Receptor kinases (RKs) are of paramount importance in transmembrane signaling that governs plant reproduction, growth, development, and adaptation to diverse environmental conditions. Receptor-like ...cytoplasmic kinases (RLCKs), which lack extracellular ligand-binding domains, have emerged as a major class of signaling proteins that regulate plant cellular activities in response to biotic abiotic stresses and endogenous extracellular signaling molecules. By associating with immune RKs, RLCKs regulate multiple downstream signaling nodes to orchestrate a complex array of defense responses against microbial pathogens. RLCKs also associate with RKs that perceive brassinosteroids and signaling peptides to coordinate growth, pollen tube guidance, embryonic and stomatal patterning, floral organ abscission, and abiotic stress responses. The activity and stability of RLCKs are dynamically regulated not only by RKs but also by other RLCK-associated proteins. Analyses of RLCK-associated components and substrates have suggested phosphorylation relays as a major mechanism underlying RK-mediated signaling.
The Arabidopsis immune receptor FLS2 perceives bacterial flagellin epitope flg22 to activate defenses through the central cytoplasmic kinase BIK1. The heterotrimeric G proteins composed of the ...non-canonical Gα protein XLG2, the Gβ protein AGB1, and the Gγ proteins AGG1 and AGG2 are required for FLS2-mediated immune responses through an unknown mechanism. Here we show that in the pre-activation state, XLG2 directly interacts with FLS2 and BIK1, and it functions together with AGB1 and AGG1/2 to attenuate proteasome-mediated degradation of BIK1, allowing optimum immune activation. Following the activation by flg22, XLG2 dissociates from AGB1 and is phosphorylated by BIK1 in the N terminus. The phosphorylated XLG2 enhances the production of reactive oxygen species (ROS) likely by modulating the NADPH oxidase RbohD. The study demonstrates that the G proteins are directly coupled to the FLS2 receptor complex and regulate immune signaling through both pre-activation and post-activation mechanisms.
The Arabidopsis immune receptor FLS2 senses the bacterial flagellin epitope flg22 to activate transient elevation of cytosolic calcium ions, production of reactive oxygen species (ROS), and other ...signaling events to coordinate antimicrobial defenses, such as stomatal closure that limits bacterial invasion. However, how FLS2 regulates these signaling events remains largely unknown. Here we show that the receptor-like cytoplasmic kinase BIK1, a component of the FLS2 immune receptor complex, not only positively regulates flg22-triggered calcium influx but also directly phosphorylates the NADPH oxidase RbohD at specific sites in a calcium-independent manner to enhance ROS generation. Furthermore, BIK1 and RbohD form a pathway that controls stomatal movement in response to flg22, thereby restricting bacterial entry into leaf tissues. These findings highlight a direct role of the FLS2 complex in the regulation of RbohD-mediated ROS production and stomatal defense.
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•The NADPH oxidase RbohD directly interacts with the FLS2 immune receptor complex•BIK1 directly phosphorylates RbohD at specific sites•BIK1 is required for flg22-induced stomatal closure•RbohD phosphorylation contributes to the BIK1-regulated stomatal defense
The FLS2 receptor complex detects bacterial flagellin to activate plant immune responses. Li et al. show that BIK1 kinase, an FLS2 complex component, directly phosphorylates an NADPH oxidase to promote the production of reactive oxygen species. This signals stomatal closure and prevents bacterial entry into plant tissues.
Microbial patterns are recognized by cell-surface receptors to initiate pattern-triggered immunity (PTI) in plants. Receptor-like cytoplasmic kinases (RLCKs), such as BIK1, and calcium-dependent ...protein kinases (CPKs) are engaged during PTI to activate the NADPH oxidase RBOHD for reactive oxygen species (ROS) production. It is unknown whether protein kinases besides CPKs and RLCKs participate in RBOHD regulation. We screened mutants in all ten Arabidopsis MAP4 kinases (MAP4Ks) and identified the conserved MAP4K SIK1 as a positive regulator of PTI. sik1 mutants were compromised in their ability to elicit the ROS burst in response to microbial features and exhibited compromised PTI to bacterial infection. SIK1 directly interacts with, phosphorylates, and stabilizes BIK1 in a kinase activity-dependent manner. Furthermore, SIK1 directly interacts with and phosphorylates RBOHD upon flagellin perception. Thus, SIK1 positively regulates immunity by stabilizing BIK1 and activating RBOHD to promote the extracellular ROS burst.
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•The conserved MAP4K SIK1 is required for PAMP-induced ROS production in Arabidopsis•SIK1 binds, phosphorylates, and stabilizes the central immune regulator BIK1•sik1 mutants display resistance to P. syringae due to high salicylic acid accumulation•SIK1 binds to and phosphorylates an NADPH oxidase to enhance ROS production for defense
Zhang et al. identify the conserved MAP4 kinase SIK1 as required for pattern-triggered immunity in plants. SIK1 associates with, phosphorylates, and stabilizes the central immune regulator BIK1. Upon perception of pathogens, SIK1 and activated BIK1 phosphorylate the NADPH oxidase RBOHD to enhance ROS production and promote defense.
Vacuolar processing enzymes (VPEs) with caspase-1-like activity are closely associated with vacuole rupture. The destruction of vacuoles is one of the characteristics of programmed cell death (PCD) ...in plants. However, whether VPE is involved in the vacuole destruction of cells during secretory cavity formation in
plants remains unclear. This research identified a
gene that encoded the VPE and utilized cytology and molecular biology techniques to explore its temporal and spatial expression characteristics during the PCD process of secretory cavity cells in the
'Tomentosa' fruit. The results showed that CgVPE1 is an enzyme with VPE and caspase-1-like activity that can self-cleave into a mature enzyme in an acidic environment.
is specifically expressed in the epithelial cells of secretory cavities. In addition, it mainly accumulates in vacuoles before it is ruptured in the secretory cavity cells. The spatial and temporal immunolocalization of CgVPE1 showed a strong relationship with the change in vacuole structure during PCD in secretory cavity cells. In addition, the change in the two types of VPE proteins from proenzymes to mature enzymes was closely related to the change in CgVPE1 localization. Our results indicate that CgVPE1 plays a vital role in PCD, causing vacuole rupture in cells during the development of the secretory cavity in
'Tomentosa' fruits.
Plants recognize pathogen-associated molecular patterns (PAMPs) via cell surface-localized pattern recognition receptors (PRRs), leading to PRR-triggered immunity (PTI). The Arabidopsis cytoplasmic ...kinase BIK1 is a downstream substrate of several PRR complexes. How plant PTI is negatively regulated is not fully understood. Here, we identify the protein phosphatase PP2C38 as a negative regulator of BIK1 activity and BIK1-mediated immunity. PP2C38 dynamically associates with BIK1, as well as with the PRRs FLS2 and EFR, but not with the co-receptor BAK1. PP2C38 regulates PAMP-induced BIK1 phosphorylation and impairs the phosphorylation of the NADPH oxidase RBOHD by BIK1, leading to reduced oxidative burst and stomatal immunity. Upon PAMP perception, PP2C38 is phosphorylated on serine 77 and dissociates from the FLS2/EFR-BIK1 complexes, enabling full BIK1 activation. Together with our recent work on the control of BIK1 turnover, this study reveals another important regulatory mechanism of this central immune component.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Cell wall degrading enzymes, including pectate lyases (PeLs), released by plant pathogens, break down protective barriers and/or activate host immunity. The direct interactions between PeLs and plant ...immune-related proteins remain unclear. We identify two PeLs, PlPeL1 and PlPeL1-like, critical for full virulence of Peronophythora litchii on litchi (Litchi chinensis). These proteins enhance plant susceptibility to oomycete pathogens in a PeL enzymatic activity-dependent manner. However, LcPIP1, a plant immune regulator secreted by litchi, binds to PlPeL1/PlPeL1-like, and attenuates PlPeL1/PlPeL1-like induced plant susceptibility to Phytophthora capsici. LcPIP1 also induces cell death and various immune responses in Nicotiana benthamiana. Conserved in plants, LcPIP1 homologs bear a conserved "VDMASG" motif and exhibit immunity-inducing activity. Furthermore, SERK3 interacts with LcPIP1 and is required for LcPIP1-induced cell death. NbPIP1 participates in immune responses triggered by the PAMP protein INF1. In summary, our study reveals the dual roles of PlPeL1/PlPeL1-like in plant-pathogen interactions: enhancing pathogen virulence through PeL enzymatic activity while also being targeted by LcPIP1, thus enhancing plant immunity.
Potato late blight, caused by Phytophthora infestans, is the most devastating disease on potato. Dissecting critical immune components in potato will be supportive for engineering P. infestans ...resistance. Upon pathogens attack, plant Ca
signature is generated and decoded by an array of Ca
sensors, among which calcineurin B-like proteins (CBLs) coupled with plant specific CBL-interacting protein kinases (CIPKs) are much less explored in plant immunity.
In this study, we identified that two differential potato CBL-CIPK modules regulate plant defense responses against Phytophthora and ROS production, respectively. By deploying virus-induced gene silencing (VIGS) system-based pathogen inoculation assays, StCBL3 was shown to negatively regulate Phytophthora resistance. Consistently, StCBL3 was further found to negatively regulate PTI and ETI responses in Nicotiana benthamiana. Furthermore, StCIPK7 was identified to act together with StCBL3 to negatively regulate Phytophthora resistance. StCIPK7 physically interacts with StCBL3 and phosphorylates StCBL3 in a Ca
-dependent manner. StCBL3 promotes StCIPK7 kinase activity. On the other hand, another StCBL3-interacting kinase StCIPK24 negatively modulating flg22-triggered accumulation of reactive oxygen species (ROS) by interacting with StRBOHB.
Together, these findings demonstrate that the StCBL3-StCIPK7 complex negatively modulates Phytophthora resistance and StCBL3-StCIPK24 complex negatively regulate ROS production. Our results offer new insights into the roles of potato CBL-CIPK in plant immunity and provide valuable gene resources to engineer the disease resistance potato in the future.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Plant cells recognize microbial patterns with the plasma‐membrane‐localized pattern‐recognition receptors consisting mainly of receptor kinases (RKs) and receptor‐like proteins (RLPs). RKs, such as ...bacterial flagellin receptor FLS2, and their downstream signaling components have been studied extensively. However, newly discovered regulatory components of RLP‐mediated immune signaling, such as the nlp20 receptor RLP23, await identification. Unlike RKs, RLPs lack a cytoplasmic kinase domain, instead recruiting the receptor‐like kinases (RLKs) BAK1 and SOBIR1. SOBIR1 specifically works as an adapter for RLP‐mediated immunity. To identify new regulators of RLP‐mediated signaling, we looked for SOBIR1‐binding proteins (SBPs) in Arabidopsis thaliana using protein immunoprecipitation and mass spectrometry, identifying two G‐type lectin RLKs, SBP1 and SBP2, that physically interacted with SOBIR1. SBP1 and SBP2 showed high sequence similarity, were tandemly repeated on chromosome 4, and also interacted with both RLP23 and BAK1. sbp1 sbp2 double mutants obtained via CRISPR‐Cas9 gene editing showed severely impaired nlp20‐induced reactive oxygen species burst, mitogen‐activated protein kinase (MAPK) activation, and defense gene expression, but normal flg22‐induced immune responses. We showed that SBP1 regulated nlp20‐induced immunity in a kinase activity‐independent manner. Furthermore, the nlp20‐induced the RLP23–BAK1 interaction, although not the flg22‐induced FLS2–BAK1 interaction, was significantly reduced in sbp1 sbp2. This study identified SBPs as new regulatory components in RLP23 receptor complex that may specifically modulate RLP23‐mediated immunity by positively regulating the interaction between the RLP23 receptor and the BAK1 co‐receptor.
A pair of closely related G‐type lectin receptor‐like kinases, the SOBIR1‐BINDING PROTEINS SBP1 and SBP2, interact with SOBIR1, BAK1 and RLP23. SBP1 and SBP2 specifically regulate RLP23‐mediated immune responses by positively modulating nlp20‐induced RLP23‐BAK1 interactions.
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