Abscisic acid, cold and salt stimulate conserved metabolic regulation in the moss Physcomitrella patens

Identification and characterization of DICER-LIKE genes and their roles in Marchantia polymorpha development and salt stress response

DICER-LIKE (DCL) proteins play a central role in plant small RNA (sRNA) biogenesis. The genome of the early land plant Marchantia polymorpha encodes four DCL proteins: MpDCL1a, MpDCL1b, MpDCL3, and MpDCL4. While MpDCL1a, MpDCL3 and MpDCL4 show high similarities to their orthologs in Physcomitrium patens and Arabidopsis thaliana, MpDCL1b shares only a limited homology with PpDCL1b, but it is very similar, in terms of functional domains, to orthologs in other moss and fern species. We generated Mpdclge mutant lines for all MpDCL genes with the CRISPR/Cas9 system and conducted phenotypic analyses under control, salt stress, and phytohormone treatments to uncover specific MpDCL functions. The mutants displayed severe developmental aberrations, altered responses to salt and phytohormones, and disturbed sexual organ development. By combining mRNA and sRNA analyses, we demonstrate that MpDCLs and their associated sRNAs play pivotal roles in regulating development, abiotic stress tolerance and phytohormone response in M. polymorpha. We identified MpDCL1a in microRNA biogenesis, MpDCL4 in trans-acting small interfering RNA generation, and MpDCL3 in the regulation of pathogen-related genes. Notably, salt sensitivity in M. polymorpha is dependent on MpDCL1b and Mpdcl1bge mutants display enhanced tolerance and reduced miRNA expression in response to salt stress. We propose that M. polymorpha employs specific mechanisms for regulating MpDCL1b associated miRNAs under high salinity conditions, potentially shared with other species harboring MpDCL1b homologs.

Physiological and metabolic responses of Sophora tonkinensis to cadmium stress

Sophora tonkinensis is a significant medicinal plant indigenous to China and Vietnam. In China, S. tonkinensis is mainly grown naturally on limestone mountains or is cultivated artificially in arable land. Heavy metal contamination in agricultural soil, particularly cadmium (Cd), poses serious threats to soil health, as well as the growth and productivity of S. tonkinensis. However, information regarding the physiological and metabolic mechanism of S. tonkinensis under Cd toxicity conditions remains limited. In this study, a hydroponic experiment was conducted to investigate the physiological and metabolic responses of S. tonkinensis to varying concentrations of Cd (0, 20, 40, 60, 80 μM), designated as T0, T1, T2, T3, and T4 respectively. The results indicated that the Cd stress significantly impaired the growth and physiological activity of S. tonkinensis. Specifically, reductions were observed in plant height (15.3% to 37.1%) along with shoot fresh weight (9.6% to 36.3%), shoot dry weight (8.2% to 34.1%), root fresh weight (6.7% to 38.2%) and root dry weight (5.1% to 51.3%). This impairment was attributed to a higher uptake and accumulation of Cd in the roots. The decrease in growth was closely linked to the increased production of reactive oxygen species (ROS), which led to cellular damage under Cd toxicity; however, increased antioxidant enzyme activities improved the stress tolerance of S. tonkinensis's stress to Cd toxicity. Non-targeted metabolomic analyses identified 380 differential metabolites (DMs) in the roots of S. tonkinensis subjected to varying level of Cd stress, including amino acids, organic acids, fatty acids, ketones, and others compounds. Further KEGG pathway enrichment analysis revealed that several pathways, such as ABC transporters, isoflavonoid biosynthesis, and pyrimidine metabolism were involved in the response to Cd. Notably, the isoflavonoid biosynthesis pathway was significantly enriched in both T0 vs. T2 and T0 vs. the higher level (80 μM) of Cd stress, highlighting its significance in the plant responses to Cd stress. In conclusion, the identification of key pathways and metabolites is crucial for understanding Cd stress tolerance in S. tonkinensis.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-024-01522-w.

Abscisic Acid Regulates the Occurrence and Recovery of the Striped Leaf Phenotype in Response to Lacking Light at the Base of Sheath in Rice by Modulating Carbohydrate Metabolism

Rice B03S mutants with intermittent leaf discoloration were developed from the photoperiod- and thermosensitive genic male sterile (PTGMS) rice line Efeng 1S. After these plants were deeply transplanted, the new leaves manifested typical stripe patterns. In this study, deep and shallow transplantation of B03S was carried out, and aluminum shading was performed directly on the leaf sheath. It was determined that the reason for the appearance of the striped leaf trait was that the base of leaf sheath lacked light, at which time the sheath transformed from the source organ to the sink organ in rice. To elucidate the related metabolic changes in glycometabolism and abscisic acid (ABA) biosynthesis and transcriptional regulation in the leaf sheath, ultra-performance liquid chromatography/tandem mass spectrometry (UPLC-MS/MS) combined with transcriptome and real-time quantitative PCR (qPCR) validation were used for analysis after deep and shallow transplantation. The result indicates that the leaf sheath may need to compete with the new leaves for sucrose produced by the photosynthesis of old leaves in response to lacking light at the base of sheath. Moreover, the ABA content increases in the leaf sheath when the gene expression of ABA2 and AAO1 is upregulated at the same time, enhancing the plant's resistance to the adverse condition of shading at the leaf sheath. Furthermore, exogenous spraying of B03S with ABA solution was carried out to help recovery under shading stress. The result indicates that the synthesis of endogenous ABA in the leaf sheath is reduced by spraying ABA. At the same time, ABA regulates sucrose metabolism by inhibiting the expression of the SUS gene. This allows for more sucrose synthesized by the old leaves to be transported to the new leaves, resulting an obvious recovery effect of the strip leaf character due to the re-balance of sugar supply and demand in B03S. These findings improve the understanding of the physiological function and metabolic mechanism of the rice leaf sheath, provide a theoretical basis for uneven leaf coloration in nature, and provide theoretical guidance for rice production via seedling transplantation or direct seeding.

Integrated multi-omic approach reveals the effect of a Graminaceae-derived biostimulant and its lighter fraction on salt-stressed lettuce plants

Plant biostimulants are widely applied in agriculture for their ability to improve plant fitness. In the present work, the impact of Graminaceae-derived protein hydrolysate (P) and its lighter molecular fraction F3 (< 1 kDa) on lettuce plants, subjected to either no salt or high salt conditions, was investigated through the combination of metabolomics and transcriptomics. The results showed that both treatments significantly modulated the transcriptome and metabolome of plants under salinity stress, highlighting an induction of the hormonal response. Nevertheless, P and F3 also displayed several peculiarities. F3 specifically modulated the response to ethylene and MAPK signaling pathway, whereas P treatment induced a down-accumulation of secondary metabolites, albeit genes controlling the biosynthesis of osmoprotectants and antioxidants were up-regulated. Moreover, according with the auxin response modulation, P promoted cell wall biogenesis and plasticity in salt-stressed plants. Notably, our data also outlined an epigenetic control of gene expression induced by P treatment. Contrarily, experimental data are just partially in agreement when not stressed plants, treated with P or F3, were considered. Indeed, the reduced accumulation of secondary metabolites and the analyses of hormone pathways modulation would suggest a preferential allocation of resources towards growth, that is not coherent with the down-regulation of the photosynthetic machinery, the CO2 assimilation rate and leaves biomass. In conclusion, our data demonstrate that, although they might activate different mechanisms, both the P and F3 can result in similar benefits, as far as the accumulation of protective osmolytes and the enhanced tolerance to oxidative stress are concerned. Notably, the F3 fraction exhibits slightly greater growth promotion effects under high salt conditions. Most importantly, this research further corroborates that biostimulants' mode of action is dependent on plants' physiological status and their composition, underscoring the importance of investigating the bioactivity of the different molecular components to design tailored applications for the agricultural practice.

BcABF1 Plays a Role in the Feedback Regulation of Abscisic Acid Signaling via the Direct Activation of BcPYL4 Expression in Pakchoi

Abscisic acid-responsive element-binding factor 1 (ABF1), a key transcription factor in the ABA signal transduction process, regulates the expression of downstream ABA-responsive genes and is involved in modulating plant responses to abiotic stress and developmental processes. However, there is currently limited research on the feedback regulation of ABF1 in ABA signaling. This study delves into the function of BcABF1 in Pakchoi. We observed a marked increase in BcABF1 expression in leaves upon ABA induction. The overexpression of BcABF1 not only spurred Arabidopsis growth but also augmented the levels of endogenous IAA. Furthermore, BcABF1 overexpression in Arabidopsis significantly decreased leaf water loss and enhanced the expression of genes associated with drought tolerance in the ABA pathway. Intriguingly, we found that BcABF1 can directly activate BcPYL4 expression, a critical receptor in the ABA pathway. Similar to BcABF1, the overexpression of BcPYL4 in Arabidopsis also reduces leaf water loss and promotes the expression of drought and other ABA-responsive genes. Finally, our findings suggested a novel feedback regulation mechanism within the ABA signaling pathway, wherein BcABF1 positively amplifies the ABA signal by directly binding to and activating the BcPYL4 promoter.

Approach strategies and application of metabolomics to biotechnology in plants

Metabolomics refers to the technology for the comprehensive analysis of metabolites and low-molecular-weight compounds in a biological system, such as cells or tissues. Metabolites play an important role in biological phenomena through their direct involvement in the regulation of physiological mechanisms, such as maintaining cell homeostasis or signal transmission through protein-protein interactions. The current review aims provide a framework for how the integrated analysis of metabolites, their functional actions and inherent biological information can be used to understand biological phenomena related to the regulation of metabolites and how this information can be applied to safety assessments of crops created using biotechnology. Advancement in technology and analytical instrumentation have led new ways to examine the convergence between biology and chemistry, which has yielded a deeper understanding of complex biological phenomena. Metabolomics can be utilized and applied to safety assessments of biotechnology products through a systematic approach using metabolite-level data processing algorithms, statistical techniques, and database development. The integration of metabolomics data with sequencing data is a key step towards improving additional phenotypical evidence to elucidate the degree of environmental affects for variants found in genome associated with metabolic processes. Moreover, information analysis technology such as big data, machine learning, and IT investment must be introduced to establish a system for data extraction, selection, and metabolomic data analysis for the interpretation of biological implications of biotechnology innovations. This review outlines the integrity of metabolomics assessments in determining the consequences of genetic engineering and biotechnology in plants.

Validation of an LC-MS/MS Method for the Determination of Abscisic Acid Concentration in a Real-World Setting

One of the most relevant aspects in evaluating the impact of natural bioactive compounds on human health is the assessment of their bioavailability. In this regard, abscisic acid (ABA) has attracted particular interest as a plant-derived molecule mainly involved in the regulation of plant physiology. Remarkably, ABA was also found in mammals as an endogenous hormone involved in the upstream control of glucose homeostasis, as evidenced by its increase after glucose load. The present work focused on the development and validation of a method for the determination of ABA in biological samples through liquid-liquid extraction (LLE), followed by liquid mass spectrometry (LC-MS) of the extract. To test method suitability, this optimized and validated method was applied to a pilot study on eight healthy volunteers' serum levels to evaluate ABA concentration after consumption of a standardized test meal (STM) and the administration of an ABA-rich nutraceutical product. The results obtained could meet the demands of clinical laboratories to determine the response to a glucose-containing meal in terms of ABA concentration. Interestingly, the detection of this endogenous hormone in such a real-world setting could represent a useful tool to investigate the occurrence of impaired ABA release in dysglycemic individuals and to monitor its eventual improvement in response to chronic nutraceutical supplementation.

The interaction of ABA and ROS in plant growth and stress resistances

The plant hormone ABA (abscisic acid) plays an extremely important role in plant growth and adaptive stress, including but are not limited to seed germination, stomatal closure, pathogen infection, drought and cold stresses. Reactive oxygen species (ROS) are response molecules widely produced by plant cells under biotic and abiotic stress conditions. The production of apoplast ROS is induced and regulated by ABA, and participates in the ABA signaling pathway and its regulated plant immune system. In this review, we summarize ABA and ROS in apoplast ROS production, plant response to biotic and abiotic stresses, plant growth regulation, ABA signal transduction, and the regulatory relationship between ABA and other plant hormones. In addition, we also discuss the effects of protein post-translational modifications on ABA and ROS related factors.

Molecular response and evolution of plant anion transport systems to abiotic stress

We propose that anion channels are essential players for green plants to respond and adapt to the abiotic stresses associated changing climate via reviewing the literature and analyzing the molecular evolution, comparative genetic analysis, and bioinformatics analysis of the key anion channel gene families. Climate change-induced abiotic stresses including heatwave, elevated CO₂, drought, and flooding, had a major impact on plant growth in the last few decades. This scenario could lead to the exposure of plants to various stresses. Anion channels are confirmed as the key factors in plant stress responses, which exist in the green lineage plants. Numerous studies on anion channels have shed light on their protein structure, ion selectivity and permeability, gating characteristics, and regulatory mechanisms, but a great quantity of questions remain poorly understand. Here, we review function of plant anion channels in cell signaling to improve plant response to environmental stresses, focusing on climate change related abiotic stresses. We investigate the molecular response and evolution of plant slow anion channel, aluminum-activated malate transporter, chloride channel, voltage-dependent anion channel, and mechanosensitive-like anion channel in green plant. Furthermore, comparative genetic and bioinformatic analysis reveal the conservation of these anion channel gene families. We also discuss the tissue and stress specific expression, molecular regulation, and signaling transduction of those anion channels. We propose that anion channels are essential players for green plants to adapt in a diverse environment, calling for more fundamental and practical studies on those anion channels towards sustainable food production and ecosystem health in the future.

Biocompatible Abscisic Acid-Sensing Supramolecular Hybridization Probe for Spatiotemporal Fluorescence Imaging in Plant Tissues

Achieving detection of the phytohormone abscisic acid (ABA) is of critical importance for understanding plant growth and development. We report a hybrid supramolecular fluorescent probe that uses bovine serum albumin (BSA) as a host. Aggregation-induced emission of fluorescent chromophores (AIEgens) enables luminescence in the presence of BSA. ABA and its aptamer act as a switch to trigger this fluorescent system, the strategy that exhibits high sensitivity to abscisic acid with a detection limit of 0.098 nM. The probe test strip also enables visualization of ABA content from plants by colorimetric observation with the naked eye. In particular, the high biocompatibility and small molecular size of the prepared fluorescent probe allow for effective monitoring of ABA in plant tissues by fluorescence imaging. This strategy provides a new perspective to achieve the detection of endogenous and exogenous ABA in plants and has important implications for plant biology research.

Advances in Plant Metabolomics and Its Applications in Stress and Single-Cell Biology

In the past two decades, the post-genomic era envisaged high-throughput technologies, resulting in more species with available genome sequences. In-depth multi-omics approaches have evolved to integrate cellular processes at various levels into a systems biology knowledge base. Metabolomics plays a crucial role in molecular networking to bridge the gaps between genotypes and phenotypes. However, the greater complexity of metabolites with diverse chemical and physical properties has limited the advances in plant metabolomics. For several years, applications of liquid/gas chromatography (LC/GC)-mass spectrometry (MS) and nuclear magnetic resonance (NMR) have been constantly developed. Recently, ion mobility spectrometry (IMS)-MS has shown utility in resolving isomeric and isobaric metabolites. Both MS and NMR combined metabolomics significantly increased the identification and quantification of metabolites in an untargeted and targeted manner. Thus, hyphenated metabolomics tools will narrow the gap between the number of metabolite features and the identified metabolites. Metabolites change in response to environmental conditions, including biotic and abiotic stress factors. The spatial distribution of metabolites across different organs, tissues, cells and cellular compartments is a trending research area in metabolomics. Herein, we review recent technological advancements in metabolomics and their applications in understanding plant stress biology and different levels of spatial organization. In addition, we discuss the opportunities and challenges in multiple stress interactions, multi-omics, and single-cell metabolomics.

Metabolome of Ceratodon purpureus (Hedw.) Brid., a cosmopolitan moss: the influence of seasonality

Ceratodon purpureus showed changes in disaccharides, flavonoids, and carotenoids throughout annual seasons. These changes indicate harsher environmental conditions during the dry period, directing metabolic precursors to enhance the antioxidant system. Bryophytes are a group of land plants comprising mosses (Bryophyta), liverworts (Marchantyophyta), and hornworts (Antocerotophyta). This study uses the molecular networking approach to investigate the influence of seasonality (dry and rainy seasons) on the metabolome and redox status of the moss Ceratodon purpureus (Hedw.) Brid., from Campos do Jordão, Brazil. Samples of C. purpureus were submitted to three extraction methods: 80% methanol producing the soluble fraction (intracellular compounds), followed by debris hydrolysis using sodium hydroxide producing the insoluble fraction (cell wall conjugated compounds), both analyzed by HPLC-MS; and extraction using pre-cooled methanol, separated into polar and non-polar fractions, being both analyzed by GC-MS. All fractions were processed using the Global Natural Product Social Molecular Network (GNPS). The redox status was assessed by the analysis of four enzyme activities combined with the analysis of the contents of ascorbate, glutathione, carotenoids, reactive oxygen species (ROS), and malondialdehyde acid (MDA). During the dry period, there was an increase of most biflavonoids, as well as phospholipids, disaccharides, long-chain fatty acids, carotenoids, antioxidant enzymes, ROS, and MDA. Results indicate that C. purpureus is under harsher environmental conditions during the dry period, mainly due to low temperature and less water availability (low rainfall).

Trehalose Ameliorates Diabetic Cardiomyopathy: Role of the PK2/PKR Pathway

Ample clinical case reports suggest a high incidence of cardiomyopathy in diabetes mellitus (DM). Recent evidence supports an essential role of trehalose (TLS) in cardiomyocyte survival signaling. Our previous study found that prokineticin2 (PK2) was involved in the process of diabetic cardiomyopathy (DCM). The present study examined the protective effects and mechanisms of TLS on DM-induced cardiomyocyte injury in mice and H9c2 cardiomyocytes. C57BL/6J mice were intraperitoneally injected with 50 mg·kg⁻¹·d⁻¹ streptozotocin for five consecutive days to establish an experimental diabetic model and then administered TLS (1 mg·g⁻¹·d⁻¹, i.p.) for two days every 4 weeks and given 2% TLS in drinking water for 24 weeks. Echocardiography, myocardial structure, apoptosis, pyroptosis, autophagy, and the PK2/PKR pathway were assessed. Cardiomyocytes exposed to high glucose (HG) were treated with TLS in the absence or presence of the PK2 antagonist PKRA7, and proteins involved in apoptosis, autophagy, and pyroptosis and the PK2/PKR pathways were evaluated using Western blot analysis. Diabetic mice demonstrated metabolic disorder, abnormal myocardial zymograms, and aberrant myocardial systolic and diastolic function, which were accompanied by pronounced apoptosis, pyroptosis, and dampened autophagy. TLS treatment relieved these effects. PK2 and receptor expressions were downregulated in diabetic mice, and TLS nullified this effect. PKRA7 eliminated the impact of TLS on cardiomyocytes. This evidence suggests that TLS rescues DM-induced myocardial function, pyroptosis, and apoptosis, likely via the PK2/PKR pathway.

Inhibition of the JAZ1 gene causes activation of camalexin biosynthesis in Arabidopsis callus cultures

Indole alkaloid camalexin has potential medicinal properties such as suppressing the viability of leukemic but not normal cells. Camalexin is not produced in plants and an external factor is required to activate its biosynthesis. In this work, we stimulated camalexin biosynthesis in Arabidopsis calli by blocking one of repressors of the jasmonate pathway, the jasmonate ZIM-domain protein 1 (JAZ1) by using amiRNA targeting JAZ1 gene transcripts. Inhibition of the JAZ1 gene led to an increase in camalexin content from trace amounts in control culture to 9 µg/g DW in the jaz1 line without affecting growth. In addition, JAZ1 silencing enhanced tolerance to cold stress with simultaneous increasing camalexin content up to 30 µg/g DW. Real-time quantitative PCR determination of marker gene expression showed that effects caused by the JAZ1 silencing might be realized through crosslinking JA, ROS, and abscisic acid signaling pathways. Thus, targeting the distal components of signaling pathways can be suggested as a tool for bioengineering of secondary metabolism, along with standard techniques for targeting biosynthetic genes or genes encoding transcription factors.

PpGRAS12 acts as a positive regulator of meristem formation in Physcomitrium patens

This study focused on the key regulatory function of Physcomitrium patens GRAS12 gene underlying an increasing plant complexity, an important step in plant terrestrialization and the evolutionary history of life. The miR171-GRAS module has been identified as a key player in meristem maintenance in angiosperms. PpGRAS12 is a member of the GRAS family and a validated target for miR171 in Physcomitrium (Physcomitrella) patens. Here we show a regulatory function of miR171 at the gametophytic vegetative growth stage and targeted deletion of the PpGRAS12 gene adversely affects sporophyte production since fewer sporophytes were produced in ΔPpGRAS12 knockout lines compared to wild type moss. Furthermore, highly specific and distinct growth arrests were observed in inducible PpGRAS12 overexpression lines at the protonema stage. Prominent phenotypic aberrations including the formation of multiple apical meristems at the gametophytic vegetative stage in response to elevated PpGRAS12 transcript levels were discovered via scanning electron microscopy. The production of multiple buds in the PpGRAS12 overexpression lines similar to ΔPpCLV1a/1b disruption mutants is accompanied by an upregulation of PpCLE and downregulation of PpCLV1, PpAPB, PpNOG1, PpDEK1, PpRPK2 suggesting that PpGRAS12 acts upstream of these genes and negatively regulates the proposed pathway to specify simplex meristem formation. As CLV signaling pathway components are not present in the chlorophytic or charophytic algae and arose with the earliest land plants, we identified a key regulatory function of PpGRAS12 underlying an increasing plant complexity, an important step in plant terrestrialization and the evolutionary history of life.

The Effect of Low Temperature Stress on the Leaves and MicroRNA Expression of Potato Seedlings

In recent years, with the wanton destruction of the ecological environment by humans and the frequent occurrence of extreme bad weather, many places that should have been warm and blooming in spring have instead experienced the phenomenon of the “April blizzard,” which has seriously affected China's crops, especially spring potato production in most areas. Potato cultivars, especially potato seedlings, are sensitive to frost, and low temperature frost has become one of the most important abiotic stresses affecting potato production. Potato cold tolerance is regulated by a complex gene network. Although some low temperature resistant microRNAs have been identified, little is known about the role of miRNAs in response to low temperature stress in potato. Therefore, the objective of this study is to clarify the influence of low temperature stress on the miRNA expression of potato by comparing the expression differences of miRNA in potato which was treated with different low temperatures. For the study, 307 known miRNAs belonging to 73 small RNA families and 211 novel miRNAs were obtained. When the temperature decreased, the number of both known and novel miRNA decreased, and the minimum temperature was −2°C. Most of the miRNAs respond to low temperature, drought, and disease stress; some conserved miRNAs were first found to respond to low temperature stress in potato, such as stu-miR530, stu-miR156d, and stu-miR167b. The Gene Ontology, Kyoto Encyclopedia of Genes, and Genomes pathway enrichment analysis of 442 different expression miRNAs target genes indicated that there existed diversified low temperature responsive pathways, but Abscisic Acid was found likely to play a central coordinating role in response to low temperature stress in many metabolism pathways. Quantitative real-time PCR assays indicated that the related targets were negatively regulated by the tested different expression miRNAs during low temperature stress. The results indicated that miRNAs may play an important coordination role in response to low temperature stress in many metabolic pathways by regulating abscisic acid and gibberellin, which provided insight into the roles of miRNAs during low temperature stress and would be helpful for alleviating low temperature stress and promoting low temperature resistant breeding in potatoes.

Physcomitrium patens Mutants in Auxin Conjugating GH3 Proteins Show Salt Stress Tolerance but Auxin Homeostasis Is Not Involved in Regulation of Oxidative Stress Factors

Salt stress is among the most challenging abiotic stress situations that a plant can experience. High salt levels do not only occur in areas with obvious salty water, but also during drought periods where salt accumulates in the soil. The moss Physcomitrium patens became a model for studying abiotic stress in non-vascular plants. Here, we show that high salt concentrations can be tolerated in vitro, and that auxin homeostasis is connected to the performance of P. patens under these stress conditions. The auxin levels can be regulated by conjugating IAA to amino acids by two members of the family of GH3 protein auxin amino acid-synthetases that are present in P. patens. Double GH3 gene knock-out mutants were more tolerant to high salt concentrations. Furthermore, free IAA levels were differentially altered during the time points investigated. Since, among the mutant lines, an increase in IAA on at least one NaCl concentration tested was observed, we treated wild type (WT) plants concomitantly with NaCl and IAA. This experiment showed that the salt tolerance to 100 mM NaCl together with 1 and 10 µM IAA was enhanced during the earlier time points. This is an additional indication that the high IAA levels in the double GH3-KO lines could be responsible for survival in high salt conditions. While the high salt concentrations induced several selected stress metabolites including phenols, flavonoids, and enzymes such as peroxidase and superoxide dismutase, the GH3-KO genotype did not generally participate in this upregulation. While we showed that the GH3 double KO mutants were more tolerant of high (250 mM) NaCl concentrations, the altered auxin homeostasis was not directly involved in the upregulation of stress metabolites.

Differential Response to Single and Combined Salt and Heat Stresses: Impact on Accumulation of Proteins and Metabolites in Dead Pericarps of Brassica juncea

Dead organs enclosing embryos, such as seed coats and pericarps, are emerging as important maternally-derived components of the dispersal unit that affect seed performance and fate. In the face of climate change and increased incidents of heatwaves, we sought to investigate the effect of salinity (S), short episodes of high temperature (HS), and combination of S + HS (SHS), at the reproductive phase, on the properties of dead pericarps of Brassica juncea. Proteome and metabolome analyses revealed multiple proteins and metabolites stored in dead pericarps whose levels and composition were altered under single and combined stress conditions. The protein profile of SHS showed a higher correlation with salt than with HS indicating the dominant effect of salt over heat stress. On the other hand, the analysis of metabolites showed that the profile of SHS has better correlation with HS than with salt. The integration of metabolic and proteomic data showed that changes in TCA cycle intermediates and certain amino acids (e.g., proline) under salt treatments (S and SHS) are highly correlated with changes in proteins involved in their biosynthetic pathways. Thus, accumulation of proteins and metabolites in dead pericarps is differently affected by single and combination of salt and heat stresses. Salinity appears to dominate plant response to combined stresses at the protein level, while heat appears to be the major factor affecting metabolite accumulation in dead pericarps.

Metabolic changes associated with differential salt tolerance in sorghum genotypes

Accumulation of specific metabolites, mainly γ-aminobutyric acid, polyamines, and proline, was essential to homeostasis regulation and differential salt tolerance in sorghum genotypes. Salinity is severe abiotic stress that limits plant growth and development in arid and semi-arid regions. Survival to abiotic stresses depends on metabolic and sometimes even morphological adjustments. We measured the growth parameters, water relations, the content of ions (Na⁺, K⁺, Cl^-), compatible solutes [some free amino acids (FAAs) including γ-aminobutyric acid (GABA) and proline and soluble carbohydrates) and polyamines (PAs), the activity of PAs metabolism enzymes, and metabolomic profile in plants after 14 days of salt stress treatment. These analyses were to evaluate the influence of metabolomic responses of sorghum genotypes exhibiting sensitivity (CSF18) or tolerance (CSF20) to salinity on plant growth. The salinity promoted growth reductions and induced increases in Na⁺ and Cl^- content and decreases in K⁺ content. The water status and osmotic potential (Ψ_o) were reduced by salt stress, but to minimize damage, especially in the CSF20, the osmolytes and PAs contributed to the osmotic adjustment. The results showed that salinity induced an increase in putrescine (Put) in the sensitive genotype. However, it raised spermidine (Spd), spermine (Spm), and cadaverine (Cad) in the tolerant genotype. In addition, the regulation of polyamine oxidase can be related to Spm and GABA biosynthesis. Differential metabolic changes to salt tolerance include metabolites associated with tricarboxylic acid (TCA) cycle intermediates and the metabolisms of sugars, FAAs, and PAs.

A Chloroplast COR413 Protein From Physcomitrella patens Is Required for Growth Regulation Under High Light and ABA Responses

COR413 genes belong to a poorly characterized group of plant-specific cold-regulated genes initially identified as part of the transcriptional activation machinery of plants during cold acclimation. They encode multispanning transmembrane proteins predicted to target the plasma membrane or the chloroplast inner membrane. Despite being ubiquitous throughout the plant kingdom, little is known about their biological function. In this study, we used reverse genetics to investigate the relevance of a predicted chloroplast localized COR413 protein (PpCOR413im) from the moss Physcomitrella patens in developmental and abiotic stress responses. Expression of PpCOR413im was strongly induced by abscisic acid (ABA) and by various environmental stimuli, including low temperature, hyperosmosis, salinity and high light. In vivo subcellular localization of PpCOR413im-GFP fusion protein revealed that this protein is localized in chloroplasts, confirming the in silico predictions. Loss-of-function mutants of PpCOR413im exhibited growth and developmental alterations such as growth retardation, reduced caulonema formation and hypersensitivity to ABA. Mutants also displayed altered photochemistry under various abiotic stresses, including dehydration and low temperature, and exhibited a dramatic growth inhibition upon exposure to high light. Disruption of PpCOR413im also caused altered chloroplast ultrastructure, increased ROS accumulation, and enhanced starch and sucrose levels under high light or after ABA treatment. In addition, loss of PpCOR413im affected both nuclear and chloroplast gene expression in response to ABA and high light, suggesting a role for this gene downstream of ABA in the regulation of growth and environmental stress responses. Developmental alterations exhibited by PpCOR413im knockout mutants had remarkable similarities to those exhibited by hxk1, a mutant lacking a major chloroplastic hexokinase, an enzyme involved in energy homeostasis. Based on these findings, we propose that PpCOR413im is involved in coordinating energy metabolism with ABA-mediated growth and developmental responses.

Quantitative Imaging Reveals Distinct Contributions of SnRK2 and ABI3 in Plasmodesmatal Permeability in Physcomitrella patens

Cell-to-cell communication is tightly regulated in response to environmental stimuli in plants. We previously used a photoconvertible fluorescent protein Dendra2 as a model reporter to study this process. This experiment revealed that macromolecular trafficking between protonemal cells in Physcomitrella patens is suppressed in response to abscisic acid (ABA). However, it remains unknown which ABA signaling components contribute to this suppression and how. Here, we show that ABA signaling components SUCROSE NON-FERMENTING 1-RELATED PROTEIN KINASE 2 (PpSnRK2) and ABA INSENSITIVE 3 (PpABI3) play roles as an essential and promotive factor, respectively, in regulating ABA-induced suppression of Dendra2 diffusion between cells (ASD). Our quantitative imaging analysis revealed that disruption of PpSnRK2 resulted in defective ASD onset itself, whereas disruption of PpABI3 caused an 81-min delay in the initiation of ASD. Live-cell imaging of callose deposition using aniline blue staining showed that, despite this onset delay, callose deposition on cross walls remained constant in the PpABI3 disruptant, suggesting that PpABI3 facilitates ASD in a callose-independent manner. Given that ABA is an important phytohormone to cope with abiotic stresses, we further explored cellular physiological responses. We found that the acquisition of salt stress tolerance is promoted by PpABI3 in a quantitative manner similar to ASD. Our results suggest that PpABI3-mediated ABA signaling may effectively coordinate cell-to-cell communication during the acquisition of salt stress tolerance. This study will accelerate the quantitative study for ABA signaling mechanism and function in response to various abiotic stresses.

From reproduction to production, stomata are the master regulators

The best predictor of leaf level photosynthetic rate is the porosity of the leaf surface, as determined by the number and aperture of stomata on the leaf. This remarkable correlation between stomatal porosity (or diffusive conductance to water vapour g_s ) and CO₂ assimilation rate (A) applies to all major lineages of vascular plants (Figure 1) and is sufficiently predictable that it provides the basis for the model most widely used to predict water and CO₂ fluxes from leaves and canopies. Yet the Ball-Berry formulation is only a phenomenological approximation that captures the emergent character of stomatal behaviour. Progressing to a more mechanistic prediction of plant gas exchange is challenging because of the diversity of biological components regulating stomatal action. These processes are the product of more than 400 million years of co-evolution between stomatal, vascular and photosynthetic tissues. Both molecular and structural components link the abiotic world of the whole plant with the turgor pressure of the epidermis and guard cells, which ultimately determine stomatal pore size and porosity to water and CO₂ exchange (New Phytol., 168, 2005, 275). In this review we seek to simplify stomatal behaviour by using an evolutionary perspective to understand the principal selective pressures involved in stomatal evolution, thus identifying the primary regulators of stomatal aperture. We start by considering the adaptive process that has locked together the regulation of water and carbon fluxes in vascular plants, finally examining specific evidence for evolution in the proteins responsible for regulating guard cell turgor.

Functional Characterization of Class I Trehalose Biosynthesis Genes in Physcomitrella patens

The function of trehalose metabolism in plants during growth and development has been extensively studied, mostly in the eudicot Arabidopsis thaliana. So far, however, not much is known about trehalose metabolism in the moss Physcomitrella patens. Here, we show that in P. patens, two active trehalose-6-phosphate synthase enzymes exist, PpTPS1 and PpTPS2. Expression of both enzymes in Saccharomyces cerevisiae can complement the glucose-growth defect of the yeast tps1∆ mutant. Truncation of N-terminal extension in PpTPS1 and PpTPS2 resulted in higher TPS activity and high trehalose levels, upon expression in yeast. Physcomitrella knockout plants were generated and analyzed in various conditions to functionally characterize these proteins. tps1∆ and tps2∆ knockouts displayed a lower amount of caulonema filaments and were significantly reduced in size of gametophores as compared to the wild type. These phenotypes were more pronounced in the tps1∆ tps2∆ mutant. Caulonema formation is induced by factors such as high energy and auxins. Only high amounts of supplied energy were able to induce caulonema filaments in the tps1∆ tps2∆ mutant. Furthermore, this mutant was less sensitive to auxins as NAA-induced caulonema development was arrested in the tps1∆ tps2∆ mutant. In contrast, formation of caulonema filaments is repressed by cytokinins. This effect was more severe in the tps1∆ and tps1∆ tps2∆ mutants. Our results demonstrate that PpTPS1 and PpTPS2 are essential for sensing and signaling sugars and plant hormones to monitor the balance between caulonema and chloronema development.

Physcomitrella as a model system for plant cell biology and organelle-organelle communication

In multicellular eukaryotic cells, metabolism and growth are sustained by the cooperative functioning of organelles in combination with cell-to-cell communication at the organism level. In land plants, multiple strategies have evolved to adapt to life outside water. As basal land plant, the moss Physcomitrella patens is used for comparative genomics, allowing to study lineage-specific features, as well as to track the evolution of fundamental parameters of plant cell organisation and physiology. P. patens is a versatile model for cell biology research, especially to investigate adaptive growth, stress biology as well as organelle dynamics and interactions. Recent advances include the use of genetically encoded biosensors for in vivo imaging of physiological parameters.

ABA-Induced Vegetative Diaspore Formation in Physcomitrella patens

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