Plant-based green synthesis of silver nanoparticles and its effective role in abiotic stress tolerance in crop plants

The development of effective and environmentally friendly methods for the green synthesis of nanoparticles (NPs) is a critical stage in the field of nanotechnology. Silver nanoparticles (AgNPs) are significant due to their unique physical, chemical, and biological properties, as well as their numerous applications. Physical, chemical, and green synthesis approaches can all be used to produce AgNPs; however, synthesis using biological precursors, particularly plant-based green synthesis, has shown outstanding results. In recent years, owing to a combination of frequent droughts, unusual rainfall, salt-affected areas, and high temperatures, climate change has changed several ecosystems. Crop yields have decreased globally as a result of these changes in the environment. Green synthesized AgNPs role in boosting antioxidant defense mechanisms, methylglyoxal (MG) detoxification, and developing tolerance for abiotic stress-induced oxidative damage has been thoroughly described in plant species over the last decade. Although various studies on abiotic stress tolerance and metallic nanoparticles (NPs) in plants have been conducted, but the details of AgNPs mediated abiotic stress tolerance have not been well summarized. Therefore, the plant responses to abiotic stress need to be well understood and to apply the gained knowledge to increase stress tolerance by using AgNPs for crop plants. In this review, we outlined the green synthesis of AgNPs extracted from plant extract. We also have updates on the most important accomplishments through exogenous application of AgNPs to improve plant tolerance to drought, salinity, low and high-temperature stresses.     

Improvement of plant abiotic stress tolerance through modulation of the polyamine pathway

Polyamines(mainly putrescine(Put),spermidine(Spd),and spermine(Spm))have been widely found in a range of physiological processes and in almost all diverse environmental stresses.In various plant species,abiotic stresses modulated the accumulation of polyamines and related gene expression.Studies using loss-of-function mutants and transgenic overexpression plants modulating polyamine metabolic pathways confirmed protective roles of polyamines during plant abiotic stress responses,and indicated the possibility to improve plant tolerance through genetic manipulation of the polyamine pathway.Additionally,putative mechanisms of polyamines involved in plant abiotic stress tolerance were thoroughly discussed and crosstalks among polyamine,abscisic acid,and nitric oxide in plant responses to abiotic stress were emphasized.Special attention was paid to the interaction between polyamine and reactive oxygen species,ion channels,amino acid and carbon metabolism,and other adaptive responses.Further studies are needed to elucidate the polyamine signaling pathway,especially polyamine-regulated downstream targets and the connections between polyamines and other stress responsive molecules.     

Improvement of plant abiotic stress tolerance through modulation of the polyamine pathway FA简

Polyamines （mainly putrescine （Put）, spermidine （Spd）, and spermine （Spin）） have been widely found in a range of physiological processes and in almost all diverse environ- mental stresses. In various plant species, abiotic stresses modulated the accumulation of polyamines and related gene expression. Studies using loss-of-function mutants and transgenic overexpression plants modulating polyamine metabolic pathways confirmed protective roles of polyamines during plant abiotic stress responses, and indicated the possibility to improve plant tolerance through genetic manipulation of the polyamine pathway. Additionally, puta- tive mechanisms of polyamines involved in plant abiotic stress tolerance were thoroughly discussed and crosstalks among polyamine, abscisic acid, and nitric oxide in plant responses to abiotic stress were emphasized. Special attention was paid to the interaction between polyamine and reactive oxygen species, ion channels, amino acid and carbon metabolism, and other adaptive responses. Further studies are needed to elucidate the polyamine signaling pathway, especially polyamine-regulated downstream tar- gets and the connections between polyamines and other stress responsive molecules.     

Role of Pathogen-Related Protein 10 (PR 10) under Abiotic and Biotic Stresses in Plants

Members of the Pathogenesis Related (PR) 10 protein family have been identified in a variety of plant species and a wide range of functions ranging from defense to growth and development has been attributed to them. PR10 protein possesses ribonuclease (RNase) activity, interacts with phytohormones, involved in hormone-mediated signalling, afforded protection against various phytopathogenic fungi, bacteria, and viruses particularly in response to biotic and abiotic stresses. The resistance mechanism of PR10 protein may include activation of defense signalling pathways through possible interacting proteins involved in mediating responses to pathogens, degradation of RNA of the invading pathogens. Moreover, several morphological changes have been shown to accompany the enhanced abiotic stress tolerance. In this review, the possible mechanism of action of PR10 protein against biotic and abiotic stress has been discussed. Furthermore, our findings also confirmed that the in vivo Nitric oxide (NO) is essential for most of environmental abiotic stresses and disease resistance against pathogen infection. The proper level of NO may be necessary and beneficial, not only in plant response to the environmental abiotic stress, but also to biotic stress. The updated information on this interesting group of proteins will be useful in future research to develop multiple stress tolerance in plants.     

Endophyte-mediated adjustments in host morphology and physiology and effects on host fitness traits in grasses

Endophytic fungi have been shown to increase tolerance of hosts to biotic and abiotic stresses and in some cases alter growth and development of plants. In this article we evaluate some effects that clavicipitaceous endophytes have on development and physiology of plant tissues. We postulate that oxidative stress protection is the fundamental underlying benefit conferred by many endophytes, accounting for frequently observed enhanced disease resistance, drought tolerance, heavy metal tolerance and tolerance to numerous additional oxidative stresses. We hypothesize that endophyte-mediated oxidative stress protection of the host is the result of at least two processes, including: (1) secretion of reactive oxygen species (ROS) from endophytic mycelia into plant cells; and (2) secretion of auxin from endophytic mycelia into plant cells. Both processes result in an increase in ROS in plant tissues; and stimulate plant tissues to increase activities of antioxidant systems. Auxin is suggested to function in suppression of plant cell death and may be important in maintaining the endophyte–plant symbiosis.     

Analysis of differentially expressed genes in abiotic stress response and their role in signal transduction pathways

The study of abiotic stress response of plants is important because they have to cope with environmental changes to survive. The plant genomes have evolved to meet environmental challenges. Salt, temperature, and drought are the main abiotic stresses. The tolerance and response to stress vary differently in plants. The idea was to analyze the genes showing differential expression under abiotic stresses. There are many pathways connecting the perception of external stimuli to cellular responses. In plants, these pathways play an important role in the transduction of abiotic stresses. In the present study, the gene expression data have been analyzed for their involvement in different steps of signaling pathways. The conserved genes were analyzed for their role in each pathway. The functional annotations of these genes and their response under abiotic stresses in other plant species were also studied. The enzymes of signal pathways, showing similarity with conserved genes, were analyzed for their role in different abiotic stresses. Our findings will help to understand the expression of genes in response to various abiotic stresses. These genes may be used to study the response of different abiotic stresses in other plant species and the molecular basis of stress tolerance.     

Emerging trends in the functional genomics of the abiotic stress response in crop plants

Plants are exposed to different abiotic stresses, such as water deficit, high temperature, salinity, cold, heavy metals and mechanical wounding, under field conditions. It is estimated that such stress conditions can potentially reduce the yield of crop plants by more than 50%. Investigations of the physiological, biochemical and molecular aspects of stress tolerance have been conducted to unravel the intrinsic mechanisms developed during evolution to mitigate against stress by plants. Before the advent of the genomics era, researchers primarily used a gene-by-gene approach to decipher the function of the genes involved in the abiotic stress response. However, abiotic stress tolerance is a complex trait and, although large numbers of genes have been identified to be involved in the abiotic stress response, there remain large gaps in our understanding of the trait. The availability of the genome sequences of certain important plant species has enabled the use of strategies, such as genome-wide expression profiling, to identify the genes associated with the stress response, followed by the verification of gene function by the analysis of mutants and transgenics. Certain components of both abscisic acid-dependent and -independent cascades involved in the stress response have already been identified. Information originating from the genome-wide analysis of abiotic stress tolerance will help to provide an insight into the stress-responsive network(s), and may allow the modification of this network to reduce the loss caused by stress and to increase agricultural productivity.     

Trehalose and its applications in plant biotechnology

Trehalose, a nonreducing disaccharide of glucose, is one of the most effective osmoprotectants. Several strategies leading to its accumulation have been envisaged in both model and crop plants using genes of bacterial, yeast and, more recently, plant origin. Significant levels of trehalose accumulation have been shown to cause abiotic stress tolerance in transgenic plants. In this review, we describe the most biologically relevant features of trehalose: chemical and biological properties; occurrence and metabolism in organisms with special reference to plants; protective role in stabilizing molecules; physiological role in plants with special reference to carbohydrate metabolism. The emphasis of this review, however, will be on manipulation of trehalose metabolism to improve abiotic stress tolerance in plants.     

GsSnRK1 interplays with transcription factor GsERF7 from wild soybean to regulate soybean stress resistance

Although the function and regulation of SnRK1 have been studied in various plants, its molecular mechanisms in response to abiotic stresses are still elusive. In this work, we identified an AP2/ERF domain-containing protein (designated GsERF7) interacting with GsSnRK1 from a wild soybean cDNA library. GsERF7 gene expressed dominantly in wild soybean roots and was responsive to ethylene, salt, and alkaline. GsERF7 bound GCC cis-acting element and could be phosphorylated on S36 by GsSnRK1. GsERF7 phosphorylation facilitated its translocation from cytoplasm to nucleus and enhanced its transactivation activity. When coexpressed in the hairy roots of soybean seedlings, GsSnRK1(wt) and GsERF7(wt) promoted plants to generate higher tolerance to salt and alkaline stresses than their mutated species, suggesting that GsSnRK1 may function as a biochemical and genetic upstream kinase of GsERF7 to regulate plant adaptation to environmental stresses. Furthermore, the altered expression patterns of representative abiotic stress-responsive and hormone-synthetic genes were determined in transgenic soybean hairy roots after stress treatments. These results will aid our understanding of molecular mechanism of how SnRK1 kinase plays a cardinal role in regulating plant stress resistances through activating the biological functions of downstream factors.     

一氧化氮在植物生长发育和抗逆过程中的作用研究进展

NO不仅在植物的抗病过程中发挥重要作用,同时也参与植物生长、发育和对干旱、高盐、高温、低温等非生物胁迫的响应等过程。该文对近年来国内外有关NO在植物生长、发育、非生物胁迫抗性过程中的作用及其与植物激素之间的互作关系等方面的研究进展进行综述,为相关研究提供信息和资料。     

植物抗旱和耐重金属基因工程研究进展

干旱和重金属污染严重影响植物的生长发育.植物耐逆相关基因的克隆和功能鉴定研究,为通过基因工程途径提高植物的抗逆性奠定了理论基础.水分亏缺、高盐、低温和重金属胁迫都能诱导LEA(late embryogenesis abundant protein)基因的表达.转基因研究表明,LEA蛋白具有抗旱保护作用、离子结合特性以及抗氧化活性;水孔蛋白存在于细胞膜和液泡膜上,在细胞乃至整个植物体水分吸收和运输过程中发挥重要作用.干旱和盐胁迫促进水孔蛋白基因转录物的积累.过量表达水孔蛋白可增强水分吸收和运输,提高植物的抗旱能力.金属转运蛋白参与重金属离子的吸收、运输和累积等过程.这些蛋白基因在改良草坪草植物的抗旱节水和耐重金属能力等方面具有潜在的应用价值.     

The pepper extracellular peroxidase CaPO2 is required for salt, drought and oxidative stress tolerance as well as resistance to fungal pathogens

In plants, biotic and abiotic stresses regulate the expression and activity of various peroxidase isoforms. Capsicum annuum EXTRACELLULAR PEROXIDASE 2 (CaPO2) was previously shown to play a role in local and systemic reactive oxygen species bursts and disease resistance during bacterial pathogen infection. Here, we report CaPO2 expression patterns and functions during conditions of biotic and abiotic stress. In pepper plants, CaPO2 expression was strongly induced by abscisic acid, but not by defense-related plant hormones such as salicylic acid, ethylene and jasmonic acid. CaPO2 was also strongly induced by abiotic and biotic stress treatments, including drought, cold, high salinity and infection by the hemibiotrophic fungal pathogen Colletotrichum coccodes. Loss-of-function of CaPO2 in virus-induced gene silenced pepper plants led to increased susceptibility to salt- and osmotic-induced stress. In contrast, CaPO2 overexpression in transgenic Arabidopsis thaliana plants conferred enhanced tolerance to high salt, drought, and oxidative stress, while also enhancing resistance to infection by the necrotrophic fungal pathogen Alternaria brassicicola. Taken together, these results provide evidence for the involvement of pepper extracellular peroxidase CaPO2 in plant defense responses to various abiotic stresses and plant fungal pathogens.     

Protein phosphatases: a genomic outlook to understand their function in plants

Protein phosphatases are the vital regulatory components of various signal transduction pathways in eukaryotes. Signaling pathways triggered during stress and development have been regulated by different classes of protein phosphatases in plants. Recently, genome-wide expressional analysis in Arabidopsis and crop plant such as rice revealed differential expression pattern for several protein phosphatases under different abiotic stresses, in various tissues and at different developmental stages. This expression pattern could be extrapolated to the possible function of protein phosphatases in abiotic stress signaling and tolerance, and during plant development. Here, we discuss organisation and expression patterns of members of the protein phosphatase gene family, and their potential functional role in plants.     

Modulation of ROS production and hormone levels by AHK5 during abiotic and biotic stress signaling

Histidine kinases have been shown to mediate responses to endogenous and exogenous stimuli in organisms such as yeast, bacteria and plants. In the model plant Arabidopsis, histidine kinases have been shown to function in hormone signaling, and abiotic and biotic stress responses. More recently, the least characterized of the Arabidopsis histidine kinases, AHK5, was demonstrated to function in resistance toward the virulent bacterium Pseudomonas syringae pv tomato DC3000 (PstDC3000) and the necrotrophic fungus Botrytis cinerea, and as a negative regulator of tolerance toward salinity. Here, we present data which indicate that AHK5 also impacts on drought stress resistance and on the outcome of an incompatible interaction with avrRpm1-expressing PstDC3000 (PstDC3000 (avrRpm1)). We present a model which proposes a role for reactive oxygen species (ROS) and hormones in integrating abiotic and biotic stress responses via AHK5.