Plasmodesmata-located Protein Research Articles

Confocal Microscopy Analysis of Protein Sorting to Plasmodesmata in Nicotiana benthamiana.

Plasmodesmata are membranous nanopores that connect the cytoplasm of adjacent plant cells and enable the cell-to-cell trafficking of nutrients, macromolecules, as well as invading viruses. Plasmodesmata play fundamental roles in the regulation of intercellular communication, contributing to plant development, environmental responses, and interactions with viral pathogens. Discovering plasmodesmal localization of plant or viral proteins could provide useful functional information about the protein and is important for understanding the mechanisms of plant-virus interactions. To facilitate these studies, we describe a protocol for confocal microscopy-based analysis of different plasmodesmal targeting proteins to select the best plasmodesmal marker for studying the virus-plasmodesmata interactions or plasmodesmal transport. Specifically, the analyses of these events are illustrated using the cell-to-cell movement protein (MP) of the Turnip vein-clearing virus (TVCV), the Arabidopsis Plasmodesmata-Localized Protein 5 (PDLP5) and Plasmodesmata Callose-Binding Protein 1 (PDCB1). The protein plasmodesmal localization data are analyzed in parallel with the global visualization of plasmodesmata using aniline blue staining of the sampled tissues. These approaches can be easily adapted to analyze the plasmodesmal localization of any cellular or pathogen proteins in planta.

Arabidopsis PDLP7 modulated plasmodesmata function is related to BG10-dependent glucosidase activity required for callose degradation

The microdomains of plasmodesmata, specialized cell-wall channels responsible for communications between neighboring cells, are composed of various plasmodesmata-located proteins (PDLPs) and lipids. Here, we found that, among all PDLP or homologous proteins in Arabidopsis thaliana genome, PDLP5 and PDLP7 possessed a C-terminal sphingolipid-binding motif, with the latter being the only member that was significantly upregulated upon turnip mosaic virus and cucumber mosaic virus infections. pdlp7 mutant plants exhibited significantly reduced callose deposition, larger plasmodesmata diameters, and faster viral transmission. These plants exhibited increased glucosidase activity but no change in callose synthase activity. PDLP7 interacted specifically with glucan endo-1,3-β-glucosidase 10 (BG10). Consistently, higher levels of callose deposition and slower virus transmission in bg10 mutants were observed. The interaction between PDLP7 and BG10 was found to depend on the presence of the Gnk2-homologous 1 (GnK2-1) domain at the N terminus of PDLP7 with Asp-35, Cys-42, Gln-44, and Leu-116 being essential. In vitro supplementation of callose was able to change the conformation of the GnK2-1 domain. Our data suggest that the GnK2-1 domain of PDLP7, in conjunction with callose and BG10, plays a key role in plasmodesmata opening and closure, which is necessary for intercellular movement of various molecules.

DsRNA-induced immunity targets plasmodesmata and is suppressed by viral movement proteins.

Emerging evidence indicates that in addition to its well-recognized functions in antiviral RNA silencing, dsRNA elicits pattern-triggered immunity (PTI), likely contributing to plant resistance against virus infections. However, compared to bacterial and fungal elicitor-mediated PTI, the mode-of-action and signaling pathway of dsRNA-induced defense remain poorly characterized. Here, using multicolor in vivo imaging, analysis of GFP mobility, callose staining, and plasmodesmal marker lines in Arabidopsis thaliana and Nicotiana benthamiana, we show that dsRNA-induced PTI restricts the progression of virus infection by triggering callose deposition at plasmodesmata, thereby likely limiting the macromolecular transport through these cell-to-cell communication channels. The plasma membrane-resident SOMATIC EMBRYOGENESIS RECEPTOR-LIKE KINASE 1, the BOTRYTIS INDUCED KINASE1/AVRPPHB SUSCEPTIBLE1-LIKE KINASE1 kinase module, PLASMODESMATA-LOCATED PROTEINs 1/2/3, as well as CALMODULIN-LIKE 41 and Ca2+ signals are involved in the dsRNA-induced signaling leading to callose deposition at plasmodesmata and antiviral defense. Unlike the classical bacterial elicitor flagellin, dsRNA does not trigger a detectable reactive oxygen species (ROS) burst, substantiating the idea that different microbial patterns trigger partially shared immune signaling frameworks with distinct features. Likely as a counter strategy, viral movement proteins from different viruses suppress the dsRNA-induced host response leading to callose deposition to achieve infection. Thus, our data support a model in which plant immune signaling constrains virus movement by inducing callose deposition at plasmodesmata and reveals how viruses counteract this layer of immunity.

Targeting of plasmodesmal proteins requires unconventional signals.

Effective cellular signaling relies on precise spatial localization and dynamic interactions among proteins in specific subcellular compartments or niches, such as cell-to-cell contact sites and junctions. In plants, endogenous and pathogenic proteins gained the ability to target plasmodesmata, membrane-lined cytoplasmic connections, through evolution to regulate or exploit cellular signaling across cell wall boundaries. For example, the receptor-like membrane protein PLASMODESMATA-LOCATED PROTEIN 5 (PDLP5), a potent regulator of plasmodesmal permeability, generates feed-forward or feed-back signals important for plant immunity and root development. However, the molecular features that determine the plasmodesmal association of PDLP5 or other proteins remain largely unknown, and no protein motifs have been identified as plasmodesmal targeting signals. Here, we developed an approach combining custom-built machine-learning algorithms and targeted mutagenesis to examine PDLP5 in Arabidopsis thaliana and Nicotiana benthamiana. We report that PDLP5 and its closely related proteins carry unconventional targeting signals consisting of short stretches of amino acids. PDLP5 contains two divergent, tandemly arranged signals, either of which is sufficient for localization and biological function in regulating viral movement through plasmodesmata. Notably, plasmodesmal targeting signals exhibit little sequence conservation but are located similarly proximal to the membrane. These features appear to be a common theme in plasmodesmal targeting.

A PDLP-NHL3 complex integrates plasmodesmal immune signaling cascades

The plant immune system relies on the perception of molecules that signal the presence of a microbe threat. This triggers signal transduction that mediates a range of cellular responses via a collection of molecular machinery including receptors, small molecules, and enzymes. One response to pathogen perception is the restriction of cell-to-cell communication by plasmodesmal closure. We previously found that while chitin and flg22 trigger specialized immune signaling cascades in the plasmodesmal plasma membrane, both execute plasmodesmal closure via callose synthesis at the plasmodesmata. Therefore, the signaling pathways ultimately converge at or upstream of callose synthesis. To establish the hierarchy of signaling at plasmodesmata and characterize points of convergence in microbe elicitor-triggered signaling, we profiled the dependence of plasmodesmal responses triggered by different elicitors on a range of plasmodesmal signaling machinery. We identified that, like chitin, flg22 signals via RESPIRATORY BURST OXIDASE HOMOLOGUE D (RBOHD) to induce plasmodesmal closure. Further, we found that PLASMODESMATA-LOCATED PROTEIN 1 (PDLP1), PDLP5, and CALLOSE SYNTHASE 1 (CALS1) are common to microbe- and salicylic acid (SA)-triggered responses, identifying PDLPs as a candidate signaling nexus. To understand how PDLPs relay a signal to CALS1, we screened for PDLP5 interactors and found NON-RACE SPECIFIC DISEASE RESISTANCE/HIN1 HAIRPIN-INDUCED-LIKE protein 3 (NHL3), which is also required for chitin-, flg22- and SA-triggered plasmodesmal responses and PDLP-mediated activation of callose synthesis. We conclude that a PDLP-NHL3 complex acts as an integrating node of plasmodesmal signaling cascades, transmitting multiple immune signals to activate CALS1 and plasmodesmata closure.

A Tale of Two Domains Pushing Lateral Roots.

Successful plant organ development depends on well-coordinated intercellular communication between the cells of the organ itself, as well as with surrounding cells. Intercellular signals often move via the symplasmic pathway using plasmodesmata. Intriguingly, brief periods of symplasmic isolation may also be necessary to promote organ differentiation and functionality. Recent findings suggest that symplasmic isolation of a subset of parental root cells and newly forming lateral root primordia (LRPs) plays a vital role in modulating lateral root development and emergence. In this opinion article we discuss how two symplasmic domains may be simultaneously established within an LRP and its overlying cells, and the significance of plasmodesmata in this process.

An evolutionarily conserved motif is required for Plasmodesmata-located protein 5 to regulate cell-to-cell movement

Numerous cell surface receptors and receptor-like proteins (RLPs) undergo activation or deactivation via a transmembrane domain (TMD). A subset of plant RLPs distinctively localizes to the plasma membrane-lined pores called plasmodesmata. Those RLPs include the Arabidopsis thaliana Plasmodesmata-located protein (PDLP) 5, which is well known for its vital function regulating plasmodesmal gating and molecular movement between cells. In this study, we report that the TMD, although not a determining factor for the plasmodesmal targeting, serves essential roles for the PDLP5 function. In addition to its role for membrane anchoring, the TMD mediates PDLP5 self-interaction and carries an evolutionarily conserved motif that is essential for PDLP5 to regulate cell-to-cell movement. Computational modeling-based analyses suggest that PDLP TMDs have high propensities to dimerize. We discuss how a specific mode(s) of TMD dimerization might serve as a common mechanism for PDLP5 and other PDLP members to regulate cell-to-cell movement.

Analysis of a novel mutant allele of GSL8 reveals its key roles in cytokinesis and symplastic trafficking in Arabidopsis

BackgroundPlant cell walls are mainly composed of polysaccharides such as cellulose and callose. Callose exists at a very low level in the cell wall; however, it plays critical roles at different stages of plant development as well as in defence against unfavorable conditions. Callose is accumulated at the cell plate, at plasmodesmata and in male and female gametophytes. Despite the important roles of callose in plants, the mechanisms of its synthesis and regulatory properties are not well understood.ResultsCALLOSE SYNTHASE (CALS) genes, also known as GLUCAN SYNTHASE-LIKE (GSL), comprise a family of 12 members in Arabidopsis thaliana. Here, we describe a new allele of GSL8 (named essp8) that exhibits pleiotropic seedling defects. Reduction of callose deposition at the cell plates and plasmodesmata in essp8 leads to ectopic endomitosis and an increase in the size exclusion limit of plasmodesmata during early seedling development. Movement of two non-cell-autonomous factors, SHORT ROOT and microRNA165/6, both required for root radial patterning during embryonic root development, are dysregulated in the primary root of essp8. This observation provides evidence for a molecular mechanism explaining the gsl8 root phenotype. We demonstrated that GSL8 interacts with PLASMODESMATA-LOCALIZED PROTEIN 5, a β-1,3-glucanase, and GSL10. We propose that they all might be part of a putative callose synthase complex, allowing a concerted regulation of callose deposition at plasmodesmata.ConclusionAnalysis of a novel mutant allele of GSL8 reveals that GSL8 is a key player in early seedling development in Arabidopsis. GSL8 is required for maintaining the basic ploidy level and regulating the symplastic trafficking. Callose deposition at plasmodesmata is highly regulated and occurs through interaction of different components, likely to be incorporated into a callose biosynthesis complex. We are providing new evidence supporting an earlier hypothesis that GSL8 might have regulatory roles apart from its enzymatic function in plasmodesmata regulation.

Histochemical Analyses Reveal That Stronger Intrinsic Defenses in Gossypium barbadense Than in G. hirsutum Are Associated With Resistance to Verticillium dahliae.

Verticillium wilt, caused by Verticillium dahliae Kleb., is a serious threat to cotton (Gossypium spp.) crop production. To enhance our understanding of the plant's complex defensive mechanism, we examined colonization patterns and interactions between V. dahliae and two cotton species, the resistant G. barbadense and the susceptible G. hirsutum. Microscopic examinations and grafting experiments showed that the progression of infection was restricted within G. barbadense. At all pre- and postinoculation sampling times, levels of salicylic acid (SA) were also higher in that species than in G. hirsutum. Comparative RNA-Seq analyses indicated that infection induced dramatic changes in the expression of thousands of genes in G. hirsutum, whereas those changes were fewer and weaker in G. barbadense. Investigations of the morphological and biochemical nature of cell-wall barriers demonstrated that depositions of lignin, phenolic compounds, and callose were significantly higher in G. barbadense. To determine the contribution of a known resistance gene to these processes, we silenced GbEDS1 and found that the transformed plants had decreased SA production, which led to the upregulation of PLASMODESMATA-LOCATED PROTEIN (PDLP) 1 and PDLP6. This was followed by a decline in callose deposition in the plasmodesmata, which then led to increased pathogen susceptibility. This comparison between resistant and susceptible species indicated that both physical and chemical mechanisms play important roles in the defenses of cotton against V. dahliae.

Ectodomain of plasmodesmata-localized protein 5 in Arabidopsis: expression, purification, crystallization and crystallographic analysis.

Plasmodesmata-localized protein 5 (PDLP5) is a cysteine-rich receptor-like protein which is localized on the plasmodesmata of Arabidopsis thaliana. Overexpression of PDLP5 can reduce the permeability of the plasmodesmata and further affect the cell-to-cell movement of viruses and macromolecules in plants. The ectodomain of PDLP5 contains two DUF26 domains; however, the function of these domains is still unknown. Here, the ectodomain of PDLP5 from Arabidopsis was cloned and overexpressed using an insect expression system and was then purified and crystallized. X-ray diffraction data were collected to 1.90 Å resolution and were indexed in space group P1, with unit-cell parameters a = 41.9, b = 48.1, c=62.2 Å, α = 97.3, β = 103.1, γ = 99.7°. Analysis of the crystal content indicated that there are two molecules in the asymmetric unit, with a Matthews coefficient of 2.51 Å3 Da-1 and a solvent content of 50.97%.

Arabidopsis thaliana Acyl-CoA-binding protein ACBP6 interacts with plasmodesmata-located protein PDLP8

ABSTRACTIn Arabidopsis thaliana, six acyl-CoA-binding proteins (ACBPs), designated as AtACBP1 to AtACBP6, have been identified to function in various events related to plant stress and development. The 10-kDa AtACBP6 is the smallest in this protein family, and recombinant AtACBP6 interacts with lipids in vitro by binding to acyl-CoA esters and phosphatidylcholine. Using anti-AtACBP6 antibodies in immunoelectron microscopy, we have localized AtACBP6 in the Arabidopsis phloem. The detection of immunogold grains in the plasmodesmata suggested that AtACBP6 could move from the companion cells to the sieve elements via the plasmodesmata. As AtACBP6 has been identified in a membrane-based interactome analysis to be a potential protein partner of Plasmodesmata-Localized Protein, PDLP8, AtACBP6-PDLP8 interaction was investigated herein utilizing isothermal titration calorimetry, as well as pull-down and bimolecular fluorescence complementation assays (BiFC). Notably, BiFC data revealed that AtACBP6-PDLP8 interaction occurred at the plasma membrane, which was unexpected as AtACBP6 has been previously identified in the cytosol. AtACBP6 expression was generally higher than PDLP8 in β-glucuronidase (GUS) assays on transgenic Arabidopsis transformed with AtACBP6 or PDLP8 promoter-driven GUS, consistent with qRT-PCR and microarray results. Furthermore, western blot analysis using anti-AtACBP6 antibodies showed a reduction in AtACBP6 expression in the pdlp8 T-DNA insertional mutant, suggesting that PDLP8 may possibly influence AtACBP6 accumulation in the sieve elements, probably in the plasmodesmata, where PDLP8 is confined and to where AtACBP6 has been immunodetected.

Expression analysis of five Arabidopsis PDLP5 homologous in watermelon subjected to biotic and abiotic stresses

Watermelon (Citrullus lanatus (Thunb.) Matsum. & Nakai var. lanatus) is an economically important crop in South Korea. Although efforts have been made to develop disease-resistant cultivars, defense signal pathways in watermelon are still unknown. GNK2 domain containing proteins in plants are involved in oxidative stress and salt stress, and in defense signaling responses to pathogens and viruses. Arabidopsis thaliana plasmodesmata-located protein 5 (PDLP5) controls cell-to-cell communication and defense signaling. We identified five Arabidopsis PDLP5 (AtPDLP5) homologous in watermelon, using the Cucurbit Genomics Database. The five putative watermelon PDLPs had two GNK2 domains and showed high sequence identities to AtPDLP5. Their mRNAs were expressed in three watermelon cultivars, PI189225, Au-Producer, and 920533. Each mRNA was differently expressed after infection of Colletotrichum orbiculare, Didymella bryoniae, and Pseudomonas syringae. In addition to pathogen infection, their expression patterns were altered when subjected to abiotic stresses (drought, salt, and cold) or salicylic acid treatment. Cla006974 mRNA was absent in the 920533 cultivar infected with D. bryoniae. Based on these findings, we propose that five putative watermelon PDLPs are involved in defense against fungal pathogens and abiotic stresses. In addition, Cla006974 could be useful as a marker for selecting Gummy stem blight-resistant cultivars via molecular screening.

The role of plasmodesma-located proteins in tubule-guided virus transport is limited to the plasmodesmata.

Intercellular spread of plant viruses involves passage of the viral genome or virion through a plasmodesma (PD). Some viruses severely modify the PD structure, as they assemble a virion carrying tubule composed of the viral movement protein (MP) inside the PD channel. Successful modulation of the host plant to allow infection requires an intimate interaction between viral proteins and both structural and regulatory host proteins. To date, however, very few host proteins are known to promote virus spread. Plasmodesmata-located proteins (PDLPs) localised in the PD have been shown to contribute to tubule formation in cauliflower mosaic virus and grapevine fanleaf virus infections. In this study, we have investigated the role of PDLPs in intercellular transport of another tubule-forming virus, cowpea mosaic virus. The MP of this virus was found to interact with PDLPs in the PD, as was shown for other tubule-forming viruses. Expression of PDLPs and MPs in protoplasts in the absence of a PD revealed that these proteins do not co-localise at the site of tubule initiation. Furthermore, we show that tubule assembly in protoplasts does not require an interaction with PDLPs at the base of the tubule, as has been observed in planta. These results suggest that a physical interaction between MPs and PDLPs is not required for assembly of the movement tubule and that the beneficial role of PDLPs in virus movement is confined to the structural context of the PD.

Mind the gap: Signal movement through plasmodesmata is critical for the manifestation of SAR

Systemic acquired resistance (SAR) is a plant defense response in which an initial localized infection affords enhanced pathogen resistance to distant, uninfected leaves. SAR requires efficient long-distance signaling between the infected leaf, where SAR signals are generated, and the distant uninfected leaves that receive them. A growing body of evidence indicates that the lipid transfer protein DIR1 (Defective in Induced Resistance) is an important mediator of long-distance SAR signaling. In a recent publication, we investigated if cell-to-cell movement through plasmodesmata is required for long-distance movement of DIR1 during SAR. We determined that overexpression of Plasmodesmata-Located Proteins (PDLP1 and 5) negatively impacted long-distance DIR1 movement and SAR competence, suggesting that movement through plasmodesmata contributes to long-distance signal movement during SAR.

The plasmodesmal protein PDLP1 localises to haustoria-associated membranes during downy mildew infection and regulates callose deposition.

The downy mildew pathogen Hyaloperonospora arabidopsidis (Hpa) is a filamentous oomycete that invades plant cells via sophisticated but poorly understood structures called haustoria. Haustoria are separated from the host cell cytoplasm and surrounded by an extrahaustorial membrane (EHM) of unknown origin. In some interactions, including Hpa-Arabidopsis, haustoria are progressively encased by host-derived, callose-rich materials but the molecular mechanisms by which callose accumulates around haustoria remain unclear. Here, we report that PLASMODESMATA-LOCATED PROTEIN 1 (PDLP1) is expressed at high levels in Hpa infected cells. Unlike other plasma membrane proteins, which are often excluded from the EHM, PDLP1 is located at the EHM in Hpa-infected cells prior to encasement. The transmembrane domain and cytoplasmic tail of PDLP1 are sufficient to convey this localization. PDLP1 also associates with the developing encasement but this association is lost when encasements are fully mature. We found that the pdlp1,2,3 triple mutant is more susceptible to Hpa while overexpression of PDLP1 enhances plant resistance, suggesting that PDLPs enhance basal immunity against Hpa. Haustorial encasements are depleted in callose in pdlp1,2,3 mutant plants whereas PDLP1 over-expression elevates callose deposition around haustoria and across the cell surface. These data indicate that PDLPs contribute to callose encasement of Hpa haustoria and suggests that the deposition of callose at haustoria may involve similar mechanisms to callose deposition at plasmodesmata.

Plasmodesmata-located protein overexpression negatively impacts the manifestation of systemic acquired resistance and the long-distance movement of Defective in Induced Resistance1 in Arabidopsis.

Systemic acquired resistance (SAR) is a plant defence response that provides immunity to distant uninfected leaves after an initial localised infection. The lipid transfer protein (LTP) Defective in Induced Resistance1 (DIR1) is an essential component of SAR that moves from induced to distant leaves following a SAR-inducing local infection. To understand how DIR1 is transported to distant leaves during SAR, we analysed DIR1 movement in transgenic Arabidopsis lines with reduced cell-to-cell movement caused by the overexpression of Plasmodesmata-Located Proteins PDLP1 and PDLP5. These PDLP-overexpressing lines were defective for SAR, and DIR1 antibody signals were not observed in phloem sap-enriched petiole exudates collected from distant leaves. Our data support the idea that cell-to-cell movement of DIR1 through plasmodesmata is important during long-distance SAR signalling in Arabidopsis.

Analysis of the role of myosins in targeting proteins to plasmodesmata.

Plasmodesmata (PD) are dynamic cell wall microchannels that facilitate the intercellular trafficking of RNA and protein macromolecules playing cell nonautonomous roles in the orchestration of plant development, growth, and plant defense. The trafficking of macromolecules and organelles within cells depends on cytoskeletal components and their associated motor proteins. Plant viruses evolved to hijack this transport system to move their infectious genomes to PD. Current efforts concentrate on dissecting the role of specific myosin motors in transporting plant or viral proteins to the channels. Here we describe a method that addresses the role of specific myosins by expression of myosin tails that cause the repression of myosin activity in a dominant-negative manner. As an example, we explain the use of myosin tails from Nicotiana benthamiana to address the role of N. benthamiana myosins in the targeting of PLASMODESMATA-LOCATED PROTEIN 1 (PDLP1) to PD.

The secretory pathway and the actomyosin motility system are required for plasmodesmatal localization of the P7-1 of rice black-streaked dwarf virus

Rice black-streaked dwarf virus (RBSDV), a plant-infecting reovirus (genus Fijivirus), generally induces virus-containing tubules in infected cells. The nonstructural protein P7-1, encoded by the first open reading frame of segment 7, is involved in forming the structural matrix of these tubules. In experiments to investigate the subcellular localization of P7-1 in Nicotiana benthamiana epidermal cells, fluorescence of P7-1:eGFP was observed in the nucleus, cytoplasm and cell periphery, and in punctate points along the cell wall of plasmolyzed cells. Co-localization with plasmodesmata-located protein 1 showed that P7-1 formed the punctate points at plasmodesmata. Mutational analysis demonstrated that transmembrane domain 1 and adjacent residues were necessary and sufficient for P7-1 to form punctate structures at the cell wall in the plasmolyzed cells. Chemical drug and protein inhibitor treatments indicated that P7-1 utilized the ER-to-Golgi secretory pathway and the actomyosin motility system for its intracellular transport. The plasmodesmatal localization of RBSDV P7-1 is therefore dependent on the secretory pathway and the actomyosin motility system.

Tubule-Guided Cell-to-Cell Movement of a Plant Virus Requires Class XI Myosin Motors

Cell-to-cell movement of plant viruses occurs via plasmodesmata (PD), organelles that evolved to facilitate intercellular communications. Viral movement proteins (MP) modify PD to allow passage of the virus particles or nucleoproteins. This passage occurs via several distinct mechanisms one of which is MP-dependent formation of the tubules that traverse PD and provide a conduit for virion translocation. The MP of tubule-forming viruses including Grapevine fanleaf virus (GFLV) recruit the plant PD receptors called Plasmodesmata Located Proteins (PDLP) to mediate tubule assembly and virus movement. Here we show that PDLP1 is transported to PD through a specific route within the secretory pathway in a myosin-dependent manner. This transport relies primarily on the class XI myosins XI-K and XI-2. Inactivation of these myosins using dominant negative inhibition results in mislocalization of PDLP and MP and suppression of GFLV movement. We also found that the proper targeting of specific markers of the Golgi apparatus, the plasma membrane, PD, lipid raft subdomains within the plasma membrane, and the tonoplast was not affected by myosin XI-K inhibition. However, the normal tonoplast dynamics required myosin XI-K activity. These results reveal a new pathway of the myosin-dependent protein trafficking to PD that is hijacked by GFLV to promote tubule-guided transport of this virus between plant cells.

A Plasmodesmata-Localized Protein Mediates Crosstalk between Cell-to-Cell Communication and Innate Immunity inArabidopsis

Plasmodesmata (PD) are thought to play a fundamental role in almost every aspect of plant life, including normal growth, physiology, and developmental responses. However, how specific signaling pathways integrate PD-mediated cell-to-cell communication is not well understood. Here, we present experimental evidence showing that the Arabidopsis thaliana plasmodesmata-located protein 5 (PDLP5; also known as HOPW1-1-INDUCED GENE1) mediates crosstalk between PD regulation and salicylic acid-dependent defense responses. PDLP5 was found to localize at the central region of PD channels and associate with PD pit fields, acting as an inhibitor to PD trafficking, potentially through its capacity to modulate PD callose deposition. As a regulator of PD, PDLP5 was also essential for conferring enhanced innate immunity against bacterial pathogens in a salicylic acid-dependent manner. Based on these findings, a model is proposed illustrating that the regulation of PD closure mediated by PDLP5 constitutes a crucial part of coordinated control of cell-to-cell communication and defense signaling.