ROS-mediated abiotic stress-induced programmed cell death in plants

Melatonin Positively Regulates Both Dark- and Age-Induced Leaf Senescence by Reducing ROS Accumulation and Modulating Abscisic Acid and Auxin Biosynthesis in Cucumber Plants

Melatonin (MT), as a signaling molecule, plays a vital role in regulating leaf senescence in plants. This study aimed to verify the antioxidant roles of MT in delaying dark- or age-induced leaf senescence of cucumber plants. The results showed that endogenous MT responds to darkness and overexpression of CsASMT, the key gene of MT synthesis, and delays leaf senescence stimulated by darkness, as manifested by significantly lower malonaldehyde (MDA) and reactive oxygen species (ROS) contents as well as higher activities and gene expression of antioxidant enzymes compared to the control. Moreover, MT suppressed both age- or dark-induced leaf senescence of cucumber, as evidenced by a decrease in senescence-related gene SAG20 and cell-death-related gene PDCD expression and ROS content and an increase in antioxidant capacity and chlorophyll biosynthesis compared with the H₂O-treated seedlings. Meanwhile, the suppression of age-induced leaf senescence by melatonin was also reflected by the reduction in abscisic acid (ABA) biosynthesis and signaling pathways as well as the promotion of auxin (IAA) biosynthesis and signaling pathways in cucumber plants in the solar greenhouse. Combining the results of the two separate experiments, we demonstrated that MT acts as a powerful antioxidant to alleviate leaf senescence by activating the antioxidant system and IAA synthesis and signaling while inhibiting ABA synthesis and signaling in cucumber plants.

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.

Seed Germination Behavior, Growth, Physiology and Antioxidant Metabolism of Four Contrasting Cultivars under Combined Drought and Salinity in Soybean

Drought and salinity stresses are persistent threat to field crops and are frequently mentioned as major constraints on worldwide agricultural productivity. Moreover, their severity and frequency are predicted to rise in the near future. Therefore, in the present study we investigated the mechanisms underlying plant responses to drought (5, 10 and 15% polyethylene glycol, PEG-6000), salinity (50, 100, and 150 mM NaCl), and their combination, particularly at the seed germination stage, in terms of photosynthesis and antioxidant activity, in four soybean cultivars, viz., PI408105A (PI5A), PI567731 (PI31), PI567690 (PI90), and PI416937 (PI37). Results showed that seed germination was enhanced by 10% PEG and decreased by 15% PEG treatments compared to the control, while seed germination was drastically decreased under all levels of NaCl treatment. Furthermore, combined drought and salinity treatment reduced plant height and root length, shoot and root total weights, and relative water content compared with that of control. However, the reductions were not similar among the varieties, and definite growth retardations were observed in cultivar PI5A under drought and in PI37 under salinity. In addition, all treatments resulted in substantially reduced contents of chlorophyll pigment, anthocyanin, and chlorophyll fluorescence; and increased lipid peroxidation, electrolyte leakage, and non-photochemical quenching in all varieties of soybean as compared to the control plants. However, proline, amino acids, sugars, and secondary metabolites were increased with the drought and salinity stresses alone. Moreover, the reactive oxygen species accumulation was accompanied by improved enzymatic antioxidant activity, such as that of superoxide dismutase, peroxidase, catalase, and ascorbate peroxidase. However, the enhancement was most noticeable in PI31 and PI90 under both treatments. In conclusion, the cultivar PI31 has efficient drought and salinity stress tolerance mechanisms, as illustrated by its superior photosynthesis, osmolyte accumulation, antioxidative enzyme activity, and secondary metabolite regulation, compared to the other cultivars, when stressed.

Root/shoot responses to drought and flooding of bahiagrass at reproductive stage depends on genotype ploidy

Severe water stress is responsible for reducing plant growth and reproduction. This study aimed to evaluate the physiological and biochemical mechanisms associated with the tolerance of two genotipes of bahiagrass (Paspalum notatum Flügge) with different ploidy level to water deficit and flooding at the reproductive stage. Photosynthetic performance of diploid and tetraploid plants was not affected by flooding. In contrast, the water deficit decreased stomatal conductance, increased leaf temperature, and resulted in a decrease in the assimilation rate of the two genotypes. Despite the greater activities of antioxidant enzymes, flooded roots accumulated hydrogen peroxide and malondialdehyde. Roots of plants exposed to water deficit maintained an accumulation of biomass similar to that of control plants; however, with higher levels of total phenol content, total soluble sugars and proline. Diploid plants subjected to flooding had more inflorescences, however, the drought reduced the total number of filled florets per plant. Less starch degradation allows the maintenance and recovery of biomass in the tetraploid genotype, which allows it to maintain its reproductive performance even under drought conditions. Overall, the synthesis of osmoprotectants and activation of antioxidant machinery are important strategies in the tolerance of bahiagrass to water stress at the reproductive stage.

A rice gene encoding glycosyl hydrolase plays contrasting roles in immunity depending on the type of pathogens

Because pathogens use diverse infection strategies, plants cannot use one-size-fits-all defence and modulate defence responses based on the nature of pathogens and pathogenicity mechanism. Here, we report that a rice glycoside hydrolase (GH) plays contrasting roles in defence depending on whether a pathogen is hemibiotrophic or necrotrophic. The Arabidopsis thaliana MORE1 (Magnaporthe oryzae resistance 1) gene, encoding a member of the GH10 family, is needed for resistance against M. oryzae and Alternaria brassicicola, a fungal pathogen infecting A. thaliana as a necrotroph. Among 13 rice genes homologous to MORE1, 11 genes were induced during the biotrophic or necrotrophic stage of infection by M. oryzae. CRISPR/Cas9-assisted disruption of one of them (OsMORE1a) enhanced resistance against hemibiotrophic pathogens M. oryzae and Xanthomonas oryzae pv. oryzae but increased susceptibility to Cochliobolus miyabeanus, a necrotrophic fungus, suggesting that OsMORE1a acts as a double-edged sword depending on the mode of infection (hemibiotrophic vs. necrotrophic). We characterized molecular and cellular changes caused by the loss of MORE1 and OsMORE1a to understand how these genes participate in modulating defence responses. Although the underlying mechanism of action remains unknown, both genes appear to affect the expression of many defence-related genes. Expression patterns of the GH10 family genes in A. thaliana and rice suggest that other members also participate in pathogen defence.

Sugar metabolism during pre- and post-fertilization events in plants under high temperature stress

High temperature challenges global crop production by limiting the growth and development of the reproductive structures and seed. It impairs the developmental stages of male and female gametogenesis, pollination, fertilization, endosperm formation and embryo development. Among these, the male reproductive processes are highly prone to abnormalities under high temperature at various stages of development. The disruption of source-sink balance is the main constraint for satisfactory growth of the reproductive structures which is disturbed at the level of sucrose import and utilization within the tissue. Seed development after fertilization is affected by modulation in the activity of enzymes involved in starch metabolism. In addition, the alteration in the seed-filling rate and its duration affects the seed weight and quality. The present review critically discusses the role of sugar metabolism in influencing the various stages of gamete and seed development under high temperature stress. It also highlights the interaction of the sugars with hormones that mediate the transport of sugars to sink tissues. The role of transcription factors for the regulation of sugar availability under high temperature has also been discussed. Further, the omics-based systematic investigation has been suggested to understand the synergistic or antagonistic interactions between sugars, hormones and reactive oxygen species at various points of sucrose flow from source to sink under high temperature stress.

Subversion of Phytomyxae Cell Communication With Surrounding Environment to Control Soilborne Diseases; A Case Study of Cytosolic Ca2+ Signal Disruption in Zoospores of Spongospora subterranea

Ca2+ signaling regulates physiological processes including chemotaxis in eukaryotes and prokaryotes. Its inhibition has formed the basis for control of human disease but remains largely unexplored for plant disease. This study investigated the role of Ca2+ signaling on motility and chemotaxis of Spongospora subterranea zoospores, responsible for root infections leading to potato root and tuber disease. Cytosolic Ca2+ flux inhibition with Ca2+ antagonists were found to alter zoospore swimming patterns and constrain zoospore chemotaxis, root attachment and zoosporangia infection. LaCl3 and GdCl3, both Ca2+ channel blockers, at concentrations ≥ 50 μM showed complete inhibition of zoospore chemotaxis, root attachment and zoosporangia root infection. The Ca2+ chelator EGTA, showed efficient chemotaxis inhibition but had relatively less effect on root attachment. Conversely the calmodulin antagonist trifluoperazine had lesser effect on zoospore chemotaxis but showed strong inhibition of zoospore root attachment. Amiloride hydrochloride had a significant inhibitory effect on chemotaxis, root attachment, and zoosporangia root infection with dose rates ≥ 150 μM. As expected, zoospore attachment was directly associated with root infection and zoosporangia development. These results highlight the fundamental role of Ca2+ signaling in zoospore chemotaxis and disease establishment. Their efficient interruption may provide durable and practical control of Phytomyxea soilborne diseases in the field.

Microbial interaction mediated programmed cell death in plants

Food demand of growing population can only be met by finding solutions for sustaining the crop yield. The understanding of basic mechanisms employed by microorganisms for the establishment of parasitic relationship with plants is a complex phenomenon. Symbionts and biotrophs are dependent on living hosts for completing their life cycle, whereas necrotrophs utilize dead cells for their growth and establishment. Hemibiotrophs as compared to other microbes associate themselves with plants in two phase's, viz. early bio-phase and later necro-phase. Plants and microbes interact with each other using receptors present on host cell surface and elicitors (PAMPs and effectors) produced by microbes. Plant-microbe interaction either leads to compatible or incompatible reaction. In response to various biotic and abiotic stress factors, plant undergoes programmed cell death which restricts the growth of biotrophs or hemibiotrophs while necrotrophs as an opportunist starts growing on dead tissue for their own benefit. PCD regulation is an outcome of plant-microbe crosstalk which entirely depends on various biochemical events like generation of reactive oxygen species, nitric oxide, ionic efflux/influx, CLPs, biosynthesis of phytohormones, phytoalexins, polyamines and certain pathogenesis-related proteins. This phenomenon mostly occurs in resistant and non-host plants during invasion of pathogenic microbes. The compatible or incompatible host-pathogen interaction depends upon the presence or absence of host plant resistance and pathogenic race. In addition to host-pathogen interaction, the defense induction by beneficial microbes must also be explored and used to the best of its potential. This review highlights the mechanism of microbe- or symbiont-mediated PCD along with defense induction in plants towards symbionts, biotrophs, necrotrophs and hemibiotrophs. Here we have also discussed the possible use of beneficial microbes in inducing systemic resistance in plants against pathogenic microbes.

Biological signalling supports biotechnology - Pulsed electric fields extract a cell-death inducing factor from Chlorella vulgaris

Compared to mechanical extraction methods, pulsed electric field (PEF) treatment provides an energy-efficient and gentle alternative. However, the biological processes involved are poorly understood. The unicellular green microalga Chlorella vulgaris was used as model organism to investigate the effect of PEF treatment on biological cells. A viability assay using fluorescein diacetate measured by flow cytometry was established. The influence of developmental stage on viability could be shown in synchronised cultures when applying PEF treatment with very low specific energies where one part of cells undergoes cell death, and the other part stays viable after treatment. Reactive oxygen species generation after similar low-energy PEF treatment could be shown, indicating that PEFs could act as abiotic stress signal. Most importantly, a cell-death inducing factor could be extracted. A water-soluble extract derived from microalgae suspensions incubated for 24 h after PEF treatment caused the recipient microalgae to die, even though the recipient cells had not been subjected to PEF treatment directly. The working model assumes that low-energy PEF treatment induces programmed cell death in C.vulgaris while specifically releasing a cell-death inducing factor. Low-energy PEF treatment with subsequent incubation period could be a novel biotechnological strategy to extract soluble proteins and lipids in cascade process.

How do plants defend themselves against pathogens-Biochemical mechanisms and genetic interventions

In agro-ecosystem, plant pathogens hamper food quality, crop yield, and global food security. Manipulation of naturally occurring defense mechanisms in host plants is an effective and sustainable approach for plant disease management. Various natural compounds, ranging from cell wall components to metabolic enzymes have been reported to protect plants from infection by pathogens and hence provide specific resistance to hosts against pathogens, termed as induced resistance. It involves various biochemical components, that play an important role in molecular and cellular signaling events occurring either before (elicitation) or after pathogen infection. The induction of reactive oxygen species, activation of defensive machinery of plants comprising of enzymatic and non-enzymatic antioxidative components, secondary metabolites, pathogenesis-related protein expression (e.g. chitinases and glucanases), phytoalexin production, modification in cell wall composition, melatonin production, carotenoids accumulation, and altered activity of polyamines are major induced changes in host plants during pathogen infection. Hence, the altered concentration of biochemical components in host plants restricts disease development. Such biochemical or metabolic markers can be harnessed for the development of "pathogen-proof" plants. Effective utilization of the key metabolites-based metabolic markers can pave the path for candidate gene identification. This present review discusses the valuable information for understanding the biochemical response mechanism of plants to cope with pathogens and genomics-metabolomics-based sustainable development of pathogen proof cultivars along with knowledge gaps and future perspectives to enhance sustainable agricultural production.

De novo and comparative transcriptomic analysis explain morphological differences in Panax notoginseng taproots

Background

Panax notoginseng (Burk.) F. H. Chen (PN) belonging to the genus Panax of family Araliaceae is widely used in traditional Chinese medicine to treat various diseases. PN taproot, as the most vital organ for the accumulation of bioactive components, presents a variable morphology (oval or long), even within the same environment. However, no related studies have yet explained the molecular mechanism of phenotypic differences. To investigate the cause of differences in the taproot phenotype, de novo and comparative transcriptomic analysis on PN taproot was performed.

Results

A total of 133,730,886 and 114,761,595 paired-end clean reads were obtained based on high-throughput sequencing from oval and long taproot samples, respectively. 121,955 unigenes with contig N50 = 1,774 bp were generated by using the de novo assembly transcriptome, 63,133 annotations were obtained with the BLAST. And then, 42 genes belong to class III peroxidase (PRX) gene family, 8 genes belong to L-Ascorbate peroxidase (APX) gene family, and 55 genes belong to a series of mitogen-activated protein kinase (MAPK) gene family were identified based on integrated annotation results. Differentially expressed genes analysis indicated substantial up-regulation of PnAPX3 and PnPRX45, which are related to reactive oxygen species metabolism, and the PnMPK3 gene, which is related to cell proliferation and plant root development, in long taproots compared with that in oval taproots. Furthermore, the determination results of real-time quantitative PCR, enzyme activity, and H₂O₂ content verified transcriptomic analysis results.

Conclusion

These results collectively demonstrate that reactive oxygen species (ROS) metabolism and the PnMPK3 gene may play vital roles in regulating the taproot phenotype of PN. This study provides further insights into the genetic mechanisms of phenotypic differences in other species of the genus Panax.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-08283-w.

Reactive Oxygen Species, Antioxidant Responses and Implications from a Microbial Modulation Perspective

Simple Summary

Environmental conditions are subject to unprecedented changes due to recent progressive anthropogenic activities on our planet. Plants, as the frontline of food security, are susceptible to these changes, resulting in the generation of unavoidable byproducts of metabolism (ROS), which eventually affect their productivity. The response of plants to these unfavorable conditions is highly intricate and depends on several factors, among them are the species/genotype tolerance level, intensity, and duration of stress factors. Defensive mechanisms in plant systems, by nature, are concerned primarily with generating enzymatic and non-enzymatic antioxidants. In addition to this, plant-microbe interactions have been found to improve immune systems in plants suffering from drought and salinity stress.

Abstract

Plants are exposed to various environmental stresses in their lifespan that threaten their survival. Reactive oxygen species (ROS), the byproducts of aerobic metabolism, are essential signalling molecules in regulating multiple plant developmental processes as well as in reinforcing plant tolerance to biotic and abiotic stimuli. However, intensified environmental challenges such as salinity, drought, UV irradiation, and heavy metals usually interfere with natural ROS metabolism and homeostasis, thus aggravating ROS generation excessively and ultimately resulting in oxidative stress. Cellular damage is confined to the degradation of biomolecular structures, including carbohydrates, proteins, lipids, pigments, and DNA. The nature of the double-edged function of ROS as a secondary messenger or harmful oxidant has been attributed to the degree of existing balance between cellular ROS production and ROS removal machinery. The activities of enzyme-based antioxidants, catalase (CAT, EC 1.11.1.6), monodehydroascorbate reductase (MDHAR, E.C.1.6.5.4), dehydroascorbate reductase (DHAR, EC 1.8.5.1), superoxide dismutase (SOD, EC 1.15.1.1), ascorbate peroxidase (APX, EC 1.11.1.11), glutathione reductase (GR, EC 1.6.4.2), and guaiacol peroxidase (GPX, EC 1.11.1.7); and non-enzyme based antioxidant molecules, ascorbate (AA), glutathione (GSH), carotenoids, α-tocopherol, prolines, flavonoids, and phenolics, are indeed parts of the defensive strategies developed by plants to scavenge excess ROS and to maintain cellular redox homeostasis during oxidative stress. This review briefly summarises current knowledge on enzymatic and non-enzymatic antioxidant machinery in plants. Moreover, additional information about the beneficial impact of the microbiome on countering abiotic/biotic stresses in association with roots and plant tissues has also been provided.

Monitoring Cell Death Via Ion Leakage and PAM Fluorometry

Cell death in plants plays a major role during development as well as in response to certain biotic and abiotic stresses. For example, plant cell death can be triggered in a tightly regulated way during the hypersensitive response (HR) in defense against pathogens or be elicited by pathogenic toxin deployment. Monitoring cell death and its impact on plant health can aid in the quantification of plant disease symptoms and help to identify the underlying molecular pathways. Here, we describe our current protocol for monitoring plant cell death via ion leakage and Pulse-Amplitude-Modulation (PAM) fluorometry. We further provide a detailed protocol for the sample preparation, the measurement, and the data evaluation and discuss the complementary nature of ion leakage and PAM fluorometry as well as the potential of PAM fluorometry for high-throughput screenings.

Climate change regulated abiotic stress mechanisms in plants: a comprehensive review

Global climate change is identified as a major threat to survival of natural ecosystems. Climate change is a dynamic, multifaceted system of alterations in environmental conditions that affect abiotic and biotic components of the world. It results in alteration in environmental conditions such as heat waves, intensity of rainfall, CO₂ concentration and temperature that lead to rise in new pests, weeds and pathogens. Climate change is one of the major constraints limiting plant growth and development worldwide. It impairs growth, disturbs photosynthesis, and reduces physiological responses in plants. The variations in global climate have gained the attention of researchers worldwide, as these changes negatively affect the agriculture by reducing crop productivity and food security. With this background, this review focuses on the effects of elevated atmospheric CO₂ concentration, temperature, drought and salinity on the morphology, physiology and biochemistry of plants. Furthermore, this paper outlines an overview on the reactive oxygen species (ROS) production and their impact on the biochemical and molecular status of plants with increased climatic variations. Also additionally, different tolerance strategies adopted by plants to combat environmental adversities have been discussed.

Imaging of Potassium and Calcium Distribution in Plant Tissues and Cells to Monitor Stress Response and Programmed Cell Death

In plants, the response to stress, such as salinity, pathogen attack, drought, high concentration of metals, hyperthermia, and hypothermia, is usually accompanied by potassium ion (K⁺) leakage from the cytosol to the cell wall, mediated by plasma membrane cation conductivity. Stress-induced electrolyte leakage co-occurs with accumulation of reactive oxygen species (ROS) and calcium ions (Ca²⁺) and often results in programmed cell death (PCD). The development of X-ray and mass spectrometry (MS) based imaging techniques has enabled insight into the spatial tissue and cell-specific redistribution of major and trace elements during the stress response. In this chapter a workflow for sample preparation, imaging, and image analysis by X-ray and MS based techniques is presented.

Detection of Root Physiological Parameters and Potassium and Calcium Currents in the Rhizoplane of the Apple Rootstock Superior Line 12-2 With Improved Apple Replant Disease Resistance

The cultivation of resistant rootstocks is one of the more effective ways to mitigate apple replant disease (ARD). We performed an ion current test, a pot experiment, and a pathogen infection test on the apple rootstocks 12-2 (self-named), T337, and M26. The ion current test showed that exposure to ARD soil extract for 30 min had a significant effect on K+ ion currents at the meristem, elongation, and mature zones of the M26 rhizoplane and on Ca2+ currents in the meristem and elongation zones. ARD also had a significant effect on Ca2+ currents in the meristem, elongation, and mature zones of the T337 rhizoplane. Exposure to ARD soil extract for 5 min had a significant effect on K+ currents in the meristem, elongation, and mature zones of 12-2 and on the Ca2+ currents in the elongation and mature zones. Compared to a 5-min exposure, a 30-min exposure to ARD extract had a less pronounced effect on K+ and Ca2+ currents in the 12-2 rhizoplane. The pot experiment showed that ARD soil had no significant effect on any root architectural or physiological parameters of 12-2. By contrast, ARD soil significantly reduced some root growth indices and the dry and fresh weights of T337 and M26 compared with controls on sterilized soil. ARD also had a significant effect on root metabolic activity, root antioxidant enzyme activity (except superoxide dismutase for T337), and malondialdehyde content of T337 and M26. Pathogen infection tests showed that Fusarium proliferatum MR5 significantly affected the root structure and reduced the root metabolic activity of T337 and M26. It also reduced their root antioxidant enzyme activities (except catalase for T337) and significantly increased the root malondialdehyde content, reactive oxygen levels, and proline and soluble sugar contents. By contrast, MR5 had no such effects on 12-2. Based on these results, 12-2 has the potential to serve as an important ARD-resistant rootstock.

Phosphorylation of RAV1/2 by KIN10 is essential for transcriptional activation of CAT6/7, which underlies oxidative stress response in cassava

Related to ABI3/VP1 (RAV) transcription factors have important roles in plant stress responses; however, it is unclear whether RAVs regulates oxidative stress response in cassava (Manihot esculenta). In this study, we report that MeRAV1/2 positively regulate oxidative stress resistance and catalase (CAT) activity in cassava. Consistently, RNA sequencing (RNA-seq) identifies three MeCATs that are differentially expressed in MeRAV1/2-silenced cassava leaves. Interestingly, MeCAT6 and MeCAT7 are identified as direct transcriptional targets of MeRAV1/2 via binding to their promoters. In addition, protein kinase MeKIN10 directly interacts with MeRAV1/2 to phosphorylate them at Ser45 and Ser44 residues, respectively, to promote their direct transcriptional activation on MeCAT6 and MeCAT7. Site mutation of MeRAV1S45A or MeRAV2S44A has no significant effect on the activities of MeCAT6 and MeCAT7 promoters or on oxidative stress resistance. In summary, this study demonstrates that the phosphorylation of MeRAV1/2 by MeKIN10 is essential for its direct transcriptional activation of MeCAT6/7 in response to oxidative stress.

Mechanism of kinetin-induced death of Vicia faba ssp. minor root cortex cells

Cell death (CD) may be induced by endogenous or exogenous factors and contributes to all the steps of plant development. This paper presents results related to the mechanism of CD regulation induced by kinetin (Kin) in the root cortex of Vicia faba ssp. minor. To explain the process, 6-(2-hydroxy-3-methylbenzylamino)purine (PI-55), adenine (Ad), 5'-amine-5'-deoxyadenosine (Ado) and N-(2-chloro-4-piridylo)-N'-phenylurea (CPPU) were applied to (i) block cytokinin receptors (CKs) and inhibit the activities of enzymes of CK metabolism, i.e., (ii) phosphoribosyltransferase, (iii) kinases, and (iv) oxidases, respectively. Moreover, ethylene glycol-bis(β-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA), lanthanum chloride (LaCl3), ruthenium red (RRed) and cyclosporine A (CS-A) were applied to (i) chelate extracellular calcium ions (Ca2+) as well as blocks of (ii) plasma-, (iii) endoplasmic reticulum- (ER) membrane Ca2+ ion channels and (iv) mitochondria- (MIT) Ca2+ ions release by permeability transition por (PTP), respectively. The measured physiological effectiveness of these factors was the number of living and dying cortex cells estimated with orange acridine (OA) and ethidium bromide (EB), the amounts of cytosolic Ca2+ ions with chlortetracycline (CTC) staining and the intensity of chromatin and Ca2+-CTC complex fluorescence, respectively. Moreover, the role of sorafenib, an inhibitor of RAF kinase, on the vitality of cortex cells and ethylene levels as well as the activities of RAF-like kinase and MEK2 with Syntide-2 and Mek2 as substrates were studied. The results clarified the previously presented suggestion that Kin is converted to appropriate ribotides (5'-monophosphate ribonucleotides), which cooperate with the ethylene and Ca2+ ion signalling pathways to transduce the signal of kinetin-programmed cell death (Kin-PCD). Based on the present and previously published results related to Kin-PCD, the crosstalk between ethylene and MAP kinase signalling, as well as inhibitors of CK receptors and enzymes of their metabolism, is proposed.

A bHLH transcription factor from Chenopodium glaucum confers drought tolerance to transgenic maize by positive regulation of morphological and physiological performances and stress-responsive genes' expressions

The basic helix-loop-helix (bHLH) transcription factor has been shown to play an important role in various physiological processes. However, its functions and mechanisms in drought tolerance still remain poorly understood. Here, we reported a bHLH transcription factor - CgbHLH001 - from Chenopodium glaucum, which was able to confer drought tolerance in maize. CgbHLH001-overexpressed maize lines exhibited drought-tolerant phenotype and improved ear traits by accumulating the contents of soluble sugar and proline and elevating the activities of antioxidant enzymes (SOD, POD, and CAT) under drought stress, accompanying with the upregulation of some stress-related genes, which may balance the redox and osmotic homeostasis compared with the non-transgenic and CgbHLH001-RNAi plants. These findings suggest that CgbHLH001 can confer drought tolerance and has the potential for utilization in improving drought resistance in maize breeding.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11032-021-01267-4.

A Sustainable Alternative for Postharvest Disease Management and Phytopathogens Biocontrol in Fruit: Antagonistic Yeasts

Postharvest diseases of fruits caused by phytopathogens cause losses up to 50% of global production. Phytopathogens control is performed with synthetic fungicides, but the application causes environmental contamination problems and human and animal health in addition to generating resistance. Yeasts are antagonist microorganisms that have been used in the last years as biocontrol agents and in sustainable postharvest disease management in fruits. Yeast application for biocontrol of phytopathogens has been an effective action worldwide. This review explores the sustainable use of yeasts in each continent, the main antagonistic mechanisms towards phytopathogens, their relationship with OMIC sciences, and patents at the world level that involve yeast-based-products for their biocontrol.

Plant protease as regulator and signaling molecule for enhancing environmental stress-tolerance

Proteases are ubiquitous in prokaryotes and eukaryotes. Plant proteases are key regulators of various physiological processes, including protein homeostasis, organelle development, senescence, seed germination, protein processing, environmental stress response, and programmed cell death. Proteases are involved in the breakdown of peptide bonds resulting in irreversible posttranslational modification of the protein. Proteases act as signaling molecules that specifically regulate cellular function by cleaving and triggering receptor molecules. Peptides derived from proteolysis regulate ROS signaling under oxidative stress in the plant. It degrades misfolded and abnormal proteins into amino acids to repair the cell damage and regulates the biological process in response to environmental stress. Proteases modulate the biogenesis of phytohormones which control plant growth, development, and environmental stresses. Protein homeostasis, the overall balance between protein synthesis and proteolysis, is required for plant growth and development. Abiotic and biotic stresses are major factors that negatively impact cellular survivability, biomass production, and reduced crop yield potentials. Therefore, the identification of various stress-responsive proteases and their molecular functions may elucidate valuable information for the development of stress-resilient crops with higher yield potentials. However, the understanding of molecular mechanisms of plant protease remains unexplored. This review provides an overview of proteases related to development, signaling, and growth regulation to acclimatize environmental stress in plants.

Programmed cell death induced by modified clay in controlling Prorocentrum donghaiense bloom

Modified clay (MC), an effective material used for the emergency elimination of algal blooms, can rapidly reduce the biomass of harmful algal blooms (HABs) via flocculation. After that, MC can still control bloom population through indirect effects such as oxidative stress, which was initially proposed to be related to programmed cell death (PCD) at molecular level. To further study the MC induced cell death in residual bloom organisms, especially identifying PCD process, we studied the physiological state of the residual Prorocentrum donghaiense. The experimental results showed that flocculation changed the physiological state of the residual cells, as evidenced by growth inhibition and increased reactive oxygen species production. Moreover, this research provides biochemical and ultrastructural evidence showing that MC induces PCD in P. donghaiense. Nuclear changes were observed, and increased caspase-like activity, externalization of phosphatidylserine and DNA fragmentation were detected in MC-treated groups and quantified. And the mitochondrial apoptosis pathway was activated in both MC-treated groups. Besides, the features of MC-induced PCD in a unicellular organism were summarized and its concentration dependent manner was proved. All our preliminary results elucidate the mechanism through which MC can further control HABs by inducing PCD and suggest a promising application of PCD in bloom control.

Identification of novel drought-responsive miRNA regulatory network of drought stress response in common vetch (Vicia sativa)

Drought is among the most important natural disasters with severe effects on animals and plants. MicroRNAs are a class of noncoding RNAs that play a crucial role in plant growth, development, and response to stress factors, including drought. However, the microRNAs in drought responses in common vetch (Vicia sativa), an annual herbaceous leguminous plant commonly used for forage by including it in mixed seeding during winter and spring, have not been characterized. To explore the microRNAs’ response to drought in common vetch, we sequenced 10 small RNA (sRNA) libraries by the next-generation sequencing technology. We obtained 379 known miRNAs belonging to 38 families and 47 novel miRNAs. The two groups had varying numbers of differentially expressed miRNAs: 85 in the comparison group D5 vs C5 and 38 in the comparison group D3 vs C3. Combined analysis of mRNA and miRNA in the same samples under drought treatment identified 318 different target genes of 123 miRNAs. Functional annotation of the target genes revealed that the miRNAs regulate drought-responsive genes, such as leucine-rich repeat receptor-like kinase-encoding genes (LRR-RLKs), ABC transporter G family member 1 (ABCG1), and MAG2-interacting protein 2 (MIP2). The genes were involved in various pathways, including cell wall biosynthesis, reactive oxygen removal, and protein transport. The findings in this study provide new insights into the miRNA-mediated regulatory networks of drought stress response in common vetch.

Cold Tolerance during the Reproductive Phase in Chickpea (Cicer arietinum L.) Is Associated with Superior Cold Acclimation Ability Involving Antioxidants and Cryoprotective Solutes in Anthers and Ovules

Chickpea is sensitive to cold stress, especially at reproductive stage, resulting in flower and pod abortion that significantly reduces seed yield. In the present study, we evaluated (a) whether cold acclimation imparts reproductive cold tolerance in chickpea; (b) how genotypes with contrasting sensitivity respond to cold acclimation; and (c) the involvement of cryoprotective solutes and antioxidants in anthers and ovules in cold acclimation. Four chickpea genotypes with contrasting cold sensitivity (cold-tolerant: ICC 17258, ICC 16349; cold-sensitive: ICC 15567, GPF 2) were grown in an outdoor environment for 40 days in November (average maximum/minimum temperature 24.9/15.9 °C) before being subjected to cold stress (13/7 °C), with or without cold acclimation in a controlled environment of walk-in-growth chambers. The 42-d cold acclimation involved 7 d exposure at each temperature beginning with 23/15 °C, 21/13 °C, 20/12 °C, 20/10 °C, 18/8 °C, 15/8 °C (12 h/12 h day/night), prior to exposing the plants to cold stress (13/7 °C, 12 h/12 h day/night; 700 μmol m⁻² s⁻¹ light intensity; 65–70% relative humidity). Cold acclimation remarkably reduced low temperature-induced leaf damage (as membrane integrity, leaf water status, stomatal conductance, photosynthetic pigments, and chlorophyll fluorescence) under cold stress in all four genotypes. It only reduced anther and ovule damage in cold-tolerant genotypes due to improved antioxidative ability, measured as enzymatic (superoxide dismutase, catalase, ascorbate peroxidase, and glutathione reductase) and non-enzymatic (ascorbate and reduced glutathione), solutes (particularly sucrose and γ-aminobutyric acid) leading to improving reproductive function and yield traits, whereas cold-sensitive genotypes were not responsive. The study concluded that cold tolerance in chickpea appears to be related to the better ability of anthers and ovules to acclimate, involving various antioxidants and cryoprotective solutes. This information will be useful in directing efforts toward increasing cold tolerance in chickpea.

Selenium restores mitochondrial dysfunction to reduce Cr-induced cell apoptosis in Chinese cabbage (Brassica campestris L. ssp. Pekinensis) root tips

Chromium (Cr) disrupts the growth and physiology of plants. Selenium (Se) is considered as a promising option to help plants ameliorate Cr toxicity. To investigate the effects of exogenous Se on reactive oxygen species (ROS) burst and programmed cell death (PCD) in root tip cells under Cr stress, hydroponic experiments were carried out with Chinese cabbage seedlings grown in Hoagland solution containing 1 mg L^-1 Cr and 0.1 mg L^-1 Se. Results showed that Se scavenged the overproduction of H₂O₂ and O₂^－·, and alleviated the level of lipid peroxidation in root tips stressed by Cr. Moreover, Se effectively prevented DNA degradation and reduced the number of apoptotic cells in root tips. Compared with Cr treatment, Se supplementation reduced the content of ROS and malondialdehyde in mitochondria by 38.23% and 17.52%, respectively. Se application decreased the opening degree of mitochondrial permeability transition pores by 32.30%, increased mitochondrial membrane potential by 40.91%, alleviated the release of cyt c from mitochondria into cytosol by 18.42% and caused 57.40% decrease of caspase 3-like protease activity, and thus restored mitochondrial dysfunction caused by Cr stress. In addition, the alteration of Se on mitochondrial physiological properties maintained calcium homeostasis between mitochondria and cytosol, which further contributed to reducing the appearance of Cr-induced PCD. Findings suggested that Se restored mitochondrial dysfunction, which further rescued root tip cells from PCD, consequently activating defense strategies to protect plants from Cr toxicity and maintaining plant growth.

Plant Tolerance to Drought Stress in the Presence of Supporting Bacteria and Fungi: An Efficient Strategy in Horticulture

Increasing temperature leads to intensive water evaporation, contributing to global warming and consequently leading to drought stress. These events are likely to trigger modifications in plant physiology and microbial functioning due to the altered availability of nutrients. Plants exposed to drought have developed different strategies to cope with stress by morphological, physiological, anatomical, and biochemical responses. First, visible changes influence plant biomass and consequently limit the yield of crops. The presented review was undertaken to discuss the impact of climate change with respect to drought stress and its impact on the performance of plants inoculated with plant growth-promoting microorganisms (PGPM). The main challenge for optimal performance of horticultural plants is the application of selected, beneficial microorganisms which actively support plants during drought stress. The most frequently described biochemical mechanisms for plant protection against drought by microorganisms are the production of phytohormones, antioxidants and xeroprotectants, and the induction of plant resistance. Rhizospheric or plant surface-colonizing (rhizoplane) and interior (endophytic) bacteria and fungi appear to be a suitable alternative for drought-stress management. Application of various biopreparations containing PGPM seems to provide hope for a relatively cheap, easy to apply and efficient way of alleviating drought stress in plants, with implications in productivity and food condition.

Transcriptome and structure analysis in root of Casuarina equisetifolia under NaCl treatment

Background

High soil salinity seriously affects plant growth and development. Excessive salt ions mainly cause damage by inducing osmotic stress, ion toxicity, and oxidation stress. Casuarina equisetifolia is a highly salt-tolerant plant, commonly grown as wind belts in coastal areas with sandy soils. However, little is known about its physiology and the molecular mechanism of its response to salt stress.

Results

Eight-week-old C. equisetifolia seedlings grown from rooted cuttings were exposed to salt stress for varying durations (0, 1, 6, 24, and 168 h under 200 mM NaCl) and their ion contents, cellular structure, and transcriptomes were analyzed. Potassium concentration decreased slowly between 1 h and 24 h after initiation of salt treatment, while the content of potassium was significantly lower after 168 h of salt treatment. Root epidermal cells were shed and a more compact layer of cells formed as the treatment duration increased. Salt stress led to deformation of cells and damage to mitochondria in the epidermis and endodermis, whereas stele cells suffered less damage. Transcriptome analysis identified 10,378 differentially expressed genes (DEGs), with more genes showing differential expression after 24 h and 168 h of exposure than after shorter durations of exposure to salinity. Signal transduction and ion transport genes such as HKT and CHX were enriched among DEGs in the early stages (1 h or 6 h) of salt stress, while expression of genes involved in programmed cell death was significantly upregulated at 168 h, corresponding to changes in ion contents and cell structure of roots. Oxidative stress and detoxification genes were also expressed differentially and were enriched among DEGs at different stages.

Conclusions

These results not only elucidate the mechanism and the molecular pathway governing salt tolerance, but also serve as a basis for identifying gene function related to salt stress in C. equisetifolia.

BAK1-induced RPK1 phosphorylation is essential for RPK1-mediated cell death in Arabidopsis

Being sessile, plants must deploy highly exquisite systems to respond to various internal and external signals for modulating growth and development throughout their lifespan. Many studies on Arabidopsis have shown that leucine-rich repeat-containing receptor-like kinases, including BRI1-associated receptor kinase 1 (BAK1) and receptor-like protein kinase 1 (RPK1), are suitable for such pleiotropic demands of plants. Previously, BAK1 and RPK1 were independently proven to be involved in the regulation of premature cell death. BAK1 inhibits spontaneous cell death and promotes defense-induced cell death. Meanwhile, RPK1 mediates reactive oxygen species (ROS) production through complexation with CaM4 and RbohF in an age-dependent manner. In the present study, RPK1-induced cell death and growth retardation were abolished both with respect to the phenotype and ROS production in bak1 mutants. Moreover, BAK1 interacts with RPK1 and mediates its unidirectional phosphorylation in plants. Further, BAK1-mediated RPK1 phosphorylation is indispensable for RPK1-CaM4 interaction, which is vital for ROS production, resulting in cell death. The presence of BAK1 enhanced the expression of cell death- and senescence-related genes, such as ORE1, PR1, SAG12, and SIRK in RPK1-mediated signaling cascades. Overall, in Arabidopsis, in addition to independent cell death regulation by BAK1 and RPK1, multiple-layers control cell death and premature senescence via the coordinated action of BAK1 and RPK1.

Transcriptome analysis reveals the molecular mechanism of yield increases in maize under stable soil water supply

This study explored the physiological and molecular mechanisms of yield increase in maize under stable soil water content (SW) conditions. Results of the study showed that under SW conditions, corn yield increased by 38.72 and 44.09% in 2019 and 2020, respectively. Further, it was found that dry matter accumulation, economic coefficient and photosynthetic rate also increased by 31.24 and 25.67%, 5.45 and 15.38% as well as 29.60 and 31.83% in 2019 and 2020 respectively. However, the results showed that both the activity of antioxidant enzymes and content of osmotic adjustment substances decreased in maize under SW conditions. When compared with soil moisture content of dry and wet alternation (DW) conditions, SW could not only significantly promote growth and yield of maize but also increase the economic coefficient. Transcriptome profiles of maize leaves under the two conditions (SW and DW) were also analyzed and compared. It was found that 11 genes were highly up-regulated in the photosynthesis pathway. These genes included photosystem II protein V (PsbE), photosystem II protein VI (PsbF), photosystem II protein D1 (PsbA), photosystem II protein D2 (PsbD) and ATP synthase CF1 beta subunit (atpB). Further, it was found that four genes were up-regulated in the oxidative phosphorylation pathway., These were ATP synthase CF1 epsilon subunit (atpE), ATP synthase CF1 beta subunit (atpB), NADH dehydrogenase subunit 4L (ndhE) and NADH dehydrogenase subunit 6 (ndhG). In conclusion, the physiological mechanism of stable soil water content (SW) to increase corn yield may be the enhancement of photosynthetic capacity and energy metabolism.

Transcriptional profiling reveals changes in gene regulation and signaling transduction pathways during temperature stress in wucai (Brassica campestris L.)

Background

Wucai (Brassica campestris L. ssp. chinensis var. rosularis Tsen) is a cold-tolerant plant that is vulnerable to high temperature. This study explored the response mechanism of wucai to low temperature. In this study, wucai seedlings were treated with different temperatures, including low temperature (LT), high temperature (HT), and a control.

Results

According to transcriptomics analysis, the number of differentially expressed genes (DEGs) in HT and LT was 10,702 and 7267, respectively, compared with the control. The key genes associated with the physiological response of wucai to the treatments were analyzed. The Kyoto Encyclopedia of Genes and Genomes and Gene Ontology annotations indicated the importance of the photosynthesis and photosynthetic-antenna protein pathways. We found that a high-temperature environment greatly inhibited the expression of important genes in the photosynthetic pathway (BrLhc superfamily members, PsaD, PsaE, PsaD, PsaD, PsbO, PsbP, PsbQ, PsbR, PsbS, PsbW, PsbY, Psb27, and Psb28), whereas low temperature resulted in the expression of certain key genes (BrLhc superfamily members, Psa F, Psa H, Psb S, Psb H, Psb 28). In addition, the wucai seedlings exhibited better photosynthetic performance under low-temperature conditions than high-temperature conditions.

Conclusions

Based on the above results, we speculate that upon exposure to low temperature, the plants developed higher cold tolerance by upregulating the expression of genes related to photosynthesis. Conversely, high-temperature stress inhibited the expression of pivotal genes and weakened the self-regulating ability of the plants.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07981-9.

Plant programmed cell death meets auxin signalling

Both auxin signalling and programmed cell death (PCD) are essential components of a normally functioning plant. Auxin underpins plant growth and development, as well as regulating plant defences against environmental stresses. PCD, a genetically controlled pathway for selective elimination of redundant, damaged or infected cells, is also a key element of many developmental processes and stress response mechanisms in plants. An increasing body of evidence suggests that auxin signalling and PCD regulation are often connected. While generally auxin appears to suppress cell death, it has also been shown to promote PCD events, most likely via stimulation of ethylene biosynthesis. Intriguingly, certain cells undergoing PCD have also been suggested to control the distribution of auxin in plant tissues, by either releasing a burst of auxin or creating an anatomical barrier to auxin transport and distribution. These recent findings indicate novel roles of localized PCD events in the context of plant development such as control of root architecture, or tissue regeneration following injury, and suggest exciting possibilities for incorporation of this knowledge into crop improvement strategies.

Voltage-Dependent Anion-Selective Channels and Other Mitochondrial Membrane Proteins Form Diverse Complexes in Beetroots Subjected to Flood-Induced Programmed Cell Death

In plants, programmed cell death (PCD) is involved in both the development and the response to biotic and abiotic aggressions. In early stages of PCD, mitochondrial membranes are made permeable by the formation of permeability transition pores, whose protein composition is debated. Cytochrome c (cyt c) is then released from mitochondria, inducing the degradation of chromatin characteristic of PCD. Since flooding stress can produce PCD in several plant species, the first goal of this study was to know if flooding stress could be used to induce PCD in Beta vulgaris roots. To do this, 2-month-old beet plants were flood-stressed from 1 to 5 days, and the alterations indicating PCD in stressed beetroot cells were observed with a confocal fluorescence microscope. As expected, nuclei were deformed, and chromatin was condensed and fragmented in flooded beetroots. In addition, cyt c was released from mitochondria. After assessing that flood stress induced PCD in beetroots, the composition of mitochondrial protein complexes was observed in control and flood-stressed beetroots. Protein complexes from isolated mitochondria were separated by native gel electrophoresis, and their proteins were identified by mass spectrometry. The spectra count of three isoforms of voltage-dependent anion-selective channels (VDACs) increased after 1 day of flooding. In addition, the size of the complexes formed by VDAC was higher in flood-stressed beetroots for 1 day (∼200 kDa) compared with non-stressed ones (∼100 kDa). Other proteins, such as chaperonin CPN60-2, also formed complexes with different masses in control and flood-stressed beetroots. Finally, possible interactions of VDAC with other proteins were found performing a cluster analysis. These results indicate that mitochondrial protein complexes formed by VDAC could be involved in the process of PCD in flood-stressed beetroots. Data are available via ProteomeXchange with identifier PXD027781.

Chitosan (CTS) Alleviates Heat-Induced Leaf Senescence in Creeping Bentgrass by Regulating Chlorophyll Metabolism, Antioxidant Defense, and the Heat Shock Pathway

Chitosan (CTS) is a deacetylated derivative of chitin that is involved in adaptive response to abiotic stresses. However, the regulatory role of CTS in heat tolerance is still not fully understood in plants, especially in grass species. The aim of this study was to investigate whether the CTS could reduce heat-induced senescence and damage to creeping bentgrass associated with alterations in antioxidant defense, chlorophyll (Chl) metabolism, and the heat shock pathway. Plants were pretreated exogenously with or without CTS (0.1 g L-1) before being exposed to normal (23/18 °C) or high-temperature (38/33 °C) conditions for 15 days. Heat stress induced detrimental effects, including declines in leaf relative water content and photochemical efficiency, but significantly increased reactive oxygen species (ROS) accumulation, membrane lipid peroxidation, and Chl loss in leaves. The exogenous application of CTS significantly alleviated heat-induced damage in creeping bentgrass leaves by ameliorating water balance, ROS scavenging, the maintenance of Chl metabolism, and photosynthesis. Compared to untreated plants under heat stress, CTS-treated creeping bentgrass exhibited a significantly higher transcription level of genes involved in Chl biosynthesis (AsPBGD and AsCHLH), as well as a lower expression level of Chl degradation-related gene (AsPPH) and senescence-associated genes (AsSAG12, AsSAG39, Asl20, and Ash36), thus reducing leaf senescence and enhancing photosynthetic performance under heat stress. In addition, the foliar application of CTS significantly improved antioxidant enzyme activities (SOD, CAT, POD, and APX), thereby effectively reducing heat-induced oxidative damage. Furthermore, heat tolerance regulated by the CTS in creeping bentgrass was also associated with the heat shock pathway, since AsHSFA-6a and AsHSP82 were significantly up-regulated by the CTS during heat stress. The potential mechanisms of CTS-regulated thermotolerance associated with other metabolic pathways still need to be further studied in grass species.

Tissue-specificity of ROS-induced K+ and Ca2+ fluxes in succulent stems of the perennial halophyte Sarcocornia quinqueflora in the context of salinity stress tolerance

The ability of halophytes to thrive under saline conditions implies efficient ROS detoxification and signalling. In this work, the causal relationship between key membrane transport processes involved in maintaining plant ionic homeostasis and oxidative stress tolerance was investigated in a succulent perennial halophyte Sarcocornia quinqueflora. The flux responses to oxidative stresses induced by either hydroxyl radicals (OH^•) or hydrogen peroxide (H₂O₂) were governed largely by (1) the type of ROS applied; (2) the tissue-specific origin and function (parenchymatic or chlorenchymatic); and (3) the tissue location in respect to the suberized endodermal barrier. The latter implied significant differences in responses between outer (water storage-WS; palisade tissue-Pa) and inner (internal photosynthetic layer-IP; stele parenchyma-SP) stem tissues. The ability of the cell to retain K⁺ under OH^• stress varied between different tissues and was ranked in the following descending order: WS>Pa>IP>SP. OH^• always led to Ca²⁺ influx in all stem tissues, while treatment with H₂O₂ induced tissue-specific Ca²⁺ "signatures". The inner/outer K⁺ ratio was the highest (~2.6) under the optimum NaCl dosage (200 mM) in comparison to non-saline (~0.4) and severe (800 mM; ~0.7) conditions, implying that a higher K⁺ concentration in the inner tissues is important for optimum growth. The overall results demonstrate a clear link between plant anatomical structure and ability of its tissues to maintain ionic homeostasis, via modulating their ROS sensitivity.

RtNAC100 involved in the regulation of ROS, Na+ accumulation and induced salt-related PCD through MeJA signal pathways in recretohalophyte Reaumuria trigyna

NAM, ATAF1/2, and CUC2 (NAC) proteins regulate plant responses to salt stress. However, the molecular mechanisms by which NAC proteins regulate salt-induced programmed cell death (PCD) are unclear. We identified 56 NAC genes, 35 of which had complete open reading frames with complete NAM domain, in the R. trigyna transcriptome. Salt stress and methyl jasmonate (MeJA) mediated PCD-induced leaf senescence in R. trigyna seedlings. Salt stress accelerated endogenous JA biosynthesis, upregulating RtNAC100 expression. This promoted salt-induced leaf senescence in R. trigyna by regulating RtRbohE and RtSAG12/20 and enhancing ROS accumulation. Transgenic assays showed that RtNAC100 overexpression aggravated salt-induced PCD in transgenic lines by promoting ROS and Na⁺ accumulation, ROS-Ca²⁺ hub activation, and PCD-related gene expression. Therefore, RtNAC100 induces PCD via the MeJA signaling pathway in R. trigyna under salt stress.

Cross-Talk between Hydrogen Peroxide and Nitric Oxide during Plant Development and Responses to Stress

Nitric oxide (NO) and hydrogen peroxide (H₂O₂) are gradually becoming established as critical regulators in plants under physiological and stressful conditions. Strong spatiotemporal correlations in their production and distribution have been identified in various plant biological processes. In this context, NO and H₂O₂ act synergistically or antagonistically as signals or stress promoters depending on their respective concentrations, engaging in processes such as the hypersensitive response, stomatal movement, and abiotic stress responses. Moreover, proteins identified as potential targets of NO-based modifications include a number of enzymes related to H₂O₂ metabolism, reinforcing their cross-talk. In this review, several processes of well-characterized functional interplay between H₂O₂ and NO are discussed with respect to the most recent reported evidence on hypersensitive response-induced programmed cell death, stomatal movement, and plant responses to adverse conditions and, where known, the molecular mechanisms and factors underpinning their cross-talk.

Physcomitrium patens Infection by Colletotrichum gloeosporioides: Understanding the Fungal-Bryophyte Interaction by Microscopy, Phenomics and RNA Sequencing

Anthracnose caused by the hemibiotroph fungus Colletotrichum gloeosporioides is a devastating plant disease with an extensive impact on plant productivity. The process of colonization and disease progression of C. gloeosporioides has been studied in a number of angiosperm crops. To better understand the evolution of the plant response to pathogens, the study of this complex interaction has been extended to bryophytes. The model moss Physcomitrium patens Hedw. B&S (former Physcomitrella patens) is sensitive to known bacterial and fungal phytopathogens, including C. gloeosporioides, which cause infection and cell death. P. patens responses to these microorganisms resemble that of the angiosperms. However, the molecular events during the interaction of P. patens and C. gloeosporioides have not been explored. In this work, we present a comprehensive approach using microscopy, phenomics and RNA-seq analysis to explore the defense response of P. patens to C. gloeosporioides. Microscopy analysis showed that appressoria are already formed at 24 h after inoculation (hai) and tissue colonization and cell death occur at 24 hai and is massive at 48 hai. Consequently, the phenomics analysis showed progressing browning of moss tissues and impaired photosynthesis from 24 to 48 hai. The transcriptomic analysis revealed that more than 1200 P. patens genes were differentially expressed in response to Colletotrichum infection. The analysis of differentially expressed gene function showed that the C. gloeosporioides infection led to a transcription reprogramming in P. patens that upregulated the genes related to pathogen recognition, secondary metabolism, cell wall reinforcement and regulation of gene expression. In accordance with the observed phenomics results, some photosynthesis and chloroplast-related genes were repressed, indicating that, under attack, P. patens changes its transcription from primary metabolism to defend itself from the pathogen.

Electrical Signals, Plant Tolerance to Actions of Stressors, and Programmed Cell Death: Is Interaction Possible?

In environmental conditions, plants are affected by abiotic and biotic stressors which can be heterogenous. This means that the systemic plant adaptive responses on their actions require long-distance stress signals including electrical signals (ESs). ESs are based on transient changes in the activities of ion channels and H⁺-ATP-ase in the plasma membrane. They influence numerous physiological processes, including gene expression, phytohormone synthesis, photosynthesis, respiration, phloem mass flow, ATP content, and many others. It is considered that these changes increase plant tolerance to the action of stressors; the effect can be related to stimulation of damages of specific molecular structures. In this review, we hypothesize that programmed cell death (PCD) in plant cells can be interconnected with ESs. There are the following points supporting this hypothesis. (i) Propagation of ESs can be related to ROS waves; these waves are a probable mechanism of PCD initiation. (ii) ESs induce the inactivation of photosynthetic dark reactions and activation of respiration. Both responses can also produce ROS and, probably, induce PCD. (iii) ESs stimulate the synthesis of stress phytohormones (e.g., jasmonic acid, salicylic acid, and ethylene) which are known to contribute to the induction of PCD. (iv) Generation of ESs accompanies K⁺ efflux from the cytoplasm that is also a mechanism of induction of PCD. Our review argues for the possibility of PCD induction by electrical signals and shows some directions of future investigations in the field.

RNA-Seq analysis reveals potential regulators of programmed cell death and leaf remodelling in lace plant (Aponogeton madagascariensis)

BACKGROUND

The lace plant (Aponogeton madagascariensis) is an aquatic monocot that develops leaves with uniquely formed perforations through the use of a developmentally regulated process called programmed cell death (PCD). The process of perforation formation in lace plant leaves is subdivided into several developmental stages: pre-perforation, window, perforation formation, perforation expansion and mature. The first three emerging "imperforate leaves" do not form perforations, while all subsequent leaves form perforations via developmentally regulated PCD. PCD is active in cells called "PCD cells" that do not retain the antioxidant anthocyanin in spaces called areoles framed by the leaf veins of window stage leaves. Cells near the veins called "NPCD cells" retain a red pigmentation from anthocyanin and do not undergo PCD. While the cellular changes that occur during PCD are well studied, the gene expression patterns underlying these changes and driving PCD during leaf morphogenesis are mostly unknown. We sought to characterize differentially expressed genes (DEGs) that mediate lace plant leaf remodelling and PCD. This was achieved performing gene expression analysis using transcriptomics and comparing DEGs among different stages of leaf development, and between NPCD and PCD cells isolated by laser capture microdissection.

RESULTS

Transcriptomes were sequenced from imperforate, pre-perforation, window, and mature leaf stages, as well as PCD and NPCD cells isolated from window stage leaves. Differential expression analysis of the data revealed distinct gene expression profiles: pre-perforation and window stage leaves were characterized by higher expression of genes involved in anthocyanin biosynthesis, plant proteases, expansins, and autophagy-related genes. Mature and imperforate leaves upregulated genes associated with chlorophyll development, photosynthesis, and negative regulators of PCD. PCD cells were found to have a higher expression of genes involved with ethylene biosynthesis, brassinosteroid biosynthesis, and hydrolase activity whereas NPCD cells possessed higher expression of auxin transport, auxin signalling, aspartyl proteases, cysteine protease, Bag5, and anthocyanin biosynthesis enzymes.

CONCLUSIONS

RNA sequencing was used to generate a de novo transcriptome for A. madagascariensis leaves and revealed numerous DEGs potentially involved in PCD and leaf remodelling. The data generated from this investigation will be useful for future experiments on lace plant leaf development and PCD in planta.

Stress effects on the reactive oxygen species-dependent regulation of plant growth and development

Plant growth is mediated by cell proliferation and expansion. Both processes are controlled by a network of endogenous factors such as phytohormones, reactive oxygen species (ROS), sugars, and other signals, which influence gene expression and post-translational regulation of proteins. Stress resilience requires rapid and appropriate responses in plant growth and development as well as defence. Regulation of ROS accumulation in different cellular compartments influences growth responses to abiotic and biotic stresses. While ROS are essential for growth, they are also implicated in the stress-induced cessation of growth and, in some cases, programmed cell death. It is widely accepted that redox post-translational modifications of key proteins determine the growth changes and cell fate responses to stress, but the molecular pathways and factors involved remain poorly characterized. Here we discuss ROS as a signalling molecule, the mechanisms of ROS-dependent regulation that influence protein-protein interactions, protein function, and turnover, together with the relocation of key proteins to different intracellular compartments in a manner that can alter cell fate. Understanding how the redox interactome responds to stress-induced increases in ROS may provide a road map to tailoring the dynamic ROS interactions that determine growth and cell fate in order to enhance stress resilience.

Senescence-Associated Glycine max (Gm)NAC Genes: Integration of Natural and Stress-Induced Leaf Senescence

Leaf senescence is a genetically regulated developmental process that can be triggered by a variety of internal and external signals, including hormones and environmental stimuli. Among the senescence-associated genes controlling leaf senescence, the transcriptional factors (TFs) comprise a functional class that is highly active at the onset and during the progression of leaf senescence. The plant-specific NAC (NAM, ATAF, and CUC) TFs are essential for controlling leaf senescence. Several members of Arabidopsis AtNAC-SAGs are well characterized as players in elucidated regulatory networks. However, only a few soybean members of this class display well-known functions; knowledge about their regulatory circuits is still rudimentary. Here, we describe the expression profile of soybean GmNAC-SAGs upregulated by natural senescence and their functional correlation with putative AtNAC-SAGs orthologs. The mechanisms and the regulatory gene networks underlying GmNAC081- and GmNAC030-positive regulation in leaf senescence are discussed. Furthermore, new insights into the role of GmNAC065 as a negative senescence regulator are presented, demonstrating extraordinary functional conservation with the Arabidopsis counterpart. Finally, we describe a regulatory circuit which integrates a stress-induced cell death program with developmental leaf senescence via the NRP-NAC-VPE signaling module.

Insights into heat response mechanisms in Clematis species: physiological analysis, expression profiles and function verification

Our results provide insights into heat response mechanisms among Clematis species. Overexpressing CvHSFA2 enhanced the heat resistance of yeast and silencing NbHSFA2 reduced the heat resistance of tobacco. Clematis species are commonly grown in western and Japanese gardens. Heat stress can inhibit many physiological processes mediating plant growth and development. The mechanism regulating responses to heat has been well characterized in Arabidopsis thaliana and some crops, but not in horticultural plants, including Clematis species. In this study, we found that Clematis alpina 'Stolwijk Gold' was heat-sensitive whereas Clematis vitalba and Clematis viticella 'Polish Spirit' were heat-tolerant based on the physiological analyses in heat stress. Transcriptomic profiling identified a set of heat tolerance-related genes (HTGs). Consistent with the observed phenotype in heat stress, 41.43% of the differentially expressed HTGs between heat treatment and control were down-regulated in heat-sensitive cultivar Stolwijk Gold, but only 9.80% and 20.79% of the differentially expressed HTGs in heat resistant C. vitalba and Polish Spirit, respectively. Co-expression network, protein-protein interaction network and phylogenetic analysis revealed that the genes encoding heat shock transcription factors (HSFs) and heat shock proteins (HSPs) may played an essential role in Clematis resistance to heat stress. Two clades of heat-induced CvHSFs were further identified by phylogenetic tree, motif analysis and qRT-PCR. Ultimately, we proposed that overexpressing CvHSFA2-2 could endow yeast with high temperature resistance and silencing its homologous gene NbHSFA2 reduced the heat resistance of tobacco. This study provides first insights into the diversity of the heat response mechanisms among Clematis species.

Transcriptional Regulation and Signaling of Developmental Programmed Cell Death in Plants

Developmental programmed cell death (dPCD) has multiple functions in plant growth and development, and is of great value for industrial production. Among them, wood formed by xylem dPCD is one of the most widely used natural materials. Therefore, it is crucial to explore the molecular mechanism of plant dPCD. The dPCD process is tightly regulated by genetic networks and is involved in the transduction of signaling molecules. Several key regulators have been identified in diverse organisms and individual PCD events. However, complex molecular networks controlling plant dPCD remain highly elusive, and the original triggers of this process are still unknown. This review summarizes the recent progress on the transcriptional regulation and signaling of dPCD during vegetative and reproductive development. It is hoped that this review will provide an overall view of the molecular regulation of dPCD in different developmental processes in plants and identify specific mechanisms for regulating these dPCD events. In addition, the application of plants in industrial production can be improved by manipulating dPCD in specific processes, such as xylogenesis.

Role of Jasmonates, Calcium, and Glutathione in Plants to Combat Abiotic Stresses Through Precise Signaling Cascade

Plant growth regulators have an important role in various developmental processes during the life cycle of plants. They are involved in abiotic stress responses and tolerance. They have very well-developed capabilities to sense the changes in their external milieu and initiate an appropriate signaling cascade that leads to the activation of plant defense mechanisms. The plant defense system activation causes build-up of plant defense hormones like jasmonic acid (JA) and antioxidant systems like glutathione (GSH). Moreover, calcium (Ca2+) transients are also seen during abiotic stress conditions depicting the role of Ca2+ in alleviating abiotic stress as well. Therefore, these growth regulators tend to control plant growth under varying abiotic stresses by regulating its oxidative defense and detoxification system. This review highlights the role of Jasmonates, Calcium, and glutathione in abiotic stress tolerance and activation of possible novel interlinked signaling cascade between them. Further, phyto-hormone crosstalk with jasmonates, calcium and glutathione under abiotic stress conditions followed by brief insights on omics approaches is also elucidated.

Protein Carbonylation: Emerging Roles in Plant Redox Biology and Future Prospects

Plants are sessile in nature and they perceive and react to environmental stresses such as abiotic and biotic factors. These induce a change in the cellular homeostasis of reactive oxygen species (ROS). ROS are known to react with cellular components, including DNA, lipids, and proteins, and to interfere with hormone signaling via several post-translational modifications (PTMs). Protein carbonylation (PC) is a non-enzymatic and irreversible PTM induced by ROS. The non-enzymatic feature of the carbonylation reaction has slowed the efforts to identify functions regulated by PC in plants. Yet, in prokaryotic and animal cells, studies have shown the relevance of protein carbonylation as a signal transduction mechanism in physiological processes including hydrogen peroxide sensing, cell proliferation and survival, ferroptosis, and antioxidant response. In this review, we provide a detailed update on the most recent findings pertaining to the role of PC and its implications in various physiological processes in plants. By leveraging the progress made in bacteria and animals, we highlight the main challenges in studying the impacts of carbonylation on protein functions in vivo and the knowledge gap in plants. Inspired by the success stories in animal sciences, we then suggest a few approaches that could be undertaken to overcome these challenges in plant research. Overall, this review describes the state of protein carbonylation research in plants and proposes new research avenues on the link between protein carbonylation and plant redox biology.

Climate Change and Salinity Effects on Crops and Chemical Communication Between Plants and Plant Growth-Promoting Microorganisms Under Stress

During the last two decades the world has experienced an abrupt change in climate. Both natural and artificial factors are climate change drivers, although the effect of natural factors are lesser than the anthropogenic drivers. These factors have changed the pattern of precipitation resulting in a rise in sea levels, changes in evapotranspiration, occurrence of flood overwintering of pathogens, increased resistance of pests and parasites, and reduced productivity of plants. Although excess CO2 promotes growth of C3 plants, high temperatures reduce the yield of important agricultural crops due to high evapotranspiration. These two factors have an impact on soil salinization and agriculture production, leading to the issue of water and food security. Farmers have adopted different strategies to cope with agriculture production in saline and saline sodic soil. Recently the inoculation of halotolerant plant growth promoting rhizobacteria (PGPR) in saline fields is an environmentally friendly and sustainable approach to overcome salinity and promote crop growth and yield in saline and saline sodic soil. These halotolerant bacteria synthesize certain metabolites which help crops in adopting a saline condition and promote their growth without any negative effects. There is a complex interkingdom signaling between host and microbes for mutual interaction, which is also influenced by environmental factors. For mutual survival, nature induces a strong positive relationship between host and microbes in the rhizosphere. Commercialization of such PGPR in the form of biofertilizers, biostimulants, and biopower are needed to build climate resilience in agriculture. The production of phytohormones, particularly auxins, have been demonstrated by PGPR, even the pathogenic bacteria and fungi which also modulate the endogenous level of auxins in plants, subsequently enhancing plant resistance to various stresses. The present review focuses on plant-microbe communication and elaborates on their role in plant tolerance under changing climatic conditions.

Redox responses of Arabidopsis thaliana to the green peach aphid, Myzus persicae

The green peach aphid (Myzus persicae) is a phloem-feeding insect that causes economic damage on a wide array of crops. Using a luminol-based assay, a superoxide-responsive reporter gene (Zat12::luciferase), and a probe specific to hydrogen peroxide (HyPer), we demonstrated that this aphid induces accumulation of reactive oxygen species (ROS) in Arabidopsis thaliana. Similar to the apoplastic oxidative burst induced by pathogens, this response to aphids was rapid and transient, with two peaks occurring within 1 and 4 hr after infestation. Aphid infestation also induced an oxidative response in the cytosol and peroxisomes, as measured using a redox-sensitive variant of green fluorescent protein (roGFP2). This intracellular response began within minutes of infestation but persisted 20 hr or more after inoculation, and the response of the peroxisomes appeared stronger than the response in the cytosol. Our results suggest that the oxidative response to aphids involves both apoplastic and intracellular sources of ROS, including ROS generation in the peroxisomes, and these different sources of ROS may potentially differ in their impacts on host suitability for aphids.

Contrasting roles of GmNAC065 and GmNAC085 in natural senescence, plant development, multiple stresses and cell death responses

NACs are plant-specific transcription factors involved in controlling plant development, stress responses, and senescence. As senescence-associated genes (SAGs), NACs integrate age- and stress-dependent pathways that converge to programmed cell death (PCD). In Arabidopsis, NAC-SAGs belong to well-characterized regulatory networks, poorly understood in soybean. Here, we interrogated the soybean genome and provided a comprehensive analysis of senescence-associated Glycine max (Gm) NACs. To functionally examine GmNAC-SAGs, we selected GmNAC065, a putative ortholog of Arabidopsis ANAC083/VNI2 SAG, and the cell death-promoting GmNAC085, an ANAC072 SAG putative ortholog, for analyses. Expression analysis of GmNAC065 and GmNAC085 in soybean demonstrated (i) these cell death-promoting GmNACs display contrasting expression changes during age- and stress-induced senescence; (ii) they are co-expressed with functionally different gene sets involved in stress and PCD, and (iii) are differentially induced by PCD inducers. Furthermore, we demonstrated GmNAC065 expression delays senescence in Arabidopsis, a phenotype associated with enhanced oxidative performance under multiple stresses, higher chlorophyll, carotenoid and sugar contents, and lower stress-induced PCD compared to wild-type. In contrast, GmNAC085 accelerated stress-induced senescence, causing enhanced chlorophyll loss, ROS accumulation and cell death, decreased antioxidative system expression and activity. Accordingly, GmNAC065 and GmNAC085 targeted functionally contrasting sets of downstream AtSAGs, further indicating that GmNAC85 and GmNAC065 regulators function inversely in developmental and environmental PCD.

Evaluation of Coal Fly Ash for Modulating the Plant Growth, Yield, and Antioxidant Properties of Daucus carota (L.): A Sustainable Approach to Coal Waste Recycling

In search of a safe, cost-effective, and sustainable method for the disposal and management of coal fly ash (CFA), seeds of carrot were sown in earthen pots containing growth substrate consisting of field soil amended with different concentrations of weathered CFA at w/w % ratios. Results suggested that CFA added many essential plant nutrients to the growth substrate and improved some important soil characteristics such as pH, electric conductivity, porosity, and water holding capacity. The growth substrate containing 15% of CFA proved most suitable for growing carrots. Plants grown in 15% CFA amended soil had significantly (p ≤ 0.05) enhanced plant growth, yield, photosynthetic pigments, nitrate reductase activity, protein, and carbohydrate contents as compared to the control. The activity of antioxidant enzymes such as SOD and CAT was significantly upregulated in 15% CFA amended soil as compared to the control. The biomineralization of various elements in the edible part of the carrot was well under the limits and no toxic metal was detected in the edible part of the carrot. The present study, therefore, attempts to delineate the application of weathered CFA as a soil amendment in agroecosystems to improve the productivity of lands through a cost-effective and an ecofriendly manner.

Calcium Signaling in Plant Programmed Cell Death

Programmed cell death (PCD) is a process intended for the maintenance of cellular homeostasis by eliminating old, damaged, or unwanted cells. In plants, PCD takes place during developmental processes and in response to biotic and abiotic stresses. In contrast to the field of animal studies, PCD is not well understood in plants. Calcium (Ca²⁺) is a universal cell signaling entity and regulates numerous physiological activities across all the kingdoms of life. The cytosolic increase in Ca²⁺ is a prerequisite for the induction of PCD in plants. Although over the past years, we have witnessed significant progress in understanding the role of Ca²⁺ in the regulation of PCD, it is still unclear how the upstream stress perception leads to the Ca²⁺ elevation and how the signal is further propagated to result in the onset of PCD. In this review article, we discuss recent advancements in the field, and compare the role of Ca²⁺ signaling in PCD in biotic and abiotic stresses. Moreover, we discuss the upstream and downstream components of Ca²⁺ signaling and its crosstalk with other signaling pathways in PCD. The review is expected to provide new insights into the role of Ca²⁺ signaling in PCD and to identify gaps for future research efforts.