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

Crop damage by herbivorous insects remains a significant contributor to annual yield reductions. Following attack, maize (Zea mays) responds to herbivore-associated molecular patterns (HAMPs) and damage-associated molecular patterns (DAMPs), activating dynamic direct and indirect antiherbivore defense responses. To define underlying signaling processes, comparative analyses between plant elicitor peptide (Pep) DAMPs and fatty acid-amino acid conjugate (FAC) HAMPs were conducted. RNA sequencing analysis of early transcriptional changes following Pep and FAC treatments revealed quantitative differences in the strength of response yet a high degree of qualitative similarity, providing evidence for shared signaling pathways. In further comparisons of FAC and Pep responses across diverse maize inbred lines, we identified Mo17 as part of a small subset of lines displaying selective FAC insensitivity. Genetic mapping for FAC sensitivity using the intermated B73 × Mo17 population identified a single locus on chromosome 4 associated with FAC sensitivity. Pursuit of multiple fine-mapping approaches further narrowed the locus to 19 candidate genes. The top candidate gene identified, termed FAC SENSITIVITY ASSOCIATED (ZmFACS), encodes a leucine-rich repeat receptor-like kinase (LRR-RLK) that belongs to the same family as a rice (Oryza sativa) receptor gene previously associated with the activation of induced responses to diverse Lepidoptera. Consistent with reduced sensitivity, ZmFACS expression was significantly lower in Mo17 as compared to B73. Transient heterologous expression of ZmFACS in Nicotiana benthamiana resulted in a significantly increased FAC-elicited response. Together, our results provide useful resources for studying early elicitor-induced antiherbivore responses in maize and approaches to discover gene candidates underlying HAMP sensitivity in grain crops.

Plant peptides are a new frontier in plant biology, owing to their key regulatory roles in plant growth, development, and stress responses. Synthetic peptides are promising biological agents that can be used to improve crop growth and protection in an environmentally sustainable manner. Plant regulatory peptides identified in pioneering research, including systemin, PSK, HypSys, RALPH, AtPep1, CLV3, TDIF, CLE, and RGF/GLV/CLEL, hold promise for crop improvement as potent regulators of plant growth and defense. Mass spectrometry and bioinformatics are greatly facilitating the discovery and identification of new plant peptides. The biological functions of most novel plant peptides remain to be elucidated. Bioassays are an essential part in studying the biological activity of identified and putative plant peptides. Root growth assays and cultivated plant cell cultures are widely used to evaluate the regulatory potential of plant peptides during growth, differentiation, and stress reactions. These bioassays can be used as universal approaches for screening peptides from different plant species. Development of high-throughput bioassays can facilitate the screening of large numbers of identified and putative plant peptides, which have recently been discovered but remain uncharacterized for biological activity. [ABSTRACT FROM AUTHOR]

Lateral root initiation requires the accumulation of auxin in lateral root founder cells, yielding a local auxin maximum. The positioning of auxin maxima along the primary root determines the density and spacing of lateral roots. The GOLVEN6 (GLV6) and GLV10 signaling peptides and their receptors have been established as regulators of lateral root spacing via their inhibitory effect on lateral root initiation in Arabidopsis. However, it was unclear how these GLV peptides interfere with auxin signaling or homeostasis. Here, we show that GLV6/10 signaling regulates the expression of a subset of auxin response genes, downstream of the canonical auxin signaling pathway, while simultaneously inhibiting the establishment of auxin maxima within xylem-pole pericycle cells that neighbor lateral root initiation sites. We present genetic evidence that this inhibitory effect relies on the activity of the PIN3 and PIN7 auxin export proteins. Furthermore, GLV6/10 peptide signaling was found to enhance PIN7 abundance in the plasma membranes of xylem-pole pericycle cells, which likely stimulates auxin efflux from these cells. Based on these findings, we propose a model in which the GLV6/10 signaling pathway serves as a negative feedback mechanism that contributes to the robust patterning of auxin maxima along the primary root. [ABSTRACT FROM AUTHOR]

BRASSINOSTEROID INSENSITIVE1-ASSOCIATED KINASE1 (BAK1) is a co-receptor involved in the recognition of pattern-associated molecular patterns (PAMPs) via plasma membrane-localized pattern recognition receptors (PRRs). Absence of BAK1/SERK4 leads to the activation of autoimmunity in plants. Yu et al. recently showed that BAK-TO-LIFE 2 (BTL2) is required for the surveillance of BAK1/SERK4 integrity to maintain immune homeostasis. [ABSTRACT FROM AUTHOR]

Summary: Multicellular organisms need mechanisms for communication between cells so that they can fulfill their purpose in the organism as a whole. Over the last two decades, several small post‐translationally modified peptides (PTMPs) have been identified as components of cell‐to‐cell signaling modules in flowering plants. Such peptides most often influence growth and development of organs not universally conserved among land plants. PTMPs have been matched to subfamily XI leucine‐rich repeat receptor‐like kinases with > 20 repeats. Phylogenetic analyses, facilitated by recently published genomic sequences of non‐flowering plants, have identified seven clades of such receptors with a history back to the common ancestor of bryophytes and vascular plants. This raises a number of questions: When did peptide signaling arise during land plant evolution? Have orthologous peptide–receptor pairs preserved their biological functions? Has peptide signaling contributed to major innovations, such as stomata, vasculature, roots, seeds, and flowers? Using genomic, genetic, biochemical, and structural data and non‐angiosperm model species, it is now possible to address these questions. The vast number of peptides that have not yet found their partners suggests furthermore that we have far more to learn about peptide signaling in the coming decades. [ABSTRACT FROM AUTHOR]

Neprilysins are highly conserved ectoenzymes that hydrolyze and thus inactivate signaling peptides in the extracellular space. Herein, we focus on Neprilysin 4 from Drosophila melanogaster and evaluate the existing knowledge on the physiological relevance of the peptidase. Particular attention is paid to the role of the neprilysin in regulating feeding behavior and the expression of insulin-like peptides in the central nervous system. In addition, we assess the function of the peptidase in controlling the activity of the sarcoplasmic and endoplasmic reticulum Ca2+ ATPase in myocytes, as well as the underlying molecular mechanism in detail. [ABSTRACT FROM AUTHOR]

Asymmetric cell division (ACD) is a fundamental process that generates new cell types during development in eukaryotic species. In plant development, post‐embryonic organogenesis driven by ACD is universal and more important than in animals, in which organ pattern is preset during embryogenesis. Thus, plant development provides a powerful system to study molecular mechanisms underlying ACD. During the past decade, tremendous progress has been made in our understanding of the key components and mechanisms involved in this important process in plants. Here, we present an overview of how ACD is determined and regulated in multiple biological processes in plant development and compare their conservation and specificity among different model cell systems. We also summarize the molecular roles and mechanisms of the phytohormones in the regulation of plant ACD. Finally, we conclude with the overarching paradigms and principles that govern plant ACD and consider how new technologies can be exploited to fill the knowledge gaps and make new advances in the field. [ABSTRACT FROM AUTHOR]

SUMMARY Enterococcus faecalis is a significant resident of the gastrointestinal tract of most animals, including humans. Although generally non-pathogenic in healthy hosts, this microbe is adept at the exploitation of compromises in host immune functions, resulting in life-threatening opportunistic infections whose treatments are complicated by a high degree of intrinsic and acquired resistance to antimicrobial chemotherapy. Historically, progress in enterococcal research was limited by a lack of experimental models that replicate natural infection pathways and the relevance of in vitro studies to the natural biology of the organism. In this review, we summarize the history of enterococcal research during the 20th and early 21st centuries and describe more recent genetic and genomic tools and screens developed to address challenges in the field. We also describe how the results of recent studies reveal the importance of previously uncharacterized enterococcal genes, and we provide examples of interesting determinants that have emerged as important contributors to enterococcal biology. These factors may also serve as targets for future vaccines and chemotherapeutic agents to combat life-threatening hospital infections.

Plant receptors constitute a large protein family that regulates various aspects of development and responses to external cues. Functional characterization of this protein family and the identification of their ligands remain major challenges in plant biology. Previously, we identified plasma membrane-intrinsic sucrose-induced receptor kinase 1 (SIRK1) and Qian Shou kinase 1 (QSK1) as receptor/co-receptor pair involved in the regulation of aquaporins in response to osmotic conditions induced by sucrose. In this study, we identified a member of the elicitor peptide (PEP) family, namely PEP7, as the specific ligand of th receptor kinase SIRK1. PEP7 binds to the extracellular domain of SIRK1 with a binding constant of 1.44 ± 0.79 μM and is secreted to the apoplasm specifically in response to sucrose treatment. Stabilization of a signaling complex involving SIRK1, QSK1, and aquaporins as substrates is mediated by alterations in the external sucrose concentration or by PEP7 application. Moreover, the presence of PEP7 induces the phosphorylation of aquaporins in vivo and enhances water influx into protoplasts. Disturbed water influx, in turn, led to delayed lateral root development in the pep7 mutant. The loss-of-function mutant of SIRK1 is not responsive to external PEP7 treatment regarding kinase activity, aquaporin phosphorylation, water influx activity, and lateral root development. Taken together, our data indicate that the PEP7/SIRK1/QSK1 complex represents a crucial perception and response module that mediates sucrose-controlled water flux in plants and lateral root development. SIRK1 is a receptor kinase and, together with the co-receptor QSK1, activates the channel activity of aquaporins. In this work, the authors identify the small peptide PEP7 as a ligand of the SIRK1-QSK1 receptor complex. Using combined methods of biochemistry, biophysics and physiology, the authors show that PEP7 binds to the extracellular domain of SIRK1 and can activate SIRK1 in the presence of QSK1, resulting in activated activity of aquaporins to promote lateral root development. [ABSTRACT FROM AUTHOR]

Increasing evidence has revealed that plant secretory peptides are involved in the long-distance signaling pathways that help to regulate plant development and signal stress responses. In this study, we purified small peptides from soybean (Glycine max) xylem sap via o-chlorophenol extraction and conducted an in-depth peptidomic analysis using a mass spectrometry (MS) and bioinformatics approach. We successfully identified 14 post-translationally modified peptide groups belonging to the peptide families CEP (C-terminally encoded peptides), CLE (CLAVATA3/embryo surrounding region-related), PSY (plant peptides containing tyrosine sulfation), and XAP (xylem sap-associated peptides). Quantitative PCR (qPCR) analysis showed unique tissue expression patterns among the peptide-encoding genes. Further qPCR analysis of some of the peptide-encoding genes showed differential stress-response profiles toward various abiotic stress factors. Targeted MS-based quantification of the nitrogen deficiency-responsive peptides, GmXAP6a and GmCEP-XSP1, demonstrated upregulation of peptide translocation in xylem sap under nitrogen-deficiency stress. Quantitative proteomic analysis of GmCEP-XSP1 overexpression in hairy soybean roots revealed that GmCEP-XSP1 significantly impacts stress response-related proteins. This study provides new insights that root-to-shoot peptide signaling plays important roles in regulating plant stress-response mechanisms. [ABSTRACT FROM AUTHOR]

Phtheirospermum japonicum is a hemiparasitic plant of the Orobanchaceae, the largest family of parasitic plants. It extracts water and nutrients from other plants through haustoria along its roots. Haustoriogenesis, the formation of haustoria, is initiated by host-derived haustorium-inducing factors (HIFs). The first step in haustoriogenesis is the development of parasitically inactive protohaustoria. Here, we report that an endogenous peptide hormone, CLAVATA3/Embryo Surrounding Region 1 ( Pj CLE1), is sufficient to induce protohaustorium formation. Pj CLE1 hyperactivated HIF-responses and caused prolific protohaustoria formation. PjCLE1 expression and activation by the subtilisin-type protease Pj SBT1.2.3 occur in fully developed, mature haustoria, suggesting that Pj CLE1 acts as an internal signal produced by mature haustoria to stimulate additional protohaustorium formation for effective extraction of resources from hosts. Pj CLE1 is similar in sequence to CLEs regulating nodulation in legumes and part of a regulatory system for haustoria formation in parasitic plants., Competing Interests: Competing interests statement:The authors declare no competing interest.

The root system of a plant provides vital functions including resource uptake, storage, and anchorage in soil. The uptake of macro-nutrients like nitrogen (N), phosphorus (P), potassium (K), and sulphur (S) from the soil is critical for plant growth and development. Small signaling peptide (SSP) hormones are best known as potent regulators of plant growth and development with a few also known to have specialized roles in macronutrient utilization. Here we describe a high throughput phenotyping platform for testing SSP effects on root uptake of multiple nutrients. The SSP, CEP1 (C-TERMINALLY ENCODED PEPTIDE) enhanced nitrate uptake rate per unit root length in Medicago truncatula plants deprived of N in the high-affinity transport range. Single structural variants of M. truncatula and Arabidopsis thaliana specific CEP1 peptides, MtCEP1D1:hyp4,11 and AtCEP1:hyp4,11, enhanced uptake not only of nitrate, but also phosphate and sulfate in both model plant species. Transcriptome analysis of Medicago roots treated with different MtCEP1 encoded peptide domains revealed that hundreds of genes respond to these peptides, including several nitrate transporters and a sulfate transporter that may mediate the uptake of these macronutrients downstream of CEP1 signaling. Likewise, several putative signaling pathway genes including LEUCINE-RICH REPEAT RECPTOR-LIKE KINASES and Myb domain containing transcription factors, were induced in roots by CEP1 treatment. Thus, a scalable method has been developed for screening synthetic peptides of potential use in agriculture, with CEP1 shown to be one such peptide.

The root system of a plant provides vital functions including resource uptake, storage, and anchorage in soil. The uptake of macro-nutrients like nitrogen (N), phosphorus (P), potassium (K), and sulphur (S) from the soil is critical for plant growth and development. Small signaling peptide (SSP) hormones are best known as potent regulators of plant growth and development with a few also known to have specialized roles in macronutrient utilization. Here we describe a high throughput phenotyping platform for testing SSP effects on root uptake of multiple nutrients. The SSP, CEP1 (C-TERMINALLY ENCODED PEPTIDE) enhanced nitrate uptake rate per unit root length in Medicago truncatula plants deprived of N in the high-affinity transport range. Single structural variants of M. truncatula and Arabidopsis thaliana specific CEP1 peptides, MtCEP1D1:hyp4,11 and AtCEP1:hyp4,11, enhanced uptake not only of nitrate, but also phosphate and sulfate in both model plant species. Transcriptome analysis of Medicago roots treated with different MtCEP1 encoded peptide domains revealed that hundreds of genes respond to these peptides, including several nitrate transporters and a sulfate transporter that may mediate the uptake of these macronutrients downstream of CEP1 signaling. Likewise, several putative signaling pathway genes including LEUCINE-RICH REPEAT RECPTOR-LIKE KINASES and Myb domain containing transcription factors, were induced in roots by CEP1 treatment. Thus, a scalable method has been developed for screening synthetic peptides of potential use in agriculture, with CEP1 shown to be one such peptide. [ABSTRACT FROM AUTHOR]

Wounding is a general stress in plants that results from various pest and pathogenic infections in addition to environment-induced mechanical damages. Plants have sophisticated molecular mechanisms to recognize and respond to wounding, with those of monocots being distinct from dicots. Here, we show the involvement of two distinct categories of temporally separated, endogenously derived peptides, namely, plant elicitor peptides (PEPs) and phytosulfokine (PSK), mediating wound responses in rice. These peptides trigger a dynamic signal relay in which a receptor kinase involved in PSK perception named OsPSKR plays a major role. Perturbation of OsPSKR expression in rice leads to compromised development and constitutive autoimmune phenotypes. OsPSKR regulates the transitioning of defense to growth signals upon wounding. OsPSKR displays mutual antagonism with the OsPEPR1 receptor involved in PEP perception. Collectively, our work indicates the presence of a stepwise peptide-mediated signal relay that regulates the transition from defense to growth upon wounding in monocots. [Display omitted] • Wounding in rice triggers a signal relay between the small peptides OsPep3 and PSK • OsPSKR receptor perceives PSK and plays a key role in rice growth and development • OsPSKR dictates gene expression and promotes transition of wound responses • OsPSKR counters OsPEPR1-mediated signaling leading to balanced growth and defense Harshith et al. show that rice wound responses involve small-peptide-mediated signal relay between defense signaling PEPs and growth signaling by a PSK peptide hormone. OsPSKR receptor perceives PSK and maintains balance between growth and defense signaling during homeostasis and promotes growth post-wounding. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Receptor endocytosis is important for signal activation, transduction, and deactivation. However, how a receptor interprets conflicting signals to adjust cellular output is not clearly understood. Using genetic, cell biological, and pharmacological approaches, we report here that ERECTA-LIKE1 (ERL1), the major receptor restricting plant stomatal differentiation, undergoes dynamic subcellular behaviors in response to different EPIDERMAL PATTERNING FACTOR (EPF) peptides. Activation of ERL1 by EPF1 induces rapid ERL1 internalization via multivesicular bodies/late endosomes to vacuolar degradation, whereas ERL1 constitutively internalizes in the absence of EPF1. The co-receptor, TOO MANY MOUTHS is essential for ERL1 internalization induced by EPF1 but not by EPFL6. The peptide antagonist, Stomagen, triggers retention of ERL1 in the endoplasmic reticulum, likely coupled with reduced endocytosis. In contrast, the dominant-negative ERL1 remained dysfunctional in ligand-induced subcellular trafficking. Our study elucidates that multiple related yet unique peptides specify cell fate by deploying the differential subcellular dynamics of a single receptor.

Post-translationally modified peptides are involved in many aspects of plant growth and development. The maturation of these peptides from their larger precursors is still poorly understood. We show here that the biogenesis of CLEL6 and CLEL9 peptides in Arabidopsis thaliana requires a series of processing events in consecutive compartments of the secretory pathway. Following cleavage of the signal peptide upon entry into the endoplasmic reticulum (ER), the peptide precursors are processed in the cis-Golgi by the subtilase SBT6.1. SBT6.1-mediated cleavage within the variable domain allows for continued passage of the partially processed precursors through the secretory pathway, and for subsequent post-translational modifications including tyrosine sulfation and proline hydroxylation within, and proteolytic maturation after exit from the Golgi. Activation by subtilases including SBT3.8 in post-Golgi compartments depends on the N-terminal aspartate of the mature peptides. Our work highlights the complexity of post-translational precursor maturation allowing for stringent control of peptide biogenesis.

Summary: Cyst nematodes induce a multicellular feeding site within roots called a syncytium. It remains unknown how root cells are primed for incorporation into the developing syncytium. Furthermore, it is unclear how CLAVATA3/EMBRYO SURROUNDING REGION (CLE) peptide effectors secreted into the cytoplasm of the initial feeding cell could have an effect on plant cells so distant from where the nematode is feeding as the syncytium expands.Here we describe a novel translocation signal within nematode CLE effectors that is recognized by plant cell secretory machinery to redirect these peptides from the cytoplasm to the apoplast of plant cells.We show that the translocation signal is functionally conserved across CLE effectors identified in nematode species spanning three genera and multiple plant species, operative across plant cell types, and can traffic other unrelated small peptides from the cytoplasm to the apoplast of host cells via a previously unknown post‐translational mechanism of endoplasmic reticulum (ER) translocation.Our results uncover a mechanism of effector trafficking that is unprecedented in any plant pathogen to date, andthey illustrate how phytonematodes can deliver effector proteins into host cells and then hijack plant cellular processes for their export back out of the cell to function as external signaling molecules to distant cells. See also the Commentary on this article by Frei dit Frey & Favery 229: 11–13. [ABSTRACT FROM AUTHOR]

SUMMARY: Plant elicitor peptides (Peps) are conserved regulators of defense responses and models for the study of damage‐associated molecular pattern‐induced immunity. Although present as multigene families in most species, the functional relevance of these multigene families remains largely undefined. While Arabidopsis Peps appear largely redundant in function, previous work examining Pep‐induced responses in maize (Zm) implied specificity of function. To better define the function of individual ZmPeps and their cognate receptors (ZmPEPRs), activities were examined by assessing changes in defense‐associated phytohormones, specialized metabolites and global gene expression patterns, in combination with heterologous expression assays and analyses of CRISPR/Cas9‐generated knockout plants. Beyond simply delineating individual ZmPep and ZmPEPR activities, these experiments led to a number of new insights into Pep signaling mechanisms. ZmPROPEP and other poaceous precursors were found to contain multiple active Peps, a phenomenon not previously observed for this family. In all, seven new ZmPeps were identified and the peptides were found to have specific activities defined by the relative magnitude of their response output rather than by uniqueness. A striking correlation was observed between individual ZmPep‐elicited changes in levels of jasmonic acid and ethylene and the magnitude of induced defense responses, indicating that ZmPeps may collectively regulate immune output through rheostat‐like tuning of phytohormone levels. Peptide structure–function studies and ligand–receptor modeling revealed structural features critical to the function of ZmPeps and led to the identification of ZmPep5a as a potential antagonist peptide able to competitively inhibit the activity of other ZmPeps, a regulatory mechanism not previously observed for this family. Significance Statement: Characterization of the maize plant elicitor peptides reveals new insights into signaling mechanisms not previously observed for this family, including antagonist peptide activity, precursors harboring multiple bioactive peptides and rheostat‐like regulation of phytohormone production and immune output. Together this demonstrates that although the general function of Peps as immunoregulatory signals is widely conserved there are unique signaling features within individual species that are not discoverable by focusing on model plants alone. [ABSTRACT FROM AUTHOR]

Stomata are epidermal valves that facilitate gas exchange between plants and their environment. Stomatal patterning is regulated by the EPIDERMAL PATTERING FACTOR (EPF) family of secreted peptides: EPF1 enforces stomatal spacing, whereas EPIDERMAL PATTERNING FACTOR-LIKE9 (EPFL9), also known as Stomagen, promotes stomatal development. It remains unknown, however, how far these signaling peptides act. Utilizing Cre-lox recombinationbased mosaic sectors that overexpress either EPF1 or Stomagen in Arabidopsis cotyledons, we reveal a range within the epidermis and across the cell layers in which these peptides influence patterns. To determine their effective ranges quantitatively, we developed a computational pipeline, SPACE (stomata patterning autocorrelation on epidermis), that describes probabilistic two-dimensional stomatal distributions based upon spatial autocorrelation statistics used in astrophysics. The SPACE analysis shows that, whereas both peptides act locally, the inhibitor EPF1 exerts longer range effects than the activator Stomagen. Furthermore, local perturbation of stomatal development has little influence on global two-dimensional stomatal patterning. Our findings conclusively demonstrate the nature and extent of EPF peptides as non-cell autonomous local signals and provide a means for quantitative characterization of complex spatial patterns in development. [ABSTRACT FROM AUTHOR]

Plant reproduction relies on the highly regulated growth of the pollen tube for sperm delivery. This process is controlled by secreted RALF signaling peptides, which have previously been shown to be perceived by Catharanthus roseus RLK1-like (CrRLK1Ls) membrane receptor-kinases/LORELEI-like GLYCOLPHOSPHATIDYLINOSITOL (GPI)-ANCHORED PROTEINS (LLG) complexes, or by leucine-rich repeat (LRR) extensin proteins (LRXs). Here, we demonstrate that RALF peptides fold into bioactive, disulfide bond-stabilized proteins that bind the LRR domain of LRX proteins with low nanomolar affinity. Crystal structures of LRX2-RALF4 and LRX8-RALF4 complexes at 3.2- and 3.9-Å resolution, respectively, reveal a dimeric arrangement of LRX proteins, with each monomer binding one folded RALF peptide. Structure-based mutations targeting the LRX- RALF4 complex interface, or the RALF4 fold, reduce RALF4 binding to LRX8 in vitro and RALF4 function in growing pollen tubes. Mutants targeting the disulfide-bond stabilized LRX dimer interface fail to rescue lrx infertility phenotypes. Quantitative biochemical assays reveal that RALF4 binds LLGs and LRX cell-wall modules with drastically different binding affinities, and with distinct and mutually exclusive binding modes. Our biochemical, structural, and genetic analyses reveal a complex signaling network by which RALF ligands instruct different signaling proteins using distinct targeting mechanisms. [ABSTRACT FROM AUTHOR]

RALFs are secreted peptides that are perceived by various CrRLK1L–LRE/LLG receptor complexes. The mechanistic basis of this perception has now been elucidated showing that the co-receptor LLG binds RALF23 to nucleate a FER receptor complex. This interaction likely occurs in other tissues where RALFs meet CrRLK1L receptors and LRE/LLG co-receptors. [ABSTRACT FROM AUTHOR]

Plants respond to various environmental stimuli in sophisticated ways. Takahashi et al. (2018) revealed that CLAVATA3/EMBRYO SURROUNDING REIGON-related 25 (CLE25) peptide is produced in roots under drought stress and transported to shoots, where it induces abscisic acid biosynthesis, resulting in drought resistance in Arabidopsis . However, the drought-related function of the CLE26 peptide, which has the same amino acid sequence as CLE25 (except for one amino acid substitution), is still unknown. In this study, a phenotypic analysis of Arabidopsis plants under repetitive drought stress treatment indicates that CLE26 is associated with drought stress memory and promotes survival rate at the second dehydration event. Additionally, we find that a loss-of-function mutant of a cell-wall-modifying gene, XYLANASE1 ( XYN1 ), exhibits improved resistance to drought, which is suppressed by the mutation of CLE26 . XYN1 is down-regulated in response to drought in wild-type plants. A further analysis shows that the synthetic CLE26 peptide is well transported in both xyn1 and drought-pretreated wild-type plants but not in untreated wild-type plants. These results suggest a novel cell wall function in drought stress memory; short-term dehydration down-regulates XYN1 in xylem cells, leading to probable cell wall modification, which alters CLE26 peptide transport, resulting in drought resistance under subsequent long-term dehydration., (© The Author(s) 2024. Published by Oxford University Press on behalf of National Academy of Sciences.)

Plant genomes contain thousands of short open reading frames that encode putative peptides. Some of these peptides play important signaling roles in response to environmental stress. Here we describe a pipeline used to identify the CTNIP/SMALL PHYTOCYTOKINES REGULATING DEFENSE AND WATER LOSS (SCREW) family of phytocytokines, based upon their transcriptional upregulation during biotic stress. Moreover, we describe approaches to assay their activity in planta by measuring increases in cytoplasmic calcium concentration, reactive oxygen species production, and mitogen-activated protein kinase phosphorylation., (© 2024. The Author(s), under exclusive license to Springer Science+Business Media, LLC, part of Springer Nature.)

Plasma membrane-resident receptor kinases (RKs) are crucial for plants to sense endogenous and exogenous signals in regulating growth, development, and stress response. Upon perception of ligands by the extracellular domain, RKs are usually activated by auto- and/or trans-phosphorylation of the cytoplasmic kinase domain, which in turn phosphorylates downstream substrates to relay the signaling. Therefore, monitoring ligand-induced in vivo phosphorylation dynamics of RKs and their associated proteins provides mechanistic insight into RK activation and downstream signal transduction. Phos-tag specifically binds phosphomonoester dianions of phosphorylated serine, threonine, and tyrosine residues, which enables Phos-tag-containing SDS-PAGE gels to separate phosphorylated proteins from non-phosphorylated form. Here, we describe a detailed method of Mn 2+ -Phos-tag SDS-PAGE analysis to detect the ligand-induced in vivo phosphorylation of RKs and associated proteins., (© 2024. The Author(s), under exclusive license to Springer Science+Business Media, LLC, part of Springer Nature.)

Leucine-rich repeat receptor-like kinases (LRR-RLKs) represent the largest subfamily of receptor-like kinases (RLKs) and play important roles in regulating growth, development, and stress responses in plants. In this study, 246 LRR-RLK genes were identified in the potato (Solanum tuberosum) genome, which were further classified into 14 subfamilies. Gene structure analysis revealed that genes within the same subgroup shared similar exon/intron structures. A signature small peptide recognition motif (RxR) was found to be largely conserved within members of subfamily IX, suggesting that these members may recognize peptide signals as ligands. 26 of the 246 StLRR-RLK genes were found to have arisen from tandem or segmental duplication events. Expression profiling revealed that StLRR-RLK genes were differentially expressed in various organs/tissues, and several genes were found to be responsive to different stress treatments. Furthermore, StLRR-RLK117 was found to be able to form homodimers and heterodimers with StLRR-RLK042 and StLRR-RLK052. Notably, the overlapping expression region of StLRR-RLK117 with Solanum tuberosum WUSCHEL (StWUS) suggested that the CLV3-CLV1/BAM-WUS feedback loop may be conserved in potato to maintain stem cell homeostasis within the shoot apical meristem. [ABSTRACT FROM AUTHOR]

Contents Summary 901 I. Introduction 901 II. Biochemistry and structure of plant SBTs 902 III. Phylogeny of plant SBTs and family organization 903 IV. Physiological roles of plant SBTs 905 V. Conclusions and outlook 911 Acknowledgements 912 References 912 Summary: Subtilases (SBTs) are serine peptidases that are found in all three domains of life. As compared with homologs in other Eucarya, plant SBTs are more closely related to archaeal and bacterial SBTs, with which they share many biochemical and structural features. However, in the course of evolution, functional diversification led to the acquisition of novel, plant‐specific functions, resulting in the present‐day complexity of the plant SBT family. SBTs are much more numerous in plants than in any other organism, and include enzymes involved in general proteolysis as well as highly specific processing proteases. Most SBTs are targeted to the cell wall, where they contribute to the control of growth and development by regulating the properties of the cell wall and the activity of extracellular signaling molecules. Plant SBTs affect all stages of the life cycle as they contribute to embryogenesis, seed development and germination, cuticle formation and epidermal patterning, vascular development, programmed cell death, organ abscission, senescence, and plant responses to their biotic and abiotic environments. In this article we provide a comprehensive picture of SBT structure and function in plants. [ABSTRACT FROM AUTHOR]

The abscission of sepals, petals and stamens in Arabidopsis flowers is controlled by a peptide signal called IDA (Inflorescence Deficient in Abscission). IDA belongs to the large group of small post-translationally modified signaling peptides that are synthesized as larger precursors and require proteolytic processing and specific side chain modifications for signal biogenesis. Using tissue-specific expression of proteinase inhibitors as a novel approach for loss-of-function analysis, we recently identified the peptidases responsible for IDA maturation within the large family of subtilisin-like proteinases (subtilases; SBTs). Further biochemical and physiological assays identified three SBTs (AtSBT5.2, AtSBT4.12, AtSBT4.13) that cleave the IDA precursor to generate the N-terminus of the mature peptide. The C-terminal processing enzyme(s) remain(s) to be identified. While proline hydroxylation was suggested as additional post-translational modification required for IDA maturation, hydroxylated and non-hydroxylated IDA peptides were found to be equally active in bioassays for abscission.

Development of stomata, valves on the plant epidermis for optimal gas exchange and water control, is fine-tuned by multiple signaling peptides with unique, overlapping, or antagonistic activities. EPIDERMAL PATTERNING FACTOR1 (EPF1) is a founding member of the secreted peptide ligands enforcing stomatal patterning. Yet, its exact role remains unclear. Here, we report that EPF1 and its primary receptor ERECTA-LIKE1 (ERL1) target MUTE, a transcription factor specifying the proliferation-to-differentiation switch within the stomatal cell lineages. In turn, MUTE directly induces ERL1. The absolute co-expression of ERL1 and MUTE, with the co-presence of EPF1, triggers autocrine inhibition of stomatal fate. During normal stomatal development, this autocrine inhibition prevents extra symmetric divisions of stomatal precursors likely owing to excessive MUTE activity. Our study reveals the unexpected role of self-inhibition as a mechanism for ensuring proper stomatal development and suggests an intricate signal buffering mechanism underlying plant tissue patterning.

Plants both generate and shed organs throughout their lifetime. Cell separation is in function during opening of anthers to release pollen; floral organs are detached after pollination when they have served their purpose; unfertilized flowers are shed; fruits and seeds are abscised from the mother plant to secure the propagation of new generations. Organ abscission takes place in specialized abscission zone (AZ) cells where the middle lamella between adjacent cell files is broken down. The plant hormone ethylene has a well-documented promoting effect on abscission, but mutation in ethylene receptor genes in Arabidopsis thaliana only delays the abscission process. Microarray and RNA sequencing have identified a large number of genes differentially expressed in the AZs, especially genes encoding enzymes involved in cell wall remodelling and disassembly. Mutations in such genes rarely give a phenotype, most likely due to functional redundancy. In contrast, mutation in the INFLORESCENCE DEFICIENT IN ABSCISSION (IDA) blocks floral organ abscission in Arabidopsis. IDA encodes a small peptide that signals through the leucine-rich repeat receptor-like kinases HAESA (HAE) and HAE-LIKE2 (HSL2) to control floral organ abscission and facilitate lateral root emergence. Untimely abscission is a severe problem in many crops, and in a more applied perspective, it is of interest to investigate whether IDA-HAE/HSL2 is involved in other cell separation processes and other species. Genes encoding IDA and HSL2 orthologues have been identified in all orders of flowering plants. Angiosperms have had enormous success, with species adapted to all kinds of environments, adaptations which include variation with respect to which organs they shed. Here we review, from an evolutionary perspective, the properties of the IDA-HAE/HSL2 signaling module and the evidence for its hypothesized involvement in various cell separation processes in angiosperms.

CLV3/ ESR ( CLE) proteins are important signaling peptides in plants. The short CLE peptide (12-13 amino acids) is cleaved from a larger pre-propeptide and functions as an extracellular ligand. The CLE family is large and has resisted attempts at classification because the CLE domain is too short for reliable phylogenetic analysis and the pre-propeptide is too variable., We used a model-based search for CLE domains from 57 plant genomes and used the entire pre-propeptide for comprehensive clustering analysis., In total, 1628 CLE genes were identified in land plants, with none recognizable from green algae. These CLEs form 12 groups within which CLE domains are largely conserved and pre-propeptides can be aligned. Most clusters contain sequences from monocots, eudicots and Amborella trichopoda, with sequences from Picea abies, Selaginella moellendorffii and Physcomitrella patens scattered in some clusters. We easily identified previously known clusters involved in vascular differentiation and nodulation. In addition, we found a number of discrete groups whose function remains poorly characterized. Available data indicate that CLE proteins within a cluster are likely to share function, whereas those from different clusters play at least partially different roles., Our analysis provides a foundation for future evolutionary and functional studies. [ABSTRACT FROM AUTHOR]

With stunning ocean views over Osaka Bay, Awaji Island played host to the first Cold Spring Harbor Asia Plant Biology meeting in Japan. The meeting, 'Latest Advances in Plant Development and Environmental Response' (CSHAPB), provided a platform to promote scientific communication and collaboration in the pan-pacific region. The event welcomed almost 200 scientists from around the world to showcase their cutting-edge research. Exemplary speakers from diverse research fields presented their latest discoveries, ranging from developmental mechanisms to host-pathogen interactions, environmental responses and stress memory. Here we seek to review the meeting and highlight some of the salient themes that emerged over the course of the 3 d. [ABSTRACT FROM AUTHOR]

The phytosulfokine peptide receptor PSKR1 is modified by phosphorylation of its cytoplasmic kinase domain. We analyzed defined phosphorylation sites by site-directed mutagenesis with regard to kinase activity in vitro and receptor activity in planta. S696 and S698 in the juxtamembrane (JM) domain are phosphorylated in planta. The phosphomimetic S696D/S698D replacements resulted in reduced transphosphorylation activity of PSKR1 kinase in vitro but did not reduce autophosphorylation activity. Growth-promoting activity of the PSKR1(S696D/S698D) receptor isoform was impaired in the shoot but not in the root. The JM domain thus seems to be important for phosphorylation of a target protein required for shoot growth promotion. The phosphomimetic replacement T998D at the C-terminus (CT) abolished kinase activity in vitro but not receptor function in planta, indicating that additional levels of regulation exist in planta. A possible mode of receptor regulation is the interaction with regulatory proteins such as the calcium sensor calmodulin (CaM). We show that the previously reported binding of CaM2 to PSKR1 is calcium-dependent, occurs predominately to the hypophosphorylated soluble PSKR1 kinase, and does not significantly change PSKR1 kinase activity. In conclusion, our results show that peptide signaling of growth by PSKR1 is regulated by differential phosphorylation of the juxtamembrane and C-terminal domains of the intracellular receptor part and suggest that interaction of PSKR1 with CaM serves a function other than the regulation of kinase activity. [ABSTRACT FROM AUTHOR]

The peptide INFLORESCENCE DEFICIENT IN ABSCISSION (IDA), which signals through the leucine-rich repeat receptor-like kinases HAESA (HAE) and HAESA-LIKE2 (HSL2), controls different cell separation events in Arabidopsis thaliana. We hypothesize the involvement of this signaling module in abscission processes in other plant species even though they may shed other organs than A. thaliana. As the first step towards testing this hypothesis from an evolutionarily perspective we have identified genes encoding putative orthologues of IDA and its receptors by BLAST searches of publically available protein, nucleotide and genome databases for angiosperms. Genes encoding IDA or IDA-LIKE (IDL) peptides and HSL proteins were found in all investigated species, which were selected as to represent each angiosperm order with available genomic sequences. The 12 amino acids representing the bioactive peptide in A. thaliana have virtually been unchanged throughout the evolution of the angiosperms; however, the number of IDL and HSL genes varies between different orders and species. The phylogenetic analyses suggest that IDA, HSL2 and the related HSL1 gene, were present in the species that gave rise to the angiosperms. HAE has arisen from HSL1 after a genome duplication that took place after the monocot - eudicots split. HSL1 has also independently been duplicated in the monocots, while HSL2 has been lost in gingers (Zingiberales) and grasses (Poales). IDA has been duplicated in eudicots to give rise to functionally divergent IDL peptides. We postulate that the high number of IDL homologs present in the core eudicots is a result of multiple whole genome duplications. We substantiate the involvement of IDA and HAE/HSL2 homologs in abscission by providing gene expression data of different organ separation events from various species.

Unlike animals, plants often have an indefinite genetic potency to form new organs throughout their entire lifespan. Growth and organogenesis are driven by cell divisions in meristems at distinct sites within the plant. Since the meristems contributing to axial thickening in dicots (cambia) are separated from places where axes elongate (apical meristems); there is a need of communication to coordinate growth. In their behavior, some meristematic cells resemble animal stem cells whose daughter cells either maintain the capacity to divide over a long period of time or undergo differentiation. The behavior of stem cells is regulated by their microenvironment, the so called niche. The stem- and niche-cell concept is now also widely accepted for apical meristems. An integral part of the cambial niche has recently been localized to the phloem. It steers cell division activity in the cambium via the release of a peptide signal and may be a hub to integrate signals from other stem cell populations to coordinate growth. Although these signals have yet to be determined, the discovery of the cambial niche cells will pave the way for a better understanding of inter-meristematic communication and cambial stem cell behavior. [ABSTRACT FROM AUTHOR]

Stem cell maintenance in plants depends on the activity of small secreted signaling peptides of the CLAVATA3/ EMBRYO SURROUNDING REGION (CLE) family, which, in the shoot, act through at least three kinds of receptor complexes, CLAVATA1 (CLV1) homomers, CLAVATA2 (CLV2) / CORYNE (CRN) heteromers, and CLV1/CLV2/CRN multimers. In the root, the CLV2/CRN receptor complexes function in the proximal meristem to transmit signals from the CLE peptide CLE40. While CLV1 consists of an extracellular receptor domain and an intracellular kinase domain, CLV2, a leucine-rich repeat (LRR) receptor-like protein, and CRN, a protein kinase, have to interact to form a receptor-kinase complex. The kinase domain of CRN has been reported to be catalytically inactive, and it is not yet known how the CLV2/CRN complex can relay the perceived signal into the cells, and whether the kinase domain is necessary for signal transduction at all. In this study we show that the kinase domain of CRN is actively involved in CLV3 signal transduction in the shoot apical meristem of Arabidopsis, but it is dispensable for CRN protein function in root meristem maintenance. Hence, we provide an example of a catalytically inactive pseudokinase that is involved in two homologous pathways, but functions in distinctively different ways in each of them. [ABSTRACT FROM AUTHOR]

The members of RRNPP family of bacterial regulators sense population density-specific secreted oligopeptides and modulate the expression of genes involved in cellular processes, such as sporulation, competence, virulence, biofilm formation, conjugative plasmid transfer and antibiotic resistance. Signaling by RRNPP regulators include several steps: generation and secretion of the signaling oligopeptides, re-internalization of the signaling molecules into the cytoplasm, signal sensing by the cytosolic RRNPP regulators, signal-specific allosteric structural changes in the regulators, and interaction of the regulators with their respective regulatory target and gene regulation. The recently determined structures of the RRNPP regulators provide insight into the mechanistic aspects for several steps in this signaling circuit. In this review, we discuss the structural principles underlying peptide specificity, regulatory target recognition, and ligand-induced allostery in RRNPP regulators and its impact on gene regulation. Despite the conserved tertiary structure of these regulators, structural analyses revealed unexpected diversity in the mechanism of activation and molecular strategies that couple the peptide-induced allostery to gene regulation. Although these structural studies provide a sophisticated understanding of gene regulation by RRNPP regulators, much needs to be learned regarding the target DNA binding by yet-to-be characterized RNPP regulators and the several aspects of signaling by Rgg regulators. [ABSTRACT FROM AUTHOR]

Although the last common unicellular ancestor of plants and animals diverged several billion years ago, and while having developed unique developmental programs that facilitate differentiation and proliferation specific to plant and animal systems, there still exists a high degree of conservation in the logic regulating these developmental processes within these two seemingly diverse kingdoms. Stomatal differentiation in plants involves a series of orchestrated cell division events mediated by a family of closely related bHLH transcription factors ( TFs) to create a pair of mature guard cells. These TFs are in turn regulated by a number of upstream signaling components that ultimately function to achieve lineage specific differentiation and organized tissue patterning on the plant epidermis. The logic involved in the specification of the myogenic differentiation program in animals is intriguingly similar to stomatal differentiation in plants: Closely-related myogenic bHLHs, known as MRFs (Myogenic Regulatory Factors) provide lineage specificity essential for cell-fate determination. These MRFs, similar to the bHLHs in plants, are regulated by several upstream signaling cascades that succinctly regulate each differentiation step, leading to the production of mature muscle fibers. This review aims at providing a perspective on the emerging parallels in the logic employed by key bHLH transcription factors and their upstream signaling components that function to precisely regulate key cell-state transition events in the stomatal as well as myogenic cell lineages. [ABSTRACT FROM AUTHOR]

Stomata are dispersed pores found in the epidermis of land plants that facilitate gas exchange for photosynthesis while minimizing water loss. Stomata are formed from progenitor cells, which execute a series of differentiation events and stereotypical cell divisions. The sequential activation of master regulatory basic-helix-loop-helix (bHLH) transcription factors controls the initiation, proliferation and differentiation of stomatal cells. Cell-cell communication mediated by secreted peptides, receptor kinases, and downstream mitogenactivated kinase cascades enforces proper stomatal patterning, and an intrinsic polarity mechanism ensures asymmetric cell divisions. As we review here, recent studies have provided insights into the intrinsic and extrinsic factors that control stomatal development. These findings have also highlighted striking similarities between plants and animals with regards to their mechanisms of specialized cell differentiation. [ABSTRACT FROM AUTHOR]

Key message: EA1-box protein classification. Abstract: Success in reproduction and vegetative development in flowering plants strongly depends on precise cell-to-cell signaling events mediated by secreted peptides. A small peptide family named as EA1-like (EAL) has been first described 10 years ago and includes EA1 involved in pollen tubes attraction by the female gametophyte and EAL1-regulating germ cell identity in maize. EALs consist of an N-terminal endoplasmic reticulum-targeting motif, the highly conserved EA1-box and a short C-terminal alanine-rich domain. Whereas EAL peptides are exclusively found in the Gramineae, the EA1-box is widely distributed throughout the plant kingdom. Based on in silico analysis and subcellular localization studies, we report here a new classification of EA1-box proteins in flowering plants. They can be distinguished into three protein classes: the already defined EAL proteins, the EAG (EA1-box glycine-rich) proteins and the EAC (EA1-box-containing) proteins. While fusion proteins of EAL and EAC classes locate to the secretory pathway, EAGs are cytoplasmic and locate also to the nucleus. Moreover, we further show that the third EAL protein of Zea mays, EAL2, appears to be also involved in processes related to late embryogenic development as its peptide level increases after formation of leaf primordia. Immunohistochemical studies indicate its presence in the scutellar parenchyma and around the vasculature, where it is secreted to the extracellular space. In conclusion, the members of the maize EAL family possess very diverse functions during reproduction and it will now be exciting to elucidate the functions of EAGs and EACs in plants. [ABSTRACT FROM AUTHOR]

Microorganisms adapt to the lab environment by eliminating unnecessary genetic systems. In Bacillus subtilis, such adaptation resulted in the lab strain being unable to form complex, matrix-associated structures known as biofilms. We recently showed that the ancestor of the lab strain, which is considered by the research community to be a stereotypical 'wild' strain, carries an atypical mutation in the RapP-PhrP quorum-sensing system. We have found that this mutation has profound effects on the biofilm phenotype of the ancestral strain. Here we discuss these recent findings and present more data that focuses on the lessons that can be learned from this work on the domestication of microorganisms. [ABSTRACT FROM AUTHOR]

The peptide INFLORESCENCE DEFICIENT IN ABSCISSION (IDA), which signals through the leucine-rich repeat receptor-like kinases HAESA (HAE) and HAESA-LIKE2 (HSL2), controls different cell separation events in Arabidopsis thaiiana. We hypothesize the involvement of this signaling module in abscission processes in other plant species even though they may shed other organs than A. thaiiana. As the first step toward testing this hypothesis from an evolutionarily perspective we have identified genes encoding putative orthologs of IDA and its receptors by BLAST searches of publically available protein, nucleotide and genome databases for angiosperms. Genes encoding IDA or IDA-LIKE (IDL) peptides and HSL proteins were found in all investigated species, which were selected as to represent each angiosperm order with available genomic sequences. The 12 amino acids representing the bioactive peptide in A. thaiiana have virtually been unchanged throughout the evolution of the angiosperms; however, the number of IDL and HSL genes varies between different orders and species. The phylogenetic analyses suggest that IDA, HSL2, and the related HSL1 gene, were present in the species that gave rise to the angiosperms. HAE has arisen from HSL1 after a genome duplication that took place after the monocot--eudicots split. HSL1 has also independently been duplicated in the monocots, while HSL2 has been lost in gingers (Zingiberales) and grasses (Poales). IDA has been duplicated in eudicots to give rise to functionally divergent IDL peptides. We postulate that the high number of IDL homologs present in the core eudicots is a result of multiple whole genome duplications (WGD). We substantiate the involvement of IDA and HAE/HSL2 homologs in abscission by providing gene expression data of different organ separation events from various species. [ABSTRACT FROM AUTHOR]

Small, post-translationally modified and secreted peptides regulate diverse plant developmental processes. Due to low natural abundance, it is difficult to isolate and identify these peptides. Using an improved peptide isolation protocol and Orbitrap mass spectrometry, nine 15-amino-acid CEP peptides were identified that corresponded to the two domains encoded by Medicago truncatula CEP1 (MtCEP1). Novel arabinosylated and hydroxylated peptides were identified in root cultures overexpressing MtCEP1. The five most abundant CEP peptides were hydroxylated and these species were detected also in low amounts in vector control samples. Synthetic peptides with different hydroxylation patterns differentially affected root development. Notably, the domain 1 peptide hydroxylated at Pro4 and Pro11 (D1:HyP4,11) imparted the strongest inhibition of lateral root emergence when grown with 5 mM KNO3 and stimulated the highest increase in nodule number when grown with 0 mM KNO3. Inhibition of lateral root emergence by D1:HyP4,11 was not alleviated by removing peptide exposure. In contrast, the domain 2 peptide hydroxylated at Pro11 (D2:HyP11) increased stage III-IV lateral root primordium numbers by 6-fold (P < 0.001) which failed to emerge. Auxin addition at levels which stimulated lateral root formation in wild-type plants had little or no ameliorating effect on CEP peptide-mediated inhibition of lateral root formation or emergence. Both peptides increased and altered the root staining pattern of the auxin-responsive reporter GH3:GUS suggesting CEPs alter auxin sensitivity or distribution. The results showed that CEP primary sequence and post-translational modifications influence peptide activities and the improved isolation procedure effectively and reproducibly identifies and characterises CEPs. [ABSTRACT FROM AUTHOR]

Growing agricultural demands in the face of impending inorganic phosphate (Pi) shortages underscore a need for a better understanding of plant development under conditions of Pi deprivation. Pi is an essential nutrient that is a major component of fertilizer. Plants have evolved strategies to improve the acquisition of this nutrient by altering root development under shortage conditions. We show that signaling peptides thought to act redundantly in Arabidopsis thaliana development have distinct functions in response to Pi deprivation., Using microscopy and confocal imaging, roots were analyzed for growth rate and cellular composition. Using expression microarrays, genes influencing development in response to phosphate deprivation were identified., ROOT GROWTH FACTOR1 ( RGF1) and RGF2 influenced different aspects of root development under conditions of Pi deprivation. We found that RGF2 influenced the longitudinal growth rate in the primary root in response to Pi deprivation, whereas RGF1 affected circumferential cell number in the root meristem., These data suggest that the mechanisms controlling adaptive development can depend on disparate functions of genes thought to act redundantly, thus elucidating new functions for important developmental regulators. [ABSTRACT FROM AUTHOR]

Plant root systems arise de novo from a single embryonic root. Complex and highly coordinated developmental networks are required to ensure the formation of lateral organs maximises plant fitness. The Arabidopsis root is well suited to dissection of regulatory and developmental networks due to its highly ordered, predictable structure. A myriad of regulatory signalling networks control the development of plant roots, from the classical hormones such as auxin and cytokinin to short-range positional signalling molecules that relay information between neighbouring cells. Small signaling peptides are a growing class of regulatory molecules involved in many aspects of root development including meristem maintenance, the gravitropic response, lateral root development and vascular formation. Here, recent findings on the roles of regulatory peptides in these aspects of root development are discussed.