RESUMEN

FLAGELLIN SENSING 2 (FLS2) encodes a pattern recognition receptor that perceives bacterial flagellin. While putative FLS2 orthologs are broadly conserved in plants, their functional characterization remains limited. Here, we report the identification of orthologs in cucumber (Cucumis sativus) and melon (C. melo), named CsFLS2 and CmFLS2, respectively. Homology searching identified CsFLS2, and virus-induced gene silencing (VIGS) demonstrated that CsFLS2 is required for flg22-triggered ROS generation. Interestingly, genome re-sequencing of melon cv. Lennon and subsequent genomic PCR revealed that Lennon has two CmFLS2 haplotypes, haplotype I encoding full-length CmFLS2 and haplotype II encoding a truncated form. We show that VIGS-mediated knockdown of CmFLS2 haplotype I resulted in a significant reduction in both flg22-triggered ROS generation and immunity to a bacterial pathogen in melon cv. Lennon. Remarkably, genomic PCR of CmFLS2 revealed that 68% of tested commercial melon cultivars possess only CmFLS2 haplotype II: these cultivars thus lack functional CmFLS2. To explore evolutionary aspects of CmFLS2 haplotype II occurrence, we genotyped the CmFLS2 locus in 142 melon accessions by genomic PCR and analyzed 437 released sequences. The results suggest that CmFLS2 haplotype II is derived from C. melo subsp. melo. Furthermore, we suggest that the proportion of CmFLS2 haplotype II increased among the improved melo group compared with the primitive melo group. Collectively, these findings suggest that the deleted FLS2 locus generated in the primitive melo subspecies expanded after domestication, resulting in the spread of commercial melon cultivars defective in flagellin recognition, which is critical for bacterial immunity.

Asunto(s)

RESUMEN

The S-locus lectin receptor kinases (G-LecRKs) have been suggested as receptors for microbe/damage-associated molecular patterns (MAMPs/DAMPs) and to be involved in the pathogen defense responses, but the functions of most G-LecRKs in biotic stress response have not been characterized. Here, we identified a member of this family, G-LecRK-I.2, that positively regulates flg22- and Pseudomonas syringae pv. tomato (Pst) DC3000-induced stomatal closure. G-LecRK-I.2 was rapidly phosphorylated under flg22 treatment and could interact with the FLS2/BAK1 complex. Two T-DNA insertion lines, glecrk-i.2-1 and glecrk-i.2-2, had lower levels of reactive oxygen species (ROS) and nitric oxide (NO) production in guard cells, as compared with the wild-type Col-0, under Pst DC3000 infection. Also, the immunity marker genes CBP60g and PR1 were induced at lower levels under Pst DC3000 hrcC- infection in glecrk-i.2-1 and glecrk-i.2-2. The GUS reporter system also revealed that G-LecRK-I.2 was expressed only in guard cells. We also found that G-LecRK-I.2 could interact H+-ATPase AHA1 to regulate H+-ATPase activity in the guard cells. Taken together, our results show that G-LecRK-I.2 plays an important role in regulating stomatal closure under flg22 and Pst DC3000 treatments and in ROS and NO signaling specifically in guard cells.

Asunto(s)

RESUMEN

The receptor-like kinase FLAGELLIN-SENSITIVE 2 (FLS2) functions as a bacterial flagellin receptor localized on the cell membrane of plants. In Arabidopsis, the co-receptor BRI1-ASSOCIATED RECEPTOR KINASE 1 (BAK1) cooperates with FLS2 to detect the flagellin epitope flg22, resulting in formation of a signaling complex that triggers plant defense responses. However, the co-receptor responsible for recognizing and signaling the flg22 epitope in rice remains to be determined, and the precise structural mechanism underlying FLS2-mediated signal activation and transduction has not been clarified. This study presents the structural characterization of a kinase-dead mutant of the intracellular kinase domain of OsFLS2 (OsFLS2-KDD1013A) in complex with ATP or ADP, resolved at resolutions of 1.98 Å and 2.09 Å, respectively. Structural analysis revealed that OsFLS2 can adopt an active conformation in the absence of phosphorylation, although it exhibits only weak basal catalytic activity for autophosphorylation. Subsequent investigations demonstrated that OsSERK2 effectively phosphorylates OsFLS2, which reciprocally phosphorylates OsSERK2, leading to complete activation of OsSERK2 and rapid phosphorylation of the downstream substrate receptor-like cytoplasmic kinases OsRLCK176 and OsRLCK185. Through mass spectrometry experiments, we successfully identified critical autophosphorylation sites on OsSERK2, as well as sites transphosphorylated by OsFLS2. Furthermore, we demonstrated the interaction between OsSERK2 and OsFLS2, which is enhanced in the presence of flg22. Genetic evidence suggests that OsRLCK176 and OsRLCK185 may function downstream of the OsFLS2-mediated signaling pathway. Our study reveals the molecular mechanism by which OsFLS2 mediates signal transduction pathways in rice and provides a valuable example for understanding RLK-mediated signaling pathways in plants.

Asunto(s)

RESUMEN

Phloem is a critical tissue for transport of photosynthates and extracellular signals in vascular plants. However, it also represents an ideal environment for pathogens seeking access to valuable host nutrients. Although many vascular pathogens induce economically relevant crop damage, there is still little known about the mechanisms by which immune signaling operates through the phloem. An existing phosphoproteomic dataset was mined to identify proteins that were both phosphorylated in response to the defense-elicitor flagellin (flg22) and expressed in vascular cells. A single candidate, OCTOPUS (OPS), is polarly associated with the plasma membrane of sieve element cells and has been characterized as an inhibitor of brassinosteroid insensitive-2 in promotion of brassinosteroid-related phytohormone signaling. The observation that OPS is differentially phosphorylated in response to flg22 led us to the examine whether OPS may also regulate flg22-induced immune signaling. Two independent alleles of ops exhibited enhanced immunity outputs across multiple signaling branches of PAMP-triggered immunity (PTI), constitutively and in response to flg22 treatment. Together with our observation that interactions between OPS and brassinosteroid insensitive-2 were disrupted by induction of salicylic acid and depletion of brassinosteriod, these data support a model whereby OPS modulates brassinolide and immune signaling to control downstream responses. We present OPS as a novel addition to the list of proteins with documented roles in PAMP-PTI signaling. These results further indicate that immune signaling in the phloem may be a significant and unique component of the host detection and response to pathogens in vascular plants.

RESUMEN

Temporospatial regulation of immunity components is essential for properly activating plant defense response. Flagellin-sensing 2 (FLS2) is a surface-localized receptor that recognizes bacterial flagellin. The immune function of FLS2 is compromised in early stages of shoot development. However, the underlying mechanism for the age-dependent FLS2 signaling is not clear. Here, we show that the reduced basal immunity of juvenile leaves against Pseudomonas syringae pv. tomato DC3000 is independent of FLS2. The flg22-induced marker gene expression and reactive oxygen species activation were comparable in juvenile and adult stages, but callose deposition was more evident in the adult stage than the juvenile stage. We further demonstrated that microRNA156, a master regulator of plant aging, does not influence the expression of FLS2 and FRK1 (Flg22-induced receptor-like kinase 1) but mildly suppresses callose deposition in juvenile leaves. Our experiments revealed an intrinsic mechanism that regulates the amplitude of FLS2-mediated resistance during aging. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Asunto(s)

RESUMEN

A prophage tail-like protein (Bg_9562) of Burkholderia gladioli strain NGJ1 possesses broad-spectrum antifungal activity, and it is required for the bacterial ability to forage over fungi. Here, we analyzed whether heterologous overexpression of Bg_9562 or exogenous treatment with purified protein can impart disease tolerance in tomato. The physiological relevance of Bg_9562 during endophytic growth of NGJ1 was also investigated. Bg_9562 overexpressing lines demonstrate fungal and bacterial disease tolerance. They exhibit enhanced expression of defense genes and activation of mitogen-activated protein kinases. Treatment with Bg_9562 protein induces defense responses and imparts immunity in wild-type tomato. The defense-inducing ability lies within 18-51 aa region of Bg_9562 and is due to sequence homology with the bacterial flagellin epitope. Interaction studies suggest that Bg_9562 is perceived by FLAGELLIN-SENSING 2 homologs in tomato. The silencing of SlSERK3s (BAK1 homologs) prevents Bg_9562-triggered immunity. Moreover, type III secretion system-dependent translocation of Bg_9562 into host apoplast is important for elicitation of immune responses during colonization of NGJ1. Our study emphasizes that Bg_9562 is important for the endophytic growth of B. gladioli, while the plant perceives it as an indirect indicator of the presence of bacteria to mount immune responses. The findings have practical implications for controlling plant diseases.

Asunto(s)

RESUMEN

Through crosstalk, FLAGELLIN SENSITIVE 2 (FLS2) and RESPIRATORY BURST OXIDASE HOMOLOG D (RBOHD) are involved in regulating the homeostasis of cellular reactive oxygen species (ROS) and are linked to the metabolic response of plants toward both biotic and abiotic stress. In the present study, we examined the metabolome of Arabidopsis seedlings under drought and salt conditions to better understand the potential role of FLS2 and RBOHD-dependent signaling in the regulation of abiotic stress response. We identified common metabolites and genes that are regulated by FLS2 and RBOHD, and are involved in the response to drought and salt stress. Under drought conditions, D-aspartic acid and the expression of associated genes, such as ASPARAGINE SYNTHASE 2 (ASN2), increased in both fls2 and robed/f double mutants. The accumulation of amino acids, carbohydrates, and hormones, such as L-proline, D-ribose, and indoleacetaldehyde increased in both fls2 and rbohd/f double mutants under salt conditions, as did the expression of related genes, such as PROLINE IMINOPEPTIDASE, PHOSPHORIBOSYL PYROPHOSPHATE SYNTHASE 5, and NITRILASE 3. Collectively, these results indicate that the FLS2-RBOHD module regulates plant response to drought and salt stress through ROS signaling by adjusting the accumulation of metabolites and expression of genes related to metabolite synthesis.

RESUMEN

Plant receptor kinases are key transducers of extracellular stimuli, such as the presence of beneficial or pathogenic microbes or secreted signaling molecules. Receptor kinases are regulated by numerous post-translational modifications.1,2,3 Here, using the immune receptor kinases FLS24 and EFR,5 we show that S-acylation at a cysteine conserved in all plant receptor kinases is crucial for function. S-acylation involves the addition of long-chain fatty acids to cysteine residues within proteins, altering their biochemical properties and behavior within the membrane environment.6 We observe S-acylation of FLS2 at C-terminal kinase domain cysteine residues within minutes following the perception of its ligand, flg22, in a BAK1 co-receptor and PUB12/13 ubiquitin ligase-dependent manner. We demonstrate that S-acylation is essential for FLS2-mediated immune signaling and resistance to bacterial infection. Similarly, mutating the corresponding conserved cysteine residue in EFR suppressed elf18-triggered signaling. Analysis of unstimulated and activated FLS2-containing complexes using microscopy, detergents, and native membrane DIBMA nanodiscs indicates that S-acylation stabilizes, and promotes retention of, activated receptor kinase complexes at the plasma membrane to increase signaling efficiency.

Asunto(s)

RESUMEN

In eukaryotes, EPSINs are Epsin N-terminal Homology (ENTH) domain-containing proteins that serve as monomeric clathrin adaptors at the plasma membrane (PM) or the trans-Golgi Network (TGN)/early endosomes (EE). The model plant Arabidopsis thaliana encodes for seven ENTH proteins, of which so far, only AtEPSIN1 (AtEPS1) and MODIFIED TRANSPORT TO THE VACUOLE1 (AtMTV1) localize to the TGN/EE and contribute to cargo trafficking to both the cell surface and the vacuole. However, relatively little is known about role(s) of any plant EPSIN in governing physiological responses. We have recently shown that AtEPS1 is a positive modulator of plant immune signaling and pattern-triggered immunity against flagellated Pseudomonas syringae pv. tomato (Pto) DC3000 bacteria. In eps1 mutants, impaired immune responses correlate with reduced accumulation of the receptor FLAGELLIN SENSING2 (AtFLS2) and the convergent immune co-receptor BRASSINOSTEROID INSENTIVE1-ASSOCIATED RECEPTOR KINASE1 (AtBAK1) in the PM. Here, we report that in contrast to AtEPS1, the TGN/EE-localized AtMTV1 did not contribute significantly to immunity against pathogenic Pto DC3000 bacteria. We also compared the amino acid sequences, peptide motif structures and in silico tertiary structures of the ENTH domains of AtEPS1 and AtMTV1 in more detail. We conclude that despite sharing the classical tertiary alpha helical ENTH-domain structure and clathrin-binding motifs, the overall low amino acid identity and differences in peptide motifs may explain their role(s) in trafficking of some of the same as well as distinct cargo components to their site of function, with the latter potentially contributing to differences in physiological responses.

Asunto(s)

RESUMEN

In eukaryotes, dynamins and dynamin-related proteins (DRPs) are high-molecular weight GTPases responsible for mechanochemical fission of organelles or membranes. Of the six DRP subfamilies in Arabidopsis thaliana, AtDRP1 and AtDRP2 family members serve as endocytic accessory proteins in clathrin-mediated endocytosis. Most studies have focused on AtDRP1A and AtDRP2B as critical modulators of plant pattern-triggered immunity (PTI) against pathogenic, flagellated Pseudomonas syringae pv. tomato DC3000 bacteria and immune signaling in response to the bacterial flagellin peptide flg22. Much less is known about AtDRP2A, the closely related paralog of AtDRP2B. AtDRP2A and AtDRP2B are the only classical, or bona fide, dynamins in Arabidopsis, based on their evolutionary conserved domain structure with mammalian dynamins functioning in endocytosis. AtDRP2B but not AtDRP2A is required for robust ligand-induced endocytosis of the receptor kinase FLAGELLIN SENSING2 for dampening of early flg22 signaling. Here, we utilized Arabidopsis drp2a null mutants to identify AtDRP2A as a positive contributor to effective PTI against P. syringae pv. tomato DC3000 bacteria, consistent with reduced PATHOGEN RELATED1 (PR1) messenger RNA accumulation. We provide evidence that AtDRP2A is a novel modulator of late flg22 signaling, contributing positively to PR1 gene induction but negatively to polyglucan callose deposition. AtDRP2A has no apparent roles in flg22-elicited mitogen-activated protein kinase defense marker gene induction. In summary, this study adds the evolutionary conserved dynamin AtDRP2A to a small group of vesicular trafficking proteins with roles as non-canonical contributors in immune responses, likely due to modulating one or both the localization and activity of multiple different proteins with distinct contributions to immune signaling. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Asunto(s)

RESUMEN

Arabidopsis DYNAMIN-RELATED PROTEIN1A (AtDRP1A) and AtDRP2B are large GTPases that function together in endocytosis for effective cytokinesis, cell enlargement and development. A recent study shows that these DRPs contribute to ligand-induced endocytosis of the immune receptor FLAGELLIN SENSING2 (AtFLS2) to modulate flg22-immune signaling, and they are required for immunity against Pseudomonas syringae pv. tomato bacteria. Here, we demonstrate that atdrp1a and atdrp2b single mutants showed increased susceptibility to Botrytis cinerea indicating that AtDRP1A and AtDRP2B are necessary for effective resistance against this necrotrophic fungus. Thus, we expanded our limited understanding of clathrin endocytic accessory proteins in immunity against plant pathogens.

Asunto(s)

RESUMEN

The oomycete pathogen Phytophthora capsici encodes hundreds of RXLR effectors that enter the plant cells and suppress host immunity. Only a few of these genes are conserved across different strains and species. Such core effectors might target hub genes and immune pathways in hosts. Here, we describe the functional characterization of the core P. capsici RXLR effector RXLR242. The expression of RXLR242 was up-regulated during infection, and its ectopic expression in Nicotiana benthamiana, an experimental plant host, further promoted Phytophthora infection. RXLR242 physically interacted with a group of RAB proteins that belong to the small GTPase family and play a role in regulating transport pathways in the intracellular membrane trafficking system. In addition, RXLR242 impeded the secretion of PATHOGENESIS-RELATED 1 (PR1) protein to the apoplast. This phenomenon resulted from the competitive binding of RXLR242 to RABE1-7. We also found that RXLR242 interfered with the association between RABA4-3 and its binding protein, thereby disrupting the trafficking of the membrane receptor FLAGELLIN-SENSING 2. Thus, RXLR242 manipulates plant immunity by targeting RAB proteins and disrupting protein trafficking in the host plants.

Asunto(s)

RESUMEN

Pattern recognition receptor (PRR) trafficking to the plasma membrane and endocytosis plays a crucial role in pattern triggered immunity (PTI). Dynamin-related proteins (DRPs) participate in endocytosis and recycling. In Arabidopsis, DRP1 and DRP2 are involved in plasma membrane scission during endocytosis. They are required for the PRR FLS2 endocytosis induction and PTI activation after elicitation with flg22, the MAMP recognized by FLS2. In tomato, SlDRP2A regulates the PRR LeEIX2 endocytosis and PTI activation in response to EIX, the MAMP recognized by LeEIX2. However, it is unknown if other DRPs participate in these processes. Taking advantage of bioinformatics tools, we selected SlDRP2B among the eight DRP2 tomato orthologues to study its functionality in trafficking and plant immunity. Through transient expression of SlDRP1B and its dominant-negative mutant on Nicotiana benthamiana and Nicotiana tabacum, we analyzed SlDRP1B function. We observed that SlDRP1B is physically associated with the LeEIX2 and modifies LeEIX2 trafficking, increasing its presence in endosomes. An enhancement of EIX-elicitated defense responses accompanies the role of SlDRP1B on LeEIX endocytosis. In addition, SlDRP1B overexpression enhanced flg22-elicited defense response. With these results, we conclude that SlDRP1B regulates PRR trafficking and, therefore, plant immunity, similarly to the SlDRP2A role.

RESUMEN

Efficient plant immune responses depend on the ability to recognise an invading microbe. The 22-amino acids in the N-terminal domain and the 28-amino acids in the central region of the bacterial flagellin, called flg22 and flgII-28, respectively, are important elicitors of plant immunity. Plant immunity is activated after flg22 or flgII-28 recognition by the plant transmembrane receptors FLS2 or FLS3, respectively. There is strong selective pressure on many plant pathogenic and endophytic bacteria to overcome flagellin-triggered immunity. Here we provide an overview of recent developments in our understanding of the evasion and suppression of flagellin pattern recognition by plant-associated bacteria.

Asunto(s)

RESUMEN

As sessile organisms, plants are constantly challenged by several environmental stresses. Different kinds of stress often occur simultaneously, leading to the accumulation of reactive oxygen species (ROS) produced by respiratory burst oxidase homolog (RBOHD) and calcium fluctuation in cells. Extensive studies have revealed that flagellin sensitive 2 (FLS2) can sense the infection by pathogenic microorganisms and activate cellular immune response by regulating intracellular ROS and calcium signals, which can also be activated during plant response to abiotic stress. However, little is known about the roles of FLS2 and RBOHD in regulating abiotic stress. In this study, we found that although the fls2 mutant showed tolerance, the double mutant rbohd rbohf displayed hypersensitivity to abiotic stress, similar to its performance in response to immune stress. An analysis of the transcriptome of the fls2 mutant and rbohd rbohf double mutant revealed that phytochrome interacting factor 4 (PIF4) acted downstream of FLS2 and RBOHD to respond to the abiotic stress. Further analysis showed that both FLS2 and RBOHD regulated the response of plants to drought and salt stress by regulating the expression of PIF4. These findings revealed an FLS2-RBOHD-PIF4 module in regulating plant response to biotic and abiotic stresses.

Asunto(s)

RESUMEN

The flagellin epitope flg22, a pathogen-associated molecular pattern (PAMP), binds to the receptor-like kinase FLAGELLIN SENSING2 (FLS2), and triggers Ca2+ influx across the plasma membrane (PM). The flg22-induced increases in cytosolic Ca2+ concentration ([Ca2+ ]i ) (FICA) play a crucial role in plant innate immunity. It's well established that the receptor FLS2 and reactive oxygen species (ROS) burst undergo sensitivity adaptation after flg22 stimulation, referred to as desensitization and resensitization, to prevent over responses to pathogens. However, whether FICA also mount adaptation mechanisms to ensure appropriate and efficient responses against pathogens remains poorly understood. Here, we analysed systematically [Ca2+ ]i increases upon two successive flg22 treatments, recorded and characterized rapid desensitization but slow resensitization of FICA in Arabidopsis thaliana. Pharmacological analyses showed that the rapid desensitization might be synergistically regulated by ligand-induced FLS2 endocytosis as well as the PM depolarization. The resensitization of FICA might require de novo FLS2 protein synthesis. FICA resensitization appeared significantly slower than FLS2 protein recovery, suggesting additional regulatory mechanisms of other components, such as flg22-related Ca2+ permeable channels. Taken together, we have carefully defined the FICA sensitivity adaptation, which will facilitate further molecular and genetic dissection of the Ca2+ -mediated adaptive mechanisms in PAMP-triggered immunity.

Asunto(s)

RESUMEN

Membrane-localized leucine-rich repeat receptor kinases (LRR-RKs) sense diverse extracellular signals, and coordinate and specify cellular functions in plants. However, functional understanding and identification of the cellular signaling of most LRR-RKs remain a major challenge owing to their genetic redundancy, the lack of ligand information, and subtle phenotypes of LRR-RK overexpression. Here, we report an engineered rapamycin-inducible dimerization (RiD) receptor system that triggers a receptor-specific LRR-RK signaling independent of their cognate ligands or endogenous receptors. Using the RiD-receptors, we demonstrated that the rapamycin-mediated association of chimeric cytosolic kinase domains from the BRI1/BAK1 receptor/co-receptor, but not the BRI1/BRI1 or BAK1/BAK1 homodimer, is sufficient to activate downstream brassinosteroid signaling and physiological responses. Furthermore, we showed that the engineered RiD-FLS2/BAK1 could activate flagellin-22-mediated immune signaling and responses. Using the RiD system, we also identified the potential function of an unknown orphan receptor in immune signaling and revealed the differential activities of SERK co-receptors of LRR-RKs. Our results indicate that the RiD method can serve as a synthetic biology tool for precise temporal manipulation of LRR-RK signaling and for understanding LRR-RK biology.

Asunto(s)

RESUMEN

The alternative splicing of pattern recognition receptor genes regulates immune signalling in mammals, but in plants its role is still unknown. Here, we detected alternatively spliced introns (exitrons) in the first annotated exons of FLAGELLIN-SENSING 2 (FLS2) genes in all the examined dicot plants across nine families. The 5' splice site (SS) regions were conserved and with rare synonymous substitutions. Point mutations and gene swaps indicated that the position and efficiency of exitron splicing primarily depended on the nucleotide sequences of FLS2 genes. Single-nucleotide mutations in the invariable codon carrying 5' SS dramatically altered the accumulation of poplar and tomato FLS2 transcripts, indicating the 5'-proximal exitrons of FLS2 function as stimulatory introns on gene expression. The 3' SSs of exitrons are diverse and can be changed by 1-2 nucleotide mutations in Salicaceae FLS2. The alternative transcripts (ATs) of poplar and tobacco FLS2, which encode small secreted proteins, were specifically induced by flg22, and one such AT from tobacco FLS2 suppressed flg22-induced response. Our results indicated that the exitrons of FLS2 genes regulate the accumulation of transcripts by an intron mediated enhancement (IME) mechanism and some ATs have the potential to encode suppressors for FLS2 pathway.

Asunto(s)

RESUMEN

The plasma membrane (PM)-localized receptor kinase FLAGELLIN SENSING 2 (FLS2) recognizes bacterial flagellin or its immunogenic epitope flg22, and initiates microbe-associated molecular pattern-triggered immunity, which inhibits infection by bacterial pathogens. The localization, abundance and activity of FLS2 are under dynamic control. Here, we demonstrate that Arabidopsis thaliana EXO70B1, a subunit of the exocyst complex, plays a critical role in FLS2 signaling that is independent of the truncated Toll/interleukin-1 receptor-nucleotide binding sequence protein TIR-NBS2 (TN2). In the exo70B1-3 mutant, the abundance of FLS2 protein at the PM is diminished, consistent with the impaired flg22 response of this mutant. EXO70B1-GFP plants showed increased FLS2 accumulation at the PM and therefore enhanced FLS2 signaling. The EXO70B1-mediated trafficking of FLS2 to the PM is partially independent of the PENETRATION 1 (PEN1)-containing secretory pathway. In addition, EXO70B1 interacts with EXO70B2, a close homolog of EXO70B1, and both proteins associate with FLS2 and contribute to the accumulation of FLS2 at the PM. Taken together, our data suggest that the exocyst complex subunits EXO70B1 and EXO70B2 regulate the trafficking of FLS2 to the PM, which represents a new layer of regulation of FLS2 function in plant immunity.

Asunto(s)

RESUMEN

The plasma membrane (PM)-localized receptor-like kinases (RLKs) play important roles in pathogen defense. One of the first cloned RLKs is the Arabidopsis receptor kinase FLAGELLIN SENSING 2 (FLS2), which specifically recognizes a conserved 22 amino acid N-terminal sequence of Pseudomonas syringae pv．tomato DC3000 (Pst) flagellin protein (flg22). Although extensively studied in Arabidopsis, the functions of RLKs in crop plants remain largely uninvestigated. To understand the roles of RLKs in soybean (Glycine max), GmFLS2 was silenced via virus induced gene silencing (VIGS) mediated by Bean pod mottle virus (BPMV). No significant morphological differences were observed between GmFLS2-silenced plants and the vector control plants. However, silencing GmFLS2 significantly enhanced the susceptibility of the soybean plants to Pseudomonas syringae pv．glycinea (Psg). Kinase activity assay showed that silencing GmFLS2 significantly reduced the phosphorylation level of GmMPK6 in response to flg22 treatment. However, reduced phosphorylation level of both GmMPK3 and GmMPK6 in response to Psg infection was observed in GmFLS2-silenced plants, implying that defense response is likely transduced through activation of the downstream GmMAPK signaling pathway upon recognition of bacterial pathogen by GmFLS2. The core peptides of flg22 from Pst and Psg were highly conserved and only 4 amino acid differences were seen at their N-termini. Interestingly, it appeared that the Psg-flg22 was more effective in activating soybean MAPKs than activating Arabidopsis MAPKs, and conversely, Pst-flg22 was more effective in activating Arabidopsis MAPKs than activating soybean MAPKs, suggesting that the cognate recognition is more potent than heterologous recognition in activating downstream signaling. Taken together, our results suggest that the function of FLS2 is conserved in immunity against bacteria pathogens across different plant species.

Asunto(s)