Polyamine Function in Plants: Metabolism, Regulation on Development, and Roles in Abiotic Stress Responses

The humidity level matters during the desiccation of Norway spruce somatic embryos

In Norway spruce, as in many other conifers, the germination capacity of somatic embryos is strongly influenced by the desiccation phase inserted after maturation. The intensity of drying during desiccation eminently affected the formation of emblings (i.e., seedlings developed from somatic embryos). Compared to non-desiccated embryos, the germination capacity of embryos desiccated at 100% relative humidity was about three times higher, but the reduction of relative humidity to 95 and 90% had a negative effect on the subsequent embryo development. The water loss observed in these embryos did not lead to an increase in lipid peroxidation, as shown by malondialdehyde levels. Another metabolic pathway in plants that mediates a response to abiotic stresses is directed toward the biosynthesis of polyamines (PAs). The activities of PA biosynthetic enzymes increased steadily in embryos during desiccation at 100% relative humidity, whereas they decreased at lower humidity. The total content of free PAs in the embryos gradually decreased throughout desiccation. The increase in free putrescine (Put) and perchloric acid-insoluble Put conjugates was observed in embryos desiccated at lower humidity. These changes were accompanied to some extent by the transcription of the genes for the PA biosynthesis enzymes. Desiccation at 100% relative humidity increased the activity of the cell wall-modifying enzymes β-1,3-glucanases and chitinases; the activities of these enzymes were also significantly suppressed at reduced humidity. The same pattern was observed in the transcription of some β-1,3-glucanase and chitinase genes. Desiccation treatments triggered metabolic processes that responded to water availability, suggesting an active response of the embryo to the reduction in humidity. A positive effect was demonstrated only for desiccation at high relative humidity. Some of the physiological characteristics described can be used as markers of inappropriate relative humidity during somatic embryo desiccation.

Elucidating the dialogue between arbuscular mycorrhizal fungi and polyamines in plants

The most dominant arbuscular mycorrhizal (AM) symbiont can be established on roots of most terrestrial plants by beneficial AM fungi. A type of polycationic and aliphatic compounds, polyamines (PAs), are involved in plant physiological activities including stress responses. Interestingly, small amounts of PAs such as putrescine (Put) and spermidine (Spd) were found in AM fungal spores, and they are considered to be a component involved in mycorrhizal development, including mycorrhizal colonization, appressoria formation, spore germination and mycelial growth. Thus, PAs are regulatory factors in plant-AM symbiosis. Inoculation of AM fungi also affects the metabolism of endogenous PAs in host plants, including PAs synthesis and catabolism, thus, regulating various physiological events of the host. As a result, there seems to be a dialogue between PAs and AM fungi. Existing knowledge makes us understand that endogenous or exogenous PAs are an important regulator factor in the growth of AM fungi, as well as a key substance to colonize roots, which further enhances mycorrhizal benefits in plant growth responses and root architecture. The presence of AM symbiosis in roots alters the dynamic balance of endogenous PAs, triggering osmotic adjustment and antioxidant defense systems, maintaining charge balance and acting as a stress signalling molecule, which affects various physiological activities, such as plant growth, nutrient acquisition, stress tolerance and improvement of root architecture. This review mainly elucidated (i) what is the role of fungal endogenous PAs in fungal growth and colonization of roots in host plants? (ii) how AM fungi and PAs interact with each other to alter the growth of fungi and plants and subsequent activities, providing the reference for the future combined use of AM fungi and PAs in agricultural production, although there are still many unknown events in the dialogue.

Strain-specific transcriptional responses overshadow salinity effects in a marine diatom sampled along the Baltic Sea salinity cline

The salinity gradient separating marine and freshwater environments represents a major ecological divide for microbiota, yet the mechanisms by which marine microbes have adapted to and ultimately diversified in freshwater environments are poorly understood. Here, we take advantage of a natural evolutionary experiment: the colonization of the brackish Baltic Sea by the ancestrally marine diatom Skeletonema marinoi. To understand how diatoms respond to low salinity, we characterized transcriptomic responses of acclimated S. marinoi grown in a common garden. Our experiment included eight strains from source populations spanning the Baltic Sea salinity cline. Gene expression analysis revealed that low salinities induced changes in the cellular metabolism of S. marinoi, including upregulation of photosynthesis and storage compound biosynthesis, increased nutrient demand, and a complex response to oxidative stress. However, the strain effect overshadowed the salinity effect, as strains differed significantly in their response, both regarding the strength and the strategy (direction of gene expression) of their response. The high degree of intraspecific variation in gene expression observed here highlights an important but often overlooked source of biological variation associated with how diatoms respond to environmental change.

Plant Growth Regulators Improve Grain Production and Water Use Efficiency of Foeniculum vulgare Mill. under Water Stress

The development of methods increasing plant water use efficiency (WUE) would enhance the ability to grow wild aromatic and medicinally important species. The aim of this research was to determine the effect of plant growth regulators (PGRs) applied by spraying on stress resistance and WUE of fennel subjected to water stress. Plants in the generative stage were more drought tolerant than those in the vegetative stage. Water stress at vegetative stage decreased plant biomass and grain yield by 60% and 61%, respectively. Severe water stress in vegetative stage reduced grain production by 56%, and grains had 43% lower mass than those from non-stressed plants. Application of PGRs at both stages of growth increased grain yield and biomass, but the magnitude of increase depended on the type and application time of PGRs. Plants grown in well-watered conditions and sprayed with methyl jasmonate during the vegetative stage had the highest grain production (2.7 g plant⁻¹), whereas under moderate water stress, plants yielded the best (2.1 g plant⁻¹) when sprayed with epibrassinolide. The maximum WUE for grain (0.91 g L⁻¹) and essential oil production (20 mg L⁻¹) was noted in plants exposed to moderate stress and treated with methyl jasmonate during the vegetative stage.

Nucleosome destabilization by polyamines

The roles and molecular interactions of polyamines (PAs) in the nucleus are not fully understood. Here their effect on nucleosome stability, a key regulatory factor in eukaryotic gene control, is reported, as measured in agarose embedded nuclei of H2B-GFP expressor HeLa cells. Nucleosome stability was assessed by quantitative microscopy [1,2] in situ, in close to native state of chromatin, preserving the nucleosome constrained topology of the genomic DNA. A robust destabilizing effect was observed in the millimolar concentration range in the case of spermine, spermidine as well as putrescine, which was strongly pH and salt concentration-dependent, and remained significant also at neutral pH. The integrity of genomic DNA was not affected by PA treatment, excluding DNA break-elicited topological relaxation as a factor in destabilization. The binding of PAs to DNA was demonstrated by the displacement of ethidium bromide, both from deproteinized nuclear halos and from plasmid DNA. The possibility that DNA methylation patterns may be influenced by PA levels is contemplated in the context of gene expression and DNA methylation correlations identified in the NCI-60 panel-based CellMiner database: methylated loci in subsets of high-ODC1 cell lines and the dependence of PER3 DNA methylation on PA metabolism.

Soil Microorganisms and Seaweed Application With Supplementary Irrigation Improved Physiological Traits and Yield of Two Dryland Wheat Cultivars

To evaluate the effect of useful soil microorganisms and organic compounds on physiological characteristics and yield of two wheat cultivars under supplementary irrigation conditions, a study was conducted in the Agriculture Research Farm of Kurdistan University during the two cropping seasons of 2017-2018 and 2018-2019. A split-split plot-based study on a randomized complete block design with four replicates was used as an experimental design. The main factor was irrigation at three levels, including control without irrigation, supplementary irrigation in the booting stage, and supplementary irrigation in the booting and flowering stages. Two wheat cultivars, namely, Sardari and Sirvan, as sub-factors and application of bio-fertilizers in eight levels, including the use of bio-fertilizers containing: Mycorrhiza, Seaweed extract, Nitrozist and Phosphozist, Mycorrhiza + Nitrozist and Phosphozist, Seaweed extract + Nitrozist and Phosphozist, Mycorrhiza + Seaweed extract, Mycorrhiza + Nitrozist and Phosphozist + Seaweed extract, and non-application of bio-fertilizers, were considered as sub-factors. The results of both seasons of the experiment showed that the application of bio-fertilizers compared to the control treatment at all irrigation levels increased root volume, leaf relative water content (RWC), membrane stability index (MSI), and photosynthetic pigment content. The highest amount of H2O2, proline, and soluble carbohydrates were obtained in wheat under dry land conditions, and supplementary irrigation, especially two-time irrigation, significantly reduced the values of these traits. Supplementary irrigation also increased grain yield, so that in the conditions of two-time irrigation compared to the non-irrigation treatment (dry land), in the first and second seasons, the grain yield increased by 79.51 and 78.69%, respectively. Application of bio-fertilizers (Mycorrhiza + Nitrozist and Phosphozist + Seaweed extract) in comparison with the non-application of these fertilizers, due to increased root volume, RWC, MSI, and content of photosynthetic pigments, increased the grain yield in the first and second seasons of the experiment by 8.04 and 6.96%, respectively. As a result, suitable microorganisms and seaweed can improve wheat resistance mechanisms to water deficit, which along with using supplementary irrigation that saves water consumption improves plant growth and yield in areas faced with water shortage.

Hydrogen sulphide alleviates cadmium stress in Trigonella foenum-graecum by modulating antioxidant enzymes and polyamine content

Cadmium (Cd) toxicity reduces growth and yield of crops grown in metal-polluted sites. Research was conducted to estimate the potential of hydrogen sulphide (H₂ S) to mitigate toxicity caused by Cd in fenugreek seedlings (Trigonella foenum-graecum L.). Different concentrations of CdCl₂ (Cd1-1 mM, Cd2-1.5 mM, Cd3-2mM) and H₂ S (HS1-100 µM, HS2-150 µM, HS3-200 µM) were assessed. Seeds of fenugreek were primed with sodium hydrosulphide (NaHS), as H₂ S donor. Seedlings growing in Cd-spiked media treated with H₂ S were harvested after 2 weeks. Cd stress affected growth of fenugreek seedlings. Cd toxicity decreased leaf relative water content (LRWC), intercellular CO₂ concentration, net photosynthesis, stomatal conductance and transpiration. However, application of H₂ S significantly improved seedling morphological attributes by increasing the activity of antioxidant enzymes, i.e. APX, CAT and SOD, in Cd-contaminated soil. H₂ S treatment also regulated phenolic and flavonoid content. H₂ S-induced biosynthesis of spermidine (Spd) and putrescine (Put) could account for the enhancement of growth and physiological performance of fenugreek seedlings under Cd stress. H₂ S treatment also reduced H₂ O₂ production (38%) and electrolyte leakage (EL, 51%) in seedlings grown in different concentrations of Cd. It is recommended to evaluate the efficacy of H₂ S in alleviating Cd toxicity in other crop plants.

The effect of polyamines and silver thiosulphate on micropropagation of date palm followed by genetic stability assessment

There are some limitations in date palm micropropagation. These include low multiplication efficiency, low rooting rate, and high mortality experienced by in vitro raised plantlets during laboratory to soil transfer. The objective of the study was to determine the effect of the polyamines and Silver Thiosulphate (STS) on the enhancement of shoot multiplication and genetic stability of in vitro cultures of date palm cultivar Quntar. Media supplemented with 75 mg L^-1 SPD in combination with 10 mg L^-1 STS gave the highest percentage of callus producing buds (83.34%) and average bud formation (16.3) per jar. The addition of PUT and STS to the medium was most effective on root formation and the number of roots per shoot, where the best result, 91.67% and 6.37 roots per shoot, respectively, were obtained using 75 mg L^-1 PUT and 10 mg L^-1 STS, resulting in fast-growing plantlets during acclimatization phase, reaching 80% of plant survival. The genetic fidelity assessment of plants derived from micropropagation was confirmed by RAPD analysis. Four operon primers were used, and all of them showed amplified unambiguous (OPA02, OPC-04, OPD-07, and OPE-15). All generated bands were monomorphic and had no variation among the tissue culture-derived plants tested. Accordingly, these results indicate that adding polyamines and silver thiosulfate to the nutrient medium of date palm cv. Quntar was beneficial to improving shoot organogenesis, rooting, and production of genetically stable date palm plants.

Insights into polyamine metabolism: homospermidine is double-oxidized in two discrete steps by a single copper-containing amine oxidase in pyrrolizidine alkaloid biosynthesis

Polyamines are important metabolites in plant development and abiotic and biotic stress responses. Copper-containing amine oxidases (CuAOs) are involved in the regulation of polyamine levels in the cell. CuAOs oxidize primary amines to their respective aldehydes and hydrogen peroxide. In plants, aldehydes are intermediates in various biosynthetic pathways of alkaloids. CuAOs are thought to oxidize polyamines at only one of the primary amino groups, a process frequently resulting in monocyclic structures. These oxidases have been postulated to be involved in pyrrolizidine alkaloid (PA) biosynthesis. Here, we describe the identification and characterization of homospermidine oxidase (HSO), a CuAO of Heliotropium indicum (Indian heliotrope), involved in PA biosynthesis. Virus-induced gene silencing of HSO in H. indicum leads to significantly reduced PA levels. By in vitro enzyme assays after transient in planta expression, we show that this enzyme prefers Hspd over other amines. Nuclear magnetic resonance spectroscopy and mass spectrometry analyses of the reaction products demonstrate that HSO oxidizes both primary amino groups of homospermidine (Hspd) to form a bicyclic structure, 1-formylpyrrolizidine. Using tracer feeding, we have further revealed that 1-formylpyrrolizidine is an intermediate in the biosynthesis of PAs. Our study therefore establishes that HSO, a canonical CuAO, catalyzes the second step of PA biosynthesis and provides evidence for an undescribed and unusual mechanism involving two discrete steps of oxidation that might also be involved in the biosynthesis of complex structures in other alkaloidal pathways.

Role of Spermidine in Photosynthesis and Polyamine Metabolism in Lettuce Seedlings under High-Temperature Stress

High temperature is a huge threat to lettuce production in the world, and spermidine (Spd) has been shown to improve heat tolerance in lettuce, but the action mechanism of Spd and the role of polyamine metabolism are still unclear. The effects of Spd and D-arginine (D-arg) on hydroponic lettuce seedlings under high-temperature stress by foliar spraying of Spd and D-arg were investigated. The results showed that high-temperature stress significantly inhibited the growth of lettuce seedlings, with a 33% decrease in total fresh weight and total dry weight; photosynthesis of lettuce seedlings was inhibited by high-temperature stress, and the inhibition was greater in the D-arg treatment, while the Spd recovery treatment increased net photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr), stomatal limit value (Ls), and intercellular CO2 concentration (Ci). High-temperature stress significantly reduced the maximum photochemical efficiency (Fv/Fm), photochemical quenching coefficient (qP), electron transport rate (ETR), and photochemical efficiency of PSII (ΦPSII), increased the non-photochemical burst coefficient (NPQ) and reduced the use of light energy, which was alleviated by exogenous Spd. The increase in polyamine content may be due to an increase in polyamine synthase activity and a decrease in polyamine oxidase activity, as evidenced by changes in the expression levels of genes related to polyamine synthesis and metabolism enzymes. This evidence suggested that D-arg suppressed endogenous polyamine levels in lettuce and reduced its tolerance, whereas exogenous Spd promoted the synthesis and accumulation of polyamines in lettuce and increased its photosynthetic and oxidative stress levels, which had an impact on the tolerance of lettuce seedlings.

Enhancement of Bioactive Constituents in Fresh Cauliflower By-Products in Challenging Climate Conditions

In order to mitigate the detrimental impact that climate change is having on plants, the study of new practices that allow for the reduction of such effects has become imperative. In addition, the revaluation of the promotion of healthy plant by-products has also markedly increased in importance in recent years. In this work, the modifications in biomass and some antioxidant compounds of cauliflower by-products treated with putrescine under extreme temperatures in two different CO₂ scenarios (the control (400 ppm) and a high concentration of CO₂ (1000 ppm)) were studied. Additionally, the compositions of inner and outer leaves were also compared. According to results found in this work, cauliflower grown under elevated CO₂ and treated with putrescine (2.5 mM) prior to heat stress showed the highest biomass accumulation (20%) compared to the control. Moreover, in the outer leaves from cauliflower grown under elevated CO₂ and treated with putrescine prior to high temperature exposure, the highest biosynthesis of sugars (20%) was recorded. Although cauliflower by-products turned out to be rich in polyamines (208.6 nmoles g⁻¹ fresh weight (FW) and 124.3 nmoles g⁻¹ FW for outer and inner leaves, respectively) and phenolic compounds (1070.2 mg gallic acid equivalents ( (GAE) 100 g⁻¹ FW in outer leaves and 772.0 mg GAE 100 g⁻¹ FW in inner leaves), it was the outer leaves that after applying the new strategy showed the greatest increase in polyamines (68%) and phenolic compounds (39%), obtaining here the highest increase in antioxidant activity (3%). Thus, they should no longer be regarded as mere by-products and should be used for pharmaceutical or nutraceutical purposes. The novel strategy presented in this work may allow us to take advantage of both the continued increase in CO₂ and heat waves that are becoming more frequent.

Arginine-Dependent Nitric Oxide Generation and S-Nitrosation in the Non-Photosynthetic Unicellular Alga Polytomella parva

Nitric oxide (NO) acts as a key signaling molecule in higher plants, regulating many physiological processes. Several photosynthetic algae from different lineages are also known to produce NO. However, it remains unclear whether this messenger is produced by non-photosynthetic algae. Among these organisms, the colorless alga Polytomella parva is a special case, as it has lost not only its plastid genome, but also nitrate reductase and nitrite reductase. Up to now, the question of whether NO synthesis occurs in the absence of functional nitrate reductase (NR) and the assimilation of nitrates/nitrites in P. parva has not been elucidated. Using spectrofluorometric assays and confocal microscopy with NO-sensitive fluorescence dye, we demonstrate L-arginine-dependent NO synthesis by P. parva cells. Based on a pharmacological approach, we propose the existence of arginine-dependent NO synthase-like activity in this non-photosynthetic alga. GC-MS analysis provides primary evidence that P. parva synthesizes putrescine, which is not an NO source in this alga. Moreover, the generated NO causes the S-nitrosation of protein cysteine thiol groups. Together, our data argue for NR-independent NO synthesis and its active role in S-nitrosation as an essential post-translational modification in P. parva.

Isolation of heavy metal-immobilizing and plant growth-promoting bacteria and their potential in reducing Cd and Pb uptake in water spinach

Heavy metal-immobilizing bacteria are normally capable of stabilizing metals and affecting their absorption by plants. However, few studies have elucidated the mechanisms employed by novel heavy metal-immobilizing and plant growth-promoting bacteria to immobilize Cd and Pb and reduce their uptake by vegetables. In this study, polyamine (PA)-producing strains were isolated and their effects on biomass and metal accumulation in water spinach (Ipomoea aquatica Forssk.) and the underlying mechanisms were investigated. Two PA-producing strains, Enterobacter bugandensis XY1 and Serratia marcescens X43, were isolated. Strains XY1 and X43 reduced the aqueous Cd and Pb levels (49%-52%) under 10 mg L^-1 Cd and 20 mg L^-1 Pb because of metal ion chelation by bacterially produced PAs and cell adsorption. Further evidence showed that Cd and Pb were bound and precipitated on the bacterial cell surface in the form of Cd(OH)₂, CdCO₃ and PbO. Compared with strain-free water spinach, greens inoculated with strains XY1 and X43 showed 51%-80% lower Cd and Pb contents. The rhizosphere soil pH and PA contents were significantly higher, and lower contents of the rhizosphere soil acid-soluble fractions of Cd (18%-39%) and Pb (31%-37%) were observed compared to the noninoculated control. Moreover, inoculation with XY1 reduced the diversity of the bacterial community, but the relative abundances of plant growth-promoting and PA-producing bacteria in rhizosphere soil were enriched, which enhanced water spinach resistance to Cd and Pb toxicity. Our findings describe novel heavy metal-immobilizing bacteria that could be used to improve the habitat of vegetables and reduce their uptake of heavy metals.

Spermine-mediated polyamine metabolism enhances arsenic-stress tolerance in Phaseolus vulgaris by expression of zinc-finger proteins related genes and modulation of mineral nutrient homeostasis and antioxidative system

The contamination of groundwater and agricultural land by metalloids especially arsenic (As) is one of the most serious threats to people and plants worldwide. Therefore, the present study was design to explore the role of spermine (Spm)- mediated polyamine metabolism in the alleviation of arsenic (As) toxicity in common bean (Phaseolus vulgaris L.). It was noted that As stress caused reduction in the intracellular CO₂ concentration, stomatal conductivity and transpiration rate as compared to the control treatment and also impairedplant growth attributes and mineral nutrient homeostasis (sulfur, phosphorus, potassium and calcium). However, the exogenous application of Spm resulted in a considerable enhance in the content of glutathione and nitric oxide, and the activity of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), glutathione-reductase (GR), ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR) in P. vulgaris seedlings grown As-contaminated soil. In addition, Spm application significantly improved the endogenous production of putrescine and spermidine accompanied along with reduction in malondialdehyde, electrolyte leakage, hydrogen peroxide, superoxide level besides enhanced methylglyoxal (MG) detoxification. Moreover, Spm treatment elevated the expression level of zinc-finger proteins related genes (PvC3H24, PvC3H25, PvC3H26 and PvC3H27) involved in abiotic stress response. The study concluded that Spm acted as an enhancing agent and improved tolerance to As-toxicity by upregulating the expression of zinc-finger proteins related genes, polyamine metabolism, Mg detoxification and antioxidant system in P. vulgaris.

Metabolite Profiling in Green Microalgae with Varying Degrees of Desiccation Tolerance

Trebouxiophyceae are microalgae occupying even extreme environments such as polar regions or deserts, terrestrial or aquatic, and can occur free-living or as lichen photobionts. Yet, it is poorly understood how environmental factors shape their metabolism. Here, we report on responses to light and temperature, and metabolic adjustments to desiccation in Diplosphaera epiphytica, isolated from a lichen, and Edaphochlorella mirabilis, isolated from Tundra soil, assessed via growth and photosynthetic performance parameters. Metabolite profiling was conducted by GC-MS. A meta-analysis together with data from a terrestrial and an aquatic Chlorella vulgaris strain reflected elements of phylogenetic relationship, lifestyle, and relative desiccation tolerance of the four algal strains. For example, compatible solutes associated with desiccation tolerance were up-accumulated in D. epiphytica, but also sugars and sugar alcohols typically produced by lichen photobionts. The aquatic C. vulgaris, the most desiccation-sensitive strain, showed the greatest variation in metabolite accumulation after desiccation and rehydration, whereas the most desiccation-tolerant strain, D. epiphytica, showed the least, suggesting that it has a more efficient constitutive protection from desiccation and/or that desiccation disturbed the metabolic steady-state less than in the other three strains. The authors hope that this study will stimulate more research into desiccation tolerance mechanisms in these under-investigated microorganisms.

Exogenously applied spermidine alleviates hypoxia stress in Phyllostachys praecox seedlings via changes in endogenous hormones and gene expression

BACKGROUND

Hypoxia stress is thought to be one of the major abiotic stresses that inhibits the growth and development of higher plants. Phyllostachys pracecox is sensitive to oxygen and suffers soil hypoxia during cultivation; however, the corresponding solutions to mitigate this stress are still limited in practice. In this study, Spermidine (Spd) was tested for regulating the growth of P. praecox seedlings under the hypoxia stress with flooding.

RESULTS

A batch experiment was carried out in seedlings treated with 1 mM and 2 mM Spd under flooding for eight days. Application of 1 mM and 2 mM Spd could alleviate plant growth inhibition and reduce oxidative damage from hypoxia stress. Exogenous Spd significantly (P < 0.05) increased proline, soluble protein content, catalase (CAT), superoxide dismutase (SOD), and S-adenosylmethionine decarboxylase (SAMDC) activity, enhanced abscisic acid (ABA) and indole-3-acetic acid (IAA) content, and reduced ethylene emission, hydrogen peroxide (H₂O₂), superoxide radical (O₂^·-) production rate, ACC oxidase (ACO) and ACC synthase (ACS) to protect membranes from lipid peroxidation under flooding. Moreover, exogenous Spd up-regulated the expression of auxin-related genes auxin responsive factor1 (ARF1), auxin1 protein (AUX1), auxin2 protein (AUX2), auxin3 protein (AUX3) and auxin4 protein (AUX4), and down-regulated the expression of ethylene-related ACO and ACS genes during flooding.

CONCLUSION

The results indicated that exogenous Spd altered hormone concentrations and the expression of hormone-related genes, thereby protecting the bamboo growth under flooding. Our data suggest that Spd can be used to reduce hypoxia-induced cell damage and improve the adaptability of P. praecox to flooding stress.

Comparative transcriptomic analysis and antioxidant defense mechanisms in clusterbean (Cyamopsis tetragonoloba (L.) Taub.) genotypes with contrasting drought tolerance

To understand drought tolerance mechanism(s) in clusterbean (Cyamopsis tetragonoloba), we conducted physiological, biochemical, and de novo comparative transcriptome analysis of drought-tolerant (RGC-1002) and drought-sensitive (RGC-1066) genotypes subjected to 30 days of drought stress. Relative water content (RWC) was maintained in tolerant genotype but was reduced in sensitive genotype. Leaf pigment concentrations were higher in tolerant genotype. Net photosynthesis was significantly decreased in sensitive genotype but insignificant reduction was found in tolerant genotype. Enzymatic antioxidant (GR, APX, DHAR) activities were enhanced in tolerant genotype, while there were insignificant changes in these enzymes in sensitive genotype. The ratios of antioxidant molecules (ASC/DHA and GSH/GSSG) were higher in tolerant genotype as compared to sensitive genotype. In sensitive genotype, 6625 differentially expressed genes (DEGs) were upregulated and 5365 genes were downregulated. In tolerant genotype, 5206 genes were upregulated and 2793 genes were downregulated. In tolerant genotype, transketolase family protein, phosphoenolpyruvate carboxylase 3, temperature-induced lipocalin, and cytochrome oxidase were highly upregulated. Moreover, according to Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis, the drought tolerance may be attributed to upregulated starch and sucrose metabolism-related genes in tolerant genotype. Finally, quantitative real-time PCR confirmed the reproducibility of the RNA-seq data.

Exogenous Putrescine Increases Heat Tolerance in Tomato Seedlings by Regulating Chlorophyll Metabolism and Enhancing Antioxidant Defense Efficiency

Crops around the world are facing a diversity of environmental problems, of which high temperatures are proving to be the most serious threat to crops. Polyamine putrescine (Put) acts as a master growth regulator that contributes to optimal plant growth and development and increased stress tolerance. Here, the current study aimed to elucidate how Put functions in regulating chlorophyll (Chl) metabolism, oxidative stress, and antioxidant defense, as well as to characterize the expression of genes related to heat stress in tomato seedlings under such stress. The results revealed that Put treatment significantly attenuates heat-induced damage by promoting biomass production, increasing photosynthetic efficiency, and inhibiting excessive production of oxidative stress markers. Heat stress markedly decreased the Chl content in the tomato leaf and accelerated the leaf yellowing process. However, Put-treated tomato seedlings showed a higher Chl content, which could be associated with the functions of Put in elevating PBGD activity (Chl biosynthesis enzyme) and suppressing the activity of the Chl catabolic enzyme (Chlase and MDCase). Under high-temperature stress, the expression levels of the gene encoding factors involved in Chl biosynthesis and Chl catabolism were significantly down- and upregulated, respectively, and this trend was reversed in Put-treated heat-stressed seedlings. In addition, exogenous application of Put boosted the activity of antioxidant enzymes, along with the levels of expression of their encoding genes, only in plants that were heat stressed. Furthermore, the expression levels of heat-shock-related genes (HSP90, HSP70, and HsfA1) were elevated in Put-treated, high-temperature-stressed tomato seedlings. Taken together, our results indicate that Put treatment significantly increases the heat tolerance of tomato seedlings, by elevating Chl concentrations and suppressing Chl catabolic enzyme activity, modulating endogenous free PA content, increasing antioxidant defense efficiency, and upregulating the expression of heat-shock-related genes.

Piriformospora indica recruits host-derived putrescine for growth promotion in plants

Growth promotion induced by the endosymbiont Piriformospora indica has been observed in various plants; however, except growth phytohormones, specific functional metabolites involved in P. indica-mediated growth promotion are unknown. Here, we used a gas chromatography-mass spectrometry-based untargeted metabolite analysis to identify tomato (Solanum lycopersicum) metabolites whose levels were altered during P. indica-mediated growth promotion. Metabolomic multivariate analysis revealed several primary metabolites with altered levels, with putrescine (Put) induced most significantly in roots during the interaction. Further, our results indicated that P. indica modulates the arginine decarboxylase (ADC)-mediated Put biosynthesis pathway via induction of SlADC1 in tomato. Piriformospora indica did not promote growth in Sladc1-(virus-induced gene silencing of SlADC1) lines of tomato and showed less colonization. Furthermore, using LC-MS/MS we showed that Put promoted growth by elevation of auxin (indole-3-acetic acid) and gibberellin (GA4 and GA7) levels in tomato. In Arabidopsis (Arabidopsis thaliana) adc knockout mutants, P. indica colonization also decreased and showed no plant growth promotion, and this response was rescued upon exogenous application of Put. Put is also important for hyphal growth of P. indica, indicating that it is co-adapted by both host and microbe. Taken together, we conclude that Put is an essential metabolite and its biosynthesis in plants is crucial for P. indica-mediated plant growth promotion and fungal growth.

A comparative whole-genome approach identifies bacterial traits for marine microbial interactions

Microbial interactions shape the structure and function of microbial communities with profound consequences for biogeochemical cycles and ecosystem health. Yet, most interaction mechanisms are studied only in model systems and their prevalence is unknown. To systematically explore the functional and interaction potential of sequenced marine bacteria, we developed a trait-based approach, and applied it to 473 complete genomes (248 genera), representing a substantial fraction of marine microbial communities. We identified genome functional clusters (GFCs) which group bacterial taxa with common ecology and life history. Most GFCs revealed unique combinations of interaction traits, including the production of siderophores (10% of genomes), phytohormones (3-8%) and different B vitamins (57-70%). Specific GFCs, comprising Alpha- and Gammaproteobacteria, displayed more interaction traits than expected by chance, and are thus predicted to preferentially interact synergistically and/or antagonistically with bacteria and phytoplankton. Linked trait clusters (LTCs) identify traits that may have evolved to act together (e.g., secretion systems, nitrogen metabolism regulation and B vitamin transporters), providing testable hypotheses for complex mechanisms of microbial interactions. Our approach translates multidimensional genomic information into an atlas of marine bacteria and their putative functions, relevant for understanding the fundamental rules that govern community assembly and dynamics.

Advances in Understanding Silicon Transporters and the Benefits to Silicon-Associated Disease Resistance in Plants

Silicon (Si) is the second most abundant element after oxygen in the earth’s crust and soil. It is available for plant growth and development, and it is considered as quasi-essential for plant growth. The uptake and transport of Si is mediated by Si transporters. With the study of the molecular mechanism of Si uptake and transport in higher plants, different proteins and coding genes with different characteristics have been identified in numerous plants. Therefore, the accumulation, uptake and transport mechanisms of Si in various plants appear to be quite different. Many studies have reported that Si is beneficial for plant survival when challenged by disease, and it can also enhance plant resistance to pathogens, even at low Si accumulation levels. In this review, we discuss the distribution of Si in plants, as well as Si uptake, transport and accumulation, with a focus on recent advances in the study of Si transporters in different plants and the beneficial roles of Si in disease resistance. Finally, the application prospects are reviewed, leading to an exploration of the benefits of Si uptake for plant resistance against pathogens.

Metabolic adjustment and regulation of gene expression are essential for increased resistance to severe water deficit and resilience post-stress in soybean

Background

Soybean is the main oilseed crop grown in the world; however, drought stress affects its growth and physiology, reducing its yield. The objective of this study was to characterize the physiological, metabolic, and genetic aspects that determine differential resistance to water deficit in soybean genotypes.

Methods

Three soybean genotypes were used in this study, two lineages (L11644 and L13241), and one cultivar (EMBRAPA 48-C48). Plants were grown in pots containing 8 kg of a mixture of soil and sand (2:1) in a greenhouse under sunlight. Soil moisture in the pots was maintained at field capacity until the plants reached the stage of development V4 (third fully expanded leaf). At this time, plants were subjected to three water treatments: Well-Watered (WW) (plants kept under daily irrigation); Water Deficit (WD) (withholding irrigation until plants reached the leaf water potential at predawn of -1.5 ± 0.2 MPa); Rewatered (RW) (plants rehydrated for three days after reached the water deficit). The WW and WD water treatments were evaluated on the eighth day for genotypes L11644 and C48, and on the tenth day for L13241, after interruption of irrigation. For the three genotypes, the treatment RW was evaluated after three days of resumption of irrigation. Physiological, metabolic and gene expression analyses were performed.

Results

Water deficit inhibited growth and gas exchange in all genotypes. The accumulation of osmolytes and the concentrations of chlorophylls and abscisic acid (ABA) were higher in L13241 under stress. The metabolic adjustment of lineages in response to WD occurred in order to accumulate amino acids, carbohydrates, and polyamines in leaves. The expression of genes involved in drought resistance responses was more strongly induced in L13241. In general, rehydration provided recovery of plants to similar conditions of control treatment. Although the C48 and L11644 genotypes have shown some tolerance and resilience responses to severe water deficit, greater efficiency was observed in the L13241 genotype through adjustments in morphological, physiological, genetic and metabolic characteristics that are combined in the same plant. This study contributes to the advancement in the knowledge about the resistance to drought in cultivated plants and provides bases for the genetic improvement of the soybean culture.

Transcriptome and metabolome analyses revealed that narrowband 280 and 310 nm UV-B induce distinctive responses in Arabidopsis

In plants, the UV-B photoreceptor UV RESISTANCE LOCUS8 (UVR8) perceives UV-B and induces UV-B responses. UVR8 absorbs a range of UV-B (260–335 nm). However, the responsiveness of plants to each UV-B wavelength has not been intensively studied so far. Here, we performed transcriptome and metabolome analyses of Arabidopsis using UV light emitting diodes (LEDs) with peak wavelengths of 280 and 310 nm to investigate the differences in the wavelength-specific UV-B responses. Irradiation with both UV-LEDs induced gene expression of the transcription factor ELONGATED HYPOCOTYL 5 (HY5), which has a central role in the UVR8 signaling pathway. However, the overall transcriptomic and metabolic responses to 280 and 310 nm UV-LED irradiation were different. Most of the known UV-B-responsive genes, such as defense-related genes, responded only to 280 nm UV-LED irradiation. Lipids, polyamines and organic acids were the metabolites most affected by 280 nm UV-LED irradiation, whereas the effect of 310 nm UV-LED irradiation on the metabolome was considerably less. Enzymatic genes involved in the phenylpropanoid pathway upstream in anthocyanin biosynthesis were up-regulated only by 280 nm UV-LED irradiation. These results revealed that the responsivenesses of Arabidopsis to 280 and 310 nm UV-B were significantly different, suggesting that UV-B signaling is mediated by more complex pathways than the current model.

Putrescine: A Key Metabolite Involved in Plant Development, Tolerance and Resistance Responses to Stress

Putrescine (Put) is the starting point of the polyamines (PAs) pathway and the most common PA in higher plants. It is synthesized by two main pathways (from ornithine and arginine), but recently a third pathway from citrulline was reported in sesame plants. There is strong evidence that Put may play a crucial role not only in plant growth and development but also in the tolerance responses to the major stresses affecting crop production. The main strategies to investigate the involvement of PA in plant systems are based on the application of competitive inhibitors, exogenous PAs treatments, and the most efficient approaches based on mutant and transgenic plants. Thus, in this article, the recent advances in understanding the role of this metabolite in plant growth promotion and protection against abiotic and biotic stresses will be discussed to provide an overview for future research.

Investigating Phragmites australis response to copper exposure using physiologic, Fourier Transform Infrared and metabolomic approaches

Phragmites australis (Cav.) Trin. ex Steud is a landscape plant with resistance to heavy metals that has significance in phytoremediation. However, little is known about the metabolomic background of the heavy metal resistance mechanisms of Phragmites . We studied copper stress on Phragmites and monitored physiological indicators such as malondialdehyde (MDA) and electrolyte leakage (EL). In addition, Fourier Transform Infrared (FTIR) was used to study the related chemical composition in the roots, stems, and leaves under copper stress. Furthermore, LC-MS technology was used to analyse the plants metabolic profile. Results showed that increased copper concentration in Phragmites led to the accumulation of MDA and EL. FTIR spectrum detected the presence of O-H and C=O stretching. O-H stretching was related to the presence of flavonoids, while C=O stretching reflected the presence of protein amide I. The latter was related to the change of amino acid composition. Both flavonoids and amino acids are regarded as contributors to the antioxidant of Phragmites under copper stress. Metabolomics analysis revealed that arginine and ayarin were accumulated and Phragmites leaves responded to copper stress with changes in the pool size of arginine and ayarin. It is speculated that they could improve resistance. Arginine is accumulated through two pathways: the citrulline decomposition and conversion pathway; and the circular pathway composed of ornithine, citrulline, l -argininosuccinate and arginine. Ayarin is synthesised through the quercetin methylation pathway. This study elucidates the antioxidant mechanisms for enhancing its resistance to heavy metal stress, thus improving of phytoremediation efficiency.

Gibberellic acid interacts with salt stress on germination, growth and polyamine gene expression in fennel (Foeniculum vulgare Mill.) seedlings

This study aimed to rigorously investigate and integrate the underlying hypothesis that an enhancing effect of gibberellic acid (GA3, 3 µM) with increased growth actually leads to a modification of the physiological role of polyamines during salinity stress (NaCl, 100 mM) in fennel. These analyses concern both reserve tissues (cotyledons) and embryonic axes in growth. Physiological results indicate a restriction of germination, growth, mineral nutrition and damages to membranes of salt-treated seedlings. This was partially attenuated in seedlings treated with an interaction effect of GA3 and NaCl. Peroxidase and catalase activities showed a reduction or an augmentation according to the treatments and organs. The three main polyamines (PA): putrescine, spermidine and spermine were elevated in the salt-treated seedlings. Meanwhile, GA3 seed priming was extremely efficient in reducing PA levels in salt-stressed seedlings compared to the control. Response of PA genes to salinity was variable. Up-regulation was noted for SPMS1, ODC1, and ADC1 in hypocotyls and cotyledons (H + C) and down-regulation for SAMDC1 in the radicle. Interaction of salt/GA3 treatment showed different responses, only ODC1 in (H + C) and ADC1 in both radicle and (H + C) were overexpressed. Concerning other genes, no change in mRNA abundance was observed in both organs compared to the salt-treated seedlings. From these results, it could be inferred that the fennel seedlings were NaCl sensitive. This sensitivity was mitigated when GA3 applied for seed priming and applied in combination with NaCl, which resulted in a reduction of the PA content.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-022-01140-4.

Exogenous application of spermidine mitigates the adverse effects of drought stress in faba bean (Vicia faba L.)

In Tunisia, drought stress is a major environmental factor limiting crop production and causing relatively low and unstable faba bean yields. In the present study, we explored the putative role of spermidine (0.5, 1, 1.5 and 2mM) in ameliorating the effects of drought stress induced by polyethylene glycol (PEG-6000, -0.58MPa) in faba bean seedlings. Drought stress reduced photosynthetic performance, chlorophyll and relative water content in leaves of faba bean variety Badii. Moreover, drought increased proline, electrolyte leakage and malondialdehyde content by inducing reactive oxygen species (hydrogen peroxide) generation in leaves. However, applying spermidine increased the activities of catalase, superoxide dismutase, ascorbate peroxidase and guaiacol peroxidase. The results show that the application of spermidine especially at a rate of 1.5mM effectively reduces oxidative damage and alleviates negative effects caused by drought stress. In addition, exogenous spermidine increased the expression of polyamine biosynthetic enzymes' genes (VfADC , VfSAMDC and VfSPDS ), and reduced the expression of VfSPMS suggesting that exogenous spermidine can regulate polyamines' metabolic status under drought challenge, and consequently may enhance drought stress tolerance in faba bean. Real-time quantitative polymerase chain reaction analysis revealed that some drought responsive genes (VfNAC , VfHSP , VfNCED , VfLEA , VfCAT , VfAPX , VfRD22 , VfMYB , VfDHN , VfERF , VfSOD and VfWRKY ) from various metabolic pathways were differentially expressed under drought stress. Overall, these genes were more abundantly transcribed in the spermidine-treated plants compared to untreated suggesting an important role of spermidine in modulating faba bean drought stress response and tolerance.

The Complex Metabolomics Crosstalk Triggered by Four Molecular Elicitors in Tomato

The elicitation of plant secondary metabolism may offer interesting opportunities in the framework of sustainable approaches in plant science and in terms of their ability to prime resistance to biotic and abiotic stressors. The broad metabolic reprogramming triggered by different molecular elicitors, namely salicylate (SA), polyamines (PAs), and chitosan, was comprehensively investigated using a metabolomics approach and the tomato (Solanum lycopersicum L.) as the model crop. Six different treatments were compared: a negative control (no treatments), a second negative control treated with 1 M acetic acid (the reference for chitosan, since chitosan was solubilized in acetic acid), and four molecular elicitors, 1 mM 2,1,3-benzothiadiazole (BTH, a positive control), 10 mg/mL chitosan, 0.01 mM SA, and a 0.1 mM PA (putrescine, spermidine, and spermine). All treatments determined a slight increase in biomass, in particular following PA treatment. A broad reprogramming of secondary metabolism could be observed, including membrane lipid remodeling, phenylpropanoid antioxidants, and phytohormone crosstalk. Overall, our results suggest that PAs, SA, and BTH shared a systemic acquired resistance (SAR)-related response, whereas chitosan induced a more distinct induced systemic resistance (ISR)-like jasmonate-related response. These results pave the way towards the possible use of elicitors as a sustainable tool in plant science and agriculture by increasing crop resilience to biotic and abiotic stressors without detrimental effects on plant biomass.

The kinetochore protein NNF1 has a moonlighting role in the vegetative development of Arabidopsis thaliana

The kinetochore is a supramolecular protein complex assembled on the chromosomes, essential for faithful segregation of the genome during cell divisions. More than 100 proteins are known to constitute the eukaryotic kinetochore architecture, primarily identified using non-plant organisms. A majority of them are fast evolving and are under positive selection. Thus, functional characterization of the plant kinetochore proteins is limited as only a few conserved orthologs sharing sequence similarity with their animal counterparts have been examined. Here, we report the functional characterization of the Arabidopsis thaliana homolog of the yeast NNF1/human PMF1 outer kinetochore protein and show that it has both kinetochore and non-kinetochore functions in plant growth and development. Knockout of NNF1 causes embryo lethality implying its essential role in cell division. AtNNF1 interacts with MIS12 in Y2H and co-immunoprecipitation assays, confirming it is one of the constituents of the plant MIS12 complex. GFP-NNF1 localizes to the kinetochore, rescuing the embryo lethal nnf1-1-/- phenotype, but the rescued plants (GFP-NNF1^nnf1-/- ) are dwarf, displaying hypomorphic phenotypes with no evidence of mitotic or meiotic segregation defects. GFP-NNF1^nnf1-/- dwarf plants have reduced levels of endogenous polyamines, which are partially rescued to wild-type levels upon exogenous application of polyamines. Mutations in the putative leucine zipper-like binding motif of NNF1 gave rise to a dominant-negative tall plant phenotype reminiscent of constitutive gibberellic acid (GA) action. These contrasting hypomorphic dwarf and antimorphic tall phenotypes facilitated us to attribute a moonlighting role to Arabidopsis NNF1 affecting polyamine and GA metabolism apart from its primary role in kinetochores.

Polyamines: Α bioenergetic smart switch for plant protection and development

The present review highlights the bioenergetic role of polyamines in plant protection and development and proposes a universal model for describing polyamine-mediated stress responses. Any stress condition induces an excitation pressure on photosystem II by reforming the photosynthetic apparatus. To control this phenomenon, polyamines act directly on the molecular structure and function of the photosynthetic apparatus as well as on the components of the chemiosmotic proton-motive force (ΔpH/Δψ), thus regulating photochemical (qP) and non-photochemical quenching (NPQ) of energy. The review presents the mechanistic characteristics that underline the key role of polyamines in the structure, function, and bioenergetics of the photosynthetic apparatus upon light adaptation and/or under stress conditions. By following this mechanism, it is feasible to make stress-sensitive plants to be tolerant by simply altering their polyamine composition (especially the ratio of putrescine to spermine), either chemically or by light regulation.

Spermine reduces the harmful effects of salt stress in Tropaeolum majus

Flowers, leaves, fruits and buds of Tropaeolum majus are used for ornamental, medicinal and food purposes. However, salt stress limits the development and productivity of T. majus due to biochemical, physiological and anatomical disturbances. Polyamine application is an alternative for mitigating the harmful effects of salt stress. Thus, the objective of this work was to evaluate the effects of spermine application in T. majus grown under salt stress. The experiment was carried out in a completely randomized design, in a 3 × 2 factorial scheme, with 0, 40 mM (moderate salt stress) and 80 mM (severe salt stress) NaCl, and 0 and 1 mM spermine, and with five replicates. Growth (plant height, stem diameter, number of leaves, number of flowers, number of buds, leaf dry mass, stem dry mass and flower dry mass), gas exchange (gs, A, E, Ci and WUE), relative water content, contents of free amino acids, phenolic compounds, reducing and non-reducing sugars, lipid peroxidation and enzymatic activities (CAT, POD and APX) were evaluated. Spermine application decreased the harmful effects of salt stress on the growth and gas exchange and increased flowering in T. majus. Furthermore, the relative water content of T. majus increased under severe salt stress conditions. Spermine application reduced the contents of total phenolic compounds, free amino acids, reducing sugars and non-reducing sugars on leaves of T. majus. Spermine application increased CAT and POD activities in plants under severe salt stress and POD and APX in plants under moderate salt stress.

The Spermidine Synthase Gene SPD1: A Novel Auxotrophic Marker for Chlamydomonas reinhardtii Designed by Enhanced CRISPR/Cas9 Gene Editing

Biotechnological application of the green microalga Chlamydomonas reinhardtii hinges on the availability of selectable markers for effective expression of multiple transgenes. However, biological safety concerns limit the establishment of new antibiotic resistance genes and until today, only a few auxotrophic markers exist for C. reinhardtii. The recent improvements in gene editing via CRISPR/Cas allow directed exploration of new endogenous selectable markers. Since editing frequencies remain comparably low, a Cas9-sgRNA ribonucleoprotein (RNP) delivery protocol was strategically optimized by applying nitrogen starvation to the pre-culture, which improved successful gene edits from 10% to 66% after pre-selection. Probing the essential polyamine biosynthesis pathway, the spermidine synthase gene (SPD1) is shown to be a potent selectable marker with versatile biotechnological applicability. Very low levels of spermidine (0.75 mg/L) were required to maintain normal mixotrophic and phototrophic growth in newly designed spermidine auxotrophic strains. Complementation of these strains with a synthetic SPD1 gene was achieved when the mature protein was expressed in the cytosol or targeted to the chloroplast. This work highlights the potential of new selectable markers for biotechnology as well as basic research and proposes an effective pipeline for the identification of new auxotrophies in C. reinhardtii.

Transcriptomic Reprogramming, Alternative Splicing and RNA Methylation in Potato (Solanum tuberosum L.) Plants in Response to Potato Virus Y Infection

Plant-virus interactions are greatly influenced by environmental factors such as temperatures. In virus-infected plants, enhanced temperature is frequently associated with more severe symptoms and higher virus content. However, the mechanisms involved in controlling the temperature regulation of plant-virus interactions are poorly characterised. To elucidate these further, we analysed the responses of potato plants cv Chicago to infection by potato virus Y (PVY) at normal (22 °C) and elevated temperature (28 °C), the latter of which is known to significantly increase plant susceptibility to PVY. Using RNAseq analysis, we showed that single and combined PVY and heat-stress treatments caused dramatic changes in gene expression, affecting the transcription of both protein-coding and non-coding RNAs. Among the newly identified genes responsive to PVY infection, we found genes encoding enzymes involved in the catalysis of polyamine formation and poly ADP-ribosylation. We also identified a range of novel non-coding RNAs which were differentially produced in response to single or combined PVY and heat stress, that consisted of antisense RNAs and RNAs with miRNA binding sites. Finally, to gain more insights into the potential role of alternative splicing and epitranscriptomic RNA methylation during combined stress conditions, direct RNA nanopore sequencing was performed. Our findings offer insights for future studies of functional links between virus infections and transcriptome reprogramming, RNA methylation and alternative splicing.

MiRNA fine tuning for crop improvement: using advance computational models and biotechnological tools

MiRNAs modulate target genes expression at post-transcriptional levels, by reducing spatial abundance of mRNAs. MiRNAs regulats plant metabolism, and emerged as regulators of plant stress responses. Which make miRNAs promising candidates for fine tuning to affectively alter crop stress tolerance and other important traits. With recent advancements in the computational biology and biotechnology miRNAs structure and target prediction is possible resulting in pin point editing; miRNA modulation can be done by up or down regulating miRNAs using recently available biotechnological tools (CRISPR Cas9, TALENS and RNAi). In this review we have focused on miRNA biogenesis, miRNA roles in plant development, plant stress responses and roles in signaling pathways. Additionally we have discussed latest computational prediction models for miRNA to target gene interaction and biotechnological systems used recently for miRNA modulation. We have also highlighted setbacks and limitations in the way of miRNA modulation; providing entirely a new direction for improvement in plant genomics primarily focusing miRNAs.

Metallophores production by bacteria isolated from heavy metal-contaminated soil and sediment at Lerma-Chapala Basin

Environmental pollution as a result of heavy metals (HMs) is a worldwide problem and the implementation of eco-friendly remediation technologies is thus required. Metallophores, low molecular weight compounds, could have important biotechnological applications in the fields of agriculture, medicine, and bioremediation. This study aimed to isolate HM-resistant bacteria from soils and sediments of the Lerma-Chapala Basin and evaluated their abilities to produce metallophores and to promote plant growth. Bacteria from the Lerma-Chapala Basin produced metallophores for all the tested metal ions, presented a greater production of As³⁺ metallophores, and showed high HM resistance especially to Zn²⁺, As⁵⁺, and Ni²⁺. A total of 320 bacteria were isolated with 170 strains showing siderophores synthesis. Members of the Delftia and Pseudomonas genera showed above 92 percent siderophore units (psu) during siderophores production and hydroxamate proved to be the most common functional group among the analyzed siderophores. Our results provided evidence that Lerma-Chapala Basin bacteria and their metallophores could potentially be employed in bioremediation processes or may even have potential for applications in other biotechnological fields.

Grafting Watermelon Onto Pumpkin Increases Chilling Tolerance by Up Regulating Arginine Decarboxylase to Increase Putrescine Biosynthesis

Low temperature is a major environmental factor that severely impairs plant growth and productivity. Watermelon (Citrullus lanatus) is a chilling-sensitive crop. Grafting of watermelon onto pumpkin rootstock is an effective technique to increase the chilling tolerance of watermelon when exposure to short-time chilling stress. However, the mechanism by which pumpkin rootstock increases chilling tolerance remains poorly understood. Under 10°C/5°C (day/night) chilling stress treatment, pumpkin-grafted watermelon seedlings showed higher chilling tolerance than self-grafted watermelon plants with significantly reduced lipid peroxidation and chilling injury (CI) index. Physiological analysis revealed that pumpkin rootstock grafting led to the notable accumulation of putrescine in watermelon seedlings under chilling conditions. Pre-treat foliar with 1 mM D-arginine (inhibitor of arginine decarboxylase, ADC) increased the electrolyte leakage (EL) of pumpkin-grafted watermelon leaves under chilling stress. This result can be ascribed to the decrease in transcript levels of ADC, ornithine decarboxylase, spermidine synthase, and polyamine oxidase genes involved in the synthesis and metabolism of polyamines. Transcriptome analysis showed that pumpkin rootstock improved chilling tolerance in watermelon seedlings by regulating differential gene expression under chilling stress. Pumpkin-grafted seedling reduced the number and expression level of differential genes in watermelon scion under chilling stress. It specifically increased the up-regulated expression of ADC (Cla97C11G210580), a key gene in the polyamine metabolism pathway, and ultimately promoted the accumulation of putrescine. In conclusion, pumpkin rootstock grafting increased the chilling tolerance of watermelon through transcription adjustments, up regulating the expression level of ADC, and promoting the synthesis of putrescine, which ultimately improved the chilling tolerance of pumpkin-grafted watermelon plants.

Male Fertility under Environmental Stress: Do Polyamines Act as Pollen Tube Growth Protectants?

Although pollen structure and morphology evolved toward the optimization of stability and fertilization efficiency, its performance is affected by harsh environmental conditions, e.g., heat, cold, drought, pollutants, and other stressors. These phenomena are expected to increase in the coming years in relation to predicted environmental scenarios, contributing to a rapid increase in the interest of the scientific community in understanding the molecular and physiological responses implemented by male gametophyte to accomplish reproduction. Here, after a brief introduction summarizing the main events underlying pollen physiology with a focus on polyamine involvement in its development and germination, we review the main effects that environmental stresses can cause on pollen. We report the most relevant evidence in the literature underlying morphological, cytoskeletal, metabolic and signaling alterations involved in stress perception and response, focusing on the final stage of pollen life, i.e., from when it hydrates, to pollen tube growth and sperm cell transport, with these being the most sensitive to environmental changes. Finally, we hypothesize the molecular mechanisms through which polyamines, well-known molecules involved in plant development, stress response and adaptation, can exert a protective action against environmental stresses in pollen by decoding the essential steps and the intersection between polyamines and pollen tube growth mechanisms.

Tissue-specific transcriptomics reveal functional differences in floral development

Flowers are produced by floral meristems, groups of stem cells that give rise to floral organs. In grasses, including the major cereal crops, flowers (florets) are contained in spikelets, which contain one to many florets, depending on the species. Importantly, not all grass florets are developmentally equivalent, and one or more florets are often sterile or abort in each spikelet. Members of the Andropogoneae tribe, including maize (Zea mays), produce spikelets with two florets; the upper and lower florets are usually dimorphic, and the lower floret is greatly reduced compared to the upper floret. In maize ears, early development appears identical in both florets but the lower floret ultimately aborts. To gain insight into the functional differences between florets with different fates, we used laser capture microdissection coupled with RNA-sequencing to globally examine gene expression in upper and lower floral meristems in maize. Differentially expressed genes were involved in hormone regulation, cell wall, sugar, and energy homeostasis. Furthermore, cell wall modifications and sugar accumulation differed between the upper and lower florets. Finally, we identified a boundary domain between upper and lower florets, which we hypothesize is important for floral meristem activity. We propose a model in which growth is suppressed in the lower floret by limiting sugar availability and upregulating genes involved in growth repression. This growth repression module may also regulate floret fertility in other grasses and potentially be modulated to engineer more productive cereal crops.

Elicitation Effects on Some Secondary Metabolites and Antioxidant Activity in Callus Cultures of Allium jesdianum Boiss. & Buhse.: Methyl Jasmonate and Putrescine

Allium jesdianum Boiss. & Buhse. is the most important species of the Amaryllidaceae family with various pharmacological properties. Three subsequent experiments (germination, callogenesis, and elicitation) were carried out as a completely randomized design with six replication. At the first study, the highest seed germination (78.33%) was achieved at chemical pre-treatment including the combination of α-naphthalene acetic acid (1 mg L-1) and benzylaminopurine (3 mg L-1) under in vitro condition. The highest callus induction (86.7%) was observed at MS/2 media, which was supplemented by NAA (1 mg L-1) and BAP (3 mg L-1) from hypocotyl explants. Then, two chemical elicitors including methyl jasmonate (MeJ) (0, 25, 50, and 100 µM) and putrescine (Pu) (0, 0.5, and 1 mM) were used to investigate their effects on different biochemical traits under callus culture. The results showed the superiority of MeJ over Pu for increasing the secondary metabolites and antioxidant activity in calluses of Allium jesdianum, compared to the control. The highest contents for total phenolics (6.02 mg GAE g-1 FW), total flavonoids (0.52 mg QE g-1 FW), and total flavonols (0.39 mg QE g-1 FW) were observed under 50 µM of MeJ. Meanwhile, the highest value for anthocyanin (8.99 µ mol g-1 FW) was achieved at 25 µM of MeJ. The highest 2,2-diphenyl-1-picrylhydrazyl activities were observed at 50 and 100 µM of MeJ. Putrescine (0.5 mM) elicitation showed only superiority for callus growth rate (0.53 mm day-1). Enhancement of desired secondary metabolites at 50 µM MeJ could be suitable for future studies in biotechnological aspects of this medicinal plant.

Changes in Metabolic Profiles of Pea (Pisum sativum L.) as a Result of Repeated Short-Term Soil Drought and Subsequent Re-Watering

The metabolic re-arrangements of peas (Pisum sativum L.) under soil drought and re-watering are still not fully explained. The search for metabolic markers of the stress response is important in breeding programs, to allow for the selection drought-resistant cultivars. During the present study, changes in the polar metabolite content in pea plant shoots were measured under repeated short-term soil drought and subsequent re-watering. A gas chromatograph, equipped with a mass spectrometer (GC-MS), was used for the metabolite profiling of pea plants during their middle stage of vegetation (14-34 days after sowing, DAS). The major changes occurred in the concentration of amino acids and some soluble carbohydrates. Among them, proline, γ-aminobutyric acid (GABA), branched-chain amino acids, hydroxyproline, serine, myo-inositol, and raffinose were accumulated under each soil drought and decreased after re-watering. Besides, the obtained results show that the first drought/re-watering cycle increased the ability of pea plants to restore a metabolic profile similar to the control after the second similar stress. The accumulation of proline seems to be an important part of drought memory in pea plants. However, confirmation of this suggestion requires metabolite profiling studies on a broader spectrum of pea cultivars.

Functions of Redox Signaling in Pollen Development and Stress Response

Cellular redox homeostasis is crucial for normal plant growth and development. Each developmental stage of plants has a specific redox mode and is maintained by various environmental cues, oxidants, and antioxidants. Reactive oxygen species (ROS) and reactive nitrogen species are the chief oxidants in plant cells and participate in cell signal transduction and redox balance. The production and removal of oxidants are in a dynamic balance, which is necessary for plant growth. Especially during reproductive development, pollen development depends on ROS-mediated tapetal programmed cell death to provide nutrients and other essential substances. The deviation of the redox state in any period will lead to microspore abortion and pollen sterility. Meanwhile, pollens are highly sensitive to environmental stress, in particular to cell oxidative burst due to its peculiar structure and function. In this regard, plants have evolved a series of complex mechanisms to deal with redox imbalance and oxidative stress damage. This review summarizes the functions of the main redox components in different stages of pollen development, and highlights various redox protection mechanisms of pollen in response to environmental stimuli. In continuation, we also discuss the potential applications of plant growth regulators and antioxidants for improving pollen vigor and fertility in sustaining better agriculture practices.

Physiological and Multi-Omics Approaches for Explaining Drought Stress Tolerance and Supporting Sustainable Production of Rice

Drought differs from other natural disasters in several respects, largely because of the complexity of a crop's response to it and also because we have the least understanding of a crop's inductive mechanism for addressing drought tolerance among all abiotic stressors. Overall, the growth and productivity of crops at a global level is now thought to be an issue that is more severe and arises more frequently due to climatic change-induced drought stress. Among the major crops, rice is a frontline staple cereal crop of the developing world and is critical to sustaining populations on a daily basis. Worldwide, studies have reported a reduction in rice productivity over the years as a consequence of drought. Plants are evolutionarily primed to withstand a substantial number of environmental cues by undergoing a wide range of changes at the molecular level, involving gene, protein and metabolite interactions to protect the growing plant. Currently, an in-depth, precise and systemic understanding of fundamental biological and cellular mechanisms activated by crop plants during stress is accomplished by an umbrella of -omics technologies, such as transcriptomics, metabolomics and proteomics. This combination of multi-omics approaches provides a comprehensive understanding of cellular dynamics during drought or other stress conditions in comparison to a single -omics approach. Thus a greater need to utilize information (big-omics data) from various molecular pathways to develop drought-resilient crop varieties for cultivation in ever-changing climatic conditions. This review article is focused on assembling current peer-reviewed published knowledge on the use of multi-omics approaches toward expediting the development of drought-tolerant rice plants for sustainable rice production and realizing global food security.

Citrus sinensis CBF1 Functions in Cold Tolerance by Modulating Putrescine Biosynthesis through Regulation of Arginine Decarboxylase

C-repeat (CRT) binding factors (CBFs) are well known to act as crucial transcription factors that function in cold stress response. Arginine decarboxylase (ADC)- mediated putrescine (Put) biosynthesis has been reported to be activated in plants exposed to cold conditions, but it remains elusive whether CBFs can regulate ADC expression and Put accumulation. In this study, we show that cold upregulated ADC gene (Citrus sinensis ADC;CsADC) and elevated endogenous Put content in sweet orange (C.sinensis). The promoter of CsADC contains two CRT sequences that are canonical elements recognized by CBFs. Sweet orange genome contains four CBFs (CsCBF1-4), in which CsCBF1 was significantly induced by cold. CsCBF1, located in the nucleus, was demonstrated to bind directly and specifically to the promoter of CsADC and acted as a transcriptional activator. Overexpression of CsCBF1 led to notable elevation of CsADC and Put levels in sweet orange transgenic plants, along with remarkably enhanced cold tolerance, relative to the wild type. However, pretreatment with D-arginine, an ADC inhibitor, caused a prominent reduction of endogenous Put levels in the overexpressing lines, accompanied by greatly compromised cold tolerance. Taken together, these results demonstrate that the CBF1 of sweet orange directly regulates ADC expression and modulates Put synthesis for orchestrating the cold tolerance. Our findings shed light on the transcriptional regulation of Put accumulation through targeting the ADC gene in the presence of cold stress. Meanwhile, this study illustrates a new mechanism underlying the CBF-mediated cold stress response.

Unravelling the multi-faceted regulatory role of polyamines in plant biotechnology, transgenics and secondary metabolomics

Polyamines (PAs) are ubiquitous low-molecular-weight, aliphatic compounds with wide as well as complex application in fundamental areas of plant growth and development. PAs are mediator of basic metabolism of organisms which include cell division and differentiation, biotic and abiotic stress tolerance, reversal of oxidative damage, stabilization of nucleic acids, and protein and phospholipid binding. In plants, it attributes in direct and indirect organogenesis, endogenous phytohormone regulation, cellular compartmentalization, fruit and flower development, senescence, and secondary metabolite production which are highly tuned as first line of defense response. There are several aspects of polyamine-directed mechanism that regulate overall plant growth in vitro and in vivo. In the present review, we have critically discussed the role played by polyamine on the enhanced production of bioactive natural products and how the same polyamines are functioning against different environmental stress conditions, i.e., salinity, drought, high CO₂ content, herbivory, and physical wounding. The role of polyamines on elicitation process has been highlighted previously, but it is important to note that its activity as growth regulator under in vitro condition is correlated with an array of intertwined mechanism and physiological tuning. Medicinal plants under different developmental stages of micropropagation are characterized with different functional aspects and regulatory changes during embryogenesis and organogenesis. The effect of precursor molecules as well as additives and biosynthetic inhibitors of polyamines in rhizogenesis, callogenesis, tuberization, embryogenesis, callus formation, and metabolite production has been discussed thoroughly. The beneficial effect of exogenous application of PAs in elicitation of secondary metabolite production, plant growth and morphogenesis and overall stress tolerance are summarized in this present work. KEY POINTS: • Polyamines (PAs) play crucial roles in in vitro organogenesis. • PAs elicitate bioactive secondary metabolites (SMs). • Transgenic studies elucidate and optimize PA biosynthetic genes coding SMs.

Selection and validation of reference genes for measuring gene expression in Piper species at different life stages using RT-qPCR analysis

The secondary metabolism of Piper species is known to produce a myriad of natural products from various biosynthetic pathways which, represent a rich source of previously uncharacterized chemical compounds. The determination of gene expression profiles in multiple tissue/organ samples could provide valuable clues towards understanding the potential biological functions of chemical changes in these plants. Studies on gene expression by RT-qPCR require particularly careful selection of suitable reference genes as a control for normalization. Here, we provide a study for the identification of reliable reference genes in P. arboreum, P. gaudichaudianum, P. malacophyllum, and P. tuberculatum, at two different life stages: 2-month-old seedlings and adult plants. To do this, annotated sequences were recovered from transcriptome datasets of the above listed Piper spp. These sequences were subjected to expression analysis using RT-qPCR, followed by analysis using the geNorm and NormFinder algorithms. A set of five genes were identified showing stable expression: ACT7 (Actin-7), Cyclophilin (Peptidyl-prolyl cis-trans isomerase), EF1α (Elongation factor 1-alpha), RNABP (RNA-binding protein), and UBCE (Ubiquitin conjugating enzyme). The universality of these genes was then validated using two target genes, ADC (arginine decarboxylase) and SAMDC (S-adenosylmethionine decarboxylase), which are involved in the biosynthesis of polyamines. We showed that normalization genes varied according to Piper spp., and we provide a list of recommended pairs of the best combination for each species. This study provides the first set of suitable candidate genes for gene expression studies in the four Piper spp. assayed, and the findings will facilitate subsequent transcriptomic and functional gene research.

Mitogen-Activated Protein Kinase 4-Regulated Metabolic Networks

Mitogen-activated protein kinase 4 (MPK4) was first identified as a negative regulator of systemic acquired resistance. It is also an important kinase involved in many other biological processes in plants, including cytokinesis, reproduction, and photosynthesis. Arabidopsis thaliana&nbsp;mpk4 mutant is dwarf and sterile. Previous omics studies including genomics, transcriptomics, and proteomics have revealed new functions of MPK4 in different biological processes. However, due to challenges in metabolomics, no study has touched upon the metabolomic profiles of the mpk4 mutant. What metabolites and metabolic pathways are potentially regulated by MPK4 are not known. Metabolites are crucial components of plants, and they play important roles in plant growth and development, signaling, and defense. Here we used targeted and untargeted metabolomics to profile metabolites in the wild type and the mpk4 mutant. We found that in addition to the jasmonic acid and salicylic acid pathways, MPK4 is involved in polyamine synthesis and photosynthesis. In addition, we also conducted label-free proteomics of the two genotypes. The integration of metabolomics and proteomics data allows for an insight into the metabolomic networks that are potentially regulated by MPK4.