The Plant Peptidome: An Expanding Repertoire of Structural Features and Biological Functions

Root-derived small peptides: Key regulators of plant development, stress resilience, and nutrient acquisition

Small peptides (SPs), emerging as crucial signaling molecules in plants, regulate diverse processes such as plant development, stress tolerance, and nutrient acquisition. Consisting of fewer than 100 amino acids, SPs are classified into two main groups: precursor-derived SPs and small open reading frame (sORF)-encoded SPs, including miRNA-encoded SPs. SPs are secreted from various plant parts, with root-derived SPs playing particularly significant roles in stress tolerance and nutrient uptake. Even at low concentrations, root-derived SPs are highly effective signaling molecules that influence the distribution and effects of phytohormones, particularly auxin. For instance, under low phosphorus conditions, CLAVATA3/Embryo-Surrounding Region-Related (CLE/CLV), a root-derived SP, enhances root apical meristem differentiation and root architecture to improve phosphate acquisition. By interacting with CLV2 and PEPR2 receptors, it modulates auxin-related pathways, directing root morphology changes to optimize nutrient uptake. During nitrogen (N) starvation, root-derived SPs are transported to the shoot, where they interact with leucine-rich repeat receptor kinases (LRR-RKs) to alleviate nitrogen deficiency. Similarly, C-terminally Encoded Peptides (CEPs) are involved in primary root growth and N-acquisition responses. Despite the identification of many SPs, countless others remain to be discovered, and the functions of those identified so far remain elusive. This review focuses on the functions of root-derived SPs, such as CLE, CEP, RALF, RGF, PSK, PSY, and DVL, and discusses the receptor-mediated signaling pathways involved. Additionally, it explores the roles of SPs in root architecture, plant development, and their metabolic functions in nutrient signaling.

MhIDA small peptides modulate the growth and development of roots in Malus hupehensis

KEY MESSAGE

MhIDA small peptides promote apple root growth by enhancing auxin synthesis and cell wall remodeling gene expression, revealing a peptide-based strategy to improve root architecture. Although small peptides have been well documented as crucial regulators of plant growth and development, the molecular mechanisms underlying lateral root morphogenesis in Malus hupehensis remain poorly understood. In this research, exogenous application of 1 µM MhIDA-Like family peptides increased primary root (PR) length by 14.31-19.96% and lateral root (LR) number by 124.54-149.08%. MhIDA, predominant expression in the root tip and lateral root primordium, demonstrated the most substantial promoting effects on PR elongation, LR number and density when the treatment concentration reached 1 µM. Furthermore, similar effects were found in MhIDA-overexpression transgenic apple seedlings, with the number and density of transgenic LRs increase by 80.52 and 126.86%, respectively, compared with wild-type seedlings. More importantly, 1 µM MhIDA treatment induced significant hormonal alterations, with the content of auxin, salicylic acid and gibberellic acid increasing by 1.5-fold, 1.4-fold, and 2.1-fold, respectively, compared to control. The qRT-PCR results showed that MhIDA could induce the expression of auxin synthesis genes (MhTAA1 and MhYUCC1) that were up-regulated by about twofold, and the cell wall remodeling-related genes (MhEXP17, MhXTR6, MhPGAZAT and MhPGLR) were upregulated by about 2- to 4-fold after 1 µM MhIDA treatment, thereby regulating LR emergence and formation of Malus hupehensis. Overall, these findings suggested the MhIDA peptide can promote the growth and development of roots, laying the foundation for cultivating apple rootstocks with strong roots and higher resistance to abiotic stress.

lncRNA-Encoded Small Peptide Promotes Viral Infection

The small open reading frames (ORFs) embedded in lncRNA have been identified to encode biologically functional peptides in many species. However, the function of lncRNA-encoded small peptides in the plant antiviral response remains unclear. In this study, an lncRNA Talnc54748 was identified, which encodes the small peptide ORF4. Transgenic Nicotiana benthamiana overexpressing ORF4 could enhance wheat yellow mosaic virus (WYMV) infection. RNA-sequencing analysis revealed that many genes in plant hormone signalling and MAPK signalling pathways were reduced in ORF4-overexpressing lines. The function of SAUR21 and MKK2, involved in plant hormone signalling and MAPK signalling pathways, respectively, was investigated by virus-induced gene silencing assay. Silencing SAUR21 or MKK2 in wheat and N. benthamiana enhanced WYMV infection. Transgenic overexpression of ORF4 not only enhanced the accumulation of tobacco mosaic virus (TMV) and tomato mosaic virus (ToMV), but also promoted Phytophthora capsici or Pseudomonas syringae pv. tomato DC3000 infection. Our results demonstrated that an lncRNA-encoded small peptide plays an important role in plant immunity and provides new insights into the roles of this lncRNA-encoded small peptide in the plant antiviral response.

Comprehensive review of plant small signaling peptides: From stress adaptation mechanisms to practical solutions for crop resilience

Small signaling peptides (SSPs), short proteins of fewer than 100 amino acids, serve as pivotal signaling molecules with diverse structural features, post-translational modifications, and functional roles. They regulate various aspects of plant growth and development by modulating specific cellular signaling pathways. Research has shown that many SSPs are essential for mediating responses to environmental stresses. This review presents the structure, characteristics, and classification of plant SSPs and elucidates their roles in resistance signaling pathways through interactions with their specific receptors. We then summarize recent findings on the biological functions and regulatory mechanisms of SSPs in response to both biotic and abiotic stresses. Finally, we discuss the potential applications and future prospects of these peptides in plant protection. This review offers valuable insights for enhancing plant resilience to environmental stress and advancing sustainable agricultural practices, while also providing key references and perspectives to accelerate research on SSPs in plants.

A novel peptide encoded by a rice circular RNA confers broad-spectrum disease resistance in rice plants

Circular RNAs (circRNAs) are a significant class of endogenous RNAs that exert crucial biological functions in human and animal systems, but little is currently understood regarding their roles in plants. Here, we identified a circRNA originating from the back-splicing of exon 4 and exon 5 of a rice gene, OsWRKY9, and named it circ-WRKY9. It is upregulated in rice stripe mosaic virus (RSMV)-infected rice plants. Notably, circ-WRKY9 contains two open reading frames with an internal ribosome entry site. We found that circ-WRKY9 encoded a peptide of 88 amino acids (aa) and named it WRKY9-88aa. Overexpression of WRKY9-88aa suppresses RSMV infection in rice plants, with increased reactive oxygen species production. Furthermore, WRKY9-88aa enhances resistance to blast disease and bacterial leaf blight, suggesting its potential to provide broad-spectrum disease resistance. Our findings provide the first evidence of a peptide encoded by a circRNA in planta and highlight its potential application to control a wide spectrum of plant diseases.

A plant peptide with dual activity against multidrug-resistant bacterial and fungal pathogens

Multidrug-resistant (MDR) bacteria pose a major threat to public health, and additional sources of antibacterial candidates are urgently needed. Noncanonical peptides (NCPs), derived from noncanonical small open reading frames, represent small biological molecules with important roles in biology. However, the antibacterial activity of NCPs remains largely unknown. Here, we discovered a plant-derived noncanonical antibacterial peptide (NCBP1) against both Gram-positive and Gram-negative bacteria. NCBP1 is composed of 11 amino acid residues with cationic surface potential and favorable safety and stability. Mechanistic studies revealed that NCBP1 displayed antibacterial activity by targeting phosphatidylglycerol and cardiolipin in bacterial membrane, resulting in membrane damage and dysfunction. Notably, NCBP1 showed promising efficacy in mice. Furthermore, NCBP1 effectively inhibited the growth of plant fungal pathogens and enhanced disease resistance in maize. Our results demonstrate the unexplored antimicrobial potential of plant-derived NCPs and provide an accessible source for the discovery of antimicrobial substances against MDR bacterial and fungal pathogens.

Decoding small peptides: Regulators of plant growth and stress resilience

Small peptides (SPs) are pivotal signaling molecules that play essential roles in the precise regulation of plant growth, development, and stress responses. Recent advancements in sequencing technologies, bioinformatics approaches, and biochemical and molecular techniques have significantly enhanced the accuracy of SP identification, unveiling their diverse biological functions in plants. This review provides a comprehensive overview of the characteristics and methodologies for identifying SPs in plants. It highlights recent discoveries regarding the biological roles and signaling pathways of SPs in regulating plant growth, development, and plant-microbial interactions, as well as their contributions to plant resilience under various environmental stresses, including abiotic stress, nutrient deficiencies, and biotic challenges. Additionally, we discuss current insights into the potential applications of SPs and outline future research directions aimed at leveraging these molecules to enhance plant adaptation to environmental challenges. By integrating recent findings, this review lays a foundation for advancing the understanding and utilization of SPs to improve plant resilience and productivity.

Phytocytokine genes newly discovered in Malus domestica and their regulation in response to Erwinia amylovora and acibenzolar-S-methyl

Phytocytokines belong to a category of small secreted peptides with signaling functions that play pivotal roles in diverse plant physiological processes. However, due to low levels of sequence conservation across plant species and poorly understood biological functions, the accurate detection and annotation of corresponding genes is challenging. The availability of a high-quality apple (Malus domestica) genome has enabled the exploration of five phytocytokine gene families, selected on the basis of their altered expression profiles in response to biotic stresses. These include phytosulfokine, inflorescence deficient in abscission/-like, pathogen-associated molecular pattern induced secreted peptide, plant peptide containing sulfated tyrosine, and C-terminally encoded peptide. The genes encoding the precursors of these five families of signaling peptides were identified using a customized bioinformatics protocol combining genome mining, homology searches, and peptide motif detection. Transcriptomic analyses showed that these peptides were deregulated in response to Erwinia amylovora, the causal agent of fire blight in pome fruit trees, and in response to a chemical elicitor (acibenzolar-S-methyl). Finally, gene family evolution and the orthology relationships with Arabidopsis thaliana homologs were investigated.

Engineering crop performance with upstream open reading frames

Plants intricately regulate the expression of protein-coding genes at multiple stages - including mRNA transcription, translation, decay, and protein degradation - to control growth, development, and responses to environmental challenges. Recent research highlights the importance of translational reprogramming as a pivotal mechanism in regulating gene expression across diverse physiological scenarios. This regulatory mechanism bears practical implications, particularly in bolstering crop productivity by manipulating RNA regulatory elements (RREs) to modulate heterologous gene expression through transgene and endogenous gene expression through gene editing. Here, we elucidate the potential of upstream open reading frames (uORFs), a prominent and stringent class of RREs, in optimizing crop performance, exemplifying the efficacy of translational control in enhancing agricultural yields.

Comparative analysis of small secreted peptide signaling during defense response: insights from vascular and non-vascular plants

Small secreted peptides (SSPs) play an important role in modulating immune responses in all land plants. However, the evolution of stress peptide signaling in different plant phyla remains poorly understood. Here, we compared the expression of SSP genes in the pathogen-induced transcriptomes of vascular and non-vascular plants. We found 13, 19, 15, and 28 SSP families that were differentially expressed during infection in Physcomitrium patens, Zea mays, Brassica napus, and Solanum tuberosum, respectively. A comparative study of peptide motifs and predicted three-dimensional structures confirmed the similarity of SSPs across the examined plant species. In both vascular and non-vascular plants. However, only the RALF peptide family was differentially regulated under infection. We also found that EPFL peptides, which are involved in growth and development processes in angiosperms, were differentially regulated in P. patens in response to pathogen infection. The search for novel immune-specific peptides revealed a family of PSY-like peptides that are differentially regulated during infection in P. patens. The treatment with synthetic tyrosine-modified and non-modified PSY, and PSY-like peptides, as well as recombinant EPFL and MEG, validated their roles in the immune response and growth regulation. Thus, our study showed the complex nature of SSP signaling and shed light on the regulation of SSPs in different plant lineages during infection.

Evaluation of Salt-Tolerant Germplasms and Identification of Salt Tolerance-Related Proteins in Upland Cotton at the Seedling Stage

Currently, developing cotton cultivation in saline-alkali soils is a vital focus for restructuring the cotton industry in China. The seedling stage, specifically the three-leaf stage, is a crucial period for assessing the salt tolerance of cotton. This research examined 430 natural populations of upland cotton, including 45 semi-wild germlines of Gossypium purpurascens. We measured the phenotypic responses of salt stress injury on seedlings as well as potassium (K), calcium (Ca), sodium (Na), and magnesium (Mg) concentrations in the roots, stems, and leaves following a 72 h exposure. The comprehensive salt tolerance index (CSTI) was determined using a membership function, principal component analysis, and cluster analysis based on 48 phenotypic traits related to salt tolerance. The results revealed significant variations in the phenotypic traits of the ion group under salt stress. Salt stress greatly affected the relative contents of Mg, K, and Ca ions in the aboveground parts of cotton, and correlations were observed among the 48 indices. The CSTI was calculated using seven principal component indexes, identifying 30 salt-tolerant, 114 weakly salt-tolerant, 39 salt-sensitive, and 4 highly sensitive materials based on cluster analysis. Among the 45 G. purpurascens cotton resources, 28 were weakly salt-tolerant, while 17 were salt-sensitive. Through TMT (Tandem Mass Tag)-based quantitative analysis, we identified 3107 unique peptides among 28,642 detected peptides, resulting in 203,869 secondary mass spectra, with 50,039 spectra successfully matched to peptides. Additionally, we identified several salt tolerance-related pathways (carbon metabolism; glutathione metabolism; the biosynthesis of amino acids, etc.) and proteins classified within the CAZy (Carbohydrate-Active EnZYme) family and expansin proteins. The results of this study concerning salt-tolerant materials provide a crucial theoretical foundation for the identification and evaluation of salt-tolerant breeding parents in cultivated cotton.

Genome-Wide Identification and Functional Analysis of CLAVATA3/EMBRYO SURROUNDING REGION-RELATED (CLE) in Three Populus Species

Intercellular communication mediated by CLAVATA3/EMBRYO SURROUNDING REGION-RELATED (CLE) peptides and their receptors is crucial for plant development and environmental adaptation. In this study, 45 and 89 CLEs were identified in Populus tomentosa and Populus alba × Populus glandulosa, respectively, and, together with the 52 CLEs in Populus trichocarpa, the chromosome localization, gene and protein characteristics, collinearity and gene duplication events, cis-acting regulatory elements in promoters and evolutionary relationships of CLEs in these three poplar species were analyzed. The CLEs of three poplar species were divided into four subfamilies. Among them, the CLEs in subfamilies I, II and IV were A-type CLEs, while those in subfamily III were B-type CLEs. During the evolutionary process of poplar, the selection pressure faced by whole-genome duplication or segmental duplication was purifying selection, and the duplication events led to the expansion of the CLE family in poplar. The exogenous addition of a certain concentration of poplar CLE13 peptides inhibits the root growth of Arabidopsis thaliana and poplar and simultaneously reduces the expression levels of ARFs and LBDs in the roots. In addition, drought stress induces the expression of PtrCLE13A. The overexpression of preCLE13A significantly enhances the osmotic and drought tolerance in Populus tomentosa. These results have provided valuable information for further research on the molecular mechanisms of CLE peptide signaling pathways in the woody model plant poplar regarding plant growth and stress resistance.

Datura alba seed proteins effect on snake venom enzymes with antioxidant and antibacterial activities

Objective

This study assessed the inhibitory potential of proteins extracted from Datura alba seeds on snake venom toxic enzymes along with their potential antioxidant and antibacterial activities.

Methods

Crude proteins were extracted using common biological buffers (20 mM acetate, 20 mM phosphate and 20 mM Tris) at a ratio of 1:5 followed by 80 % ammonium sulfate precipitation, dialysis, and lyophilization. Then the lyophilized extracts were resolved on 15 % sodium dodecyl sulfate polyacrylamide electrophoresis (SDS-PAGE) gels. The Tris extract showing the maximum number of protein bands on the SDS gel was further assessed for inhibitory bioactivities. Specifically, the agar well diffusion method was performed to assess the inhibitory activities of phospholipase A2 (PLA2), protease, and α-amylase using 2 % egg yolk, 5 % skim milk and 1 % starch as substrates, respectively. Naja naja, Echis carinatus venom, and human saliva were used as sources of PLA2, protease, and amylase, respectively, to test the inhibitory activity of the extract on these enzymes. Antioxidant activity was determined by the 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging assay using ascorbic acid as a standard. Antibacterial activity was assessed by the agar well diffusion method using Escherichia coli and Staphylococcus aureus as bacterial sources.

Results

The Tris extract of seed proteins exhibited 19 % inhibition of snake venom PLA2 at a concentration of 125 μg/μL concentration, whereas no venom protease inhibition or antibacterial activity was observed at the highest concentrations analyzed. Significant antioxidant activity (44.9 %) was observed at 600 μg/μL, while α-amylase-enhancing activity in a concentration-dependent manner was noted.

Conclusion

The results of this study demonstrated snake venom PLA2 neutralization, which is a major toxic enzyme present in snake venom, along with significant antioxidant properties. This study highlights the potential of Datura seed proteins as an antiophidic along with other therapeutically important applications.

Natural variation in root exudate composition in the genetically structured Arabidopsis thaliana in the Iberian Peninsula

Plant root exudates are involved in nutrient acquisition, microbial partnerships, and inter-organism signaling. Yet, little is known about the genetic and environmental drivers of root exudate variation at large geographical scales, which may help understand the evolutionary trajectories of plants in heterogeneous environments. We quantified natural variation in the chemical composition of Arabidopsis thaliana root exudates in 105 Iberian accessions. We identified up to 373 putative compounds using ultra-high-performance liquid chromatography coupled with mass spectrometry. We estimated the broad-sense heritability of compounds and conducted a genome-wide association (GWA) study. We associated variation in root exudates to variation in geographic, environmental, life history, and genetic attributes of Iberian accessions. Only 25 of 373 compounds exhibited broad-sense heritability values significantly different from zero. GWA analysis identified polymorphisms associated with 12 root exudate compounds and 26 known genes involved in metabolism, defense, signaling, and nutrient transport. The genetic structure influenced root exudate composition involving terpenoids. We detected five terpenoids related to plant defense significantly varying in mean abundances in two genetic clusters. Our study provides first insights into the extent of root exudate natural variation at a regional scale depicting a diversified evolutionary trajectory among A. thaliana genetic clusters chiefly mediated by terpenoid composition.

The Small Key to the Treasure Chest: Endogenous Plant Peptides Involved in Symbiotic Interactions

Plant growth and development are inextricably connected with rhizosphere organisms. Plants have to balance between strong defenses against pathogens while modulating their immune responses to recruit beneficial organisms such as bacteria and fungi. In recent years, there has been increasing evidence that regulatory peptides are essential in establishing these symbiotic relationships, orchestrating processes that include nutrient acquisition, root architecture modification, and immune modulation. In this review, we provide a comprehensive summary of the peptide families that facilitate beneficial relationships between plants and rhizosphere organisms.

Peptide hormones in plants

Peptide hormones are defined as small secreted polypeptide-based intercellular communication signal molecules. Such peptide hormones are encoded by nuclear genes, and often go through proteolytic processing of preproproteins and post-translational modifications. Most peptide hormones are secreted out of the cell to interact with membrane-associated receptors in neighboring cells, and subsequently activate signal transductions, leading to changes in gene expression and cellular responses. Since the discovery of the first plant peptide hormone, systemin, in tomato in 1991, putative peptide hormones have continuously been identified in different plant species, showing their importance in both short- and long-range signal transductions. The roles of peptide hormones are implicated in, but not limited to, processes such as self-incompatibility, pollination, fertilization, embryogenesis, endosperm development, stem cell regulation, plant architecture, tissue differentiation, organogenesis, dehiscence, senescence, plant-pathogen and plant-insect interactions, and stress responses. This article, collectively written by researchers in this field, aims to provide a general overview for the discoveries, functions, chemical natures, transcriptional regulations, and post-translational modifications of peptide hormones in plants. We also updated recent discoveries in receptor kinases underlying the peptide hormone sensing and down-stream signal pathways. Future prospective and challenges will also be discussed at the end of the article.

An evaluation study on screening, partial purification, and characterization of proteins and antioxidant peptides from two varieties of Clitoria Ternatea

This study focused on the unexplored bioactive proteins derived from the flower of Clitoria ternatea. The profiling of blue and white C. ternatea flowers was compared. After extraction, the samples underwent ultrafiltration and the isolation of the protein peptides was done by using four different buffers. The highest yield was found in the case of phosphate buffered-based extracts in blue C. ternatea flower. The single HPLC peak at 220 nm with a high area percentage confirmed the presence of peptides in all the 3 kDa filtrates of C. ternatea. These 3 kDa filtrates were concentrated by using a C-18 zip tip method, with alpha-cyano-4-hydroxycinnamic acid as a substrate for MALDI-TOF-MS-based peptide mass analysis. To determine the antioxidant activity of the peptides, four different assays including DPPH, ABTS, FRAP and NOS were used and it was observed that the blue C. ternatea flower exhibited the potential activity when compared to the white C. ternatea flower. Among all, the phosphate buffer filtrate exhibited the highest antioxidant activity. The binding affinity of the identified protein peptides APCPNR, LGLFR, LIPQE and SISWSS from blue and white flower were evaluated against amyloid beta (Aβ) and acetylcholinesterase (AChE) targets of Alzheimer's disease by in silico analysis.

Peptide AEDL and Glutathione Stimulates Root Development Nicotiana tabacum

Reactive oxygen species (ROS) are essential molecules involved in intercellular communication, signal transduction, and metabolic processes. Abiotic stresses cause the accumulation of excess ROS in plant cells. The issue of regulating the antioxidant protection of plants using natural and synthetic compounds with antioxidant activity still remains one of the most important and relevant areas of fundamental and applied research. Glutathione (GSH) plays an important role in the stress resistance and redox homeostasis of plant cells and effectively protects the cell from the stress-induced generation of ROS. An increase in the GSH content in plant cells can contribute to an increase in plant resistance to various types of stressors. We have shown that growing Nicotiana tabacum in the presence of tetrapeptide AEDL (AlaGluAspLeu) contributes to an increase in the GSH content by 3.24 times. At the same time, the tobacco plant was more developed, especially its root system. A scheme of the mechanism behind the regulation of the redox balance in the stem cell niche and the participation of the AEDL and GSH peptides in the regulation of the fate of stem cells was proposed.

SCOOP10 and SCOOP12 peptides act through MIK2 receptor-like kinase to antagonistically regulate Arabidopsis leaf senescence

Leaf senescence plays a critical role in a plant's overall reproductive success due to its involvement in nutrient remobilization and allocation. However, our current understanding of the molecular mechanisms controlling leaf senescence remains limited. In this study, we show that the receptor-like kinase MALE DISCOVERER 1-INTERACTING RECEPTOR-LIKE KINASE 2 (MIK2) functions as a negative regulator of leaf senescence. We found that the SERINE-RICH ENDOGENOUS PEPTIDE 12, previously known to physically interact with MIK2, competes with SCOOP10 to regulate MIK2-dependent leaf senescence. We observed that increased expression of SCOOP10 or the application of exogenous SCOOP10 peptides accelerated leaf senescence in a MIK2-dependent manner. Conversely, SCOOP12 acted as a suppressor of MIK2-dependent leaf senescence regulation. Biochemical assays showed that SCOOP12 enhances while SCOOP10 diminishes MIK2 phosphorylation. Thus, the SCOOP12-MIK2 module might function antagonistically on SCOOP10-MIK2 signaling at late senescing stages, allowing for fine-tuned modulation of the leaf senescence process. Our study sheds light on the complex mechanisms underlying leaf senescence and provides valuable insights into the interplay between receptors, peptides, and the regulation of plant senescence.

An emerging connected view: Phytocytokines in regulating stomatal, apoplastic, and vascular immunity

Foliar pathogens exploit natural openings, such as stomata and hydathodes, to invade plants, multiply in the apoplast, and potentially spread through the vasculature. To counteract these threats, plants dynamically regulate stomatal movement and apoplastic water potential, influencing hydathode guttation and water transport. This review highlights recent advances in understanding how phytocytokines, plant small peptides with immunomodulatory functions, regulate these processes to limit pathogen entry and proliferation. Additionally, we discuss the coordinated actions of stomatal movement, hydathode guttation, and the vascular system in restricting pathogen entry, multiplication, and dissemination. We also explore future perspectives and key questions arising from these findings, aiming to advance our knowledge of plant immunity and improve disease resistance strategies.

Transcriptional junk: Waste or a key regulator in diverse biological processes?

Plant genomes, through their evolutionary journey, have developed a complex composition that includes not only protein-coding sequences but also a significant amount of non-coding DNA, repetitive sequences, and transposable elements, traditionally labeled as "junk DNA". RNA molecules from these regions, labeled as "transcriptional junk," include non-coding RNAs, alternatively spliced transcripts, untranslated regions (UTRs), and short open reading frames (sORFs). However, recent research shows that this genetic material plays crucial roles in gene regulation, affecting plant growth, development, hormonal balance, and responses to stresses. Additionally, some of these regulatory regions encode small proteins, such as miRNA-encoded peptides (miPEPs) and microProteins (miPs), which interact with DNA or nuclear proteins, leading to chromatin remodeling and modulation of gene expression. This review aims to consolidate our understanding of the diverse roles that these so-called "transcriptional junk" regions play in regulating various physiological processes in plants.

Chickpea NCR13 disulfide cross-linking variants exhibit profound differences in antifungal activity and modes of action

Small cysteine-rich antifungal peptides with multi-site modes of action (MoA) have potential for development as biofungicides. In particular, legumes of the inverted repeat-lacking clade express a large family of nodule-specific cysteine-rich (NCR) peptides that orchestrate differentiation of nitrogen-fixing bacteria into bacteroids. These NCRs can form two or three intramolecular disulfide bonds and a subset of these peptides with high cationicity exhibits antifungal activity. However, the importance of intramolecular disulfide pairing and MoA against fungal pathogens for most of these plant peptides remains to be elucidated. Our study focused on a highly cationic chickpea NCR13, which has a net charge of +8 and contains six cysteines capable of forming three disulfide bonds. NCR13 expression in Pichia pastoris resulted in formation of two peptide folding variants, NCR13_PFV1 and NCR13_PFV2, that differed in the pairing of two out of three disulfide bonds despite having an identical amino acid sequence. The NMR structure of each PFV revealed a unique three-dimensional fold with the PFV1 structure being more compact but less dynamic. Surprisingly, PFV1 and PFV2 differed profoundly in the potency of antifungal activity against several fungal plant pathogens and their multi-faceted MoA. PFV1 showed significantly faster fungal cell-permeabilizing and cell entry capabilities as well as greater stability once inside the fungal cells. Additionally, PFV1 was more effective in binding fungal ribosomal RNA and inhibiting protein translation in vitro. Furthermore, when sprayed on pepper and tomato plants, PFV1 was more effective in reducing disease symptoms caused by Botrytis cinerea, causal agent of gray mold disease in fruits, vegetables, and flowers. In conclusion, our work highlights the significant impact of disulfide pairing on the antifungal activity and MoA of NCR13 and provides a structural framework for design of novel, potent antifungal peptides for agricultural use.

A comprehensive atlas of endogenous peptides in maize

In this study, we present a comprehensive peptidomic atlas of 13 maize tissues, covering both vegetative and reproductive phases. Using a three-frame translation of canonical coding sequences, we identified 6100 nonredundant endogenous peptides, significantly expanding the known plant peptide repertoire. By integrating peptidomic coexpression profiles with previously reported proteomic profiles, we found that the peptide abundance did not consistently correlate with the abundance of their source proteins, suggesting the presence of complex regulatory mechanisms. This integrated peptidomic and proteomic map can serve as a valuable resource for exploring the functional roles of endogenous peptides in maize development and facilitates the investigation of the functional relationship among genes, peptides, and proteins across various biological contexts.

The parallel narrative of RGF/GLV/CLEL peptide signalling

Plant peptide families share distinct characteristics, and many members are in homologous signalling pathways controlling development and responses to external signals. The root meristem growth factor (RGF) peptides/GOLVEN (GLV)/CLAVATA3-ESR-related like (CLEL) are a family of short signalling peptides that are derived from a precursor protein and undergo post-translational modifications. Their role in root meristem development is well established and recent efforts have identified subtilase processing pathways and several downstream signalling components. This discovery has enabled the convergence of previously distinct pathways and enhanced our understanding of plant developmental processes. Here, we review the structure-function relationship of RGF peptides, the post-translational modification pathways, and the downstream signalling mechanisms and highlight components of these pathways that are known in non-RGF-mediated pathways.

Functional Characterization of Plant Peptide-Containing Sulfated Tyrosine (PSY) Family in Wheat (Triticum aestivum L.)

The plant peptide-containing sulfated tyrosine (PSY) family plays critical roles in plant cell proliferation and stress responses. However, the functional characterization of the PSY peptide family in wheat remains unclear. This study systematically identified a total of 29 TaPSY genes at the genome-wide level, classifying them into six subgroups based on PSY-like motifs. These peptides contain a highly conserved active peptide domain, closely resembling the Arabidopsis AtPSY1 motif. All TaPSY homologs are predicted to have a sulfated tyrosine catalyzed by plant tyrosylprotein sulfotransferase (TPST). The TaPSY genes displayed distinct expression patterns across various tissues, with most genes showing higher expression levels in roots and stems. Synthetic sulfated TaPSY peptides enhanced root growth in both wild-type Arabidopsis and the tpst-1 mutant plants. In wheat, exogenous application of TaPSY peptides also promoted root growth, with the synthetic TaPSY5 peptide affecting reactive oxygen species levels in wheat taproots to stimulate primary root growth. Furthermore, transgenic Arabidopsis plants overexpressing TaPSY10 exhibited longer primary roots and increased lateral root numbers. These findings provide insights into the physiological roles of TaPSY peptides in regulating wheat root growth.

A mass spectrometry-based peptidomic dataset of the spermosphere in common bean (Phaseolus vulgaris L.) seeds

The spermosphere, a dynamic microenvironment surrounding germinating seeds, is shaped by the complex interactions between natural compounds exuded by seeds and seed-associated microbial communities. While peptides exuded by plants are known to influence microbiota diversity, little is known about those specifically exuded by seeds. In this study, we characterised the peptidome profile of the spermosphere for the first time using seeds from eight genotypes of common bean (Phaseolus vulgaris) grown in two contrasting production regions. An untargeted LC-MS/MS peptidomic analysis revealed 3,258 peptides derived from 414 precursor proteins of common bean in the spermosphere. This comprehensive peptidomic dataset provides valuable insights into the characteristics of peptides exuded by common bean seeds in the spermosphere. It can be used to identify peptides with potential antimicrobial or other biological activities, advancing our understanding of the functional roles of seed-exuded peptides in the spermosphere.

CLE peptide signaling in plant-microbe interactions

Cell-cell communication is essential for both unicellular and multicellular organisms. Secreted peptides that act as diffusive ligands are utilized by eukaryotic organisms to transduce information between cells to coordinate developmental and physiological processes. In plants, The CLAVATA3/EMBRYO SURROUNDING REGION-RELATED (CLE) genes encode a family of secreted small peptides which play pivotal roles in stem cell homeostasis in various types of meristems. Accumulated evidence has revealed that CLE peptides mediate trans-kingdom interactions between plants and microbes, including pathogens and symbionts. This review highlights the emerging roles of CLE peptide signaling in plant-microbe interactions, focusing on their involvement in nodulation, immunity, and symbiosis with arbuscular mycorrhizal fungi. Understanding these interactions provides insights into the sophisticated regulatory networks to balance plant growth and defense, enhancing our knowledge of plant biology and potential agricultural applications.

Genome-Wide Identification of the RALF Gene Family and Expression Pattern Analysis in Zea mays (L.) under Abiotic Stresses

Rapid Alkalization Factor (RALF) is a signaling molecule in plants that plays a crucial role in growth and development, reproductive processes, and responses to both biotic and abiotic stresses. Although RALF peptides have been characterized in Arabidopsis and rice, a comprehensive bioinformatics analysis of the ZmRALF gene family in maize is still lacking. In this study, we identified 20 RALF genes in the maize genome. Sequence alignment revealed significant structural variation among the ZmRALF family genes. Phylogenetic analysis indicates that RALF proteins from Arabidopsis, rice, and maize can be classified into four distinct clades. Duplication events suggest that the expansion of the RALF gene family in maize primarily relies on whole-genome duplication. ZmRALF genes are widely expressed across various tissues; ZmRALF1/15/18/19 are highly expressed in roots, while ZmRALF6/11/14/16 are predominantly expressed in anthers. RNA-seq and RT-qPCR demonstrated that the expression levels of ZmRALF7, ZmRALF9, and ZmRALF13 were significantly up-regulated and down-regulated in response to PEG and NaCl stresses, respectively. Overall, our study provides new insights into the role of the RALF gene family in abiotic stress.

Complex of Defense Polypeptides of Wheatgrass (Elytrigia elongata) Associated with Plant Immunity to Biotic and Abiotic Stress Factors

Plant defense polypeptides play a crucial role in providing plants with constitutive immunity against various biotic and abiotic stressors. In this study, we explored a complex of proteins from wheatgrass (Elytrigia elongata) spikelets to estimate their role in the plant's tolerance to various environmental factors. The current research shows that in vitro protein extracts from E. elongata spikelets possess antifungal activity against certain Fusarium species, which are specific cereal pathogens, at concentrations of 1-2 mg/mL. In this study, we reproduced these antifungal activities using a 4 mg/mL extract in artificial fungal infection experiments on wheat grain (Triticum aestivum) under controlled laboratory conditions. Furthermore, the tested extract demonstrated a protective effect on Saccharomyces cerevisiae exposed to hyper-salinity stress at a concentration of 2 mg/mL. A combined scheme of fractionation and structural identification was applied for the estimation of the diversity of defense polypeptides. Defensins, lipid-transfer proteins, hydrolase inhibitors (cereal bifunctional trypsin/alpha-amylase inhibitors from a Bowman-Birk trypsin inhibitor), and high-molecular-weight disease resistance proteins were isolated from the extract. Thus, wheatgrass spikelets appear to be a reservoir of defense polypeptides. Our findings contribute to a deeper understanding of plant defense proteins and peptides and their involvement in the adaptation to various stress factors, and they reveal the regulatory effect at the ecosystem level.

NCPbook: A comprehensive database of noncanonical peptides

Noncanonical peptides (NCPs) are a class of peptides generated from regions previously thought of as noncoding, such as introns, 5' UTRs, 3' UTRs, and intergenic regions. In recent years, the significance and diverse functions of NCPs have come to light, yet a systematic and comprehensive NCP database remains absent. Here, we developed NCPbook (https://ncp.wiki/ncpbook/), a database of evidence-supported NCPs, which aims to provide a resource for efficient exploration, analysis, and manipulation of NCPs. NCPbook incorporates data from diverse public databases and scientific literature. The current version of NCPbook includes 180,676 NCPs across 29 different species, evidenced by MS, ribosome profiling, or molecular experiments. These NCPs are distributed across kingdoms, comprising 123,408 from 14 plant species, 56,999 from 7 animal species, and 269 from 8 microbial species. Furthermore, NCPbook encompasses 9,166 functionally characterized NCPs playing important roles in immunity, stress resistance, growth, and development. Equipped with a user-friendly interface, NCPbook allows users to search, browse, visualize, and retrieve data, making it an indispensable platform for researching NCPs in various plant, animal, and microbial species.

Comparative Genomics Screens Identify a Novel Small Secretory Peptide, SlSolP12, which Activates Both Local and Systemic Immune Response in Tomatoes and Exhibits Broad-Spectrum Activity

Small secreted peptides (SSPs) are essential for defense mechanisms in plant-microbe interactions, acting as danger-associated molecular patterns (DAMPs). Despite the first discovery of SSPs over three decades ago, only a limited number of SSP families, particularly within Solanaceae plants, have been identified due to inefficient approaches. This study employed comparative genomics screens with Solanaceae proteomes (tomato, tobacco, and pepper) to discover a novel SSP family, SolP. Bioinformatics analysis suggests that SolP may serve as an endogenous signal initiating the plant PTI response. Interestingly, SolP family members from tomato, tobacco, and pepper share an identical sequence (VTSNALALVNRFAD), named SlSolP12 (also referred to as NtSolP15 or CaSolP1). Biochemical and phenotypic analyses revealed that synthetic SlSolP12 peptide triggers multiple defense responses: ROS burst, MAPK activation, callose deposition, stomatal closure, and expression of immune defense genes. Furthermore, SlSolP12 enhances systemic resistance against Botrytis cinerea infection in tomato plants and interferes with classical peptides, flg22 and Systemin, which modulate the immune response. Remarkably, SolP12 activates ROS in diverse plant species, such as Arabidopsis thaliana, soybean, and rice, showing a broad spectrum of biological activities. This study provides valuable approaches for identifying endogenous SSPs and highlights SlSolP12 as a novel DAMP that could serve as a useful target for crop protection.

Plant proteins, peptides, and non-protein amino acids: Toxicity, sources, and analysis

Plants have evolved various mechanisms to synthesize diverse range of substances that contribute to their survival against pests, pathogens, predators, and adverse environmental conditions. Although several plant metabolites possess therapeutic potential, some can be potentially harmful to human and animal health when consumed in large proportion. Proteins, peptides, and non-protein amino acids are products of plant biochemical pathways with proven beneficial and nutritional effects. Despite these benefits, the in vivo toxicities associated with certain plant-derived proteins, peptides, and non-protein amino acids pose a significant risk to humans and animals. Symptoms of poisoning include nausea, vomiting, diarrhea, hair and weight loss, goiter, cataracts, and infertility. Even though plant processing methods such as soaking and drying can reduce the amount of toxin contained in plants, complete riddance is often impossible. As such, food regulatory bodies need to prevent uncontrolled consumption of the listed and many other toxin-containing plant species to keep the public safe. For this purpose, this review collates crucial insights into the sources, and in vivo toxicity associated with certain plant-derived proteins, peptides, and non-protein amino acids that have the clear potential to adversely affect human health. Additionally, this review provides information on analytical methods suitable for the detection of these substances in plants.

smAMPsTK: a toolkit to unravel the smORFome encoding AMPs of plant species

The pervasive repertoire of plant molecules with the potential to serve as a substitute for conventional antibiotics has led to obtaining better insights into plant-derived antimicrobial peptides (AMPs). The massive distribution of Small Open Reading Frames (smORFs) throughout eukaryotic genomes with proven extensive biological functions reflects their practicality as antimicrobials. Here, we have developed a pipeline named smAMPsTK to unveil the underlying hidden smORFs encoding AMPs for plant species. By applying this pipeline, we have elicited AMPs of various functional activity of lengths ranging from 5 to 100 aa by employing publicly available transcriptome data of five different angiosperms. Later, we studied the coding potential of AMPs-smORFs, the inclusion of diverse translation initiation start codons, and amino acid frequency. Codon usage study signifies no such codon usage biases for smORFs encoding AMPs. Majorly three start codons are prominent in generating AMPs. The evolutionary and conservational study proclaimed the widespread distribution of AMPs encoding genes throughout the plant kingdom. Domain analysis revealed that nearly all AMPs have chitin-binding ability, establishing their role as antifungal agents. The current study includes a developed methodology to characterize smORFs encoding AMPs, and their implications as antimicrobial, antibacterial, antifungal, or antiviral provided by SVM score and prediction status calculated by machine learning-based prediction models. The pipeline, complete package, and the results derived for five angiosperms are freely available at https://github.com/skbinfo/smAMPsTK.Communicated by Ramaswamy H. Sarma.

Functionality of Reactive Oxygen Species (ROS) in Plants: Toxicity and Control in Poaceae Crops Exposed to Abiotic Stress

Agriculture and changing environmental conditions are closely related, as weather changes could adversely affect living organisms or regions of crop cultivation. Changing environmental conditions trigger different abiotic stresses, which ultimately cause the accumulation of reactive oxygen species (ROS) in plants. Common ROS production sites are the chloroplast, endoplasmic reticulum, plasma membrane, mitochondria, peroxisomes, etc. The imbalance in ROS production and ROS detoxification in plant cells leads to oxidative damage to biomolecules such as lipids, nucleic acids, and proteins. At low concentrations, ROS initiates signaling events related to development and adaptations to abiotic stress in plants by inducing signal transduction pathways. In plants, a stress signal is perceived by various receptors that induce a signal transduction pathway that activates numerous signaling networks, which disrupt gene expression, impair the diversity of kinase/phosphatase signaling cascades that manage the stress response in the plant, and result in changes in physiological responses under various stresses. ROS production also regulates ABA-dependent and ABA-independent pathways to mitigate drought stress. This review focuses on the common subcellular location of manufacturing, complex signaling mechanisms, and networks of ROS, with an emphasis on cellular effects and enzymatic and non-enzymatic antioxidant scavenging mechanisms of ROS in Poaceae crops against drought stress and how the manipulation of ROS regulates stress tolerance in plants. Understanding ROS systems in plants could help to create innovative strategies to evolve paths of cell protection against the negative effects of excessive ROS in attempts to improve crop productivity in adverse environments.

Wound-induced small-peptide-mediated signaling cascade, regulated by OsPSKR, dictates balance between growth and defense in rice

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.

Small Peptides: Orchestrators of Plant Growth and Developmental Processes

Small peptides (SPs), ranging from 5 to 100 amino acids, play integral roles in plants due to their diverse functions. Despite their low abundance and small molecular weight, SPs intricately regulate critical aspects of plant life, including cell division, growth, differentiation, flowering, fruiting, maturation, and stress responses. As vital mediators of intercellular signaling, SPs have garnered significant attention in plant biology research. This comprehensive review delves into SPs' structure, classification, and identification, providing a detailed understanding of their significance. Additionally, we summarize recent findings on the biological functions and signaling pathways of prominent SPs that regulate plant growth and development. This review also offers a perspective on future research directions in peptide signaling pathways.

Proline Analogues

Within the canonical repertoire of the amino acid involved in protein biogenesis, proline plays a unique role as an amino acid presenting a modified backbone rather than a side-chain. Chemical structures that mimic proline but introduce changes into its specific molecular features are defined as proline analogues. This review article summarizes the existing chemical, physicochemical, and biochemical knowledge about this peculiar family of structures. We group proline analogues from the following compounds: substituted prolines, unsaturated and fused structures, ring size homologues, heterocyclic, e.g., pseudoproline, and bridged proline-resembling structures. We overview (1) the occurrence of proline analogues in nature and their chemical synthesis, (2) physicochemical properties including ring conformation and cis/trans amide isomerization, (3) use in commercial drugs such as nirmatrelvir recently approved against COVID-19, (4) peptide and protein synthesis involving proline analogues, (5) specific opportunities created in peptide engineering, and (6) cases of protein engineering with the analogues. The review aims to provide a summary to anyone interested in using proline analogues in systems ranging from specific biochemical setups to complex biological systems.

Genome-wide Characterization of Small Secreted Peptides in Nicotiana tabacum and Functional Assessment of NtLTP25 in Plant Immunity

Small secreted peptides (SSPs), serving as signaling molecules for intercellular communication, play significant regulatory roles in plant growth, development, pathogen immunity, and responses to abiotic stress. Despite several SSPs, such as PIP, PSK, and PSY having been identified to participate in plant immunity, the majority of SSPs remain understudied, necessitating the exploration and identification of SSPs regulating plant immunity from vast genomic resources. Here we systematically characterized 756 putative SSPs across the genome of Nicotiana tabacum. 173 SSPs were further annotated as established SSPs, such as nsLTP, CAPE, and CEP. Furthermore, we detected the expression of 484 putative SSP genes in five tissues, with 83 SSPs displaying tissue-specific expression. Transcriptomic analysis of tobacco roots under plant defense hormones revealed that 46 SSPs exhibited specific responsiveness to salicylic acid (SA), and such response was antagonistically regulated by methyl jasmonate. It's worth noting that among these 46 SSPs, 16 members belong to nsLTP family, and one of them, NtLTP25, was discovered to enhance tobacco's resistance against Phytophthora nicotianae. Overexpression of NtLTP25 in tobacco enhanced the expression of ICS1, subsequently stimulating the biosynthesis of SA and the expression of NPR1 and pathogenesis-related genes. Concurrently, NtLTP25 overexpression activated genes associated with ROS scavenging, consequently mitigating the accumulation of ROS during the subsequent phases of pathogenesis. These discoveries indicate that these 46 SSPs, especially the 16 nsLTPs, might have a vital role in governing plant immunity that relies on SA signaling. This offers a valuable source for pinpointing SSPs involved in regulating plant immunity.

CEPs suppress auxin signaling but promote cytokinin signaling to inhibit root growth in Arabidopsis

C-terminally encoded peptides (CEPs) are peptide hormones that function as mobile signals coordinating crucial developmental programs in plants. Previous studies have revealed that CEPs exert negative regulation on root development through interaction with CEP receptors (CEPRs), CEP DOWNSTREAMs (CEPDs), the cytokinin receptor ARABIDOPSIS HISTIDINE KINASE (AHKs) and the transcriptional repressor Auxin/Indole-3-Acetic Acid (AUX/IAA). However, the precise molecular mechanisms underlying CEPs-mediated regulation of root development via auxin and cytokinin signaling pathways still necessitate further detailed investigation. In this study, we examined prior research and elucidated the underlying molecular mechanisms. The results showed that both synthetic AtCEPs and overexpression of AtCEP5 markedly supressed primary root elongation and lateral root (LR) formation in Arabidopsis. Molecular biology and genetics elucidated how CEPs inhibit root growth by suppressing auxin signaling while promoting cytokinin signaling. In summary, this study elucidated the inhibitory effects of AtCEPs on Arabidopsis root growth and provided insights into their potential molecular mechanisms, thus enhancing our comprehension of CEP-mediated regulation of plant growth and development.

Rice small secreted peptide, OsRALF26, recognized by FERONIA-like receptor 1 induces immunity in rice and Arabidopsis

Rapid alkalinization factors (RALFs), belonging to a family of small secreted peptides, have been considered as important signaling molecules in diverse biological processes, including immunity. Current studies on RALF-modulated immunity mainly focus on Arabidopsis, but little is reported in crop plants. The rice immune receptor XA21 confers immunity to the bacterial blight pathogen, Xanthomonas oryzae pv. oryzae (Xoo). Here, we pursued functional characterization of rice RALF26 (OsRALF26) up-regulated by Xoo during XA21-mediated immune response. When applied exogenously as a recombinant peptide, OsRALF26 induced a series of immune responses, including pathogenesis-related genes (PRs) induction, reactive oxygen species (ROS) production, and callose deposition in rice and/or Arabidopsis. Transgenic rice and Arabidopsis overexpressing OsRALF26 exhibited significantly enhanced resistance to Xoo and Pseudomonas syringae pv. tomato DC3000 (Pst DC3000), respectively. In yeast two-hybrid, pull-down assays, and co-immunoprecipitation analyses, rice FER-like receptor 1 (OsFLR1) was identified as a receptor of OsRALF26. Transient expression of OsFLR1 in Nicotiana benthamiana leaves displayed significantly increased ROS production and callose deposition after OsRALF26 treatment. Together, we propose that OsRALF26 induced by Xoo in an XA21-dependent manner is perceived by OsFLR1 and may play a novel role in the enforcement of XA21-mediated immunity.

Specialized metabolite modifications in Brassicaceae seeds and plants: diversity, functions and related enzymes

Covering: up to 2023Specialized metabolite (SM) modifications and/or decorations, corresponding to the addition or removal of functional groups (e.g. hydroxyl, methyl, glycosyl or acyl group) to SM structures, contribute to the huge diversity of structures, activities and functions of seed and plant SMs. This review summarizes available knowledge (up to 2023) on SM modifications in Brassicaceae and their contribution to SM plasticity. We give a comprehensive overview on enzymes involved in the addition or removal of these functional groups. Brassicaceae, including model (Arabidopsis thaliana) and crop (Brassica napus, Camelina sativa) plant species, present a large diversity of plant and seed SMs, which makes them valuable models to study SM modifications. In this review, particular attention is given to the environmental plasticity of SM and relative modification and/or decoration enzymes. Furthermore, a spotlight is given to SMs and related modification enzymes in seeds of Brassicaceae species. Seeds constitute a large reservoir of beneficial SMs and are one of the most important dietary sources, providing more than half of the world's intake of dietary proteins, oil and starch. The seed tissue- and stage-specific expressions of A. thaliana genes involved in SM modification are presented and discussed in the context of available literature. Given the major role in plant phytochemistry, biology and ecology, SM modifications constitute a subject of study contributing to the research and development in agroecology, pharmaceutical, cosmetics and food industrial sectors.

Histone modification-dependent production of peptide hormones facilitates acquisition of pluripotency during leaf-to-callus transition in Arabidopsis

Chromatin configuration is critical for establishing tissue identity and changes substantially during tissue identity transitions. The crucial scientific and agricultural technology of in vitro tissue culture exploits callus formation from diverse tissue explants and tissue regeneration via de novo organogenesis. We investigated the dynamic changes in H3ac and H3K4me3 histone modifications during leaf-to-callus transition in Arabidopsis thaliana. We analyzed changes in the global distribution of H3ac and H3K4me3 during the leaf-to-callus transition, focusing on transcriptionally active regions in calli relative to leaf explants, defined by increased accumulation of both H3ac and H3K4me3. Peptide signaling was particularly activated during callus formation; the peptide hormones RGF3, RGF8, PIP1 and PIPL3 were upregulated, promoting callus proliferation and conferring competence for de novo shoot organogenesis. The corresponding peptide receptors were also implicated in peptide-regulated callus proliferation and regeneration capacity. The effect of peptide hormones in plant regeneration is likely at least partly conserved in crop plants. Our results indicate that chromatin-dependent regulation of peptide hormone production not only stimulates callus proliferation but also establishes pluripotency, improving the overall efficiency of two-step regeneration in plant systems.

Metabolite-mediated adaptation of crops to drought and the acquisition of tolerance

Drought is one of the major and growing threats to agriculture productivity and food security. Metabolites are involved in the regulation of plant responses to various environmental stresses, including drought stress. The complex drought tolerance can be ascribed to several simple metabolic traits. These traits could then be used for detecting the genetic architecture of drought tolerance. Plant metabolomes show dynamic differences when drought occurs during different developmental stages or upon different levels of drought stress. Here, we reviewed the major and most recent findings regarding the metabolite-mediated plant drought response. Recent progress in the development of drought-tolerant agents is also discussed. We provide an updated schematic overview of metabolome-driven solutions for increasing crop drought tolerance and thereby addressing an impending agricultural challenge.

Small but mighty: Peptides regulating abiotic stress responses in plants

Throughout evolution, plants have developed strategies to confront and alleviate the detrimental impacts of abiotic stresses on their growth and development. The combat strategies involve intricate molecular networks and a spectrum of early and late stress-responsive pathways. Plant peptides, consisting of fewer than 100 amino acid residues, are at the forefront of these responses, serving as pivotal signalling molecules. These peptides, with roles similar to phytohormones, intricately regulate plant growth, development and facilitate essential cell-to-cell communications. Numerous studies underscore the significant role of these small peptides in coordinating diverse signalling events triggered by environmental challenges. Originating from the proteolytic processing of larger protein precursors or directly translated from small open reading frames, including microRNA (miRNA) encoded peptides from primary miRNA, these peptides exert their biological functions through binding with membrane-embedded receptor-like kinases. This interaction initiates downstream cellular signalling cascades, often involving major phytohormones or reactive oxygen species-mediated mechanisms. Despite these advances, the precise modes of action for numerous other small peptides remain to be fully elucidated. In this review, we delve into the dynamics of stress physiology, mainly focusing on the roles of major small signalling peptides, shedding light on their significance in the face of changing environmental conditions.

The Mechanism of Ovule Abortion in Self-Pollinated 'Hanfu' Apple Fruits and Related Gene Screening

Apples exhibit S-RNase-mediated self-incompatibility and typically require cross-pollination in nature. 'Hanfu' is a cultivar that produces abundant fruit after self-pollination, although it also shows a high rate of seed abortion afterwards, which greatly reduces fruit quality. In this study, we investigated the ovule development process and the mechanism of ovule abortion in apples after self-pollination. Using a DIC microscope and biomicroscope, we found that the abortion of apple ovules occurs before embryo formation and results from the failure of sperm-egg fusion. Further, we used laser-assisted microdissection (LAM) cutting and sperm and egg cell sequencing at different periods after pollination to obtain the genes related to ovule abortion. The top 40 differentially expressed genes (DEGs) were further verified, and the results were consistent with switching the mechanism at the 5' end of the RNA transcript (SMART-seq). Through this study, we can preliminarily clarify the mechanism of ovule abortion in self-pollinated apple fruits and provide a gene reserve for further study and improvement of 'Hanfu' apple fruit quality.

Modeling alternative translation initiation sites in plants reveals evolutionarily conserved cis-regulatory codes in eukaryotes

mRNA translation relies on identifying translation initiation sites (TISs) in mRNAs. Alternative TISs are prevalent across plant transcriptomes, but the mechanisms for their recognition are unclear. Using ribosome profiling and machine learning, we developed models for predicting alternative TISs in the tomato (Solanum lycopersicum). Distinct feature sets were predictive of AUG and nonAUG TISs in 5' untranslated regions and coding sequences, including a novel CU-rich sequence that promoted plant TIS activity, a translational enhancer found across dicots and monocots, and humans and viruses. Our results elucidate the mechanistic and evolutionary basis of TIS recognition, whereby cis-regulatory RNA signatures affect start site selection. The TIS prediction model provides global estimates of TISs to discover neglected protein-coding genes across plant genomes. The prevalence of cis-regulatory signatures across plant species, humans, and viruses suggests their broad and critical roles in reprogramming the translational landscape.

Intrinsically disordered Prosystemin discloses biologically active repeat motifs

The in-depth studies over the years on the defence barriers by tomato plants have shown that the Systemin peptide controls the response to a wealth of environmental stress agents. This multifaceted stress reaction seems to be related to the intrinsic disorder of its precursor protein, Prosystemin (ProSys). Since latest findings show that ProSys has biological functions besides Systemin sequence, here we wanted to assess if this precursor includes peptide motifs able to trigger stress-related pathways. Candidate peptides were identified in silico and synthesized to test their capacity to trigger defence responses in tomato plants against different biotic stressors. Our results demonstrated that ProSys harbours several repeat motifs which triggered plant immune reactions against pathogens and pest insects. Three of these peptides were detected by mass spectrometry in plants expressing ProSys, demonstrating their effective presence in vivo. These experimental data shed light on unrecognized functions of ProSys, mediated by multiple biologically active sequences which may partly account for the capacity of ProSys to induce defense responses to different stress agents.

Improved super-resolution ribosome profiling reveals prevalent translation of upstream ORFs and small ORFs in Arabidopsis

A crucial step in functional genomics is identifying actively translated ORFs and linking them to biological functions. The challenge lies in identifying short ORFs, as their identification is greatly influenced by data quality and depth. Here, we improved the coverage of super-resolution Ribo-seq in Arabidopsis (Arabidopsis thaliana), revealing uncharacterized translation events for nuclear, chloroplastic, and mitochondrial genes. Assisted by a transcriptome assembly, we identified 7,751 unconventional translation events, comprising 6,996 upstream ORFs (uORFs) and 209 downstream ORFs on annotated protein-coding genes, as well as 546 ORFs in presumed noncoding RNAs. Proteomic data confirmed the production of stable proteins from some of these unannotated translation events. We present evidence of active translation from primary transcripts of trans-acting small interfering RNAs (TAS1-4) and microRNAs (pri-MIR163 and pri-MIR169) and periodic ribosome stalling supporting cotranslational decay. Additionally, we developed a method for identifying extremely short uORFs, including 370 minimum uORFs (AUG-stop), and 2,921 tiny uORFs (2 to 10 amino acids) and 681 uORFs that overlap with each other. Remarkably, these short uORFs exhibit strong translational repression as do longer uORFs. We also systematically discovered 594 uORFs regulated by alternative splicing, suggesting widespread isoform-specific translational control. Finally, these prevalent uORFs are associated with numerous important pathways. In summary, our improved Arabidopsis translational landscape provides valuable resources to study gene expression regulation.

Detection of the Arabidopsis Proteome and Its Post-translational Modifications and the Nature of the Unobserved (Dark) Proteome in PeptideAtlas

This study describes a new release of the Arabidopsis thaliana PeptideAtlas proteomics resource (build 2023-10) providing protein sequence coverage, matched mass spectrometry (MS) spectra, selected post-translational modifications (PTMs), and metadata. 70 million MS/MS spectra were matched to the Araport11 annotation, identifying ∼0.6 million unique peptides and 18,267 proteins at the highest confidence level and 3396 lower confidence proteins, together representing 78.6% of the predicted proteome. Additional identified proteins not predicted in Araport11 should be considered for the next Arabidopsis genome annotation. This release identified 5198 phosphorylated proteins, 668 ubiquitinated proteins, 3050 N-terminally acetylated proteins, and 864 lysine-acetylated proteins and mapped their PTM sites. MS support was lacking for 21.4% (5896 proteins) of the predicted Araport11 proteome: the "dark" proteome. This dark proteome is highly enriched for E3 ligases, transcription factors, and for certain (e.g., CLE, IDA, PSY) but not other (e.g., THIONIN, CAP) signaling peptides families. A machine learning model trained on RNA expression data and protein properties predicts the probability that proteins will be detected. The model aids in discovery of proteins with short half-life (e.g., SIG1,3 and ERF-VII TFs) and for developing strategies to identify the missing proteins. PeptideAtlas is linked to TAIR, tracks in JBrowse, and several other community proteomics resources.

Origins, Technological Advancement, and Applications of Peptidomics

Peptidomics is the comprehensive characterization of peptides from biological sources instead of heading for a few single peptides in former peptide research. Mass spectrometry allows to detect a multitude of peptides in complex mixtures and thus enables new strategies leading to peptidomics. The term was established in the year 2001, and up to now, this new field has grown to over 3000 publications. Analytical techniques originally developed for fast and comprehensive analysis of peptides in proteomics were specifically adjusted for peptidomics. Although it is thus closely linked to proteomics, there are fundamental differences with conventional bottom-up proteomics. Fundamental technological advancements of peptidomics since have occurred in mass spectrometry and data processing, including quantification, and more slightly in separation technology. Different strategies and diverse sources of peptidomes are mentioned by numerous applications, such as discovery of neuropeptides and other bioactive peptides, including the use of biochemical assays. Furthermore, food and plant peptidomics are introduced similarly. Additionally, applications with a clinical focus are included, comprising biomarker discovery as well as immunopeptidomics. This overview extensively reviews recent methods, strategies, and applications including links to all other chapters of this book.