Isolation of Natural Fungal Pathogens from Marchantia polymorpha Reveals Antagonism between Salicylic Acid and Jasmonate during Liverwort-Fungus Interactions

Coronatine-treated seedlings increase the tolerance of cotton to low-temperature stress

Coronatine, an analog of Jasmonic acid (JA), has been shown to enhance crop tolerance to abiotic stresses, including chilling stress. However, the underlying molecular mechanism remains largely unknown. In this study, we investigated the effect of Coronatine on cotton seedlings under low temperature using transcriptomic and metabolomics analysis. Twelve cDNA libraries from cotton seedlings were constructed, and pairwise comparisons revealed a total of 48,322 differentially expressed genes (DEGs). Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis identified the involvement of these unigenes in various metabolic pathways, including Starch and sucrose metabolism, Sesquiterpenoid and triterpenoid biosynthesis, Phenylpropanoid biosynthesis, alpha-Linolenic acid metabolism, ABC transporters, and Plant hormone signal transduction. Additionally, substantial accumulations of jasmonates (JAs), abscisic acid and major cell wall metabolites were observed. Transcriptome analysis revealed differential expression of regulatory genes, and qRT-PCR analysis confirmed the expression patterns of 9 selected genes. Co-expression analysis showed that the JA-responsive genes might form a network module with ABA biosynthesis genes or cell wall biosynthesis genes, suggesting the existence of a COR-JA-cellulose and COR-JA-ABA-cellulose regulatory pathway in cotton seedlings. Collectively, our findings uncover new insights into the molecular basis of coronatine--associated cold tolerance in cotton seedlings.

The crane fly glycosylated triketide δ-lactone cornicinine elicits akinete differentiation of the cyanobiont in aquatic Azolla fern symbioses

The restriction of plant-symbiont dinitrogen fixation by an insect semiochemical had not been previously described. Here we report on a glycosylated triketide δ-lactone from Nephrotoma cornicina crane flies, cornicinine, that causes chlorosis in the floating-fern symbioses from the genus Azolla. Only the glycosylated trans-A form of chemically synthesized cornicinine was active: 500 nM cornicinine in the growth medium turned all cyanobacterial filaments from Nostoc azollae inside the host leaf-cavities into akinetes typically secreting CTB-bacteriocins. Cornicinine further inhibited akinete germination in Azolla sporelings, precluding re-establishment of the symbiosis during sexual reproduction. It did not impact development of the plant Arabidopsis thaliana or several free-living cyanobacteria from the genera Anabaena or Nostoc but affected the fern host without cyanobiont. Fern-host mRNA sequencing from isolated leaf cavities confirmed high NH4-assimilation and proanthocyanidin biosynthesis in this trichome-rich tissue. After cornicinine treatment, it revealed activation of Cullin-RING ubiquitin-ligase-pathways, known to mediate metabolite signaling and plant elicitation consistent with the chlorosis phenotype, and increased JA-oxidase, sulfate transport and exosome formation. The work begins to uncover molecular mechanisms of cyanobiont differentiation in a seed-free plant symbiosis important for wetland ecology or circular crop-production today, that once caused massive CO2 draw-down during the Eocene geological past.

Reviewing bryophyte-microorganism association: insights into environmental optimization

Bryophytes, the second-largest group of plants, play a crucial role as early colonizers of land and are a prolific source of naturally occurring substances with significant economic potential. Microorganisms, particularly bacteria, cyanobacteria, fungi form intricate associations with plants, notably bryophytes, contributing to the ecological functioning of terrestrial ecosystems and sometimes it gives negative impact also. This review elucidates the pivotal role of endophytic bacteria in promoting plant growth, facilitating nutrient cycling, and enhancing environmental health. It comprehensively explores the diversity and ecological significance of fungal and bacterial endophytes across various ecosystems. Furthermore, it highlights the moss nitrogen dynamics observed in select moss species. Throughout the review, emphasis is placed on the symbiotic interdependence between bryophytes and microorganisms, offering foundational insights for future research endeavors. By shedding light on the intricate bryophyte-microorganism associations, this study advances our understanding of the complex interplay between plants, microbes, and their environment, paving the way for further research and applications in environmental and biotechnological realms.

Analysis of Marchantia polymorpha-microorganism interactions: basis for understanding plant-microbe and plant-pathogen interactions

Marchantia polymorpha is a bryophyte gaining significance as a model plant in evolutionary studies in recent years. This is attributed to its small-sequenced genome, standardized transformation methodology, global distribution, and easy and rapid in vitro culturing. As an evolutionary model, M. polymorpha contributes to our understanding of the evolution of plant defensive responses and the associated hormonal signaling pathways. Through its interaction with microorganisms, M. polymorpha serves as a valuable source of knowledge, yielding insights into new microbial species and bioactive compounds. Bibliographic analysis involved collecting, reading, and categorizing documents obtained from the Scopus and Web of Science databases using different search terms. The review was based on 30 articles published between 1995 and 2023, with Japanese and Spanish authors emerging as the most prolific contributors in this field. These articles have been grouped into four main themes: antimicrobial metabolites produced by M. polymorpha; identification and characterization of epiphytic, endophytic, and pathogenic microorganisms; molecular studies of the direct interaction between M. polymorpha and microorganisms; and plant transformation using bacterial vectors. This review highlights the key findings from these articles and identifies potential future research directions.

Evolution of immunity networks across embryophytes

Land plants (embryophytes), including vascular (tracheophytes) and non-vascular plants (bryophytes), co-evolved with microorganisms since descendants of an algal ancestor colonized terrestrial habitats around 500 million years ago. To cope with microbial pathogen infections, embryophytes evolved a complex immune system for pathogen perception and activation of defenses. With the growing number of sequenced genomes and transcriptome datasets from algae, bryophytes, tracheophytes, and available plant models, comparative analyses are increasing our understanding of the evolution of molecular mechanisms underpinning immune responses in different plant lineages. In this review, recent progress on plant immunity networks is highlighted with emphasis on the identification of key components that shaped immunity against pathogens in bryophytes compared to angiosperms during plant evolution.

Jasmonates and salicylic acid: Evolution of defense hormones in land plants

The emergence of plant hormone signaling pathways is deeply intertwined with land plant evolution. In angiosperms, two plant hormones, salicylic Acid (SA) and Jasmonates (JAs), play a key role in plant defense, where JAs-mediated defenses are typically activated in response to herbivores and necrotrophic pathogens, whereas SA is prioritized against hemi/biotrophic pathogens. Thus, studying the evolution of SA and JAs and their crosstalk is essential to understand the evolution of molecular plant-microbe interactions (EvoMPMI) in land plants. Recent advances in the evolution of SA and JAs biosynthesis, signaling, and crosstalk in land plants illustrated that the insight gained in angiosperms does not necessarily apply to non-seed plant lineages, where the receptors perceive different ligands and the hormones activate pathways independently on the canonical receptors. In this review, recent findings on the two main defense hormones (JAs and SA) in non-seed plants, including functional studies in the bryophyte model Marchantia polymorpha, will be discussed.

Bryo-FIGHTs: Emerging insights and principles acquired from non-vascular plant-pathogen interactions

Since the dawn of land plant evolution, pathogenic microbes have impacted plant health and threatened their survival. Though much of our knowledge on plant-pathogen interactions is derived from flowering plants, emerging research leveraging evolutionarily divergent non-vascular/non-seed bryophytes is beginning to shed light on the history and diversity of plant immune and infection processes. Here, we highlight key bryophyte-microbe pathosystems used to address fundamental questions on plant health. To this end, we outline the idea that core molecular aspects impacting plant infection and immunity are likely conserved across land plants. We discuss recent advances in the emerging field of Evo-MPMI (evolutionary molecular plant-microbe interactions) and highlight future opportunities that will clarify our understanding of the evolutionary framework that underpins host-pathogen interactions across the full spectrum of plant evolution.

Plant-pathogen interactions: The need to evolve to stay the same

Plants and microorganisms have a long-standing relationship involving mutual and continuous adaptations. A new study shows that several molecular tools plants use to recognize their pathogens were already present when plants colonized the land.

Impact of in vitro phytohormone treatments on the metabolome of the leafy liverwort Radula complanata (L.) Dumort

INTRODUCTION

Liverworts are a group of non-vascular plants that possess unique metabolism not found in other plants. Many liverwort metabolites have interesting structural and biochemical characteristics, however the fluctuations of these metabolites in response to stressors is largely unknown.

OBJECTIVES

To investigate the metabolic stress-response of the leafy liverwort Radula complanata.

METHODS

Five phytohormones were applied exogenously to in vitro cultured R. complanata and an untargeted metabolomic analysis was conducted. Compound classification and identification was performed with CANOPUS and SIRIUS while statistical analyses including PCA, ANOVA, and variable selection using BORUTA were conducted to identify metabolic shifts.

RESULTS

It was found that R. complanata was predominantly composed of carboxylic acids and derivatives, followed by benzene and substituted derivatives, fatty acyls, organooxygen compounds, prenol lipids, and flavonoids. The PCA revealed that samples grouped based on the type of hormone applied, and the variable selection using BORUTA (Random Forest) revealed 71 identified and/or classified features that fluctuated with phytohormone application. The stress-response treatments largely reduced the production of the selected primary metabolites while the growth treatments resulted in increased production of these compounds. 4-(3-Methyl-2-butenyl)-5-phenethylbenzene-1,3-diol was identified as a biomarker for the growth treatments while GDP-hexose was identified as a biomarker for the stress-response treatments.

CONCLUSION

Exogenous phytohormone application caused clear metabolic shifts in Radula complanata that deviate from the responses of vascular plants. Further identification of the selected metabolite features can reveal metabolic biomarkers unique to liverworts and provide more insight into liverwort stress responses.

Chemical and Biological Studies of Endophytes Isolated from Marchantia polymorpha

Natural bioresources, predominantly plants, have always been regarded as the richest source of drugs for diseases threatening humanity. Additionally, microorganism-originating metabolites have been extensively explored as weapons against bacterial, fungal, and viral infections. However, the biological potential of metabolites produced by plant endophytes still remains understudied, despite significant efforts reflected in recently published papers. Thus, our goal was to evaluate the metabolites produced by endophytes isolated from Marchantia polymorpha and to study their biological properties, namely anticancer and antiviral potential. The cytotoxicity and anticancer potential were assessed using the microculture tetrazolium technique (MTT) against non-cancerous VERO cells and cancer cells-namely the HeLa, RKO, and FaDu cell lines. The antiviral potential was tested against the human herpesvirus type-1 replicating in VERO cells by observing the influence of the extract on the virus-infected cells and measuring the viral infectious titer and viral load. The most characteristic metabolites identified in the ethyl acetate extract and fractions obtained by use of centrifugal partition chromatography (CPC) were volatile cyclic dipeptides, cyclo(l-phenylalanyl-l-prolyl), cyclo(l-leucyl-l-prolyl), and their stereoisomers. In addition to the diketopiperazine derivatives, this liverwort endophyte also produced arylethylamides and fatty acids amides. The presence of N-phenethylacetamide and oleic acid amide was confirmed. The endophyte extract and isolated fractions showed a potential selective anticancer influence on all tested cancer cell lines. Moreover, the extract and the first separated fraction noticeably diminished the formation of the HHV-1-induced cytopathic effect and reduced the virus infectious titer by 0.61-1.16 log and the viral load by 0.93-1.03 log. Endophytic organisms produced metabolites with potential anticancer and antiviral activity; thus, future studies should aim to isolate pure compounds and evaluate their biological activities.

Controlling stomatal aperture, a potential strategy for managing plant bacterial disease

Bacterial blight of crucifers caused by Pseudomonas cannabina pv. alisalensis (Pcal) inflicts great damage on crucifer production. To explore efficient and sustainable strategies for Pcal disease control, we here investigated and screened for amino acids with reduced disease development. We found that exogenous foliar application with multiple amino acids reduced disease symptoms and bacterial populations in cabbage after spray-inoculation, but not syringe-inoculation. These results indicate that these amino acids showed a protective effect before Pcal entered plants. Therefore, we observed stomatal responses, which is a main gateway for Pcal entry into the apoplast, after amino acid treatments. As a results, we found several amino acids induce stomatal closure. Moreover, our findings demonstrated that reducing stomatal aperture width can limit bacterial entry into plants, leading to reduced disease symptoms. Indeed, Cys, Glu, and Lys, which showed a protective effect on cabbage, reduced stomatal aperture width and bacterial entry. Therefore, managing stomatal aperture can be a powerful strategy for controlling bacterial disease.

Crossroads in the evolution of plant specialized metabolism

The monophyletic group of embryophytes (land plants) stands out among photosynthetic eukaryotes: they are the sole constituents of the macroscopic flora on land. In their entirety, embryophytes account for the majority of the biomass on land and constitute an astounding biodiversity. What allowed for the massive radiation of this particular lineage? One of the defining features of all land plants is the production of an array of specialized metabolites. The compounds that the specialized metabolic pathways of embryophytes produce have diverse functions, ranging from superabundant structural polymers and compounds that ward off abiotic and biotic challenges, to signaling molecules whose abundance is measured at the nanomolar scale. These specialized metabolites govern the growth, development, and physiology of land plants-including their response to the environment. Hence, specialized metabolites define the biology of land plants as we know it. And they were likely a foundation for their success. It is thus intriguing to find that the closest algal relatives of land plants, freshwater organisms from the grade of streptophyte algae, possess homologs for key enzymes of specialized metabolic pathways known from land plants. Indeed, some studies suggest that signature metabolites emerging from these pathways can be found in streptophyte algae. Here we synthesize the current understanding of which routes of the specialized metabolism of embryophytes can be traced to a time before plants had conquered land.

A potential role of salicylic acid in the evolutionary behavior of Trichoderma as a plant pathogen: from Marchantia polymorpha to Arabidopsis thaliana

Recognition of the interaction of Trichoderma during the evolution of land plants plays a potential key role in the development of the salicylic acid defense pathway and the establishment of a mutualistic relationship. Marchantia polymorpha is a common liverwort considered in recent years as a model plant for evolutionary studies on plant-microorganism interactions. Despite the lack of research, remarkable results have been reported regarding the understanding of metabolic and evolutionary processes of beneficial and/or harmful interactions, owing to a better understanding of the origin and evolution of different plant defense pathways. In this study, we have carried out work on the direct and indirect interactions (exudates and volatiles) of M. polymorpha with different species of the fungal genus Trichoderma. These interactions showed different outcomes, including resistance or even growth promotion and disease. We have analyzed the level of tissue colonization and defense-related gene expression. Furthermore, we have used the pteridophyte Dryopteris affinis and the angiosperm Arabidopsis thaliana, as subsequent steps in plant evolution, together with the plant pathogen Rhizoctonia solani as a control of plant pathogenicity. Trichoderma virens, T. brevicompactum and T. hamatum are pathogens of M. polymorpha, while exudates of T. asperellum are harmful to the plant. The analysis of the expression of several defense genes in M. polymorpha and A. thaliana showed that there is a correlation of the transcriptional activation of SA-related genes with resistance or susceptibility of M. polymorpha to Trichoderma. Moreover, exogenous SA provides resistance to the virulent Trichoderma species. This beneficial fungus may have had an evolutionary period of interaction with plants in which it behaved as a plant pathogen until plants developed a defense system to limit its colonization through a defense response mediated by SA.

The renaissance and enlightenment of Marchantia as a model system

The liverwort Marchantia polymorpha has been utilized as a model for biological studies since the 18th century. In the past few decades, there has been a Renaissance in its utilization in genomic and genetic approaches to investigating physiological, developmental, and evolutionary aspects of land plant biology. The reasons for its adoption are similar to those of other genetic models, e.g. simple cultivation, ready access via its worldwide distribution, ease of crossing, facile genetics, and more recently, efficient transformation, genome editing, and genomic resources. The haploid gametophyte dominant life cycle of M. polymorpha is conducive to forward genetic approaches. The lack of ancient whole-genome duplications within liverworts facilitates reverse genetic approaches, and possibly related to this genomic stability, liverworts possess sex chromosomes that evolved in the ancestral liverwort. As a representative of one of the three bryophyte lineages, its phylogenetic position allows comparative approaches to provide insights into ancestral land plants. Given the karyotype and genome stability within liverworts, the resources developed for M. polymorpha have facilitated the development of related species as models for biological processes lacking in M. polymorpha.

Enhanced volatile emissions and anti-herbivore functions mediated by the synergism between jasmonic acid and salicylic acid pathways in tea plants

The interaction between jasmonic acid (JA) and salicylic acid (SA) pathways, which affects plant stress resistance, is mainly considered to be antagonistic. Using an established theoretical model, we investigated how tea plant (Camellia sinensis) volatiles induced by exogenous elicitors of the JA and SA pathways are affected by the sequence of elicitor application, elicitor identity, and the applied concentrations. We also examined the effects of the volatiles mediated by the JA-SA synergistic interaction on the behaviors of a tea leaf-chewing herbivore (Ectropis grisescens) and its parasitic wasp (Apanteles sp.). The JA and SA pathway interactions were almost always reciprocally synergistic when the two pathways were elicited at different times, except at high JA elicitor concentrations. However, the JA pathway antagonized the SA pathway when they were elicited simultaneously. The elicitor identity affected the degree of JA-SA interaction. The volatiles induced by the JA pathway in the JA-SA reciprocal synergism treatments included up to 11 additional compounds and the total amount of volatiles was up to 7.9-fold higher. Similarly, the amount of emitted volatiles induced by the SA pathway in the reciprocal synergism treatments increased by up to 4.2-fold. Compared with the volatiles induced by either pathway, the enriched volatiles induced by the JA-SA reciprocal synergism similarly repelled E. grisescens, but attracted Apanteles sp. more strongly. Thus, non-simultaneous activation is important for optimizing the JA-SA reciprocal synergism. This reciprocal synergism enables plants to induce multifarious responses, leading to increased biotic stress resistance.

CRISPR/Cas9-mediated disruption of ALLENE OXIDE SYNTHASE results in defective 12-oxo-phytodienoic acid accumulation and reduced defense against spider mite (Tetranychus urticae) in liverwort (Marchantia polymorpha)

Allene oxide synthase (AOS) is a key enzyme involved in the biosynthesis of 12-oxo-phytodienoic acid (OPDA) and jasmonic acid and plays an important role in plant defense against herbivore attacks. In the liverwort, Marchantia polymorpha, we previously identified cytosol-type MpAOS1 and chloroplast-type MpAOS2 that show AOS activities. However, there is no direct evidence to show the subcellular localization of MpAOSs and their contribution to plant defense via OPDA production in M. polymorpha. In this study, we generated M. polymorpha mutants, with the MpAOS1 and MpAOS2 genes disrupted via CRISPR/Cas9-mediated genome editing; the loss of OPDA production was analyzed in double-knockout mutants. On AOS mutants, the survival rate and oviposition of spider mites (Tetranychus urticae) increased relative to those on wild-type plants. Overall, these findings suggest that defense systems via OPDA-signaling pathways in response to spider mites have been established in M. polymorpha.

Marchantia polymorpha model reveals conserved infection mechanisms in the vascular wilt fungal pathogen Fusarium oxysporum

Root-infecting vascular fungi cause wilt diseases and provoke devastating losses in hundreds of crops. It is currently unknown how these pathogens evolved and whether they can also infect nonvascular plants, which diverged from vascular plants over 450 million years ago. We established a pathosystem between the nonvascular plant Marchantia polymorpha (Mp) and the root-infecting vascular wilt fungus Fusarium oxysporum (Fo). On angiosperms, Fo exhibits exquisite adaptation to the plant xylem niche as well as host-specific pathogenicity, both of which are conferred by effectors encoded on lineage-specific chromosomes. Fo isolates displaying contrasting lifestyles on angiosperms - pathogenic vs endophytic - are able to infect Mp and cause tissue maceration and host cell killing. Using isogenic fungal mutants we define a set of conserved fungal pathogenicity factors, including mitogen activated protein kinases, transcriptional regulators and cell wall remodelling enzymes, that are required for infection of both vascular and nonvascular plants. Markedly, two host-specific effectors and a morphogenetic regulator, which contribute to vascular colonisation and virulence on tomato plants are dispensable on Mp. Collectively, these findings suggest that vascular wilt fungi employ conserved infection strategies on nonvascular and vascular plant lineages but also have specific mechanisms to access the vascular niche of angiosperms.

Genome-wide identification and expression analysis of the coronatine-insensitive 1 (COI1) gene family in response to biotic and abiotic stresses in Saccharum

Background

The coronatine insensitive 1 (COI1) gene is the core member of jasmonate signaling pathway, which is closely related to plant biotic and abiotic resistance. However, there have been no reports on COI1 in sugarcane (Sacharum spp.). Hence, systematically investigating the characteristics of the COI1 multigene family in sugarcane can provide a means to study and manipulate the jasmonic acid signaling pathway.

Results

A total of 156 COI1 proteins were obtained from the genomes of 19 land plants, while none were obtained from five algae species. A phylogenetic tree demonstrated that these COI1 proteins were classified into four groups, while 31 proteins of SsCOI1 from Saccharum spontaneum, SbCOI1 from Sorghum bicolor, and ShCOI1 from Saccharum spp. hybrid cultivar R570 clustered into three groups. Synteny analysis and duplication patterns revealed that COI1 genes expanded through various genome replication events and could have experienced strong purifying selective pressure during evolution in S. spontaneum, S. bicolor, and R570. An investigation of cis-acting elements suggests that COI1 genes may be involved in plant growth and development and response to various stresses. Expression analysis implied that 21 SsCOI1 genes were constitutively expressed, and had positive responses to drought, cold, and Sporisorium scitamineum stresses with different expression patterns. Among them, seven SsCOI1 haplotype genes may play different roles in response to methyl jasmonate. Furthermore, the ShCOI1–4, ShCOI1–5, and ShCOI1–6 genes were cloned from Saccharum spp. hybrid cultivar ROC22. Real-time quantitative PCR (RT-qPCR) analysis demonstrated that these three ShCOI1 genes had divergent expression profiles in response to salicylic acid, abscisic acid, polyethylene glycol, cold, and S. scitamineum.

Conclusions

These results suggest that COI1 genes may act in sugarcane growth, development, and response to various stresses via different regulatory mechanisms, which laying a foundation for the functional identification of the sugarcane COI1 gene.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-08255-0.

Agrobacterium-Mediated Transient Transformation of Marchantia Liverworts

Agrobacterium-mediated transient gene expression is a rapid and useful approach for characterizing functions of gene products in planta. However, the practicability of the method in the model liverwort Marchantia polymorpha has not yet been thoroughly described. Here we report a simple and robust method for Agrobacterium-mediated transient transformation of Marchantia thalli and its applicability. When thalli of M. polymorpha were co-cultured with Agrobacterium tumefaciens carrying β-glucuronidase (GUS) genes, GUS staining was observed primarily in assimilatory filaments and rhizoids. GUS activity was detected 2 days after infection and saturated 3 days after infection. We were able to transiently co-express fluorescently tagged proteins with proper localizations. Furthermore, we demonstrate that our method can be used as a novel pathosystem to study liverwort-bacteria interactions. We also provide evidence that air chambers support bacterial colonization.

Transcriptional profiling reveals conserved and species-specific plant defense responses during the interaction of Physcomitrium patens with Botrytis cinerea

Evolutionary conserved defense mechanisms present in extant bryophytes and angiosperms, as well as moss-specific defenses are part of the immune response of Physcomitrium patens. Bryophytes and tracheophytes are descendants of early land plants that evolved adaptation mechanisms to cope with different kinds of terrestrial stresses, including drought, variations in temperature and UV radiation, as well as defense mechanisms against microorganisms present in the air and soil. Although great advances have been made on pathogen perception and subsequent defense activation in angiosperms, limited information is available in bryophytes. In this study, a transcriptomic approach uncovered the molecular mechanisms underlying the defense response of the bryophyte Physcomitrium patens (previously Physcomitrella patens) against the important plant pathogen Botrytis cinerea. A total of 3.072 differentially expressed genes were significantly affected during B. cinerea infection, including genes encoding proteins with known functions in angiosperm immunity and involved in pathogen perception, signaling, transcription, hormonal signaling, metabolic pathways such as shikimate and phenylpropanoid, and proteins with diverse role in defense against biotic stress. Similarly as in other plants, B. cinerea infection leads to downregulation of genes involved in photosynthesis and cell cycle progression. These results highlight the existence of evolutionary conserved defense responses to pathogens throughout the green plant lineage, suggesting that they were probably present in the common ancestors of land plants. Moreover, several genes acquired by horizontal transfer from prokaryotes and fungi, and a high number of P. patens-specific orphan genes were differentially expressed during B. cinerea infection, suggesting that they are important players in the moss immune response.

Phytohormone biosynthesis and signaling pathways of mosses

Most known phytohormones regulate moss development. We present a comprehensive view of the synthesis and signaling pathways for the most investigated of these compounds in mosses, focusing on the model Physcomitrium patens. The last 50 years of research have shown that most of the known phytohormones are synthesized by the model moss Physcomitrium patens (formerly Physcomitrella patens) and regulate its development, in interaction with responses to biotic and abiotic stresses. Biosynthesis and signaling pathways are best described in P. patens for the three classical hormones auxins, cytokinins and abscisic acid. Furthermore, their roles in almost all steps of development, from early filament growth to gametophore development and sexual reproduction, have been the focus of much research effort over the years. Evidence of hormonal roles exist for ethylene and for CLE signaling peptides, as well as for salicylic acid, although their possible effects on development remain unclear. Production of brassinosteroids by P. patens is still debated, and modes of action for these compounds are even less known. Gibberellin biosynthesis and signaling may have been lost in P. patens, while gibberellin precursors such as ent-kaurene derivatives could be used as signals in a yet to discover pathway. As for jasmonic acid, it is not used per se as a hormone in P. patens, but its precursor OPDA appears to play a corresponding role in defense against abiotic stress. We have tried to gather a comprehensive view of the biosynthesis and signaling pathways for all these compounds in mosses, without forgetting strigolactones, the last class of plant hormones to be reported. Study of the strigolactone response in P. patens points to a novel signaling compound, the KAI2-ligand, which was likely employed as a hormone prior to land plant emergence.

Non-Targeted Metabolite Profiling Reveals Host Metabolomic Reprogramming during the Interaction of Black Pepper with Phytophthora capsici

Phytophthora capsici is one of the most destructive pathogens causing quick wilt (foot rot) disease in black pepper (Piper nigrum L.) to which no effective resistance has been defined. To better understand the P. nigrum-P. capsici pathosystem, we employed metabolomic approaches based on flow-infusion electrospray-high-resolution mass spectrometry. Changes in the leaf metabolome were assessed in infected and systemic tissues at 24 and 48 hpi. Principal Component Analysis of the derived data indicated that the infected leaves showed a rapid metabolic response by 24 hpi whereas the systemic leaves took 48 hpi to respond to the infection. The major sources of variations between infected leaf and systemic leaf were identified, and enrichment pathway analysis indicated, major shifts in amino acid, tricarboxylic acid cycle, nucleotide and vitamin B6 metabolism upon infection. Moreover, the individual metabolites involved in defensive phytohormone signalling were identified. RT-qPCR analysis of key salicylate and jasmonate biosynthetic genes indicated a transient reduction of expression at 24 hpi but this increased subsequently. Exogenous application of jasmonate and salicylate reduced P. capsici disease symptoms, but this effect was suppressed with the co-application of abscisic acid. The results are consistent with abscisic acid reprogramming, salicylate and jasmonate defences in infected leaves to facilitate the formation of disease. The augmentation of salicylate and jasmonate defences could represent an approach through which quick wilt disease could be controlled in black pepper.

Pathogen Effectors: Exploiting the Promiscuity of Plant Signaling Hubs

Pathogens produce effectors to overcome plant immunity, thereby threatening crop yields and global food security. Large-scale interactomic studies have revealed that pathogens from different kingdoms of life target common plant proteins during infection, the so-called effector hubs. These hubs often play central roles in numerous plant processes through their ability to interact with multiple plant proteins. This ability arises partly from the presence of intrinsically disordered domains (IDDs) in their structure. Here, we highlight the role of the TEOSINTE BRANCHED1/CYCLOIDEA/PROLIFERATING CELL FACTOR (TCP) and JASMONATE-ZIM DOMAIN (JAZ) transcription regulator families as plant signaling and effector hubs. We consider different evolutionary hypotheses to rationalize the existence of diverse effectors sharing common targets and the possible role of IDDs in this interaction.

Possible role of small secreted peptides (SSPs) in immune signaling in bryophytes

Plants utilize a plethora of peptide signals to regulate their immune response. Peptide ligands and their cognate receptors involved in immune signaling share common motifs among many species of vascular plants. However, the origin and evolution of immune peptides is still poorly understood. Here, we searched for genes encoding small secreted peptides in the genomes of three bryophyte lineages-mosses, liverworts and hornworts-that occupy a critical position in the study of land plant evolution. We found that bryophytes shared common predicted small secreted peptides (SSPs) with vascular plants. The number of SSPs is higher in the genomes of mosses than in both the liverwort Marchantia polymorpha and the hornwort Anthoceros sp. The synthetic peptide elicitors-AtPEP and StPEP-specific for vascular plants, triggered ROS production in the protonema of the moss Physcomitrella patens, suggesting the possibility of recognizing peptide ligands from angiosperms by moss receptors. Mass spectrometry analysis of the moss Physcomitrella patens, both the wild type and the Δcerk mutant secretomes, revealed peptides that specifically responded to chitosan treatment, suggesting their role in immune signaling.