Unraveling salt stress signaling in plants

Salt stress is a maior environmental factor limiting plant growth and productivity. A better understanding of the mechanisms mediating salt resistance will help researchers design ways to improve crop performance under adverse environmental conditions. Salt stress can lead to ionic stress, osmotic stress and secondary stresses, particularly oxidative stress, in plants. Therefore, to adapt to salt stress, plants rely on signals and pathways that re-establish cellular ionic, osmotic, and reactive oxygen species （ROS） homeostasis. Over the past two decades, genetic and biochemical analyses have revealed several core stress signaling pathways that participate in salt resistance. The Salt Overly Sensitive signaling pathway plays a key role in maintaining ionic homeostasis, via extruding sodium ions into the apoplast. Mitogenactivated protein kinase cascades mediate ionic, osmotic, and ROS homeostasis. SnRK2 （sucrose nonfermenting l-related protein kinase 2） proteins are involved in maintaining osmotic homeostasis. In this review, we discuss recent progress in identifying the components and pathways involved in the plant＇s response to salt stress and their regulatory mechanisms. We also review progress in identifying sensors involved in salt-induced stress signaling in plants.

Molecular Mechanisms Regulating Rapid Stress Signaling Networks in Arabidopsis

As sessile organisms plants must ronmental conditions. To survive cope with ever changing enviplants have evolved elaborate mechanisms to perceive and rapidly respond to a diverse range of abiotic and biotic stresses. Central to this response is the ability to modulate gene expression at both the transcriptional and posttranscriptional levels. This review will focus on recent progress that has been made towards understanding the rapid reprogramming of the transcriptome that occurs in response to stress as well as emerging mechanisms underpinning the reprogramming of gene expression in response to stress,

Targeting Glycinebetaine for Abiotic Stress Tolerance in Crop Plants:Physiological Mechanism,Molecular Interaction and Signaling

In the era of climate change,abiotic stresses(e.g.,salinity,drought,extreme temperature,flooding,metal/metalloid(s),UV radiation,ozone,etc.)are considered as one of the most complex environmental constraints that restricts crop production worldwide.Introduction of stress-tolerant crop cultivars is the most auspicious way of surviving this constraint,and to produce these types of tolerant crops.Several bioengineering mechanisms involved in stress signaling are being adopted in this regard.One example of this kind of manipulation is the osmotic adjustment.The quarternary ammonium compound glycinebetaine(GB),also originally referred to as betaine is a methylated glycine derivative.Among the betaines,GB is the most abundant one in plants,which is mostly produced in response to dehydration caused by different abiotic stresses like drought,salinity,and extreme temperature.Glycinebetaine helps in decreased accumulation and detoxification of ROS,thereby restoring photosynthesis and reducing oxidative stress.It takes part in stabilizing membranes and macromolecules.It is also involved in the stabilization and protection of photosynthetic components,such as ribulose-1,5-bisphosphate carboxylase/oxygenase,photosystem II and quarternary enzyme and protein complex structures under environmental stresses.Glycinebetaine was found to perform in chaperone-induced protein disaggregation.In addition,GB can confer stress tolerance in very low concentrations,and it acts in activating defense responsive genes with stress protection.Recently,field application of GB has also shown protective effects against environmental adversities increasing crop yield and quality.In this review,we will focus on the role of GB in conferring abiotic stress tolerance and the possible ways to engineer GB biosynthesis in plants.

Effects of abiotic stress and hormones on the expressions of five13-CmLOXs and enzyme activity in oriental melon(Cucumis melo var.makuwa Makino)

Lipoxygenases（LOXs） are a group of non-heme,iron-containing enzymes and extensively involved in plant growth and development,ripening and senescence,stress responses,biosynthesis of regulatory molecules and defense reaction.In our previous study,18 LOXs in melon genome were screened and identified,and five 13-LOX genes（CmLOX08,CmLOX10,CmLOX12,CmLOX13 and CmLOX18） were predicted to locate in chloroplast.Phylogenetic analysis result showed that the five genes have high homology with jasmonic acid（JA） biosynthesis-related LOXs from other plants.In addition,promoter analysis revealed that motifs of the five genes participate in gene expression regulated by hormones and stresses.Therefore,we analyzed the expressions of the five genes and LOX activity in leaves of four-leaf stage seedlings of oriental melon cultivar Yumeiren under abiotic stress：wounding,cold,high temperature and hydrogen peroxide（H_2O_2）,and signal molecule treatments：methyl jasmonate（MeJA）,abscisic acid（ABA） and salicylic acid（SA）.Real time qPCR revealed that wounding and H_2O_2 induced the expressions of all the five genes.Only CmLOX08 was induced by cold while only CmLOX13 was suppressed by high temperature.ABA induced the expressions of CmLOXIO and CmLOX12 while inhibited CmLOX13 and CmLOX18.MeJA increased the 3 genes expressions except CmLOX08 and CmLOX13,whereas SA decreased the effect,apart from CmLOX12.All the abiotic stresses and signal molecules treatments increased the LOX activity in leaves of oriental melon.In summary,the results suggest that the five genes have diverse functions in abiotic stress and hormone responses,and might participate in defense response.The data generated in this study will be helpful in subcellular localization and transgenic experiment to understand their precise roles in plant defense response.

Growth retrieval of stressed bacterial cells: logic and contradictions

Study of bacterial stress response against an array of stress signals like heat shock and oxidative stress has been well accomplished so far.Several stress factors cause microorganisms to go under the viable but nonculturable state.However,the growth resuscitation of bacterial cells from such viable but nonculturable state is still obscure.Current review briefly focused on the growth revival of the viable but nonculturable cells and placed the possible model of growth resuscitation.The significance of such type of study on the viable but nonculturable cells principally relies upon clinical sectors whereby some pathogens are found to be latent for many days and thereby imparting the false negative results as well as in the food industries whereby the viable but nonculturable cells may cause massive damage in the public health upon their resuscitation.

Adaptive response of resistant cancer cells to chemotherapy

Despite advances in cancer therapeutics and the integration of personalized medicine,the development of chemoresistance in many patients remains a significant contributing factor to cancer mortality.Upon treatment with chemotherapeutics,the disruption of homeostasis in cancer cells triggers the adaptive response which has emerged as a key resistance mechanism.In this review,we summarize the mechanistic studies investigating the three major components of the adaptive response,autophagy,endoplasmic reticulum(ER)stress signaling,and senescence,in response to cancer chemotherapy.We will discuss the development of potential cancer therapeutic strategies in the context of these adaptive resistance mechanisms,with the goal of stimulating research that may facilitate the development of effective cancer therapy.

Reactive oxygen species signaling and stomatal movement in plant responses to drought stress and pathogen attack

Stomata, the pores formed by a pair of guard cells, are the main gateways for water transpiration and photosynthetic CO2 exchange, as well as pathogen invasion in land plants. Guard cell movement is regulated by a combination of environmental factors, including water status, light, CO2 levels and pathogen attack, as well as endogenous signals, such as abscisic acid and apoplastic reactive oxygen species （ROS）. Under abiotic and biotic stress conditions, extracellular ROS are mainly produced by plasma membrane-localized NADPH oxidases, whereas intracellular ROS are produced in multiple organelles. These ROS form a sophisticated cellular signaling network, with the accumulation of apoplastic ROS an early hallmark of stomatal movement. Here, we review recent progress in understanding the molecular mechanisms of the ROS signaling network, primarily during drought stress and pathogen attack. We summarize the roles of apoplastic ROS in regulating stomatal movement, ABA and CO2 signaling, and immunity responses. Finally, we discuss ROS accumulation and communication between organelles and cells. This information provides a conceptual framework for understanding how ROS signaling is integrated with various signaling pathways during plant responses to abiotic and biotic stress stimuli.

c-Abl-MST1 Signaling Pathway Mediates Oxidative Stress Induced Neuronal Cell Death

Oxidative stress influences cell survival and homeostasis, but the mechanisms underlying the biological effects of oxidative stress remain to be elucidated. We have defined that the

Deletion of an Endoplasmic Reticulum Stress Response Element in a ZmPP2C-A Gene Facilitates Drought Tolerance of Maize Seedlings

Drought is a major abiotic stress that causes the yearly yield loss of maize, a crop cultured worldwide. Breeding drought-tolerant maize cultivars is a priority requirement of world agriculture. Clade A PP2C phosphatases （PP2C-A）, which are conserved in most plant species, play important roles in abscisic acid （ABA） signaling and plant drought response. However, natural variations of PP2C-A genes that are directly associated with drought tolerance remain to be elucidated. Here, we conducted a candidate gene association analysis of the ZmPP2C-A gene family in a maize panel consisting of 368 varieties collected worldwide, and identified a drought responsive gene ZmPP2C-AIO that is tightly associated with drought tolerance. We found that the degree of drought tolerance of maize cultivars negatively corre- lates with the expression levels of ZmPP2C-AIO. ZmPP2C-A10, like its Arabidopsis orthologs, interacts with ZmPYL ABA receptors and ZmSnRK2 kinases, suggesting that ZmPP2C-A10 is involved in mediating ABA signaling in maize. Transgenic studies in maize and Arabidopsis confirmed that ZmPP2C-A10 functions as a negative regulator of drought tolerance. Further, a causal natural variation, deletion allele-338, which bears a deletion of ERSE （endoplasmic reticulum stress response element） in the 51-UTR region of ZmPP2C-AIO, was detected. This deletion causes the loss of endoplasmic reticulum （ER） stress-induced expression of ZmPP2C-AIO, leading to increased plant drought tolerance. Our study provides direct evidence linking ER stress signaling with drought tolerance and genetic resources that can be used directly in breeding drought-tolerant maize cultivars.

Gene Networks in Plant Ozone Stress Response and Tolerance

For many plant species ozone stress has become much more severe in the last decade. The accumulating evidence for the significant effects of ozone pollutant on crop and forest yield situate ozone as one of the most important environmental stress factors that limits plant productivity worldwide. Today, transcriptomic approaches seem to give the best coverage of genome level responses. Therefore, microarray serves as an invaluable tool for global gene expression analyses, unravelling new information about gene pathways, in-species and cross-species gene expression comparison, and for the characterization of unknown relationships between genes. In this review we summarize the recent progress in the transcriptomics of ozone to demonstrate the benefits that can be harvested from the application of integrative and systematic analytical approaches to study ozone stress response. We focused our consideration on microarray analyses identifying gene networks responsible for response and tolerance to elevated ozone concentration. From these analyses it is now possible to notice how plant ozone defense responses depend on the interplay between many complex signaling pathways and metabolite signals.

Force-dependent calcium signaling and its pathway of human neutrophils on P-selectin in flow

P-selectin engagement of P-selectin glycoprotein Iigand-1 （PSGL-1） causes circulating leukocytes to roll on and adhere to the vascular surface, and mediates intracellular calcium flux, a key but unclear event for subsequent arresting firmly at and migrating into the infection or injured tissue. Using a parallel plate flow chamber technique and intracellular calcium ion detector （Fluo-4 AM）, the intracellular calcium flux of firmly adhered neutrophils on immobilized P-selectin in the absence of chemokines at various wall shear stresses was investigated here in real time by fluorescence microscopy. The results demon- strated that P-selectin engagement of PSGL-1 induced the intracellular calcium flux of firmly adhered neutrophils in flow, increasing P-selectin concentration enhanced cellu- lar calcium signaling, and, force triggered, enhanced and quickened the cytoplasmic calcium bursting of neu- trophils on immobilized P-selectin. This P-selectin-induced calcium signaling should come from intracellular calcium release rather than extracellular calcium influx, and be along the mechano-chemical signal pathway involving the cytoskeleton, moesin and Spleen tyrosine kinase （Syk）. These results provide a novel insight into the mechano-chemical regulation mechanism for P-selectininduced calcium signaling of neutrophils in flow.

Regulation Mechanisms of Stomatal Oscillation

Stomata function as the gates between the plant and the atmospheric environment. Stomatal movement, including stomatal opening and closing, controls CO2 absorption as the raw material for photosynthesis and water loss through transpiration. How to reduce water loss and maintain enough CO2 absorption has been an interesting research topic for some time. Simple stomatal opening may elevate CO2 absorption, but, in the meantime, promote the water loss, whereas simple closing of stomatal pores may reduce both water loss and CO2 absorption, resulting in impairment of plant photosynthesis. Both processes are not economical to the plant. As a special rhythmic stomatal movement that usually occurs at smaller stomatal apertures, stomatal oscillation can keep CO2 absorption at a sufficient level and reduce water loss at the same time, suggesting a potential improvement in water use efficiency. Stomatal oscillation is usually found after a sudden change in one environmental factor in relatively constant environments. Many environmental stimuli can induce stomatal oscillation. It appears that, at the physiological level, feedback controls are involved in stomatal oscillation. At the cellular level, possibly two different patterns exist： （i） a quicker responsive pattern; and （ii） a slower response. Both involve water potential changes and water channel regulation, but the mechanisms of regulation of the two patterns are different. Some evidence suggests that the regulation of water channels may play a vital and primary role in stomatal oscillation. The present review summarizes studies on stomatal oscillation and concludes with some discussion regarding the mechanisms of regulation of stomatal oscillation.

Surviving the odds: From perception to survival of fungal phytopathogens under host-generated oxidative burst

Fungal phytopathogens pose a serious threat to global crop production.Only a handful of strategies are available to combat these fungal infections,and the increasing incidence of fungicide resistance is making the situation worse.Hence,the molecular understanding of plant–fungus interactions remains a primary focus of plant pathology.One of the hallmarks of host–pathogen interactions is the overproduction of reactive oxygen species(ROS)as a plant defense mechanism,collectively termed the oxidative burst.In general,high accumulation of ROS restricts the growth of pathogenic organisms by causing localized cell death around the site of infection.To survive the oxidative burst and achieve successful host colonization,fungal phytopathogens employ intricate mechanisms for ROS perception,ROS neutralization,and protection from ROS-mediated damage.Together,these countermeasures maintain the physiological redox homeostasis that is essential for cell viability.In addition to intracellular antioxidant systems,phytopathogenic fungi also deploy interesting effector-mediated mechanisms for extracellular ROS modulation.This aspect of plant–pathogen interactions is significantly under-studied and provides enormous scope for future research.These adaptive responses,broadly categorized into“escape”and“exploitation”mechanisms,are poorly understood.In this review,we discuss the oxidative stress response of filamentous fungi,their perception signaling,and recent insights that provide a comprehensive understanding of the distinct survival mechanisms of fungal pathogens in response to the host-generated oxidative burst.

A Major Role of the MEKK1-MKK1/2-MPK4 Pathway in ROS Signalling

Over the last few years, it has become evident that reactive oxygen species （ROS） signalling plays an important role in various physiological responses, including pathogen defense and stomatal opening/closure. On the other hand, ROS overproduction is detrimental for proper plant growth and development, indicating that the regulation of an appropriate redox balance is essential for plants. ROS homeostasis in plants involves the mitogen-activated protein kinase （MAPK） pathway consisting of the MAPK kinase kinase MEKK1 and the MAPK MPK4. Phenotypic and molecular analysis revealed that the MAPK kinases MKK1 and MKK2 are part of a cascade, regulating ROS and salicylic acid （SA） accumulation. Gene expression analysis shows that of 32 transcription factors reported to be highly responsive to multiple ROS-inducing conditions, 20 are regulated by the MEKK1, predominantly via the MEKK1-MKK1/2-MPK4 pathway. However, MEKK1 also functions on other as yet unknown pathways and part of the MEKK1-dependent MPK4 responses are regulated independently of MKK1 and MKK2. Overall, this analysis emphasizes the central role of this MAPK cascade in oxidative stress signalling, but also indicates the high level of complexity revealed by this signalling network.

Yishen Jiangzhuo Granules(益肾降浊冲剂) Affect Tubulointerstitial Fibrosis via A Mitochondrion-Mediated Apoptotic Pathway

Objective： To investigate the effect of Yishen Jiangzhuo Granules （益肾降浊冲剂 , YSJZG） on mitochondrial injury and regeneration and renal tubular epithelial cell apoptosis in chronic renal failure （CRF） rats and explore its mechanism from molecular pathology, gene, protein levels, and relative pathway. Methods： The CRF rat model was established using 5/6 nephrectomy. Sixty rats were randomly divided into six groups： sham-operation group, model （CRF） group, Niaoduqing Granules （尿毒清颗粒）-treated group [5 g/（kg.day）], low-, moderate-, and high-dose [L-YSJZG, M-YSJZG, H-YSJZG at 3, 6, and 9 g/（kg-day）] YSJZG-treated group （n=10 each）. The levels of serum creatinine （Scr）, blood urea nitrogen （BUN）, and 24-h urine protein were assessed after 10 weeks of treatment. The tubulointerstitial injury and collagen deposition were evaluated using periodic acid-schiff stain and Masson staining. Renal tubular epithelial cell apoptosis was assessed using the terminal deoxynucleotidyl transferase dUTP nick end labeling assay, mitochondrial injury was observed using an electron microscope, and superoxide dismutase （SOD）, glutathione （GSH） and malondialdehyde （MDA） levels were assessed using chromometry. Transforming growth factor- 1 β（TGF-β 1） expression was assessed using immunohistochemistry. The expressions of Bax, Bcl-2, peroxisome proliferator-activated receptor γ coactivator-1 α （PGC-1α）, mitochondrial transcription factor A （Tfam）, mitogen-activated protein kinases （MAPK） phosphorylation were evaluated by Western blot. Results： YSJZG decreased the 24-h urine protein, BUN, Scr, remnant kidney weight-to-body weight ratio, renal tubular injury, deposition of collagen, and the apoptosis of renal tubular epithelial cells in a dose-dependent manner. YSJZG dose-dependently restored the number and structure of mitochondria and the expression of Tfam and PCG-1 α, up-regulated the expression of Bcl-2, and inhibited the expression of Bax. YSJZG also dose-dependently inhibited TGF- 13 1 expression, increased SOD and GSH activity, decreased the MDA level, and inhibited p38MAPK and pERK1/2 phosphorylation （all P〈0.01）. Conclusion： YSJZG improved the renal function in rats with CRF and inhibited the progression of tubulointerstitial fibrosis by dose-dependently alleviating mitochondrial injury, restoring the expression of Tfam and PCG-1α , and inhibiting renal tubular epithelial cell apoptosis through inhibiting activation of reactive oxygen species-MAPK signaling.

The WUSCHEL Related Homeobox Protein WOX7 Regulates the Sugar Response of Lateral Root Development in Arabidopsis thaliana

Sugars promote lateral root formation at low levels but become inhibitory at high C/N or C/P ratios. How sugars suppress lateral root formation is unclear, however. Here we report that WOX7, a member of the WUSCHEL related homeobox （WOX） family transcription factors, inhibits lateral root development in a sugar-dependent manner. The number of lateral root primordia increased in wox7 mutants but decreased in plants over-expressing WOX7o Plants expressing the WOX7-VP16 fusion protein produced even more lateral roots than wox7, suggesting that WOX7 acts as a transcriptional repressor in lateral root develop- ment. WOX7 is expressed at all stages of lateral root development, but it is primarily involved in lateral root initiation. Consistent with this, the wox7 mutant had a higher mitotic activity only at early stages of lateral root development. Further studies suggest that WOX7 regulates lateral root development through direct repression of cell cycle genes, particularly CYCD6;1. WOX7 expression was enhanced by sugar, reduced by auxin, but did not respond to salt and mannitoh In the wox7 mutant, the effect of sugar on lateral root formation was mitigated. These results together suggest that WOX7 plays an important role in coupling the lateral root development program and sugar status in plants.