Conserved Biochemical Defenses Underpin Host Responses to Oomycete Infection in an Early-Divergent Land Plant Lineage

Contrasting and conserved roles of NPR pathways in diverged land plant lineages

The NPR proteins function as salicylic acid (SA) receptors in Arabidopsis thaliana. AtNPR1 plays a central role in SA-induced transcriptional reprogramming whereby positively regulates SA-mediated defense. NPRs are found in the genomes of nearly all land plants. However, we know little about the molecular functions and physiological roles of NPRs in most plant species. We conducted phylogenetic and alignment analyses of NPRs from 68 species covering the significant lineages of land plants. To investigate NPR functions in bryophyte lineages, we generated and characterized NPR loss-of-function mutants in the liverwort Marchantia polymorpha. Brassicaceae NPR1-like proteins have characteristically gained or lost functional residues identified in AtNPRs, pointing to the possibility of a unique evolutionary trajectory for the Brassicaceae NPR1-like proteins. We find that the only NPR in M. polymorpha, MpNPR, is not the master regulator of SA-induced transcriptional reprogramming and negatively regulates bacterial resistance in this species. The Mpnpr transcriptome suggested roles of MpNPR in heat and far-red light responses. We identify both Mpnpr and Atnpr1-1 display enhanced thermomorphogenesis. Interspecies complementation analysis indicated that the molecular properties of AtNPR1 and MpNPR are partially conserved. We further show that MpNPR has SA-binding activity. NPRs and NPR-associated pathways have evolved distinctively in diverged land plant lineages to cope with different terrestrial environments.

The N-terminal domains of NLR immune receptors exhibit structural and functional similarities across divergent plant lineages

Nucleotide-binding domain and leucine-rich repeat (NLR) proteins are a prominent class of intracellular immune receptors in plants. However, our understanding of plant NLR structure and function is limited to the evolutionarily young flowering plant clade. Here, we describe an extended spectrum of NLR diversity across divergent plant lineages and demonstrate the structural and functional similarities of N-terminal domains that trigger immune responses. We show that the broadly distributed coiled-coil (CC) and toll/interleukin-1 receptor (TIR) domain families of nonflowering plants retain immune-related functions through translineage activation of cell death in the angiosperm Nicotiana benthamiana. We further examined a CC subfamily specific to nonflowering lineages and uncovered an essential N-terminal MAEPL motif that is functionally comparable with motifs in resistosome-forming CC-NLRs. Consistent with a conserved role in immunity, the ectopic activation of CCMAEPL in the nonflowering liverwort Marchantia polymorpha led to profound growth inhibition, defense gene activation, and signatures of cell death. Moreover, comparative transcriptomic analyses of CCMAEPL activity delineated a common CC-mediated immune program shared across evolutionarily divergent nonflowering and flowering plants. Collectively, our findings highlight the ancestral nature of NLR-mediated immunity during plant evolution that dates its origin to at least ∼500 million years ago.

Oomycete Metabolism Is Highly Dynamic and Reflects Lifestyle Adaptations

The selective pressure of pathogen-host symbiosis drives adaptations. How these interactions shape the metabolism of pathogens is largely unknown. Here, we use comparative genomics to systematically analyze the metabolic networks of oomycetes, a diverse group of eukaryotes that includes saprotrophs as well as animal and plant pathogens, with the latter causing devastating diseases with significant economic and/or ecological impacts. In our analyses of 44 oomycete species, we uncover considerable variation in metabolism that can be linked to lifestyle differences. Comparisons of metabolic gene content reveal that plant pathogenic oomycetes have a bipartite metabolism consisting of a conserved core and an accessory set. The accessory set can be associated with the degradation of defense compounds produced by plants when challenged by pathogens. Obligate biotrophic oomycetes have smaller metabolic networks, and taxonomically distantly related biotrophic lineages display convergent evolution by repeated gene losses in both the conserved as well as the accessory set of metabolisms. When investigating to what extent the metabolic networks in obligate biotrophs differ from those in hemibiotrophic plant pathogens, we observe that the losses of metabolic enzymes in obligate biotrophs are not random and that gene losses predominantly influence the terminal branches of the metabolic networks. Our analyses represent the first metabolism-focused comparison of oomycetes at this scale and will contribute to a better understanding of the evolution of oomycete metabolism in relation to lifestyle adaptation. Numerous oomycete species are devastating plant pathogens that cause major damage in crops and natural ecosystems. Their interactions with hosts are shaped by strong selection, but how selection affects adaptation of the primary metabolism to a pathogenic lifestyle is not yet well established. By pan-genome and metabolic network analyses of distantly related oomycete pathogens and their nonpathogenic relatives, we reveal considerable lifestyle- and lineage-specific adaptations. This study contributes to a better understanding of metabolic adaptations in pathogenic oomycetes in relation to lifestyle, host, and environment, and the findings will help in pinpointing potential targets for disease control. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Ectomycorrhizal fungi alter soil food webs and the functional potential of bacterial communities

Most of Earth's trees rely on critical soil nutrients that ectomycorrhizal fungi (EcMF) liberate and provide, and all of Earth's land plants associate with bacteria that help them survive in nature. Yet, our understanding of how the presence of EcMF modifies soil bacterial communities, soil food webs, and root chemistry requires direct experimental evidence to comprehend the effects that EcMF may generate in the belowground plant microbiome. To this end, we grew Pinus muricata plants in soils that were either inoculated with EcMF and native forest bacterial communities or only native bacterial communities. We then profiled the soil bacterial communities, applied metabolomics and lipidomics, and linked omics data sets to understand how the presence of EcMF modifies belowground biogeochemistry, bacterial community structure, and their functional potential. We found that the presence of EcMF (i) enriches soil bacteria linked to enhanced plant growth in nature, (ii) alters the quantity and composition of lipid and non-lipid soil metabolites, and (iii) modifies plant root chemistry toward pathogen suppression, enzymatic conservation, and reactive oxygen species scavenging. Using this multi-omic approach, we therefore show that this widespread fungal symbiosis may be a common factor for structuring soil food webs.IMPORTANCEUnderstanding how soil microbes interact with one another and their host plant will help us combat the negative effects that climate change has on terrestrial ecosystems. Unfortunately, we lack a clear understanding of how the presence of ectomycorrhizal fungi (EcMF)-one of the most dominant soil microbial groups on Earth-shapes belowground organic resources and the composition of bacterial communities. To address this knowledge gap, we profiled lipid and non-lipid metabolites in soils and plant roots, characterized soil bacterial communities, and compared soils amended either with or without EcMF. Our results show that the presence of EcMF changes soil organic resource availability, impacts the proliferation of different bacterial communities (in terms of both type and potential function), and primes plant root chemistry for pathogen suppression and energy conservation. Our findings therefore provide much-needed insight into how two of the most dominant soil microbial groups interact with one another and with their host plant.

DELLA proteins recruit the Mediator complex subunit MED15 to coactivate transcription in land plants

DELLA proteins are negative regulators of the gibberellin response pathway in angiosperms, acting as central hubs that interact with hundreds of transcription factors (TFs) and regulators to modulate their activities. While the mechanism of TF sequestration by DELLAs to prevent DNA binding to downstream targets has been extensively documented, the mechanism that allows them to act as coactivators remains to be understood. Here, we demonstrate that DELLAs directly recruit the Mediator complex to specific loci in Arabidopsis, facilitating transcription. This recruitment involves DELLA amino-terminal domain and the conserved MED15 KIX domain. Accordingly, partial loss of MED15 function mainly disrupted processes known to rely on DELLA coactivation capacity, including cytokinin-dependent regulation of meristem function and skotomorphogenic response, gibberellin metabolism feedback, and flavonol production. We have also found that the single DELLA protein in the liverwort Marchantia polymorpha is capable of recruiting MpMED15 subunits, contributing to transcriptional coactivation. The conservation of Mediator-dependent transcriptional coactivation by DELLA between Arabidopsis and Marchantia implies that this mechanism is intrinsic to the emergence of DELLA in the last common ancestor of land plants.

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.

Shared infection strategy of a fungal pathogen across diverse lineages of land plants, the Fusarium example

Plants engage with a wide variety of microorganisms either in parasitic or mutualistic relationships, which have helped them to adapt to terrestrial ecosystems. Microbial interactions have driven plant evolution and led to the emergence of complex interaction outcomes via suppression of host defenses by evolving pathogens. The evolution of plant-microbe interactions is shaped by conserved host and pathogen gene modules and fast-paced lineage-specific adaptability which determines the interaction outcome. Recent findings from different microbes ranging from bacteria, oomycetes, and fungi suggest recurrent concepts in establishing interactions with evolutionarily distant plant hosts, but also clade-specific adaptation that ultimately contributes to pathogenicity. Here, we revisit some of the latest features that illustrate shared colonization strategies of the fungal pathogen Fusarium oxysporum on distant plant lineages and lineage-specific adaptability of mini-chromosomal units encoding effectors, for shaping host-specific pathogenicity in angiosperms.

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.

Immunobiodiversity: Conserved and specific immunity across land plants and beyond

Angiosperms represent most plants that humans cultivate, grow, and eat. However, angiosperms are only one of five major land plant lineages. As a whole lineage, plants also include algal groups. All these clades represent a tremendous genetic diversity that can be investigated to reveal the evolutionary history of any given mechanism. In this review, we describe the current model of the plant immune system, discuss its evolution based on the recent literature, and propose future directions for the field. In angiosperms, plant-microbe interactions have been intensively studied, revealing essential cell surface and intracellular immune receptors, as well as metabolic and hormonal defense pathways. Exploring diversity at the genomic and functional levels demonstrates the conservation of these pathways across land plants, some of which are beyond plants. On basis of the conserved mechanisms, lineage-specific variations have occurred, leading to diversified reservoirs of immune mechanisms. In rare cases, this diversity has been harnessed and successfully transferred to other species by integration of wild immune receptors or engineering of novel forms of receptors for improved resistance to pathogens. We propose that exploring further the diversity of immune mechanisms in the whole plant lineage will reveal completely novel sources of resistance to be deployed in crops.

Comparative Analysis of Transcriptomics and Metabolomics Reveals Defense Mechanisms in Melon Cultivars against Pseudoperonospora cubensis Infection

Melon (Cucumis melo L.) represents an agriculturally significant horticultural crop that is widely grown for its flavorful fruits. Downy mildew (DM), a pervasive foliar disease, poses a significant threat to global melon production. Although several quantitative trait loci related to DM resistance have been identified, the comprehensive genetic underpinnings of this resistance remain largely uncharted. In this study, we utilized integrative transcriptomics and metabolomics approaches to identify potential resistance-associated genes and delineate the strategies involved in the defense against DM in two melon cultivars: the resistant 'PI442177' ('K10-1') and the susceptible 'Huangdanzi' ('K10-9'), post-P. cubensis infection. Even in the absence of the pathogen, there were distinctive differentially expressed genes (DEGs) between 'K10-1' and 'K10-9'. When P. cubensis was infected, certain genes, including flavin-containing monooxygenase (FMO), receptor-like protein kinase FERONIA (FER), and the HD-ZIP transcription factor member, AtHB7, displayed pronounced expression differences between the cultivars. Notably, our data suggest that following P. cubensis infection, both cultivars suppressed flavonoid biosynthesis via the down-regulation of associated genes whilst concurrently promoting lignin production. The complex interplay of transcriptomic and metabolic responses elucidated by this study provides foundational insights into melon's defense mechanisms against DM. The robust resilience of 'K10-1' to DM is attributed to the synergistic interaction of its inherent transcriptomic and metabolic reactions.

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.

Environmental gradients reveal stress hubs pre-dating plant terrestrialization

Plant terrestrialization brought forth the land plants (embryophytes). Embryophytes account for most of the biomass on land and evolved from streptophyte algae in a singular event. Recent advances have unravelled the first full genomes of the closest algal relatives of land plants; among the first such species was Mesotaenium endlicherianum. Here we used fine-combed RNA sequencing in tandem with a photophysiological assessment on Mesotaenium exposed to a continuous range of temperature and light cues. Our data establish a grid of 42 different conditions, resulting in 128 transcriptomes and ~1.5 Tbp (~9.9 billion reads) of data to study the combinatory effects of stress response using clustering along gradients. Mesotaenium shares with land plants major hubs in genetic networks underpinning stress response and acclimation. Our data suggest that lipid droplet formation and plastid and cell wall-derived signals have denominated molecular programmes since more than 600 million years of streptophyte evolution-before plants made their first steps on land.

Green land: Multiple perspectives on green algal evolution and the earliest land plants

Green plants, broadly defined as green algae and the land plants (together, Viridiplantae), constitute the primary eukaryotic lineage that successfully colonized Earth's emergent landscape. Members of various clades of green plants have independently made the transition from fully aquatic to subaerial habitats many times throughout Earth's history. The transition, from unicells or simple filaments to complex multicellular plant bodies with functionally differentiated tissues and organs, was accompanied by innovations built upon a genetic and phenotypic toolkit that have served aquatic green phototrophs successfully for at least a billion years. These innovations opened an enormous array of new, drier places to live on the planet and resulted in a huge diversity of land plants that have dominated terrestrial ecosystems over the past 500 million years. This review examines the greening of the land from several perspectives, from paleontology to phylogenomics, to water stress responses and the genetic toolkit shared by green algae and plants, to the genomic evolution of the sporophyte generation. We summarize advances on disparate fronts in elucidating this important event in the evolution of the biosphere and the lacunae in our understanding of it. We present the process not as a step-by-step advancement from primitive green cells to an inevitable success of embryophytes, but rather as a process of adaptations and exaptations that allowed multiple clades of green plants, with various combinations of morphological and physiological terrestrialized traits, to become diverse and successful inhabitants of the land habitats of Earth.

System network analysis of Rosmarinus officinalis transcriptome and metabolome-Key genes in biosynthesis of secondary metabolites

Medicinal plants contain valuable compounds that have attracted worldwide interest for their use in the production of natural drugs. The presence of compounds such as rosmarinic acid, carnosic acid, and carnosol in Rosmarinus officinalis has made it a plant with unique therapeutic effects. The identification and regulation of the biosynthetic pathways and genes will enable the large-scale production of these compounds. Hence, we studied the correlation between the genes involved in biosynthesis of the secondary metabolites in R. officinalis using proteomics and metabolomics data by WGCNA. We identified three modules as having the highest potential for the metabolite engineering. Moreover, the hub genes highly connected to particular modules, TFs, PKs, and transporters were identified. The TFs of MYB, C3H, HB, and C2H2 were the most likely candidates associated with the target metabolic pathways. The results indicated that the hub genes including Copalyl diphosphate synthase (CDS), Phenylalanine ammonia lyase (PAL), Cineole synthase (CIN), Rosmarinic acid synthase (RAS), Tyrosine aminotransferase (TAT), Cinnamate 4-hydroxylase (C4H), and MYB58 are responsible for biosynthesis of important secondary metabolites. Thus, we confirmed these results using qRT-PCR after treating R. officinalis seedlings with methyl jasmonate. These candidate genes may be employed for genetic and metabolic engineering research to increase R. officinalis metabolite production.

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.

RALF peptides modulate immune response in the moss Physcomitrium patens

BACKGROUND

RAPID ALKALINIZATION FACTOR (RALFs) are cysteine-rich peptides that regulate multiple physiological processes in plants. This peptide family has considerably expanded during land plant evolution, but the role of ancient RALFs in modulating stress responses is unknown.Results: Here, we used the moss Physcomitrium patens as a model to gain insight into the role of RALF peptides in the coordination of plant growth and stress response in non-vascular plants. The quantitative proteomic analysis revealed concerted downregulation of M6 metalloprotease and some membrane proteins, including those involved in stress response, in PpRALF1, 2 and 3 knockout (KO) lines. The subsequent analysis revealed the role of PpRALF3 in growth regulation under abiotic and biotic stress conditions, implying the importance of RALFs in responding to various adverse conditions in bryophytes. We found that knockout of the PpRALF2 and PpRALF3 genes resulted in increased resistance to bacterial and fungal phytopathogens, Pectobacterium carotovorum and Fusarium solani, suggesting the role of these peptides in negative regulation of the immune response in P. patens. Comparing the transcriptomes of PpRALF3 KO and wild-type plants infected by F. solani showed that the regulation of genes in the phenylpropanoid pathway and those involved in cell wall modification and biogenesis was different in these two genotypes.

CONCLUSION

Thus, our study sheds light on the function of the previously uncharacterized PpRALF3 peptide and gives a clue to the ancestral functions of RALF peptides in plant stress response.

Transcriptome analysis of two pepper genotypes infected with pepper mild mottle virus

Pepper mild mottle virus (PMMoV) poses a significant threat to pepper production because it is highly contagious and extremely persistent in soil. Despite this threat, little is known about the molecular processes that underlie plant responses to pepper mild mottle virus. Here, we performed RNA sequencing of tolerant ("17-p63") and susceptible ("16-217") pepper genotypes after pepper mild mottle virus or mock inoculation. Viral accumulation in systemic leaves was lower in the pepper mild mottle virus-resistant 17-p63 genotype than in the pepper mild mottle virus-sensitive 16-217 genotype, and infection symptoms were more apparent in systemic leaves of 16-217 than in those of 17-p63 at the same timepoints during the infection process. We identified 2,959 and 2,159 differentially expressed genes (DEGs) in systemic leaves of infected 16-217 and 17-p63, respectively. Through Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis of differentially expressed genes from both genotypes revealed significant enrichment of the MAPK signaling pathway, plant-pathogen interaction, and flavonoid biosynthesis. A number of differentially expressed genes showed opposite trends in relation to stress resistance and disease defense in the two genotypes. We also performed weighted gene co-expression network analysis (WGCNA) of all samples and identified modules associated with resistance to pepper mild mottle virus, as well as seven hub genes. These results identify candidate virus resistance genes and provide insight into pepper defense mechanisms against pepper mild mottle virus.

G protein controls stress readiness by modulating transcriptional and metabolic homeostasis in Arabidopsis thaliana and Marchantia polymorpha

The core G protein signaling module, which consists of Gα and extra-large Gα (XLG) subunits coupled with the Gβγ dimer, is a master regulator of various stress responses. In this study, we compared the basal and salt stress-induced transcriptomic, metabolomic and phenotypic profiles in Gα, Gβ, and XLG-null mutants of two plant species, Arabidopsis thaliana and Marchantia polymorpha, and showed that G protein mediates the shift of transcriptional and metabolic homeostasis to stress readiness status. We demonstrated that such stress readiness serves as an intrinsic protection mechanism against further stressors through enhancing the phenylpropanoid pathway and abscisic acid responses. Furthermore, WRKY transcription factors were identified as key intermediates of G protein-mediated homeostatic shifts. Statistical and mathematical model comparisons between A. thaliana and M. polymorpha revealed evolutionary conservation of transcriptional and metabolic networks over land plant evolution, whereas divergence has occurred in the function of plant-specific atypical XLG subunit. Taken together, our results indicate that the shifts in transcriptional and metabolic homeostasis at least partially act as the mechanisms of G protein-coupled stress responses that are conserved between two distantly related plants.

Indonesian Mangrove Sonneratia caseolaris Leaves Ethanol Extract Is a Potential Super Antioxidant and Anti Methicillin-Resistant Staphylococcus aureus Drug

Methicillin-resistant Staphylococcus aureus (MRSA) is an S. aureus strain that has developed resistance against ß-lactam antibiotics, resulting in a scarcity of a potent cure for treating Staphylococcus infections. In this study, the anti-MRSA and antioxidant activity of the Indonesian mangrove species Sonneratia caseolaris, Avicennia marina, Rhizophora mucronata, and Rhizophora apiculata were studied. Disk diffusion, DPPH, a brine shrimp lethality test, and total phenolic and flavonoid assays were conducted. Results showed that among the tested mangroves, ethanol solvent-based S. caseolaris leaves extract had the highest antioxidant and anti-MRSA activities. An antioxidant activity assay showed comparable activity when compared to ascorbic acid, with an IC50 value of 4.2499 ± 3.0506 ppm and 5.2456 ± 0.5937 ppm, respectively, classifying the extract as a super-antioxidant. Moreover, S. caseolaris leaves extract showed the highest content of strongly associated antioxidative and antibacterial polyphenols, with 12.4% consisting of nontoxic flavonoids with the minimum inhibitory concentration of the ethanol-based S. caseolaris leaves extract being approximately 5000 ppm. LC-MS/MS results showed that phenolic compounds such as azelaic acid and aspirin were found, as well as flavonoid glucosides such as isovitexin and quercitrin. This strongly suggested that these compounds greatly contributed to antibacterial and antioxidant activity. Further research is needed to elucidate the interaction of the main compounds in S. caseolaris leaves extract in order to confirm their potential either as single or two or more compounds that synergistically function as a nontoxic antioxidant and antibacterial against MRSA.

Evolution and function of red pigmentation in land plants

BACKGROUND

Land plants commonly produce red pigmentation as a response to environmental stressors, both abiotic and biotic. The type of pigment produced varies among different land plant lineages. In the majority of species they are flavonoids, a large branch of the phenylpropanoid pathway. Flavonoids that can confer red colours include 3-hydroxyanthocyanins, 3-deoxyanthocyanins, sphagnorubins and auronidins, which are the predominant red pigments in flowering plants, ferns, mosses and liverworts, respectively. However, some flowering plants have lost the capacity for anthocyanin biosynthesis and produce nitrogen-containing betalain pigments instead. Some terrestrial algal species also produce red pigmentation as an abiotic stress response, and these include both carotenoid and phenolic pigments.

SCOPE

In this review, we examine: which environmental triggers induce red pigmentation in non-reproductive tissues; theories on the functions of stress-induced pigmentation; the evolution of the biosynthetic pathways; and structure-function aspects of different pigment types. We also compare data on stress-induced pigmentation in land plants with those for terrestrial algae, and discuss possible explanations for the lack of red pigmentation in the hornwort lineage of land plants.

CONCLUSIONS

The evidence suggests that pigment biosynthetic pathways have evolved numerous times in land plants to provide compounds that have red colour to screen damaging photosynthetically active radiation but that also have secondary functions that provide specific benefits to the particular land plant lineage.

An Overview of PRR- and NLR-Mediated Immunities: Conserved Signaling Components across the Plant Kingdom That Communicate Both Pathways

Cell-surface-localized pattern recognition receptors (PRRs) and intracellular nucleotide-binding domain and leucine-rich repeat receptors (NLRs) are plant immune proteins that trigger an orchestrated downstream signaling in response to molecules of microbial origin or host plant origin. Historically, PRRs have been associated with pattern-triggered immunity (PTI), whereas NLRs have been involved with effector-triggered immunity (ETI). However, recent studies reveal that such binary distinction is far from being applicable to the real world. Although the perception of plant pathogens and the final mounting response are achieved by different means, central hubs involved in signaling are shared between PTI and ETI, blurring the zig-zag model of plant immunity. In this review, we not only summarize our current understanding of PRR- and NLR-mediated immunities in plants, but also highlight those signaling components that are evolutionarily conserved across the plant kingdom. Altogether, we attempt to offer an overview of how plants mediate and integrate the induction of the defense responses that comprise PTI and ETI, emphasizing the need for more evolutionary molecular plant-microbe interactions (EvoMPMI) studies that will pave the way to a better understanding of the emergence of the core molecular machinery involved in the so-called evolutionary arms race between plants and microbes.

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.

The moss-specific transcription factor PpERF24 positively modulates immunity against fungal pathogens in Physcomitrium patens

APETALA2/ethylene response factors (AP2/ERFs) transcription factors (TFs) have greatly expanded in land plants compared to algae. In angiosperms, AP2/ERFs play important regulatory functions in plant defenses against pathogens and abiotic stress by controlling the expression of target genes. In the moss Physcomitrium patens, a high number of members of the ERF family are induced during pathogen infection, suggesting that they are important regulators in bryophyte immunity. In the current study, we analyzed a P. patens pathogen-inducible ERF family member designated as PpERF24. Orthologs of PpERF24 were only found in other mosses, while they were absent in the bryophytes Marchantia polymorpha and Anthoceros agrestis, the vascular plant Selaginella moellendorffii, and angiosperms. We show that PpERF24 belongs to a moss-specific clade with distinctive amino acids features in the AP2 domain that binds to the DNA. Interestingly, all P. patens members of the PpERF24 subclade are induced by fungal pathogens. The function of PpERF24 during plant immunity was assessed by an overexpression approach and transcriptomic analysis. Overexpressing lines showed increased defenses to infection by the fungal pathogens Botrytis cinerea and Colletotrichum gloeosporioides evidenced by reduced cellular damage and fungal biomass compared to wild-type plants. Transcriptomic and RT-qPCR analysis revealed that PpERF24 positively regulates the expression levels of defense genes involved in transcriptional regulation, phenylpropanoid and jasmonate pathways, oxidative burst and pathogenesis-related (PR) genes. These findings give novel insights into potential mechanism by which PpERF24 increases plant defenses against several pathogens by regulating important players in plant immunity.

A scoping review of bryophyte microbiota: diverse microbial communities in small plant packages

Plant health depends not only on the condition of the plant itself but also on its diverse community of microbes, or microbiota. Just like the better-studied angiosperms, bryophytes (mosses, liverworts, and hornworts) harbor diverse communities of bacteria, archaea, fungi, and other microbial eukaryotes. Bryophytes are increasingly recognized as important model systems for understanding plant evolution, development, physiology, and symbiotic interactions. Much of the work on bryophyte microbiota in the past focused on specific symbiont types for each bryophyte group, but more recent studies are taking a broader view acknowledging the coexistence of diverse microbial communities in bryophytes. Therefore, this review integrates studies of bryophyte microbes from both perspectives to provide a holistic view of the existing research for each bryophyte group and on key themes. The systematic search also reveals the taxonomic and geographic biases in this field, including a severe under-representation of the tropics, very few studies on viruses or eukaryotic microbes beyond fungi, and a focus on mycorrhizal fungi studies in liverworts. Such gaps may have led to errors in conclusions about evolutionary patterns in symbiosis. This analysis points to a wealth of future research directions that promise to reveal how the distinct life cycles and physiology of bryophytes interact with their microbiota.

Moss transcription factors regulating development and defense responses to stress

Transcription factors control gene expression, leading to regulation of biological processes that determine plant development and adaptation to the environment. Land colonization by plants occurred 450-470 million years ago and was accompanied by an increase in the complexity of transcriptional regulation associated to transcription factor gene expansions. AP2/ERF, bHLH, MYB, NAC, GRAS, and WRKY transcription factor families increased in land plants compared with algae. In angiosperms, they play crucial roles in regulating plant growth and responses to environmental stressors. However, less information is available in bryophytes and only in a few cases is the functional role of moss transcription factors in stress mechanisms known. In this review, we discuss current knowledge of the transcription factor families involved in development and defense responses to stress in mosses and other bryophytes. By exploring and analysing the Physcomitrium patens public database and published transcriptional profiles, we show that a high number of AP2/ERF, bHLH, MYB, NAC, GRAS, and WRKY genes are differentially expressed in response to abiotic stresses and during biotic interactions. Expression profiles together with a comprehensive analysis provide insights into relevant transcription factors involved in moss defenses, and hint at distinct and conserved biological roles between bryophytes and angiosperms.

Stress, senescence, and specialized metabolites in bryophytes

Life on land exposes plants to varied abiotic and biotic environmental stresses. These environmental drivers contributed to a large expansion of metabolic capabilities during land plant evolution and species diversification. In this review we summarize knowledge on how the specialized metabolite pathways of bryophytes may contribute to stress tolerance capabilities. Bryophytes are the non-tracheophyte land plant group (comprising the hornworts, liverworts, and mosses) and rapidly diversified following the colonization of land. Mosses and liverworts have as wide a distribution as flowering plants with regard to available environments, able to grow in polar regions through to hot desert landscapes. Yet in contrast to flowering plants, for which the biosynthetic pathways, transcriptional regulation, and compound function of stress tolerance-related metabolite pathways have been extensively characterized, it is only recently that similar data have become available for bryophytes. The bryophyte data are compared with those available for angiosperms, including examining how the differing plant forms of bryophytes and angiosperms may influence specialized metabolite diversity and function. The involvement of stress-induced specialized metabolites in senescence and nutrient response pathways is also discussed.

Beyond Photoprotection: The Multifarious Roles of Flavonoids in Plant Terrestrialization

Plants evolved an impressive arsenal of multifunctional specialized metabolites to cope with the novel environmental pressures imposed by the terrestrial habitat when moving from water. Here we examine the multifarious roles of flavonoids in plant terrestrialization. We reason on the environmental drivers, other than the increase in UV-B radiation, that were mostly responsible for the rise of flavonoid metabolism and how flavonoids helped plants in land conquest. We are reasonably based on a nutrient-deficiency hypothesis for the replacement of mycosporine-like amino acids, typical of streptophytic algae, with the flavonoid metabolism during the water-to-land transition. We suggest that flavonoids modulated auxin transport and signaling and promoted the symbiosis between plants and fungi (e.g., arbuscular mycorrhizal, AM), a central event for the conquest of land by plants. AM improved the ability of early plants to take up nutrients and water from highly impoverished soils. We offer evidence that flavonoids equipped early land plants with highly versatile “defense compounds”, essential for the new set of abiotic and biotic stressors imposed by the terrestrial environment. We conclude that flavonoids have been multifunctional since the appearance of plants on land, not only acting as UV filters but especially improving both nutrient acquisition and biotic stress defense.

Plant-microbe interactions in the apoplast: Communication at the plant cell wall

The apoplast is a continuous plant compartment that connects cells between tissues and organs and is one of the first sites of interaction between plants and microbes. The plant cell wall occupies most of the apoplast and is composed of polysaccharides and associated proteins and ions. This dynamic part of the cell constitutes an essential physical barrier and a source of nutrients for the microbe. At the same time, the plant cell wall serves important functions in the interkingdom detection, recognition, and response to other organisms. Thus, both plant and microbe modify the plant cell wall and its environment in versatile ways to benefit from the interaction. We discuss here crucial processes occurring at the plant cell wall during the contact and communication between microbe and plant. Finally, we argue that these local and dynamic changes need to be considered to fully understand plant-microbe interactions.

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.

Symbiotic responses of Lotus japonicus to two isogenic lines of a mycorrhizal fungus differing in the presence/absence of an endobacterium

As other arbuscular mycorrhizal fungi, Gigaspora margarita contains unculturable endobacteria in its cytoplasm. A cured fungal line has been obtained and showed it was capable of establishing a successful mycorrhizal colonization. However, previous OMICs and physiological analyses have demonstrated that the cured fungus is impaired in some functions during the pre-symbiotic phase, leading to a lower respiration activity, lower ATP, and antioxidant production. Here, by combining deep dual-mRNA sequencing and proteomics applied to Lotus japonicus roots colonized by the fungal line with bacteria (B+) and by the cured line (B-), we tested the hypothesis that L. japonicus (i) activates its symbiotic pathways irrespective of the presence or absence of the endobacterium, but (ii) perceives the two fungal lines as different physiological entities. Morphological observations confirmed the absence of clear endobacteria-dependent changes in the mycorrhizal phenotype of L. japonicus, while transcript and proteomic datasets revealed activation of the most important symbiotic pathways. They included the iconic nutrient transport and some less-investigated pathways, such as phenylpropanoid biosynthesis. However, significant differences between the mycorrhizal B+/B- plants emerged in the respiratory pathways and lipid biosynthesis. In both cases, the roots colonized by the cured line revealed a reduced capacity to activate genes involved in antioxidant metabolism, as well as the early biosynthetic steps of the symbiotic lipids, which are directed towards the fungus. Similar to its pre-symbiotic phase, the intraradical fungus revealed transcripts related to mitochondrial activity, which were downregulated in the cured line, as well as perturbation in lipid biosynthesis.

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.

Laccase Directed Lignification Is One of the Major Processes Associated With the Defense Response Against Pythium ultimum Infection in Apple Roots

Apple replant disease (ARD), incited by a pathogen complex including Pythium ultimum, causes stunted growth or death of newly planted trees at replant sites. Development and deployment of resistant or tolerant rootstocks offers a cost-effective, ecologically friendly, and durable approach for ARD management. Maximized exploitation of natural resistance requires integrated efforts to identify key regulatory mechanisms underlying resistance traits in apple. In this study, miRNA profiling and degradome sequencing identified major miRNA pathways and candidate genes using six apple rootstock genotypes with contrasting phenotypes to P. ultimum infection. The comprehensive RNA-seq dataset offered an expansive view of post-transcriptional regulation of apple root defense activation in response to infection from P. ultimum. Several pairs of miRNA families and their corresponding targets were identified for their roles in defense response in apple roots, including miR397-laccase, miR398-superoxide dismutase, miR10986-polyphenol oxidase, miR482-resistance genes, and miR160-auxin response factor. Of these families, the genotype-specific expression patterns of miR397 indicated its fundamental role in developing defense response patterns to P. ultimum infection. Combined with other identified copper proteins, the importance of cellular fortification, such as lignification of root tissues by the action of laccase, may critically contribute to genotype-specific resistance traits. Our findings suggest that quick and enhanced lignification of apple roots may significantly impede pathogen penetration and minimize the disruption of effective defense activation in roots of resistant genotypes. The identified target miRNA species and target genes consist of a valuable resource for subsequent functional analysis of their roles during interaction between apple roots and P. ultimum.

The evolution of the phenylpropanoid pathway entailed pronounced radiations and divergences of enzyme families

Land plants constantly respond to fluctuations in their environment. Part of their response is the production of a diverse repertoire of specialized metabolites. One of the foremost sources for metabolites relevant to environmental responses is the phenylpropanoid pathway, which was long thought to be a land-plant-specific adaptation shaped by selective forces in the terrestrial habitat. Recent data have, however, revealed that streptophyte algae, the algal relatives of land plants, have candidates for the genetic toolkit for phenylpropanoid biosynthesis and produce phenylpropanoid-derived metabolites. Using phylogenetic and sequence analyses, we here show that the enzyme families that orchestrate pivotal steps in phenylpropanoid biosynthesis have independently undergone pronounced radiations and divergence in multiple lineages of major groups of land plants; sister to many of these radiated gene families are streptophyte algal candidates for these enzymes. These radiations suggest a high evolutionary versatility in the enzyme families involved in the phenylpropanoid-derived metabolism across embryophytes. We suggest that this versatility likely translates into functional divergence, and may explain the key to one of the defining traits of embryophytes: a rich specialized metabolism.

Transcriptomics and metabolomics reveal the induction of flavonoid biosynthesis pathway in the interaction of Stylosanthes-Colletotrichum gloeosporioides

Colletotrichum, a hemibiotrophic fungal pathogen with a broad host range, causes a yield-limiting disease called anthracnose. Stylo (Stylosanthes) is a dominant pasture legume in tropics and subtropics, and anthracnose is one of its most destructive disease. Resistance mechanisms against anthracnose in stylo are poorly understood, thus hindering the development of resistant varieties. We performed time-resolved leaf transcriptomics, metabolomics and in vitro inhibition assay to investigate the defense responses against Colletotrichum gloeosporioides in stylo. Transcriptomics demonstrated that flavonoid biosynthetic genes were significantly induced during the infection. Consistently, metabolomics also showed the increased accumulation of flavonoid compounds. In vitro assays showed that phloretin and naringenin inhibited the mycelial growth, and apigenin, daidzein, quercetin and kaempferol suppressed conidial germination of Colletotrichum strains. Together, our results suggest that stylo plants cope with C. gloeosporioides by up-regulation of genes and compounds in flavonoid biosynthesis pathway, providing potential targets for resistance breeding.

Molecular mechanisms involved in functional macroevolution of plant transcription factors

Transcription factors (TFs) are key components of the transcriptional regulation machinery. In plants, they accompanied the evolution from unicellular aquatic algae to complex flowering plants that dominate the land environment. The adaptations of the body plan and physiological responses required changes in the biological functions of TFs. Some ancestral gene regulatory networks are highly conserved, while others evolved more recently and only exist in particular lineages. The recent emergence of novel model organisms provided the opportunity for comparative studies, producing new insights to infer these evolutionary trajectories. In this review, we comprehensively revisit the recent literature on TFs of nonseed plants and algae, focusing on the molecular mechanisms driving their functional evolution. We discuss the particular contribution of changes in DNA-binding specificity, protein-protein interactions and cis-regulatory elements to gene regulatory networks. Current advances have shown that these evolutionary processes were shaped by changes in TF expression pattern, not through great innovation in TF protein sequences. We propose that the role of TFs associated with environmental and developmental regulation was unevenly conserved during land plant evolution.

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.

Pathway-based analysis of anthocyanin diversity in diploid potato

Anthocyanin biosynthesis is one of the most studied pathways in plants due to the important ecological role played by these compounds and the potential health benefits of anthocyanin consumption. Given the interest in identifying new genetic factors underlying anthocyanin content we studied a diverse collection of diploid potatoes by combining a genome-wide association study and pathway-based analyses. By using an expanded SNP dataset, we identified candidate genes that had not been associated with anthocyanin variation in potatoes, namely a Myb transcription factor, a Leucoanthocyanidin dioxygenase gene and a vacuolar membrane protein. Importantly, a genomic region in chromosome 10 harbored the SNPs with strongest associations with anthocyanin content in GWAS. Some of these SNPs were associated with multiple anthocyanin compounds and therefore could underline the existence of pleiotropic genes or anthocyanin biosynthetic clusters. We identified multiple anthocyanin homologs in this genomic region, including four transcription factors and five enzymes that could be governing anthocyanin variation. For instance, a SNP linked to the phenylalanine ammonia-lyase gene, encoding the first enzyme in the phenylpropanoid biosynthetic pathway, was associated with all of the five anthocyanins measured. Finally, we combined a pathway analysis and GWAS of other agronomic traits to identify pathways related to anthocyanin biosynthesis in potatoes. We found that methionine metabolism and the production of sugars and hydroxycinnamic acids are genetically correlated to anthocyanin biosynthesis. The results contribute to the understanding of anthocyanins regulation in potatoes and can be used in future breeding programs focused on nutraceutical food.

Plant evolution driven by interactions with symbiotic and pathogenic microbes

During 450 million years of diversification on land, plants and microbes have evolved together. This is reflected in today's continuum of associations, ranging from parasitism to mutualism. Through phylogenetics, cell biology, and reverse genetics extending beyond flowering plants into bryophytes, scientists have started to unravel the genetic basis and evolutionary trajectories of plant-microbe associations. Protection against pathogens and support of beneficial, symbiotic, microorganisms are sustained by a blend of conserved and clade-specific plant mechanisms evolving at different speeds. We propose that symbiosis consistently emerges from the co-option of protection mechanisms and general cell biology principles. Exploring and harnessing the diversity of molecular mechanisms used in nonflowering plant-microbe interactions may extend the possibilities for engineering symbiosis-competent and pathogen-resilient crops.

Bryo-Activities: A Review on How Bryophytes Are Contributing to the Arsenal of Natural Bioactive Compounds against Fungi

Usually regarded as less evolved than their more recently diverged vascular sisters, which currently dominate vegetation landscape, bryophytes seem having nothing to envy to the defensive arsenal of other plants, since they had acquired a suite of chemical traits that allowed them to adapt and persist on land. In fact, these closest modern relatives of the ancestors to the earliest terrestrial plants proved to be marvelous chemists, as they traditionally were a popular remedy among tribal people all over the world, that exploit their pharmacological properties to cure the most different diseases. The phytochemistry of bryophytes exhibits a stunning assortment of biologically active compounds such as lipids, proteins, steroids, organic acids, alcohols, aliphatic and aromatic compounds, polyphenols, terpenoids, acetogenins and phenylquinones, thus it is not surprising that substances obtained from various species belonging to such ancestral plants are widely employed as antitumor, antipyretic, insecticidal and antimicrobial. This review explores in particular the antifungal potential of the three Bryophyta divisions-mosses (Musci), hornworts (Anthocerotae) and liverworts (Hepaticae)-to be used as a sources of interesting bioactive constituents for both pharmaceutical and agricultural areas, providing an updated overview of the latest relevant insights.

The RGF/GLV/CLEL Family of Short Peptides Evolved Through Lineage-Specific Losses and Diversification and Yet Conserves Its Signaling Role Between Vascular Plants and Bryophytes

Short secreted plant peptides act as key signaling molecules and control a plethora of developmental and physiological processes. The ROOT GROWTH FACTOR (RGF)/GOLVEN (GLV)/CLE-Like (CLEL) family of peptides was discovered to be involved in root development in Arabidopsis thaliana. In contrast to active research efforts, which have been revealing receptors and downstream signaling components, little attention has been paid to evolutionary processes that shaped the RGF signaling system as we know it in angiosperms today. As a first step toward understanding how RGF signaling emerged and evolved, this study aimed to elucidate the phylogenetic distribution and functional conservation of RGF-like sequences. Using publicly available, genome and transcriptome data, RGF-like sequences were searched in 27 liverworts, 22 mosses, 8 hornworts, 23 lycophytes, 23 ferns, 38 gymnosperms, and 8 angiosperms. This led to the identification of more than four hundreds of RGF-like sequences in all major extant land plant lineages except for hornworts. Sequence comparisons within and between taxonomic groups identified lineage-specific characters. Notably, one of the two major RGF subgroups, represented by A. thaliana RGF6/GLV1/CLEL6, was found only in vascular plants. This subgroup, therefore, likely emerged in a common ancestor of vascular plants after its divergence from bryophytes. In bryophytes, our results infer independent losses of RGF-like sequences in mosses and hornworts. On the other hand, a single, highly similar RGF-like sequence is conserved in liverworts, including Marchantia polymorpha, a genetically tractable model species. When constitutively expressed, the M. polymorpha RGF-like sequence (MpRGF) affected plant development and growth both in A. thaliana and M. polymorpha. This suggests that MpRGF can exert known RGF-like effects and that MpRGF is under transcriptional control so that its potent activities are precisely controlled. These data suggest that RGFs are conserved as signaling molecules in both vascular plants and bryophytes and that lineage-specific diversification has increased sequence variations of RGFs. All together, our findings form a basis for further studies into RGF peptides and their receptors, which will contribute to our understandings of how peptide signaling pathways evolve.

Contribution of phenylpropanoid metabolism to plant development and plant-environment interactions

Phenylpropanoid metabolism is one of the most important metabolisms in plants, yielding more than 8,000 metabolites contributing to plant development and plant-environment interplay. Phenylpropanoid metabolism materialized during the evolution of early freshwater algae that were initiating terrestrialization and land plants have evolved multiple branches of this pathway, which give rise to metabolites including lignin, flavonoids, lignans, phenylpropanoid esters, hydroxycinnamic acid amides, and sporopollenin. Recent studies have revealed that many factors participate in the regulation of phenylpropanoid metabolism, and modulate phenylpropanoid homeostasis when plants undergo successive developmental processes and are subjected to stressful environments. In this review, we summarize recent progress on elucidating the contribution of phenylpropanoid metabolism to the coordination of plant development and plant-environment interaction, and metabolic flux redirection among diverse metabolic routes. In addition, our review focuses on the regulation of phenylpropanoid metabolism at the transcriptional, post-transcriptional, post-translational, and epigenetic levels, and in response to phytohormones and biotic and abiotic stresses.

Characterization of a Plant Nuclear Matrix Constituent Protein in Liverwort

The nuclear lamina (NL) is a complex network of nuclear lamins and lamina-associated nuclear membrane proteins, which scaffold the nucleus to maintain structural integrity. In animals, type V intermediate filaments are the main constituents of NL. Plant genomes do not encode any homologs of these intermediate filaments, yet plant nuclei contain lamina-like structures that are present in their nuclei. In Arabidopsis thaliana, CROWDED NUCLEI (CRWN), which are required for maintaining structural integrity of the nucleus and specific perinuclear chromatin anchoring, are strong candidates for plant lamin proteins. Recent studies revealed additional roles of Arabidopsis Nuclear Matrix Constituent Proteins (NMCPs) in modulating plants' response to pathogen and abiotic stresses. However, detailed analyses of Arabidopsis NMCP activities are challenging due to the presence of multiple homologs and their functional redundancy. In this study, we investigated the sole NMCP gene in the liverwort Marchantia polymorpha (MpNMCP). We found that MpNMCP proteins preferentially were localized to the nuclear periphery. Using CRISPR/Cas9 techniques, we generated an MpNMCP loss-of-function mutant, which displayed reduced growth rate and curly thallus lobes. At an organelle level, MpNMCP mutants did not show any alteration in nuclear morphology. Transcriptome analyses indicated that MpNMCP was involved in regulating biotic and abiotic stress responses. Additionally, a highly repetitive genomic region on the male sex chromosome, which was preferentially tethered at the nuclear periphery in wild-type thalli, decondensed in the MpNMCP mutants and located in the nuclear interior. This perinuclear chromatin anchoring, however, was not directly controlled by MpNMCP. Altogether, our results unveiled that NMCP in plants have conserved functions in modulating stress responses.

Managing enzyme promiscuity in plant specialized metabolism: A lesson from flavonoid biosynthesis: Mission of a "body double" protein clarified

Specificities of enzymes involved in plant specialized metabolism, including flavonoid biosynthesis, are generally promiscuous. This enzyme promiscuity has served as an evolutionary basis for new enzyme functions and metabolic pathways in land plants adapting to environmental challenges. This phenomenon may lead, however, to inefficiency in specialized metabolism and adversely affect metabolite-mediated plant survival. How plants manage enzyme promiscuity for efficient specialized metabolism is, thus, an open question. Recent studies of flavonoid biosynthesis addressing this issue have revealed a conserved strategy, namely, a homolog of chalcone isomerase with no catalytic activity binds to chalcone synthase, a key flavonoid pathway enzyme, to narrow (or rectify) the enzyme's highly promiscuous product specificity. Reducing promiscuity via specific protein-protein interactions among metabolic enzymes and proteins may be a solution adopted by land plants to achieve efficient operation of specialized metabolism, while the intrinsic promiscuity of enzymes has likely been retained incidentally.

A Comprehensive Toolkit for Quick and Easy Visualization of Marker Proteins, Protein-Protein Interactions and Cell Morphology in Marchantia polymorpha

Even though stable genomic transformation of sporelings and thalli of Marchantia polymorpha is straightforward and efficient, numerous problems can arise during critical phases of the process such as efficient spore production, poor selection capacity of antibiotics or low transformation efficiency. It is therefore also desirable to establish quick methods not relying on stable transgenics to analyze the localization, interactions and functions of proteins of interest. The introduction of foreign DNA into living cells via biolistic mechanisms has been first reported roughly 30 years ago and has been commonly exploited in established plant model species such as Arabidopsis thaliana or Nicotiana benthamiana. Here, we report the fast and reliable transient biolistic transformation of Marchantia thallus epidermal cells using fluorescent protein fusions. We present a catalog of fluorescent markers which can be readily used for tagging of a variety of subcellular compartments. Moreover, we report the functionality of the bimolecular fluorescence complementation (BiFC) in M. polymorpha with the example of the p-body markers MpDCP1/2. Finally, we provide standard staining procedures for live cell imaging in M. polymorpha, applicable to visualize cell boundaries or cellular structures, to complement or support protein localizations and to understand how results gained by transient transformations can be embedded in cell architecture and dynamics. Taken together, we offer a set of easy and quick tools for experiments that aim at understanding subcellular localization, protein-protein interactions and thus functions of proteins of interest in the emerging early diverging land plant model M. polymorpha.

Developmental Modulation of Root Cell Wall Architecture Confers Resistance to an Oomycete Pathogen

The cell wall is the primary interface between plant cells and their immediate environment and must balance multiple functionalities, including the regulation of growth, the entry of beneficial microbes, and protection against pathogens. Here, we demonstrate how API, a SCAR2 protein component of the SCAR/WAVE complex, controls the root cell wall architecture important for pathogenic oomycete and symbiotic bacterial interactions in legumes. A mutation in API results in root resistance to the pathogen Phytophthora palmivora and colonization defects by symbiotic rhizobia. Although api mutant plants do not exhibit significant overall growth and development defects, their root cells display delayed actin and endomembrane trafficking dynamics and selectively secrete less of the cell wall polysaccharide xyloglucan. Changes associated with a loss of API establish a cell wall architecture with altered biochemical properties that hinder P. palmivora infection progress. Thus, developmental stage-dependent modifications of the cell wall, driven by SCAR/WAVE, are important in balancing cell wall developmental functions and microbial invasion.

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The SCAR protein API controls actin and endomembrane trafficking dynamics

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SCAR proteins of several plant species can support symbiosis and pathogen infection

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A mutation in API affects specific biochemical properties of plant cell walls

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An altered wall architecture results in root resistance to Phytophthora palmivora

Plant science's next top models

BACKGROUND

Model organisms are at the core of life science research. Notable examples include the mouse as a model for humans, baker's yeast for eukaryotic unicellular life and simple genetics, or the enterobacteria phage λ in virology. Plant research was an exception to this rule, with researchers relying on a variety of non-model plants until the eventual adoption of Arabidopsis thaliana as primary plant model in the 1980s. This proved to be an unprecedented success, and several secondary plant models have since been established. Currently, we are experiencing another wave of expansion in the set of plant models.

SCOPE

Since the 2000s, new model plants have been established to study numerous aspects of plant biology, such as the evolution of land plants, grasses, invasive and parasitic plant life, adaptation to environmental challenges, and the development of morphological diversity. Concurrent with the establishment of new plant models, the advent of the 'omics' era in biology has led to a resurgence of the more complex non-model plants. With this review, we introduce some of the new and fascinating plant models, outline why they are interesting subjects to study, the questions they will help to answer, and the molecular tools that have been established and are available to researchers.

CONCLUSIONS

Understanding the molecular mechanisms underlying all aspects of plant biology can only be achieved with the adoption of a comprehensive set of models, each of which allows the assessment of at least one aspect of plant life. The model plants described here represent a step forward towards our goal to explore and comprehend the diversity of plant form and function. Still, several questions remain unanswered, but the constant development of novel technologies in molecular biology and bioinformatics is already paving the way for the next generation of plant models.

Evo-physio: on stress responses and the earliest land plants

Embryophytes (land plants) can be found in almost any habitat on the Earth's surface. All of this ecologically diverse embryophytic flora arose from algae through a singular evolutionary event. Traits that were, by their nature, indispensable for the singular conquest of land by plants were those that are key for overcoming terrestrial stressors. Not surprisingly, the biology of land plant cells is shaped by a core signaling network that connects environmental cues, such as stressors, to the appropriate responses-which, thus, modulate growth and physiology. When did this network emerge? Was it already present when plant terrestrialization was in its infancy? A comparative approach between land plants and their algal relatives, the streptophyte algae, allows us to tackle such questions and resolve parts of the biology of the earliest land plants. Exploring the biology of the earliest land plants might shed light on exactly how they overcame the challenges of terrestrialization. Here, we outline the approaches and rationale underlying comparative analyses towards inferring the genetic toolkit for the stress response that aided the earliest land plants in their conquest of land.