Plant Signaling Research Articles

Over 25 years of decrypting PIN-mediated plant development.

Identification of PIN exporters for auxin, the major coordinative signal in plants, some 25 years ago, signifies a landmark in our understanding of plant-specific mechanisms underlying development and adaptation. Auxin is directionally transported throughout the plant body; a unique feature already envisioned by Darwin and solidified by PINs' discovery and characterization. The PIN-based auxin distribution network with its complex regulations of PIN expression, localization and activity turned out to underlie a remarkable multitude of developmental processes and represents means to integrate endogenous and environmental signals. Given the recent anniversary, we here summarize past and current developments in this exciting field.

Effect of Higher Ethylene Levels Emitted by Shade-Avoider Plants on Neighboring Seedlings

Plants of several species, including crops, change their volatilome when exposed to a low ratio of red to far-red light (low R/FR) that informs about the presence of nearby plants (i.e., proximity shade). In particular, the volatile hormone ethylene was shown to be produced at higher levels in response to the low R/FR signal in shade-avoider plants. Here, we show that the shade-tolerant species Cardamine hirsuta produces more ethylene than shade avoiders such as Arabidopsis thaliana (a close relative of C. hirsuta) and tomato (Solanum lycopersicum) under white light (W). However, exposure to low R/FR (specifically to FR-supplemented W, referred to as W+FR or simulated shade) resulted in only a slight increase in ethylene emission in C. hirsuta compared to shade avoiders. Stimulation of ethylene production by growing plants in media supplemented with 1-aminocyclopropane-1-carboxylate (ACC) resulted in reduced hypocotyl growth under W+FR in both A. thaliana and C. hirsuta. ACC-dependent ethylene production also repressed hypocotyl elongation under low W and in the dark in C. hirsuta. By contrast, in A. thaliana, ACC supplementation inhibited hypocotyl elongation in the dark but stimulated it under W. Most interestingly, elongation of dark-grown A. thaliana seedlings was also repressed by exposure to the volatiles released by ACC-grown A. thaliana or tomato plants. This observation suggests that increased ethylene levels in the headspace can indeed impact the development of nearby plants. Although the amount of ethylene released by ACC-grown plants to their headspace was much higher than that released by exposure to low R/FR, our results support a contribution of this volatile hormone on the communication of proximity shade conditions to neighboring plants.

Analysis of abiotic and biotic stress-induced Ca2+ transients in the crop species Solanum tuberosum.

Secondary messengers, such as calcium ions (Ca2+), are integral parts of a system that transduces environmental stimuli into appropriate cellular responses. Different abiotic and biotic stresses as well as developmental processes trigger temporal increases in cytosolic free Ca2+ levels by an influx from external and internal stores. Stimulus-specificity is obtained by a certain amplitude, duration, oscillation and localisation of the response. Most knowledge on stress-specific Ca2+ transient, called calcium signatures, has been gained in the model plant Arabidopsis thaliana, while reports about stress-related Ca2+ signalling in crop plants are comparatively scarce. In this study, we introduced the Ca2+ biosensor apoaequorin into potato (Solanum tuberosum, Lcv.Désirée). We observed dose-dependent calcium signatures in response to a series of stress stimuli, including H2O2, NaCl, mannitol and pathogen-associated molecular patterns (PAMPs) with stimuli-specific kinetics. Direct comparison with Arabidopsis revealed differences in the kinetics and amplitude of Ca2+ transients between both species, implying species-specific sensitivity for different stress conditions. The potato line generated in this work provides a useful tool for further investigations on stress-induced signalling pathways, which could contribute to the generation of novel, stress-tolerant potato varieties.

Strigolactones Regulate Secondary Metabolism and Nitrogen/Phosphate Signaling in Tea Plants via Transcriptional Reprogramming and Hormonal Interactions.

Strigolactones (SLs) are known to regulate plant architecture formation, nitrogen (N) and phosphorus (P) responses, and secondary metabolism, but their effects in tea plants remain unclear. We demonstrated that the application of a bioactive SL analogue GR24 either to tea roots or leaves initially stimulated but later inhibited catechins, theanine, and caffeine biosynthesis. GR24 treatment also promoted the accumulation of flavonols and insoluble proanthocyanidins in a time- and dose-dependent manner. GR24 influenced flavonoid and theanine biosynthesis genes, such as up-regulating CsTT2c, CsMYB12, and CsbZIP1, modulating N-responsive and assimilation genes (CsNRT1,1, CsGSI/TS1, CsHRS1, CsPHR1, CsNLA1, and CsLBD37/38/39), and repressing N/P transport and signaling genes (CsPHO2, CsPHT1s, CsNRT2,2, CsHHO1, and CsWRKY38). GR24-induced changes in secondary metabolites were also observed in the leaves of tea plants. GR24-regulated CsLBD37a interacted with CsTT8a and CsTT2c, repressing catechins biosynthesis by interrupting MBW complex formation. GR24 regulated caffeine biosynthesis and regulator genes CsS40 and CsNAC7 and may thereby suppress caffeine production. GR24 altered the transcriptomic profiles of multiple hormone biosynthesis and signaling genes that potentially regulate tea characteristic metabolism and N/P signaling. This study provides new insights into SL-induced transcriptional reprogramming that leads to changes in N/P nutrition, secondary metabolism, and hormone signaling in tea plants.

Activation of a helper NLR by plant and bacterial TIR immune signaling.

Plant intracellular nucleotide-binding leucine-rich repeat (NLR) receptors with an N-terminal Toll/interleukin-1 receptor (TIR) domain sense pathogen effectors to initiate immune signaling. TIR domains across different kingdoms possess NADase activities and can produce phosphoribosyl adenosine monophosphate/diphosphate (pRib-AMP/ADP) or cyclic ADPR (cADPR) isomers. Lipase-like proteins, EDS1 and PAD4, transduce immune signals from sensor TIR-NLRs to a helper NLR called ADR1, which executes immune function. We report the structure and function of Arabidopsis EDS1-PAD4-ADR1 (EPA) heterotrimer in complex with pRib-AMP/ADP activated by plant or bacterial TIR signaling. 2'cADPR can be hydrolyzed into pRib-AMP and thus activates EPA signaling. Bacterial TIR domains producing 2'cADPR also activate EPA function. Our findings suggest that 2'cADPR may be the storage form of the unstable signaling molecule pRib-AMP.

Increasing stomatal CO2 conductance as a potential mechanism of photosynthetic activation by electrical signals in terrestrial plants

Increasing stomatal CO2 conductance as a potential mechanism of photosynthetic activation by electrical signals in terrestrial plants

Mechanistic study of SCOOPs recognition by MIK2-BAK1 complex reveals the role of N-glycans in plant ligand-receptor-coreceptor complex formation.

Ligand-induced receptor and co-receptor heterodimerization is a common mechanism in receptor kinase (RK) signalling activation. SERINE-RICH ENDOGENOUS PEPTIDEs (SCOOPs) mediate the complex formation of Arabidopsis RK MIK2 and co-receptor BAK1, triggering immune responses. Through structural, biochemical and genetic analyses, we demonstrate that SCOOPs use their SxS motif and adjacent residues to bind MIK2 and the carboxy-terminal GGR residues to link MIK2 to BAK1. While N-glycosylation of plant RKs is typically associated with protein maturation, plasma membrane targeting and conformation maintenance, a surprising revelation emerges from our crystal structural analysis of MIK2-SCOOP-BAK1 complexes. Specific N-glycans on MIK2 directly interact with BAK1 upon SCOOP sensing. The absence of N-glycosylation at the specific site in MIK2 neither affects its subcellular localization and protein accumulation in plant cells nor alters its structural conformation, but markedly reduces its affinity for BAK1, abolishing SCOOP-triggered immune responses. This N-glycan-mediated receptor and co-receptor heterodimerization occurs in both Arabidopsis and Brassica napus. Our findings elucidate the molecular basis of SCOOP perception by the MIK2-BAK1 immune complex and underscore the crucial role of N-glycans in plant receptor-coreceptor interactions and signalling activation, shaping immune responses.

The endosomal-vacuolar transport system acts as a docking platform for the Pmk1 MAP kinase signaling pathway in Magnaporthe oryzae.

In Magnaporthe oryzae, the Pmk1 MAP kinase signaling pathway regulates appressorium formation, plant penetration, effector secretion, and invasive growth. While the Mst11-Mst7-Pmk1 cascade was characterized two decades ago, knowledge of its signaling in the intracellular network remains limited. In this study, we demonstrate that the endosomal surface scaffolds Pmk1 MAPK signaling and Msb2 activates Ras2 on endosomes in M. oryzae. Protein colocalization demonstrated that Msb2, Ras2, Cap1, Mst50, Mst11, Mst7, and Pmk1 attach to late endosomal membranes. Damage to the endosome-vacuole transport system influences Pmk1 phosphorylation. When Msb2 senses a plant signal, it internalizes and activates Ras2 on endosome membrane surfaces, transmitting the signal to Pmk1 via Mst11 and Mst7. Signal-sensing and delivery proteins are ubiquitinated and sorted for degradation in late endosomes and vacuoles, terminating signaling. Plant penetration and lowered intracellular turgor are required for the transition from late endosomes to vacuoles in appressoria. Our findings uncover an effective mechanism that scaffolds and controls Pmk1 MAPK signaling through endosomal-vacuolar transport, offering new knowledge for the cytological and molecular mechanisms by which the Pmk1 MAPK pathway modulates development and pathogenicity in M. oryzae.

Arabidopsis RALF4 Rapidly Halts Pollen Tube Growth by Increasing ROS and Decreasing Calcium Cytoplasmic Tip Levels

In recent years, the rapid alkalinization factor (RALF) family of cysteine-rich peptides has been reported to be crucial for several plant signaling mechanisms, including cell growth, plant immunity and fertilization. RALF4 and RALF19 (RALF4/19) pollen peptides redundantly regulate the pollen tube integrity and growth through binding to their receptors ANXUR1/2 (ANX1/2) and Buddha’s Paper Seal 1 and 2 (BUPS1/2), members of the Catharanthus roseus RLK1-like (CrRLK1L) family, and, thus, are essential for plant fertilization. However, the signaling mechanisms at the cellular level that follow these binding events remain unclear. In this study, we show that the addition of synthetic peptide RALF4 rapidly halts pollen tube growth along with the excessive deposition of plasma membrane and cell wall material at the tip. The ratiometric imaging of genetically encoded ROS and Ca2+ sensors-expressing pollen tubes shows that RALF4 treatment modulates the cytoplasmic levels of reactive oxygen species (ROS) and calcium (Ca2+) in opposite ways at the tip. Thus, we propose that pollen RALF4/19 peptides bind ANX1/2 and BUPS1/2 to regulate ROS and calcium homeostasis to ensure proper cell wall integrity and control of pollen tube growth.

Sequence diversity in the monooxygenases involved in oxime production in plant defense and signaling: a conservative revision in the nomenclature of the highly complex CYP79 family.

Cytochrome P450 monooxygenases of the CYP79 family catalyze conversion of specific amino acids into oximes feeding into a variety of metabolic plant pathways. Here we present an extensive phylogenetic tree of the CYP79 family built on carefully curated sequences collected across the entire plant kingdom. Based on a monophyletic origin of the P450s, a set of evolutionarily distinct branches was identified. Founded on the functionally characterized CYP79 sequences, sequence features of the individual substrate recognition sites (SRSs) were analyzed. Co-evolving amino acid residues were identified using co-evolutionary sequence analysis. SRS4 possesses a specific sequence pattern when tyrosine is a substrate. Except for the CYP79Cs and CYP79Fs, substrate preferences toward specific amino acids could not be assigned to specific subfamilies. The highly diversified CYP79 tree, reflecting recurrent independent evolution of CYP79s, may relate to the different roles of oximes in different plant species. The sequence differences across individual CYP79 subfamilies may facilitate the in vivo orchestration of channeled metabolic pathways based on altered surface charge domains of the CYP79 protein. Alternatively, they may serve to optimize dynamic interactions with oxime metabolizing enzymes to enable optimal ecological interactions. The outlined detailed curation of the CYP79 sequences used for building the phylogenetic tree made it appropriate to make a conservative phylogenetic tree-based revision of the naming of the sequences within this highly complex cytochrome P450 family. The same approach may be used in other complex P450 subfamilies. The detailed phylogeny of the CYP79 family will enable further exploration of the evolution of function in these enzymes.

Unveiling the hidden world: How arbuscular mycorrhizal fungi and its regulated core fungi modify the composition and metabolism of soybean rhizosphere microbiome

BackgroundThe symbiosis between arbuscular mycorrhizal fungi (AMF) and plants often stimulates plant growth, increases agricultural yield, reduces costs, thereby providing significant economic benefits. AMF can also benefit plants through affecting the rhizosphere microbial community, but the underlying mechanisms remain unclear. Using Rhizophagus intraradices as a model AMF species, we assessed how AMF influences the bacterial composition and functional diversity through 16 S rRNA gene sequencing and non-targeted metabolomics analysis in the rhizosphere of aluminum-sensitive soybean that were inoculated with pathogenic fungus Nigrospora oryzae and phosphorus-solubilizing fungus Talaromyces verruculosus in an acidic soil.ResultsThe inoculation of R. intraradices, N. oryzae and T. verruculosus didn’t have a significant influence on the levels of soil C, N, and P, or various plant characteristics such as seed weight, crude fat and protein content. However, their inoculation affected the structure, function and nutrient dynamics of the resident bacterial community. The co-inoculation of T. verruculosus and R. intraradices increased the relative abundance of Pseudomonas psychrotolerans, which was capable of N-fixing and was related to cry-for-help theory (plants signal for beneficial microbes when under stress), within the rhizosphere. R. intraradices increased the expression of metabolic pathways associated with the synthesis of unsaturated fatty acids, which was known to enhance plant resistance under adverse environmental conditions. The inoculation of N. oryzae stimulated the stress response inside the soil environment by enriching the polyene macrolide antifungal antibiotic-producing bacterial genus Streptomyces in the root endosphere and upregulating two antibacterial activity metabolic pathways associated with steroid biosynthesis pathways in the rhizosphere. Although inoculation of pathogenic fungus N. oryzae enriched Bradyrhizobium and increased soil urease activity, it had no significant effects on biomass and N content of soybean. Lastly, the host niches exhibited differences in the composition of the bacterial community, with most N-fixing bacteria accumulating in the endosphere and Rhizobium vallis only detected in the endosphere.ConclusionsOur findings demonstrate that intricate interactions between AMF, associated core fungi, and the soybean root-associated ecological niches co-mediate the regulation of soybean growth, the dynamics of rhizosphere soil nutrients, and the composition, function, and metabolisms of the root-associated microbiome in an acidic soil.

Mechanistic effects of lipid binding pockets within soluble signaling proteins: Lessons from acyl-CoA-binding and START-domain-containing proteins.

While lipids serve as important energy reserves, metabolites, and cellular constituents in all forms of life, these macromolecules also function as unique carriers of information in plant communication given their diverse chemical structures. The signal transduction process involves a sophisticated interplay between messengers, receptors, signal transducers, and downstream effectors. Over the years, an array of plant signaling proteins have been identified for their crucial roles in perceiving lipid signals. However, the mechanistic effects of lipid binding on protein functions remain largely elusive. Recent literature has presented numerous fascinating models that illustrate the significance of protein-lipid interactions in mediating signaling responses. This review focuses on the category of lipophilic signaling proteins that encompass a hydrophobic binding pocket located outside of cellular membranes and provides an update on the lessons learned from two of these structures, namely the acyl-CoA-binding and START domains. It begins with a brief overview of the latest advances in understanding the functions of the two protein families in plant communication. The second part highlights five functional mechanisms of lipid ligands in concert with their target signaling proteins.

G-Quadruplex Structures as Epigenetic Regulatory Elements in Priming of Defense Genes upon Short-Term Trichoderma atroviride Inoculation in Maize.

Symbiosis establishment between Trichoderma atroviride and plant roots triggers the priming of defense responses, among other effects. Currently, there is no clear evidence regarding the molecular mechanisms that allow the plant to remain alert to future stimulus, either by pathogen attack or any other abiotic stress. Epigenetic modifications have emerged as a strategy to explain the increased defense response of plants in a priming state conferred by Trichoderma. Recently, various non-canonical structures of nucleic acids, especially G-quadruplex structures (G-quadruplexes or G4s), have been identified as potential targets during the establishment or maintenance of plant signals. In the present study, we developed a screening test for the identification of putative G4-forming sequences (PQSs) in previously identified Z. mays priming genes. Bioinformatic analysis revealed the presence of PQSs in the promoter region of five essential genes playing a critical role in priming in maize. Biophysical and spectroscopy studies showed the formation of G4s by these PQSs in vitro, and ChIP assays demonstrate their formation in vivo. Therefore, G4 formation could play a role as an epigenetic regulatory mechanism involved in the long-lasting primed state in maize plants.

Genome-Wide Identification and Expression Analysis of the MADS-Box Gene Family in Cassava (Manihot esculenta)

The MADS-box gene family constitutes a vital group of transcription factors that play significant roles in regulating plant growth, development, and signal transduction processes. However, research on the MADS-box genes in cassava (Manihot esculenta) has been relatively limited. To gain deeper insights into the functions of the MADS-box genes in cassava development, in this study, we undertook a comprehensive genome-wide identification of the MADS-box gene family in cassava. We identified a total of 86 MADS-box genes with complete domains in the cassava genome, designated as MeMADS01 to MeMADS86. Through bioinformatic analyses, we investigated the basic physicochemical properties, conserved motifs, chromosomal locations, and phylogenetic relationships of the cassava MADS-box genes. The MADS-box gene family of cassava exhibited conservation, as well as species-specific characteristics, with intron loss being a predominant mode of evolution for the MADS-box genes. Expression pattern variations in the MeMADS genes across different tissues offer insights into their potential functions. Time-ordered gene co-expression network (TO-GCN), transcriptome data, and RT-qPCR analysis suggested the responsiveness of the MADS-box genes to drought stress. Meanwhile, MeMADS12 might be involved in regulating flowering under drought conditions via an ABA (abscisic acid)-dependent pathway. These findings provide valuable resources for a deeper understanding of the biological roles of the MADS-box genes in cassava.

TaCDPK1-5A positively regulates drought response through modulating osmotic stress responsive-associated processes in wheat (Triticum aestivum).

Wheat TaCDPK1-5A plays critical roles in mediating drought tolerance through regulating osmotic stress-associated physiological processes. Calcium (Ca2+) acts as an essential second messenger in plant signaling pathways and impacts plant abiotic stress responses. This study reported the function of TaCDPK1-5A, a calcium-dependent protein kinase (CDPK) gene in T. aestivum, in mediating drought tolerance. TaCDPK1-5A sensitively responded to drought and exogenous abscisic acid (ABA) signaling, displaying induced transcripts in plants under drought and ABA treatments. Yeast two-hybrid and co-immunoprecipitation assays revealed that TaCDPK1-5A interacts with the mitogen-activated protein kinase TaMAPK4-7D whereas the latter with ABF transcription factor TaABF1-3A, suggesting that TaCDPK1-5A constitutes a signaling module with above partners to transduce signals initiated by drought/ABA stressors. Overexpression of TaCDPK1-5A, TaMAPK4-7D and TaABF1-3A enhanced plant drought adaptation by modulating the osmotic stress-related physiological indices, including increased osmolyte contents, enlarged root morphology, and promoted stomata closure. Yeast one-hybrid assays indicated the binding ability of TaABF1-3A with promoters of TaP5CS1-1B, TaPIN3-5A, and TaSLAC1-3-2A, the genes encoding P5CS enzyme, PIN-FORMED protein, and slow anion channel, respectively. ChIP-PCR and transcriptional activation assays confirmed that TaABF1-3A regulates these genes at transcriptional level. Moreover, transgene analysis indicated that these stress-responsive genes positively regulated proline biosynthesis (TaP5CS1-1B), root morphology (TaPIN3-5A), and stomata closing (TaSLAC1-3-2A) upon drought signaling. Positive correlations were observed between yield and the transcripts of TaCDPK1-5A signaling partners in wheat cultivars under drought condition, with haplotype TaCDPK1-5A-Hap1 contributing to improved drought tolerance. Our study concluded that TaCDPK1-5A positively regulates drought adaptation and is a valuable target for molecular breeding the drought-tolerant cultivars in T. aestivum.

Hormonal signaling regulates photosynthetic function of alfalfa (Medicago sativa L.) under NaHCO3 stress

The physiological and molecular mechanisms underlying salt-alkali tolerance in Medicago sativa are of significant importance for the development of animal husbandry on salt-alkali lands and the restoration of vegetation in such areas. This study utilized salt-alkali tolerance Medicago sativa 'Zhaodong' (ZD) and salt-alkali sensitive variety M. sativa 'Zhongmu No.1′ (ZM) as materials. Physiological analyses, transcriptomic sequencing, and hormone-targeted metabolomics techniques were employed to investigate the differential responses of the two alfalfa varieties to NaHCO3 stress in terms of morphology, photosynthetic functionality, and oxidative damage indicators. Additionally, weighted gene co-expression network analysis (WGCNA) was utilized to elucidate key mechanisms underlying salt-alkali tolerance in alfalfa. The results indicate that NaHCO3 stress leads to photosynthetic inhibition and oxidative damage in alfalfa leaves. Under NaHCO3 stress, PSI in alfalfa leaves exhibits higher stability compared to PSII. The salt-alkali tolerance alfalfa variety ZD demonstrates stronger tolerance compared to the salt-alkali sensitive variety ZM. Furthermore, differentially expressed genes (DEGs) between the two varieties under NaHCO3 stress are primarily enriched in KEGG pathways such as chlorophyll synthesis, photosynthesis, carbon fixation, and plant hormone synthesis and signaling. Weighted gene co-expression network analysis (WGCNA) was conducted based on physiological and transcriptomic data. Most differentially expressed genes (DEGs) in the top two modules with the highest correlation to physiological indicators such as photosynthesis are enriched in hormone synthesis and signal transduction pathways. Additionally, key transcription factors involved in hormone signal transduction were identified within these modules, such as MYC2 and ABI5, which regulate jasmonic acid (JA) and abscisic acid (ABA) signaling, respectively. These findings suggest that plant hormone signaling may play a critical role in regulating salt-alkali tolerance in alfalfa. Further analysis was conducted on plant hormone levels and gene expression involved in biosynthesis and signal transduction processes. The results indicate that NaHCO3 stress leads to significant accumulation of ABA and JA content in alfalfa leaves. The biosynthesis and signal transduction pathways of ABA and JA are activated under NaHCO3 stress. Additionally, the salt-alkali tolerance alfalfa variety ZD exhibits a more sensitive response to ABA and JA signals compared to ZM. Salicylic acid (SA) shows a positive response to NaHCO3 stress only in the ZD variety, which may be one of the key reasons for its stronger salt-alkali tolerance. Under NaHCO3 stress, overall growth-promoting hormones (IAA, GA, CK) are downregulated in ZD but upregulated in ZM, indicating that the salt-alkali tolerance alfalfa variety ZD mainly regulates the balance between growth and resistance by modulating the ratio of growth-promoting and stress-related hormones in response to NaHCO3 stress. This study reveals that hormone signaling plays a key role in regulating the photosynthetic function of alfalfa in response to salt-alkali stress, which provides theoretical basis and clues for the molecular breeding of alfalfa for salt-alkali tolerance.

Elucidating the downstream pathways triggered by H2S signaling in Arabidopsis thaliana under drought stress via transcriptome analysis

ABSTRACT Hydrogen sulfide (H2S) is a crucial signaling molecule in plants. Recent studies have shown that H2S plays an equally important role as nitric oxide (NO) and hydrogen peroxide (H2O2) in plant signaling. Previous studies have demonstrated the involvement of H2S in regulating drought and other stressful environmental conditions, but the exact downstream molecular mechanisms activated by the H2S signaling molecule remain unclear. In this study, we conducted a comprehensive genome-wide transcriptomic analysis of both wild type (WT) and double mutant (lcd/des1). Arabidopsis thaliana plants were exposed to 40% polyethylene glycol (PEG) to induce drought stress and 20 µM sodium hydrosulfide (NaHS). The resulting transcriptome data were analyzed for differentially significant genes and their statistical enrichments in the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. The results indicated significant upregulation of genes related to photosynthesis, carbon fixation, plant secondary metabolite biosynthesis, inositol and phosphatidylinositol signaling pathways, and stress-responsive pathways in mutant plants under drought stress. Mutant plants with impaired H2S signaling mechanisms displayed greater susceptibility to drought stress compared to wild-type plants. In summary, all findings highlight the pivotal role of H2S signaling in stimulating other drought-responsive signaling pathways.

L-histidine makes Ni2+ ‘visible’ for plant signalling systems: Shading the light on Ni2+-induced Ca2+ and redox signalling in plants.

Nickel is both an important nutrient and an ecotoxicant for plants. Organic ligands, such as L-histidine (His), play a key role in Ni2+ detoxification. Here, we show that His (added together with 0.01-10 mM Ni2+) decreases Ni2+ toxicity to Arabidopsis thaliana roots not only as a result of a decrease in Ni2+ activity, but also via the induction of signalling phenomena important for adaptation such as the generation of reactive oxygen species (ROS) and cytosolic Ca2+ transients. With the use of EPR spectroscopy, we demonstrate that Ni-His complexes generate hydroxyl radicals that is not detected by the addition of Ni2+ or His separately. Similarly, Ni-His complexes, but not Ni2+, activate Ca2+ influx and K+ efflux currents in patch-clamped root protoplasts resulting in distinct cytosolic Ca2+ signals and a transient K+ release. His prevented programmed cell death symptoms (cytoplasm shrinkage, protease and endonuclease activation) induced by Ni2+ and inhibited Ni2+ accumulation at [Ni2+]>0.3 mM. Intriguingly, priming of roots with Ni-His stimulated plant resistance to Ni2+. Overall, these data show that His triggers ROS-Ca2+-mediated reactions making Ni2+ ‘visible’ for plant signalling machinery and facilitating adaptation to the excess Ni2+.

Foliar application of carbon dots enhances nitrogen uptake and assimilation through CEPD1-dependent signaling in plants

The use of nitrogen (N) fertilizers increases crop yield, but the accumulation of residual N in agricultural soils poses significant environmental risks. Improving the N use efficiency (NUE) of crops can help reduce N pollution. While nanomaterials have been shown to enhance crop agronomic traits, more research is needed to clarify the regulatory mechanisms involved. In this study, foliar spraying of carbon dots (CDs, 1 mg·mL−1) derived from Salvia miltiorrhiza increased the activity of plasma membrane H+-ATPase in Arabidopsis thaliana roots, promoting the uptake, transport, and assimilation of NO3- and NH4+. The upregulation of N metabolism-related genes, such as AtAMTs and AtNRTs, was also observed in A. thaliana roots. Transcriptome analysis suggested that this regulatory effect is mediated by the shoot-to-root mobile polypeptide CEPD1 (C-terminally encoded peptide DOWNSTREAM 1) signaling pathway. Additionally, foliar application of CDs increased the NUE of sweetpotato (Ipomoea batatas (L.) Lam.) from 2.5% to 8.1%. The upregulation of genes such as CEPD1 in leaves was observed following CDs application under different N conditions. Finally, foliar spraying of CDs significantly increased field yield and enhanced tolerance to low N stress in sweetpotato. Overall, this study demonstrated that foliar application of CDs improved NUE in plants through CEPD1-dependent signaling.

Metabolite and Transcriptomic Changes Reveal the Cold Stratification Process in Sinopodophyllum hexandrum Seeds.

Sinopodophyllum hexandrum (Royle) Ying, an endangered perennial medicinal herb, exhibits morpho-physiological dormancy in its seeds, requiring cold stratification for germination. However, the precise molecular mechanisms underlying this transition from dormancy to germination remain unclear. This study integrates transcriptome and plant hormone-targeted metabolomics techniques to unravel these intricate molecular regulatory mechanisms during cold stratification in S. hexandrum seeds. Significant alterations in the physicochemical properties (starch, soluble sugars, soluble proteins) and enzyme activities (PK, SDH, G-6-PDH) within the seeds occur during stratification. To characterize and monitor the formation and transformation of plant hormones throughout this process, extracts from S. hexandrum seeds at five stratification stages of 0 days (S0), 30 days (S1), 60 days (S2), 90 days (S3), and 120 days (S4) were analyzed using UPLC-MS/MS, revealing a total of 37 differential metabolites belonging to seven major classes of plant hormones. To investigate the biosynthetic and conversion processes of plant hormones related to seed dormancy and germination, the transcriptome of S. hexandrum seeds was monitored via RNA-seq, revealing 65,372 differentially expressed genes associated with plant hormone synthesis and signaling. Notably, cytokinins (CKs) and gibberellins (GAs) exhibited synergistic effects, while abscisic acid (ABA) displayed antagonistic effects. Furthermore, key hub genes were identified through integrated network analysis. In this rigorous scientific study, we systematically elucidate the intricate dynamic molecular regulatory mechanisms that govern the transition from dormancy to germination in S. hexandrum seeds during stratification. By meticulously examining these mechanisms, we establish a solid foundation of knowledge that serves as a scientific basis for facilitating large-scale breeding programs and advancing the artificial cultivation of this highly valued medicinal plant.