Suppressing a ß-1,3-glucanase gene expression increases the seed and fibre yield in cotton.

Seeds are initiated from the carpel margin meristem (CMM) and high seed yield is top one of breeding objectives for many crops. ß-1,3-glucanases play various roles in plant growth and developmental processes; however, whether it participates in CMM development and seed formation remains largely unknown. Here, we identified a ß-1,3-glucanase gene (GLU19) as a determinant of CMM callose deposition and seed yield in cotton. GLU19 was differentially expressed in carpel tissues between Gossypium barbadense (Gb) and Gossypium hirsutum (Gh). Based on resequencing data, one interspecies-specific InDel in the promoter of GLU19 was further detected. The InDel was involved in the binding site of the CRABS CLAW (CRC) transcription factor, a regulator of carpel development. We found that the CRC binding affinity to the GLU19 promoter of G. barbadense was higher than that of G. hirsutum. Since G. barbadense yields fewer seeds than G. hirsutum, we speculated that stronger CRC binding to the GLU19 promoter activated higher expression of GLU19 which in turn suppressed seed production. Consistent with this hypothesis was that the overexpression of GhGLU19 caused reduced seed number, boll weight and less callose formation in CMM. Conversely, GhGLU19-knockdown (GhGLU19-KD) cotton led to the opposite phenotypes. By crossing GhGLU19-KD lines with several G. hirsutum and G. barbadense cotton accessions, all F1 and F2 plants carrying GhGLU19-KD transgenic loci exhibited higher seed yield than control plants without the locus. The increased seed effect was also found in the down-regulation of Arabidopsis orthologs lines, indicating that this engineering strategy may improve the seed yield in other crops.

Embryo sac development relies on symplastic signals from ovular integuments in Arabidopsis.

Ovules are female reproductive organs of angiosperms, consisting of sporophytic integuments surrounding female gametophytes, that is, embryo sacs. Synchronization between integument growth and embryo sac development requires intracellular communication. However, signaling routes through which cells of the two generations communicate are unclear. We report that symplastic signals through plasmodesmata (PDs) of integuments are critical for the development of female gametophytes. Genetic interferences of PD biogenesis either by functional loss of CHOLINE TRANSPORTER-LIKE1 (CTL1) or by integument-specific expression of a mutated CALLOSE SYNTHASE 3 (cals3m) compromised PD formation in integuments and reduced fertility. Close examination of pINO:cals3m or ctl1 ovules indicated that female gametophytic development was either arrested at various stages after the formation of functional megaspores. In both cases, defective ovules could not attract pollen tubes, leading to the failure of fertilization. Results presented here demonstrate a key role of the symplastic route in sporophytic control of female gametophytic development.

A fungal microRNA-like RNA regulated effector promotes pathogen infection by targeting a host defense-related transcription factor.

Effectors play important roles in facilitating the infection of plant pathogenic fungi. However, the gene expression regulatory mechanism of effector genes, in particular at the post-transcriptional level, is largely unknown. In this study, we uncovered the post-transcriptional regulation of an effector gene VmSP1 by a miRNA-like RNA (Vm-milR16) facilitating the infection of the apple tree Valsa canker pathogen Valsa mali. Genetic and molecular biological assays indicated that the expression of VmSP1 could be suppressed by Vm-milR16-mediated mRNA cleavage in a sequence-specific manner. During V. mali infection, Vm-milR16 was downregulated, whereas VmSP1 was upregulated, which further indicated the regulation relationship. VmSP1 was further demonstrated to be a secreted protein and could suppress plant immunity. Deletion of VmSP1 did not affect the vegetative growth but significantly reduced the virulence of V. mali. Further study indicated that VmSP1 could interact with the transcription factor MdbHLH189 of apple. Transiently overexpression of MdbHLH189 enhanced host resistance to V. mali by enhancing the expression of apple defense-related genes, together with the increased callose deposition. Silencing of MdbHLH189 compromised host resistance to V. mali. Our findings uncovered the novel epigenetic regulation mechanism of a virulence-associated effector gene mediated by a fungal milRNA at the post-transcriptional level, and the results enriched the understanding of the function and action mechanism of effectors in tree pathogenic fungi.

Disruption of BG14 results in enhanced callose deposition in developing seeds and decreases seed longevity and seed dormancy in Arabidopsis.

Seed longevity is an important trait for agriculture and the conservation of genetic resources. ß-1,3-Glucanases were first recognized as pathogenesis-related proteins involved in plant defense, but their roles in seeds are largely unknown. Here, we report a glycosylphosphatidylinositol-anchored ß-1,3-glucanase, BG14, that degrades callose in seed embryos and functions in seed longevity and dormancy in Arabidopsis. The loss of function of BG14 significantly decreased seed longevity, whereas functional reversion (RE) and overexpression (OE) lines reversed and increased the impaired phenotype, respectively. The loss of function of BG14 enhanced callose deposition in the embryos of mature seeds, confirmed by quantitative determination and the decreased callose degrading ability in bg14. The drop-and-see (DANS) assay revealed that the fluorescence signal in bg14 was significantly lower than that observed in the other three genotypes. BG14 is located on the periphery of the cell wall and can completely merge with callose at the plasmodesmata of epidermal cells. BG14 was highly expressed in developing seeds and was induced by aging and abscisic acid (ABA). The loss of function of BG14 led to a variety of phenotypes related to ABA, including reduced seed dormancy and reduced responses to treatment with ABA or pacolblltrazol, whereas OE lines showed the opposite phenotype. The reduced ABA response is because of the decreased level of ABA and the lowered expression of ABA synthesis genes in bg14. Taken together, this study demonstrated that BG14 is a bona fide BG that mediates callose degradation in the plasmodesmata of embryo cells, transcriptionally influences ABA synthesis genes in developing seeds, and positively affects seed longevity and dormancy in Arabidopsis.

Comparing Methods for Detection and Quantification of Plasmodesmal Callose in Nicotiana benthamiana Leaves During Defense Responses.

Callose, a ß-(1,3)-d-glucan polymer, is essential for regulating intercellular trafficking via plasmodesmata (PD). Pathogens manipulate PD-localized proteins to enable intercellular trafficking by removing callose at PD or, conversely, by increasing callose accumulation at PD to limit intercellular trafficking during infection. Plant defense hormones like salicylic acid regulate PD-localized proteins to control PD and intercellular trafficking during immune defense responses such as systemic acquired resistance. Measuring callose deposition at PD in plants has therefore emerged as a popular parameter for assessing likely intercellular trafficking activity during plant immunity. Despite the popularity of this metric, there is no standard for how these measurements should be made. In this study, three commonly used methods for identifying and quantifying plasmodesmal callose by aniline blue staining were evaluated to determine the most effective in the Nicotiana benthamiana leaf model. The results reveal that the most reliable method used aniline blue staining and fluorescence microscopy to measure callose deposition in fixed tissue. Manual or semiautomated workflows for image analysis were also compared and found to produce similar results, although the semiautomated workflow produced a wider distribution of data points. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Unlocking Precision in Callose Staining: Unveiling the Role of Sirofluor.

Callose is a vital component in plant biology, contributing to essential processes like pollen maturation and defense against pathogens. However, misconceptions surrounding callose staining persist, particularly regarding the role of aniline blue. It is now known that commercial aniline blue contains sirofluor, and it is this fluorophore, rather than aniline blue itself, that is responsible for the observed fluorescence during callose detection. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

A comprehensive analysis of the WRKY family in soybean and functional analysis of GmWRKY164-GmGSL7c in resistance to soybean mosaic virus.

BACKGROUND: Soybean mosaic disease caused by soybean mosaic virus (SMV) is one of the most devastating and widespread diseases in soybean producing areas worldwide. The WRKY transcription factors (TFs) are widely involved in plant development and stress responses. However, the roles of the GmWRKY TFs in resistance to SMV are largely unclear. RESULTS: Here, 185 GmWRKYs were characterized in soybean (Glycine max), among which 60 GmWRKY genes were differentially expressed during SMV infection according to the transcriptome data. The transcriptome data and RT-qPCR results showed that the expression of GmWRKY164 decreased after imidazole treatment and had higher expression levels in the incompatible combination between soybean cultivar variety Jidou 7 and SMV strain N3. Remarkably, the silencing of GmWRKY164 reduced callose deposition and enhanced virus spread during SMV infection. In addition, the transcript levels of the GmGSL7c were dramatically lower upon the silencing of GmWRKY164. Furthermore, EMSA and ChIP-qPCR revealed that GmWRKY164 can directly bind to the promoter of GmGSL7c, which contains the W-box element. CONCLUSION: Our findings suggest that GmWRKY164 plays a positive role in resistance to SMV infection by regulating the expression of GmGSL7c, resulting in the deposition of callose and the inhibition of viral movement, which provides guidance for future studies in understanding virus-resistance mechanisms in soybean.

Plant immunity suppression by an ß-1,3-glucanase of the maize anthracnose pathogen Colletotrichum graminicola.

BACKGROUND: Many phytopathogens secrete a large number of cell wall degrading enzymes (CWDEs) to decompose host cell walls in order to penetrate the host, obtain nutrients and accelerate colonization. There is a wide variety of CWDEs produced by plant pathogens, including glycoside hydrolases (GHs), which determine the virulence, pathogenicity, and host specificity of phytopathogens. The specific molecular mechanisms by which pathogens suppress host immunity remain obscure. RESULT: In this study, we found that CgEC124 encodes a glycosyl hydrolase with a signal peptide and a conserved Glyco_hydro_cc domain which belongs to glycoside hydrolase 128 family. The expression of CgEC124 was significantly induced in the early stage of Colletotrichum graminicola infection, especially at 12 hpi. Furthermore, CgEC124 positively regulated the pathogenicity, but it did not impact the vegetative growth of mycelia. Ecotopic transient expression of CgEC124 decreased the disease resistance and callose deposition in maize. Moreover, CgEC124 exhibited the ß-1,3-glucanase activity and suppresses glucan-induced ROS burst in maize leaves. CONCLUSIONS: Our results indicate that CgEC124 is required for full virulence of C. graminicola but not for vegetative growth. CgEC124 increases maize susceptibility by inhibiting host reactive oxygen species burst as well as callose deposition. Meanwhile, our data suggests that CgEC124 explores its ß-1,3-glucanase activity to prevent induction of host defenses.

Rice physical defenses and their role against insect herbivores.

MAIN CONCLUSION: Understanding surface defenses, a relatively unexplored area in rice can provide valuable insight into constitutive and induced defenses against herbivores. Plants have evolved a multi-layered defense system against the wide range of pests that constantly attack them. Physical defenses comprised of trichomes, wax, silica, callose, and lignin, and are considered as the first line of defense against herbivory that can directly affect herbivores by restricting or deterring them. Most studies on physical defenses against insect herbivores have been focused on dicots compared to monocots, although monocots include one of the most important crops, rice, which half of the global population is dependent on as their staple food. In rice, Silica is an important element stimulating plant growth, although Silica has also been found to impart resistance against herbivores. However, other physical defenses in rice including wax, trichomes, callose, and lignin are less explored. A detailed exploration of the morphological structures and functional consequences of physical defense structures in rice can assist in incorporating these resistance traits in plant breeding and genetic improvement programs, and thereby potentially reduce the use of chemicals in the field. This mini review addresses these points with a closer look at current literature and prospects on rice physical defenses.

APP1/NTL9-CalS8 module ensures proper phloem differentiation by stabilizing callose accumulation and symplastic communication.

Phloem sieve elements (PSE), the primary conduits collaborating with neighboring phloem pole pericycle (PPP) cells to facilitate unloading in Arabidopsis roots, undergo a series of developmental stages before achieving maturation and functionality. However, the mechanism that maintains the proper progression of these differentiation stages remains largely unknown. We identified a gain-of-function mutant altered phloem pole pericycle 1 Dominant (app1D), producing a truncated, nuclear-localized active form of NAC with Transmembrane Motif 1-like (NTL9). This mutation leads to ectopic expression of its downstream target CALLOSE SYNTHASE 8 (CalS8), thereby inducing callose accumulation, impeding SE differentiation, impairing phloem transport, and inhibiting root growth. The app1D phenotype could be reproduced by blocking the symplastic channels of cells within APP1 expression domain in wild-type (WT) roots. The WT APP1 is primarily membrane-tethered and dormant in the root meristem cells but entries into the nucleus in several cells in PPP near the unloading region, and this import is inhibited by blocking the symplastic intercellular transport in differentiating SE. Our results suggest a potential maintenance mechanism involving an APP1-CalS8 module, which induces CalS8 expression and modulates symplastic communication, and the proper activation of this module is crucial for the successful differentiation of SE in the Arabidopsis root.

Roles of ROS and redox in regulating cell-to-cell communication: Spotlight on viral modulation of redox for local spread.

Reactive oxygen species (ROS) are important signalling molecules that influence many aspects of plant biology. One way in which ROS influence plant growth and development is by modifying intercellular trafficking through plasmodesmata (PD). Viruses have evolved to use PD for their local cell-to-cell spread between plant cells, so it is therefore not surprising that they have found ways to modulate ROS and redox signalling to optimise PD function for their benefit. This review examines how intracellular signalling via ROS and redox pathways regulate intercellular trafficking via PD during development and stress. The relationship between viruses and ROS-redox systems, and the strategies viruses employ to control PD function by interfering with ROS-redox in plants is also discussed.

The development of pleiotropic phenotypes in powdery mildew-resistant barley and Arabidopsis thaliana mlo mutants is linked to nitrogen availability.

Powdery mildew-resistant barley (Hordeum vulgare) and Arabidopsis thaliana mlo mutant plants exhibit pleiotropic phenotypes such as the spontaneous formation of callose-rich cell wall appositions and early leaf chlorosis and necrosis, indicative of premature leaf senescence. The exogenous factors governing the occurrence of these undesired side effects remain poorly understood. Here, we characterised the formation of these symptoms in detail. Ultrastructural analysis revealed that the callose-rich cell wall depositions spontaneously formed in A. thaliana mlo mutants are indistinguishable from those induced by the bacterial pattern epitope, flagellin 22 (flg22). We further found that increased plant densities during culturing enhance the extent of the leaf senescence syndrome in A. thaliana mlo mutants. Application of a liquid fertiliser rescued the occurrence of leaf chlorosis and necrosis in both A. thaliana and barley mlo mutant plants. Controlled fertilisation experiments uncovered nitrogen as the macronutrient whose deficiency promotes the extent of pleiotropic phenotypes in A. thaliana mlo mutants. Light intensity and temperature had a modulatory impact on the incidence of leaf necrosis in the case of barley mlo mutant plants. Collectively, our data indicate that the development of pleiotropic phenotypes associated with mlo mutants is governed by various exogenous factors.

C-Type LECTIN receptor-like kinase 1 and ACTIN DEPOLYMERIZING FACTOR 3 are key components of plasmodesmata callose modulation.

Plasmodesmata (PDs) are intercellular organelles carrying multiple membranous nanochannels that allow the trafficking of cellular signalling molecules. The channel regulation of PDs occurs dynamically and is required in various developmental and physiological processes. It is well known that callose is a critical component in regulating PD permeability or symplasmic connectivity, but the understanding of the signalling pathways and mechanisms of its regulation is limited. Here, we used the reverse genetic approach to investigate the role of C-type lectin receptor-like kinase 1 (CLRLK1) in the aspect of PD callose-modulated symplasmic continuity. Here, we found that loss-of-function mutations in CLRLK1 resulted in excessive PD callose deposits and reduced symplasmic continuity, resulting in an accelerated gravitropic response. The protein interactome study also found that CLRLK1 interacted with actin depolymerizing factor 3 (ADF3) in vitro and in plants. Moreover, mutations in ADF3 result in elevated PD callose deposits and faster gravitropic response. Our results indicate that CLRLK1 and ADF3 negatively regulate PD callose accumulation, contributing to fine-tuning symplasmic opening apertures. Overall, our studies identified two key components involved in the deposits of PD callose and provided new insights into how symplasmic connectivity is maintained by the control of PD callose homoeostasis.

Drought-dependent regulation of cell coupling in Arabidopsis leaf epidermis requires plasmodesmata protein NHL12.

The cytoplasms of most plant cells are connected by membrane-lined cell wall channels, the plasmodesmata (PD). Dynamic regulation of sugar, hormone and protein diffusion through PD is essential for plant development and stress responses. Understanding this regulation requires knowledge of factors and mechanisms that control PD permeability through the modulation of callose levels in the cell wall around PD openings. We investigated PD regulation in leaf epidermis cells in relation to drought stress in Arabidopsis thaliana. Upon finding PD-mediated cell wall permeability decreased by drought stress and the hormone ABA, we tested several PD-associated genes with drought-responsive expression for their involvement in this response. Mutants of NHL12 showed relatively low PD permeability that was unaffected by drought or ABA treatment. Overexpression of NHL12 in Nicotiana benthamiana epidermis cells increased PD permeability. Moreover, we show that NHL12 can potentially interact with the callose synthase-regulator NHL3 and we explored the effect of NHL12 abundance and/or lower interface permeability on ABA signaling genes. Our results indicate that NHL12 is a drought-responsive negative regulator of PD callose levels and, thereby, interface permeability. Results are discussed with regard to PD function during drought stress and the regulation of intercellular transport.

Four-dimensional quantitative analysis of cell plate development in Arabidopsis using lattice light sheet microscopy identifies robust transition points between growth phases.

Cell plate formation during cytokinesis entails multiple stages occurring concurrently and requiring orchestrated vesicle delivery, membrane remodelling, and timely deposition of polysaccharides, such as callose. Understanding such a dynamic process requires dissection in time and space; this has been a major hurdle in studying cytokinesis. Using lattice light sheet microscopy (LLSM), we studied cell plate development in four dimensions, through the behavior of yellow fluorescent protein (YFP)-tagged cytokinesis-specific GTPase RABA2a vesicles. We monitored the entire duration of cell plate development, from its first emergence, with the aid of YFP-RABA2a, in both the presence and absence of cytokinetic callose. By developing a robust cytokinetic vesicle volume analysis pipeline, we identified distinct behavioral patterns, allowing the identification of three easily trackable cell plate developmental phases. Notably, the phase transition between phase I and phase II is striking, indicating a switch from membrane accumulation to the recycling of excess membrane material. We interrogated the role of callose using pharmacological inhibition with LLSM and electron microscopy. Loss of callose inhibited the phase transitions, establishing the critical role and timing of the polysaccharide deposition in cell plate expansion and maturation. This study exemplifies the power of combining LLSM with quantitative analysis to decode and untangle such a complex process.

Callose Deficiency Modulates Plasmodesmata Frequency and Extracellular Distance in Rice Pollen Mother and Tapetal cells.

Fertilization relies on pollen mother cells able to transit from mitosis to meiosis to supply gametes. This process involves remarkable changes at the molecular, cellular and physiological levels including (but not limited to) remodelling of the cell wall. During the meiosis onset, cellulose content at the pollen mother cell walls gradually declines with the concurrent deposition of the polysaccharide callose in anther locules. We aim to understand the biological significance of cellulose-to-callose turnover in pollen mother cells walls using electron microscopic analyses of rice flowers. Our observations indicate that in wild type rice anthers, the mitosis-to-meiosis transition coincides with a gradual reduction in the number of cytoplasmic connections called plasmodesmata. A mutant in the Oryza sativa callose synthase GSL5 (Osgsl5-3), impaired in callose accumulation in premeiotic and meiotic anthers, displayed a greater reduction in plasmodesmata frequency among pollen mother cells and tapetal cells suggesting a role for callose in plasmodesmata maintenance. In addition, a significant increase in extracellular distance between pollen mother cells and impaired premeiotic cell shaping was observed in the Osgsl5-3 mutant. The results suggest that callose-to-cellulose turnover during mitosis-meiosis transition is necessary to maintain cell-to-cell connections and optimal extracellular distance among the central anther locular cells. Findings of this study contribute to our understanding of the regulatory influence of callose metabolism during meiosis initiation in flowering plants.

α1-COP modulates plasmodesmata function through sphingolipid enzyme regulation.

Callose, a ß-1,3-glucan plant cell wall polymer, regulates symplasmic channel size at plasmodesmata (PD) and plays a crucial role in a variety of plant processes. However, elucidating the molecular mechanism of PD callose homeostasis is limited. We screened and identified an Arabidopsis mutant plant with excessive callose deposition at PD and found that the mutated gene was α1-COP, a member of the coat protein I (COPI) coatomer complex. We report that loss of function of α1-COP elevates the callose accumulation at PD by affecting subcellular protein localization of callose degradation enzyme PdBG2. This process is linked to the functions of ERH1, an inositol phosphoryl ceramide synthase, and glucosylceramide synthase through physical interactions with the α1-COP protein. Additionally, the loss of function of α1-COP alters the subcellular localization of ERH1 and GCS proteins, resulting in a reduction of GlcCers and GlcHCers molecules, which are key sphingolipid (SL) species for lipid raft formation. Our findings suggest that α1-COP protein, together with SL modifiers controlling lipid raft compositions, regulates the subcellular localization of GPI-anchored PDBG2 proteins, and hence the callose turnover at PD and symplasmic movement of biomolecules. Our findings provide the first key clue to link the COPI-mediated intracellular trafficking pathway to the callose-mediated intercellular signaling pathway through PD.

Plasma membrane-localized SEM1 protein mediates sugar movement to sink rice tissues.

The translocation of photosynthate carbohydrates, such as sucrose, is critical for plant growth and crop yield. Previous studies have revealed that sugar transporters, plasmodesmata and sieve plates act as important controllers in sucrose loading into and unloading from phloem in the vascular system. However, other pivotal steps for the regulation of sucrose movement remain largely elusive. In this study, characterization of two starch excesses in mesophyll (sem) mutants and dye and sucrose export assays were performed to provide insights into the regulatory networks that drive source-sink relations in rice. Map-based cloning identified two allelic mutations in a gene encoding a GLUCAN SYNTHASE-LIKE (GSL) protein, thus indicating a role for SEM1 in callose biosynthesis. Subcellular localization in rice showed that SEM1 localized to the plasma membrane. In situ expression analysis and GUS staining showed that SEM1 was mainly expressed in vascular phloem cells. Reduced sucrose transport was found in the sem1-1/1-2 mutant, which led to excessive starch accumulation in source leaves and inhibited photosynthesis. Paraffin section and transmission electron microscopy experiments revealed that less-developed vascular cells (VCs) in sem1-1/1-2 potentially disturbed sugar movement. Moreover, dye and sugar trafficking experiments revealed that aberrant VC development was the main reason for the pleiotropic phenotype of sem1-1/1-2. In total, efficient sucrose loading into the phloem benefits from an optional number of VCs with a large vacuole that could act as a buffer holding tank for sucrose passing from the vascular bundle sheath.

(Z)-3-hexenol primes callose deposition against whitefly-mediated begomovirus infection in tomato.

Rapid callose accumulation has been shown to mediate defense in certain plant-virus interactions. Exposure to the green leaf volatile (Z)-3-hexenol (Z-3-HOL) can prime tomato (Solanum lycopersicum) for an enhanced defense against subsequent infection by whitefly-transmitted Tomato yellow leaf curl virus (TYLCV). However, the molecular mechanisms affecting Z-3-HOL-induced resistance are poorly understood. Here, we explored the mechanisms underlying Z-3-HOL-induced resistance against whitefly-transmitted TYLCV infection and the role of callose accumulation during this process. Tomato plants pre-treated with Z-3-HOL displayed callose priming upon whitefly infestation. The callose inhibitor 2-deoxy-d-glucose abolished Z-3-HOL-induced resistance, confirming the importance of callose in this induced resistance. We also found that Z-3-HOL pre-treatment enhanced salicylic acid levels and activated sugar signaling in tomato upon whitefly infestation, which increased the expression of the cell wall invertase gene Lin6 to trigger augmented callose deposition against TYLCV infection resulting from whitefly transmission. Using virus-induced gene silencing, we demonstrated the Lin6 expression is relevant for sugar accumulation mediated callose priming in restricting whitefly-transmitted TYLCV infection in plants that have been pre-treated with Z-3-HOL. Moreover, Lin6 induced the expression of the callose synthase gene Cals12, which is also required for Z-3-HOL-induced resistance of tomato against whitefly-transmitted TYLCV infection. These findings highlight the importance of sugar signaling in the priming of callose as a defense mechanism in Z-3-HOL-induced resistance of tomato against whitefly-transmitted TYLCV infection. The results will also increase our understanding of defense priming can be useful for the biological control of viral diseases.

Danger-associate peptide regulates root immunity in Arabidopsis.

Plant elicitor peptides (Peps) are recognized by two receptor-like kinases, PEPR1 and PEPR2, and trigger plant immunity responses and root growth inhibition. In this study, we reveal that the Pep-PEPR system triggers root immunity responses in Arabidopsis. Pep1 incubation initiated callose and lignin deposition in roots of wild type but not in that of pepr1 pepr2 mutant seedlings. The plasma membrane-associated kinase BIK1, which serves downstream of the Pep-PEPR signaling pathway, was essential for Pep1-induced root immunity responses. Interestingly, disruption of PEPR1/2-associated coreceptor BAK1 enhanced the deposition of both callose and lignin induced by Pep1 in roots. Ethylene and salicylic acid signaling are involved in Pep1-induced root immunity responses. Furthermore, we showed that the successful phytopathogen, P. syringae (DC3000) could effectively suppress Pep1-trigged root callose and lignin accumulation. These results demonstrated the endogenous Pep-triggered root immunity responses and pathogenic suppression of the Pep-PEPR signaling pathway.