course of running the program, 70% have been verified. P value close to 0.8, this article will be treated as the promoter contains osmotic stress cis-elements, the expression of gene induced by osmotic stress. For thaliana, cotton and rice, programs running average time was 51s, 72s and 114s. Through the use of some commonly used bioinformatics gene mining algorithms, MEME algorithm and BioProspector algorithm for the same data have been processed, the average running time of the system is increasing with the increase of data. Running time of MEME algorithm increases from 60s to reach 198s, BioProspector algorithm increases from 45s to 150s model process used herein were 50s, 75s, 110s, 135s. At the same time, the authors can see in the three algorithms, the model algorithm used herein with respect to the first two more optimized. To ensure the accuracy rate, meanwhile has high speed and stabilization of higher.

Arabidopsis thaliana NGATHA1 transcription factor induces ABA biosynthesis by activating NCED3 gene during dehydration stress

The plant hormone abscisic acid (ABA) is accumulated after drought stress and plays critical roles in the responses to drought stress in plants, such as gene regulation, stomatal closure, seed maturation, and dormancy. Although previous reports revealed detailed molecular roles of ABA in stress responses, the factors that contribute to the drought-stress responses-in particular, regulation of ABA accumulation-remain unclear. The enzyme NINE-CIS-EPOXYCAROTENOID DIOXYGENASE 3 (NCED3) is essential for ABA biosynthesis during drought stress, and the NCED3 gene is highly induced by drought stress. In the present study, we isolated NGATHAs (NGAs) as candidate transcriptional regulators of NCED3 through a screen of a plant library harboring the transcription factors fused to a chimeric repressor domain, SRDX. The NGA proteins were directly bound to a cis-element NGA-binding element (NBE) in the 5' untranslated region (5' UTR) of the NCED3 promoter and were suggested to be transcriptional activators of NCED3 Among the single-knockout mutants of four NGA family genes, we found that the NGATHA1 (NGA1) knockout mutant was drought-stress-sensitive with a decreased expression level of NCED3 during dehydration stress. These results suggested that NGA1 essentially functions as a transcriptional activator of NCED3 among the NGA family proteins. Moreover, the NGA1 protein was degraded under nonstressed conditions, and dehydration stress enhanced the accumulation of NGA1 proteins, even in ABA-deficient mutant plants, indicating that there should be ABA-independent posttranslational regulations. These findings emphasize the regulatory mechanisms of ABA biosynthesis during early drought stress.

The transcription factor OsbHLH035 mediates seed germination and enables seedling recovery from salt stress through ABA-dependent and ABA-independent pathways, respectively

BACKGROUND

Many transcription factors (TFs), such as those in the basic helix-loop-helix (bHLH) family, are important for regulating plant growth and plant responses to abiotic stress. The expression of OsbHLH035 is induced by drought and salinity. However, its functional role in rice growth, development, and the salt response is still unknown.

RESULTS

The bHLH TF OsbHLH035 is a salt-induced gene that is primarily expressed in germinating seeds and seedlings. Stable expression of GFP-fused OsbHLH035 in rice transgenic plants revealed that this protein is predominantly localized to the nucleus. Osbhlh035 mutants show delayed seed germination, particularly under salt-stress conditions. In parallel, abscisic acid (ABA) contents are over-accumulated, and the expression of the ABA biosynthetic genes OsABA2 and OsAAO3 is upregulated; furthermore, compared with that in wild-type (WT) seedlings, the salt-induced expression of OsABA8ox1, an ABA catabolic gene, in germinating Osbhlh035 mutant seeds is downregulated. Moreover, Osbhlh035 mutant seedlings are unable to recover from salt-stress treatment. Consistently, sodium is over-accumulated in aerial tissues but slightly reduced in terrestrial tissues from Osbhlh035 seedlings after salt treatment. Additionally, the expression of the sodium transporters OsHKT1;3 and 1;5 is reduced in Osbhlh035 aerial and terrestrial tissues, respectively. Furthermore, genetic complementation can restore both the delayed seed germination and the impaired recovery of salt-treated Osbhlh035 seedlings to normal growth.

CONCLUSION

OsbHLH035 mediates seed germination and seedling recovery after salt stress relief through the ABA-dependent and ABA-independent activation of OsHKT pathways, respectively.

Overexpression of BoNAC019, a NAC transcription factor from Brassica oleracea, negatively regulates the dehydration response and anthocyanin biosynthesis in Arabidopsis

NACs are one of the largest transcription factor families in plants and are involved in the response to abiotic stress. BoNAC019, a homologue of AtNAC019, was isolated from cabbage (Brassica oleracea). BoNAC019 was localized in the nucleus and functioned as a transcriptional activator. The expression of BoNAC019 was induced by dehydration, salt, abscisic acid (ABA), and H2O2 treatments. BoNAC019 overexpressing plants were generated to explore the function of BoNAC019 in response to drought stress. Overexpression (OE) of BoNAC019 reduced drought tolerance with lower survival rate, higher water loss rate, lower proline content and ABA content. The seed germination and root length assays of BoNAC019-OE plants showed decreased sensitivity to ABA. Under drought condition, antioxidant enzymes and anthocyanin content decreased in BoNAC019 -OE plants, resulting in the accumulation of more reactive oxygen species (ROS), which cause damage to plants. Several stress-responsive genes, antioxidant enzymatic genes, anthocyanin biosynthetic genes and ABA signaling genes were down-regulated under drought condition while the ABA catabolism genes were induced in BoNAC019-OE plants under both normal and drought conditions. Our results demonstrated that BoNAC019 might participated in regulating drought tolerance by inducing ABA catabolism genes and decreasing ABA content.

COP1 plays a prominent role in drought stress tolerance in Arabidopsis and Pea

Constitutively photomorphogenic 1 (COP1) is an E3 ubiquitin ligase that has been studied extensively in the photomorphogenesis- and light-related processes in Arabidopsis. However, the possible role of COP1 in plant drought stress response remains unknown. Hence, in the present study, the stomatal behavior as one of the key elements in plant dehydration response was investigated in Arabidopsis cop1-4 and pea light-independent photomorphogenesis (lip1) mutants. We observed that water loss rate in the cop1-4 and lip1 detached leaves was significantly much faster than wild-type, resulting from failing to reduce the stomatal aperture by the mutants. But, interestingly, the cop1-4 and lip1 isolated leaves treated with abscisic acid (ABA) as well as cop1-4 and lip1 soil-grown under drought stress could close their stomata as wild-type. Hence, COP1 plays a fundamental role in the regulation of stomatal movements in response to dehydration and its function was conserved during evolution in both Arabidopsis and pea. Further evaluations showed the cop1-4 mutant was not significantly damaged from the oxidative stress derived from soil water limiting conditions when compared to wild-type. Similarly, the up-regulation level of several key stress-responsive genes was relatively lower in cop1-4 than wild-type. Therefore, COP1 might be considered as a potential key regulator of both short-and long-term dehydration response. Multiple stress-related cis-elements were also detected in the COP1 promoter region, which supported its up-regulation in response to drought, salt, and cold stresses. Besides, we figured out the constitutively open stomata of cop1-4 in darkness can be as a result of the reduced AtMYB61 expression.

Protection of photosynthesis in desiccation-tolerant resurrection plants

Inhibition of photosynthesis is a central, primary response that is observed in both desiccation-tolerant and desiccation-sensitive plants affected by drought stress. Decreased photosynthesis during drought stress can either be due to the limitation of carbon dioxide entry through the stomata and the mesophyll cells, due to increased oxidative stress or due to decreased activity of photosynthetic enzymes. Although the photosynthetic rates decrease in both desiccation-tolerant and sensitive plants during drought, the remarkable difference lies in the complete recovery of photosynthesis after rehydration in desiccation-tolerant plants. Desiccation of sensitive plants leads to irreparable damages of the photosynthetic membranes, in contrast the photosynthetic apparatus is deactivated during desiccation in desiccation-tolerant plants. Desiccation-tolerant plants employ different strategies to protect and/or maintain the structural integrity of the photosynthetic apparatus to reactivate photosynthesis upon water availability. Two major mechanisms are distinguished. Homoiochlorophyllous desiccation-tolerant plants preserve chlorophyll and thylakoid membranes and require active protection mechanisms, while poikilochlorophyllous plants degrade chlorophyll in a regulated manner but then require de novo synthesis during rehydration. Desiccation-tolerant plants, particularly homoiochlorophyllous plants, employ conserved and novel antioxidant enzymes/metabolites to minimize the oxidative damage and to protect the photosynthetic machinery. De novo synthesized, stress-induced proteins in combination with antioxidants are localized in chloroplasts and are important components of the protective network. Genome sequence informations provide some clues on selection of genes involved in protecting photosynthetic structures; e.g. ELIP genes (early light inducible proteins) are enriched in the genomes and more abundantly expressed in homoiochlorophyllous desiccation-tolerant plants. This review focuses on the mechanisms that operate in the desiccation-tolerant plants to protect the photosynthetic apparatus during desiccation.

Long non-coding RNAs of switchgrass (Panicum virgatum L.) in multiple dehydration stresses

BACKGROUND

Long non-coding RNAs (lncRNAs) play important roles in plant growth and stress responses. Studies of lncRNAs in non-model plants are quite limited, especially those investigating multiple dehydration stresses. In this study, we identified novel lncRNAs and analyzed their functions in dehydration stress memory in switchgrass, an excellent biofuel feedstock and soil-conserving plant in the Gramineae family.

RESULTS

We analyzed genome-wide transcriptional profiles of leaves of 5-week-old switchgrass plantlets grown via tissue culture after primary and secondary dehydration stresses (D1 and D2) and identified 16,551 novel lncRNAs, including 4554 annotated lncRNAs (targeting 3574 genes), and 11,997 unknown lncRNAs. Gene ontology and pathway enrichment analysis of annotated genes showed that the differentially expressed lncRNAs were related to abscisic acid (ABA) and ethylene (ETH) biosynthesis and signal transduction, and to starch and sucrose metabolism. The upregulated lncRNAs and genes were related to ABA synthesis and its signal transduction, and to trehalose synthesis. Meanwhile, lncRNAs and genes related to ETH biosynthesis and signal transduction were suppressed. LncRNAs and genes involved in ABA metabolism were verified using quantitative real-time PCR, and the endogenous ABA content was determined via high performance liquid chromatography mass spectrometry (HPLC-MS). These results showed that ABA accumulated significantly during dehydration stress, especially in D2. Furthermore, we identified 307 dehydration stress memory lncRNAs, and the ratios of different memory types in switchgrass were similar to those in Arabidopsis and maize.

CONCLUSIONS

The molecular responses of switchgrass lncRNAs to multiple dehydration stresses were researched systematically, revealing novel information about their transcriptional regulatory behavior. This study provides new insights into the response mechanism to dehydration stress in plants. The lncRNAs and pathways identified in this study provide valuable information for genetic modification of switchgrass and other crops.

Investigation of Drought and Salinity Tolerance Related Genes and their Regulatory Mechanisms in Arabidopsis (Arabidopsis thaliana)

Background:

The development of genome microarrays of the model plant;Arabidopsis thaliana, with increasing repositories of publicly available data and high-throughput data analysis tools, has opened new avenues to genome-wide systemic analysis of plant responses to environmental stresses.

Objective:

To identify differentially expressed genes and their regulatory networks inArabidopsis thalianaunder harsh environmental condition.

Methods:

Two replications of eight microarray data sets were derived from two different tissues (root and shoot) and two different time courses (control and 24 hours after the beginning of stress occurrence) for comparative data analysis through various bioinformatics tools.

Results:

Under drought stress, 2558 gene accessions in root and 3691 in shoot tissues had significantly differential expression with respect to control condition. Likewise, under salinity stress 9078 gene accessions in root and 5785 in shoot tissues were discriminated between stressed and non-stressed conditions. Furthermore, the transcription regulatory activity of differentially expressed genes was mainly due to hormone, light, circadian and stress responsivecis-acting regulatory elements among which ABRE, ERE, P-box, TATC-box, CGTCA-motif, GARE-motif, TGACG-motif, GAG-motif, GA-motif, GATA- motif, TCT-motif, GT1-motif, Box 4, G-Box, I-box, LAMP-element, Sp1, MBS, TC-rich repeats, TCA-element and HSE were the most important elements in the identified up-regulated genes.

Conclusion:

The results of the high-throughput comparative analyses in this study provide more options for plant breeders and give an insight into genes andcis-acting regulatory elements involved in plant response to drought and salinity stresses in strategic crops such as cereals.

Transcriptional and physiological data reveal the dehydration memory behavior in switchgrass (Panicum virgatum L.)

BACKGROUND

Switchgrass (Panicum virgatum L.) is a model biofuel plant because of its high biomass, cellulose-richness, easy degradation to ethanol, and the availability of extensive genomic information. However, a little is currently known about the molecular responses of switchgrass plants to dehydration stress, especially multiple dehydration stresses.

RESULTS

Studies on the transcriptional profiles of 35-day-old tissue culture plants revealed 741 dehydration memory genes. Gene Ontology and pathway analysis showed that these genes were enriched in phenylpropanoid biosynthesis, starch and sucrose metabolism, and plant hormone signal transduction. Further analysis of specific pathways combined with physiological data suggested that switchgrass improved its dehydration resistance by changing various aspects of its responses to secondary dehydration stress (D2), including the regulation of abscisic acid (ABA) and jasmonic acid (JA) biosynthesis and signal transduction, the biosynthesis of osmolytes (l-proline, stachyose and trehalose), energy metabolism (i.e., metabolic process relating to photosynthetic systems, glycolysis, and the TCA cycle), and lignin biosynthesis. The transcriptional data and chemical substance assays showed that ABA was significantly accumulated during both primary (D1) and secondary (D2) dehydration stresses, whereas JA accumulated during D1 but became significantly less abundant during D2. This suggests the existence of a complicated signaling network of plant hormones in response to repeated dehydration stresses. A homology analysis focusing on switchgrass, maize, and Arabidopsis revealed the conservation and species-specific distribution of dehydration memory genes.

CONCLUSIONS

The molecular responses of switchgrass plants to successive dehydration stresses have been systematically characterized, revealing a previously unknown transcriptional memory behavior. These results provide new insights into the mechanisms of dehydration stress responses in plants. The genes and pathways identified in this study will be useful for the genetic improvement of switchgrass and other crops.

Isolation and characterization of a promoter responsive to salt, osmotic and dehydration stresses in soybean

Drought stress is the main limiting factor of soybean yield. Currently, genetic engineering has been one important tool in the development of drought-tolerant cultivars. A widely used strategy is the fusion of genes that confer tolerance under the control of the CaMV35S constitutive promoter; however, stress-responsive promoters would constitute the best alternative to the generation of drought-tolerant crops. We characterized the promoter of α-galactosidase soybean (GlymaGAL) gene that was previously identified as highly up-regulated by drought stress. The β-glucuronidase (GUS) activity of Arabidopsis transgenic plants bearing 1000- and 2000-bp fragments of the GlymaGAL promoter fused to the uidA gene was evaluated under air-dried, polyethylene glycol (PEG) and salt stress treatments. After 24 h of air-dried and PEG treatments, the pGAL-2kb led to an increase in GUS expression in leaf and root samples when compared to the control samples. These results were corroborated by qPCR expression analysis of the uidA gene. The pGAL-1kb showed no difference in GUS activity between control and treated samples. The pGAL-2kb promoter was evaluated in transgenic soybean roots, leading to an increase in EGFP expression under air-dried treatment. Our data indicates that pGAL-2kb could be a useful tool in developing drought-tolerant cultivars by driving gene expression.

RNA-seq Analysis of Cold and Drought Responsive Transcriptomes of Zea mays ssp. mexicana L

The annual Zea mays ssp. mexicana L. is a member of teosinte, a wild relative of the Zea mays spp. mays L. This subspecies has strong growth and regeneration ability, high tiller numbers, high protein and lysine content as well as resistance to many fungal diseases, and it can be effectively used in maize improvement. In this study, we reported a Zea mays ssp. mexicana L. transcriptome by merging data from untreated control (CK), cold (4°C) and drought (PEG2000, 20%) treated plant samples. A total of 251,145 transcripts (N50 = 1,269 bp) and 184,280 unigenes (N50 = 923 bp) were predicted, which code for homologs of near 47% of the published maize proteome. Under cold conditions, 2,232 and 817 genes were up-regulated and down-regulated, respectively, while fewer genes were up-regulated (532) and down-regulated (82) under drought stress, indicating that Zea mays ssp. mexicana L. is more sensitive to the applied cold rather than to the applied drought stresses. Functional enrichment analyses identified many common or specific biological processes and gene sets in response to drought and cold stresses. The ABA dependent pathway, trehalose synthetic pathway and the ICE1-CBF pathway were up-regulated by both stresses. GA associated genes have been shown to differentially regulate the responses to cold in close subspecies in Zea mays. These findings and the identified functional genes can provide useful clues for improving abiotic stress tolerance of maize.

Comprehensive Analysis of ABA Effects on Ethylene Biosynthesis and Signaling during Tomato Fruit Ripening

ABA has been widely acknowledged to regulate ethylene biosynthesis and signaling during fruit ripening, but the molecular mechanism underlying the interaction between these two hormones are largely unexplored. In the present study, exogenous ABA treatment obviously promoted fruit ripening as well as ethylene emission, whereas NDGA (Nordihydroguaiaretic acid, an inhibitor of ABA biosynthesis) application showed the opposite biological effects. Combined RNA-seq with time-course RT-PCR analysis, our study not only helped to illustrate how ABA regulated itself at the transcription level, but also revealed that ABA can facilitate ethylene production and response probably by regulating some crucial genes such as LeACS4, LeACO1, GR and LeETR6. In addition, investigation on the fruits treated with 1-MCP immediately after ABA exposure revealed that ethylene might be essential for the induction of ABA biosynthesis and signaling at the onset of fruit ripening. Furthermore, some specific transcription factors (TFs) known as regulators of ethylene synthesis and sensibility (e.g. MADS-RIN, TAGL1, CNR and NOR) were also observed to be ABA responsive, which implied that ABA influenced ethylene action possibly through the regulation of these TFs expression. Our comprehensive physiological and molecular-level analysis shed light on the mechanism of cross-talk between ABA and ethylene during the process of tomato fruit ripening.

CmWRKY1 Enhances the Dehydration Tolerance of Chrysanthemum through the Regulation of ABA-Associated Genes

WRKY transcription factors serve as antagonistic or synergistic regulators in a variety of abiotic stress responses in plants. Here, we show that CmWRKY1, a member of the group IIb WRKY family isolated from Chrysanthemum morifolium, exhibits no transcriptional activation in yeast cells. The subcellular localization examination showed that CmWRKY1 localizes to the nucleus in vivo. Furthermore, CmWRKY1-overexpressing transgenic lines exhibit enhanced dehydration tolerance in response to polyethylene glycol (PEG) treatment compared with wild-type plants. We further confirmed that the transgenic plants exhibit suppressed expression levels of genes negatively regulated by ABA, such as PP2C, ABI1 and ABI2, and activated expression levels of genes positively regulated by ABA, such as PYL2, SnRK2.2, ABF4, MYB2, RAB18, and DREB1A. Taken together, our results indicate that CmWRKY1 plays an important role in the response to drought in chrysanthemum through an ABA-mediated pathway.

MdMYB1 Regulates Anthocyanin and Malate Accumulation by Directly Facilitating Their Transport into Vacuoles in Apples

Tonoplast transporters, including proton pumps and secondary transporters, are essential for plant cell function and for quality formation of fleshy fruits and ornamentals. Vacuolar transport of anthocyanins, malate, and other metabolites is directly or indirectly dependent on the H(+)-pumping activities of vacuolar H(+)-ATPase (VHA) and/or vacuolar H(+)-pyrophosphatase, but how these proton pumps are regulated in modulating vacuolar transport is largely unknown. Here, we report a transcription factor, MdMYB1, in apples that binds to the promoters of two genes encoding the B subunits of VHA, MdVHA-B1 and MdVHA-B2, to transcriptionally activate its expression, thereby enhancing VHA activity. A series of transgenic analyses in apples demonstrates that MdMYB1/10 controls cell pH and anthocyanin accumulation partially by regulating MdVHA-B1 and MdVHA-B2. Furthermore, several other direct target genes of MdMYB10 are identified, including MdVHA-E2, MdVHP1, MdMATE-LIKE1, and MdtDT, which are involved in H(+)-pumping or in the transport of anthocyanins and malates into vacuoles. Finally, we show that the mechanism by which MYB controls malate and anthocyanin accumulation in apples also operates in Arabidopsis (Arabidopsis thaliana). These findings provide novel insights into how MYB transcription factors directly modulate the vacuolar transport system in addition to anthocyanin biosynthesis, consequently controlling organ coloration and cell pH in plants.

Transcriptomic Analysis of Soil-Grown Arabidopsis thaliana Roots and Shoots in Response to a Drought Stress

Drought stress has a negative impact on crop yield. Thus, understanding the molecular mechanisms responsible for plant drought stress tolerance is essential for improving this beneficial trait in crops. In the current study, a transcriptional analysis was conducted of gene regulatory networks in roots of soil-grown Arabidopsis plants in response to a drought stress treatment. A microarray analysis of drought-stressed roots and shoots was performed at 0, 1, 3, 5, 7, and 9 days. Results indicated that the expression of many drought stress-responsive genes and abscisic acid biosynthesis-related genes was differentially regulated in roots and shoots from days 3 to 9. The expression of cellular and metabolic process-related genes was up-regulated at an earlier time-point in roots than in shoots. In this regard, the expression of genes involved in oxidative signaling, chromatin structure, and cell wall modification also increased significantly in roots compared to shoots. Moreover, the increased expression of genes involved in the transport of amino acids and other solutes; including malate, iron, and sulfur, was observed in roots during the early time points following the initiation of the drought stress. These data suggest that plants may utilize these signaling channels and metabolic adjustments as adaptive responses in the early stages of a drought stress. Collectively, the results of the present study increases our understanding of the differences pertaining to the molecular mechanisms occurring in roots vs. shoots in response to a drought stress. Furthermore, these findings also aid in the selection of novel genes and promoters that can be used to potentially produce crop plants with increased drought tolerance.

Transcription Factors and Plants Response to Drought Stress: Current Understanding and Future Directions

Increasing vulnerability of plants to a variety of stresses such as drought, salt and extreme temperatures poses a global threat to sustained growth and productivity of major crops. Of these stresses, drought represents a considerable threat to plant growth and development. In view of this, developing staple food cultivars with improved drought tolerance emerges as the most sustainable solution toward improving crop productivity in a scenario of climate change. In parallel, unraveling the genetic architecture and the targeted identification of molecular networks using modern "OMICS" analyses, that can underpin drought tolerance mechanisms, is urgently required. Importantly, integrated studies intending to elucidate complex mechanisms can bridge the gap existing in our current knowledge about drought stress tolerance in plants. It is now well established that drought tolerance is regulated by several genes, including transcription factors (TFs) that enable plants to withstand unfavorable conditions, and these remain potential genomic candidates for their wide application in crop breeding. These TFs represent the key molecular switches orchestrating the regulation of plant developmental processes in response to a variety of stresses. The current review aims to offer a deeper understanding of TFs engaged in regulating plant's response under drought stress and to devise potential strategies to improve plant tolerance against drought.

Salt-Related MYB1 Coordinates Abscisic Acid Biosynthesis and Signaling during Salt Stress in Arabidopsis

Abiotic stresses, such as salinity, cause global yield loss of all major crop plants. Factors and mechanisms that can aid in plant breeding for salt stress tolerance are therefore of great importance for food and feed production. Here, we identified a MYB-like transcription factor, Salt-Related MYB1 (SRM1), that negatively affects Arabidopsis (Arabidopsis thaliana) seed germination under saline conditions by regulating the levels of the stress hormone abscisic acid (ABA). Accordingly, several ABA biosynthesis and signaling genes act directly downstream of SRM1, including SALT TOLERANT1/NINE-CIS-EPOXYCAROTENOID DIOXYGENASE3, RESPONSIVE TO DESICCATION26, and Arabidopsis NAC DOMAIN CONTAINING PROTEIN19. Furthermore, SRM1 impacts vegetative growth and leaf shape. We show that SRM1 is an important transcriptional regulator that directly targets ABA biosynthesis and signaling-related genes and therefore may be regarded as an important regulator of ABA-mediated salt stress tolerance.

Global analysis of gene expression profiles in physic nut (Jatropha curcas L.) seedlings exposed to drought stress

BACKGROUND

Physic nut (Jatropha curcas L.) is a small perennial tree or large shrub, which is well-adapted to semi-arid regions and is considered to have potential as a crop for biofuel production. It is now regarded as an excellent model for studying biofuel plants. However, our knowledge about the molecular responses of this species to drought stress is currently limited.

RESULTS

In this study, genome-wide transcriptional profiles of roots and leaves of 8-week old physic nut seedlings were analyzed 1, 4 and 7 days after withholding irrigation. We observed a total of 1533 and 2900 differentially expressed genes (DEGs) in roots and leaves, respectively. Gene Ontology analysis showed that the biological processes enriched in droughted plants relative to unstressed plants were related to biosynthesis, transport, nucleobase-containing compounds, and cellular protein modification. The genes found to be up-regulated in roots were related to abscisic acid (ABA) synthesis and ABA signal transduction, and to the synthesis of raffinose. Genes related to ABA signal transduction, and to trehalose and raffinose synthesis, were up-regulated in leaves. Endoplasmic reticulum (ER) stress response genes were significantly up-regulated in leaves under drought stress, while a number of genes related to wax biosynthesis were also up-regulated in leaves. Genes related to unsaturated fatty acid biosynthesis were down-regulated and polyunsaturated fatty acids were significantly reduced in leaves 7 days after withholding irrigation. As drought stress increased, genes related to ethylene synthesis, ethylene signal transduction and chlorophyll degradation were up-regulated, and the chlorophyll content of leaves was significantly reduced by 7 days after withholding irrigation.

CONCLUSIONS

This study provides us with new insights to increase our understanding of the response mechanisms deployed by physic nut seedlings under drought stress. The genes and pathways identified in this study also provide much information of potential value for germplasm improvement and breeding for drought resistance.

RNA-Seq and Gene Network Analysis Uncover Activation of an ABA-Dependent Signalosome During the Cork Oak Root Response to Drought

Quercus suber (cork oak) is a West Mediterranean species of key economic interest, being extensively explored for its ability to generate cork. Like other Mediterranean plants, Q. suber is significantly threatened by climatic changes, imposing the need to quickly understand its physiological and molecular adaptability to drought stress imposition. In the present report, we uncovered the differential transcriptome of Q. suber roots exposed to long-term drought, using an RNA-Seq approach. 454-sequencing reads were used to de novo assemble a reference transcriptome, and mapping of reads allowed the identification of 546 differentially expressed unigenes. These were enriched in both effector genes (e.g., LEA, chaperones, transporters) as well as regulatory genes, including transcription factors (TFs) belonging to various different classes, and genes associated with protein turnover. To further extend functional characterization, we identified the orthologs of differentially expressed unigenes in the model species Arabidopsis thaliana, which then allowed us to perform in silico functional inference, including gene network analysis for protein function, protein subcellular localization and gene co-expression, and in silico enrichment analysis for TFs and cis-elements. Results indicated the existence of extensive transcriptional regulatory events, including activation of ABA-responsive genes and ABF-dependent signaling. We were then able to establish that a core ABA-signaling pathway involving PP2C-SnRK2-ABF components was induced in stressed Q. suber roots, identifying a key mechanism in this species' response to drought.

Recent advances in the dissection of drought-stress regulatory networks and strategies for development of drought-tolerant transgenic rice plants

Advances have been made in the development of drought-tolerant transgenic plants, including cereals. Rice, one of the most important cereals, is considered to be a critical target for improving drought tolerance, as present-day rice cultivation requires large quantities of water and as drought-tolerant rice plants should be able to grow in small amounts of water. Numerous transgenic rice plants showing enhanced drought tolerance have been developed to date. Such genetically engineered plants have generally been developed using genes encoding proteins that control drought regulatory networks. These proteins include transcription factors, protein kinases, receptor-like kinases, enzymes related to osmoprotectant or plant hormone synthesis, and other regulatory or functional proteins. Of the drought-tolerant transgenic rice plants described in this review, approximately one-third show decreased plant height under non-stressed conditions or in response to abscisic acid treatment. In cereal crops, plant height is a very important agronomic trait directly affecting yield, although the improvement of lodging resistance should also be taken into consideration. Understanding the regulatory mechanisms of plant growth reduction under drought stress conditions holds promise for developing transgenic plants that produce high yields under drought stress conditions. Plant growth rates are reduced more rapidly than photosynthetic activity under drought conditions, implying that plants actively reduce growth in response to drought stress. In this review, we summarize studies on molecular regulatory networks involved in response to drought stress. In a separate section, we highlight progress in the development of transgenic drought-tolerant rice plants, with special attention paid to field trial investigations.

Drought tolerance conferred to sugarcane by association with Gluconacetobacter diazotrophicus: a transcriptomic view of hormone pathways

Sugarcane interacts with particular types of beneficial nitrogen-fixing bacteria that provide fixed-nitrogen and plant growth hormones to host plants, promoting an increase in plant biomass. Other benefits, as enhanced tolerance to abiotic stresses have been reported to some diazotrophs. Here we aim to study the effects of the association between the diazotroph Gluconacetobacter diazotrophicus PAL5 and sugarcane cv. SP70-1143 during water depletion by characterizing differential transcriptome profiles of sugarcane. RNA-seq libraries were generated from roots and shoots of sugarcane plants free of endophytes that were inoculated with G. diazotrophicus and subjected to water depletion for 3 days. A sugarcane reference transcriptome was constructed and used for the identification of differentially expressed transcripts. The differential profile of non-inoculated SP70-1143 suggests that it responds to water deficit stress by the activation of drought-responsive markers and hormone pathways, as ABA and Ethylene. qRT-PCR revealed that root samples had higher levels of G. diazotrophicus 3 days after water deficit, compared to roots of inoculated plants watered normally. With prolonged drought only inoculated plants survived, indicating that SP70-1143 plants colonized with G. diazotrophicus become more tolerant to drought stress than non-inoculated plants. Strengthening this hypothesis, several gene expression responses to drought were inactivated or regulated in an opposite manner, especially in roots, when plants were colonized by the bacteria. The data suggests that colonized roots would not be suffering from stress in the same way as non-inoculated plants. On the other hand, shoots specifically activate ABA-dependent signaling genes, which could act as key elements in the drought resistance conferred by G. diazotrophicus to SP70-1143. This work reports for the first time the involvement of G. diazotrophicus in the promotion of drought-tolerance to sugarcane cv. SP70-1143, and it describes the initial molecular events that may trigger the increased drought tolerance in the host plant.

Differential expression analysis of a subset of GmNAC genes in shoots of two contrasting drought-responsive soybean cultivars DT51 and MTD720 under normal and drought conditions

NAC transcription factors are known to be involved in regulation of plant responses to drought stress. In this study, the expression of 23 drought-responsive GmNAC genes was assessed in the shoot tissues of DT51 and MTD720, the two soybean varieties with contrasting drought-responsive phenotypes, by real-time quantitative PCR (RT-qPCR) under normal and drought conditions. Results indicated that expression profile of GmNAC genes was genotype-dependent, and six GmNACs (GmNAC019, 043, 062, 085, 095 and 101) had higher transcript levels in the shoots of the drought-tolerant DT51 in comparison with the drought-sensitive MTD720 under drought. Our study suggests a positive correlation between the higher drought tolerance degree of DT51 versus MTD720 and the up-regulation of at least these six drought-responsive GmNACs in the shoot tissues. Furthermore, on the basis of our analysis, three genes, GmNAC043, 085 and 101, were identified as promising candidates for development of drought-tolerant soybean cultivars by genetic engineering.

Genome-wide identification, phylogeny, duplication, and expression analyses of two-component system genes in Chinese cabbage (Brassica rapa ssp. pekinensis)

In plants, a two component system (TCS) composed of sensor histidine kinases (HKs), histidine phosphotransfer proteins (HPs), and response regulators (RRs) has been employed in cytokinin signal transduction. A TCS exhibits important functions in diverse biological processes, including plant growth, development, and response to environmental stimuli. Conducting an exhaustive search of the Chinese cabbage genome, a total of 20 HK(L) (11 HKs and 9 HKLs), 8 HP (7 authentic and 1 pseudo), and 57 RR (21 Type-A, 17 Type-B, 4 Type-C, and 15 pseudo) proteins were identified. The structures, conserved domains, and phylogenetic relationships of these protein-coding genes were analysed in detail. The duplications, evolutionary patterns, and divergence of the TCS genes were investigated. The transcription levels of TCS genes in various tissues, organs, and developmental stages were further analysed to obtain information of the functions of these genes. Cytokinin-related binding elements were found in the putative promoter regions of Type-A BrRR genes. Furthermore, gene expression patterns to adverse environmental stresses (drought and high salinity) and exogenous phytohormones (tZ and ABA) were investigated. Numerous stress-responsive candidate genes were obtained. Our systematic analyses provided insights into the characterization of the TCS genes in Chinese cabbage and basis for further functional studies of such genes.