The OsBSK1-2-MAPK module regulates blast resistance in rice

Receptor-like cytoplasmic kinase OsBSK1-2 was reported to play an important role in regulation of response to rice blast,but the signaling pathway remained unknown.In this study,we identified OsMAPKKK18 and previously uncharacterized MAPKKKs OsMAPKKK16 and OsMAPKKK19 that interact with OsBSK1-2.Expression of all three MAPKKKs was induced by Magnaporthe oryzae infection,and all three induced cell death when transiently expressed in Nicotiana benthamiana leaves.Knockout of OsMAPKKK16 and OsMAPKKK18 compromised blast resistance and overexpression of OsMAPKKK19 increased blast resistance,indicating that all three MAPKKKs are involved in regulation of rice blast response.Furthermore,both OsMAPKKK16 and OsMAPKKK19 interacted with and phosphorylated OsMKK4 and OsMKK5,and chitin-induced MAPK activation was suppressed in osmapkkk16 and osbsk1-2 mutants.OsMAPKKK18 was earlier reported to interact with and phosphorylate OsMKK4 and affect chitin-induced MAPK activation,suggesting that OsBSK1-2 is involved in regulation of immunity through multiple MAPK signaling pathways.Unlike BSK1 in Arabidopsis,OsBSK1-2 was not involved in response to avirulent M.oryzae strains.Taken together,our results revealed important roles of OsMAPKKK16/18/19 and a OsBSK1-2-OsMAPKKK16/18/19-OsMKK4/5 module in regulating response to rice blast.

Outcomes of the Expanded Programme on Immunization Pre-Service Training Initiatives in Kenya: A Mixed Methods Study

Background: The Maternal and Child Survival Program of United States Agency for International Development conducted a study in 2017 to assess the outcome of an initiative to strengthen Expanded Programme on Immunization (EPI) pre-service training. The pre-service training initiative was undertaken by the Ministry of Health (MOH) with support from partners in 2012-2016. The overall objective of the study was to assess the adoption and effectiveness of the initiative in the competency (knowledge, skills and attitude) of graduate nurses. Methods: The study included a conveniently selected sample of 14 pre-service training institutions, 23 field practicum sites, and 29 health facilities in western Kenya, and used quantitative and qualitative methods of data collection. Results: All pre-service training institutions were found to have adapted the WHO EPI prototype curriculum. Overall, tutors followed training method in the classroom as suggested in the curriculum, except evaluation of students’ learning lacked tests or quizzes. Students had opportunities for hands-on practical experience in the field practicum sites. Graduate nurses were found to have acquired the skills for vaccinating children. However, some pre-service training institutions lacked functional skills labs for practical learning of students. In addition, students did not receive up-to-date information on EPI program, and lacked knowledge and skills on monitoring and documentation of EPI coverage during preservice training. Conclusions: It appears that the EPI pre-service training strengthening initiatives facilitated competency-based EPI training of nurses in Kenya. However, preservice training institutions still have scope for improvement in the skills lab, hand-washing practice, providing up-to-date information, and training students on coverage monitoring and documentation.

Rethinking Strategies to Address Inequity in Immunization Services towards Achieving Universal Immunization Coverage (UIC) in Karachi, Pakistan

Karachi, the largest city in Pakistan, having high population growth and a complex health care environment, has highest density of unimmunized (zero dose) and under-immunized children. The main reasons of low immunization coverage in Karachi were lack of governance and accountability in a duplicative and fragmented health management structure, weak and inequitable immunization services, and lack of demand and trust among people for immunization services. The Expanded Programme on Immunization (EPI), Ministry of Health (MOH) in Sindh Province spearheaded a structured and collaborative process to develop strategies for addressing inequity in immunization services towards achieving Universal Immunization Coverage (UIC) in Karachi. The process included a situation analysis with gathering quantitative and qualitative information on the root causes of zero-dose and inequity of the immunization services. The strategies and interventions were developed with multi-layer input and feedback of the stakeholders and partners, and focusing primarily to address gaps in three program areas: governance, leadership and accountability;immunization service delivery;and building demand and trust among the people. The interventions were further prioritized for high-risk areas;identified based on maximum number zero-dose children, presence of large slum areas, measles outbreak and on-going circulation of wild poliovirus. Finally, costing for the Roadmap activities was done through consultation with partners and aligning domestic and external (donor) resources. In this paper, we have highlighted the unique process the Sindh Government undertook in collaboration with the stakeholders and partners to develop strategies and interventions for addressing inequity in urban immunization services in Karachi towards achieving Universal Immunization Coverage (UIC). Similar processes can be adapted, as a potential model, for developing strategies to achieve universal health coverage in the cities of Pakistan and in other countries.

Characterization and Pathogenicity of Pseudopestalotiopsis vietnamensis Causing Gray Blight of Wuyi Rock Tea(Camellia sinensis)in China and Specific Mechanisms of Disease Infection

Gray blight disease(GBD)causes significant losses in tea production in China.Although genes and biological processes involved in resistance to fungal disease in tea plants have been identified,specific mechanisms of the GBD infection process remain unknown.In this study,morphological and multi-gene(TEF-TUB-ITS)phylogenetic characteristics were used to identify isolate CLBB1 of Pseudopestalotiopsis vietnamensis.Pathogenicity tests confirmed that isolate CLBB1 from tea leaves caused GBD in the susceptible tea cultivar Wuyi Rock(Camellia sinensis var.sinensis cv.Shuixian).Spores began to germinate 24 h after infection(hai),and after 48 h,elongated fungal hyphae formed from a single conidium.Transcriptome analysis revealed that 482,517,and 369 genes were differentially expressed at 24,48,and 72 hai,respectively,in Wuyi Rock tea leaves.Isolate CLBB1 infection elicited phenotype-related responses and activated defense-related pathways,including plant–pathogen interaction,MAPK signaling,and plant hormone signal transduction,suggesting a possible mechanism underlying phenotype-based susceptibility to CLBB1.Thus,a new Ps.vietnamensis strain causing GBD in the tea cultivar‘Shuixian’was discovered in this study.Transcriptome analysis indicated that pathogen invasion activated chitin-related MAPK pathways and that tea plants required a hormone to restrict CLBB1.

Diversity of Saccharomyces boulardii CNCM I-745 mechanisms of action against intestinal infections

The yeast Saccharomyces boulardii CNCM I-745 is one of the probiotics recommended for the prevention of antibiotic-associated diarrhea. Studies conducted in vivo and in vitro demonstrated that in the case of infectious diseases there are two potential sites of action of Saccharomyces boulardii CNCM I-745:(1)An action on enteropathogenic microorganisms(adhesion of bacteria and their elimination or an effect on their virulence factors: Toxins, lipopolysaccharide,etc.); and(2) a direct action on the intestinal mucosa(trophic effects, effects on epithelial reconstitution, anti-secretory effects, anti-inflammatory,immunomodulators). Oral administration of Saccharomyces boulardii CNCM I-745 to healthy subjects does not alter their microbiota. However, in the case of diseases associated with the use of antibiotics or chronic diarrhea, Saccharomyces boulardii CNCM I-745 can restore the intestinal microbiota faster. The interaction of Saccharomyces boulardii CNCM I-745 with the innate immune system have been recently demonstrated thus opening up a new therapeutic potential of this yeast in the case of diseases associated with intestinal infections but also other pathologies associated with dysbiosis such as inflammatory diseases.

Polyphosphate and associated enzymes as global regulators of stress response and virulence in Campylobacter jejuni

Campylobacter jejuni(C. jejuni),a Gram-negative microaerophilic bacterium,is a predominant cause of bacterial foodborne gastroenteritis in humans worldwide. Despite its importance as a major foodborne pathogen,our understanding of the molecular mechanisms underlying C. jejuni stress survival and pathogenesis is limited. Inorganic polyphosphate(poly P) has been shown to play significant roles in bacterial resistance to stress and virulence in many pathogenic bacteria. C. jejuni contains the complete repertoire of enzymes required for poly P metabolism. Recent work in our laboratory and others have demonstrated that poly P controls a plethora of C. jejuni properties that impact its ability to survive in the environment as well as to colonize/infect mammalian hosts. This review article summarizes the current literature on the role of poly P in C. jejuni stress survival and virulence and discusses on how poly P-related enzymes can be exploited for therapeutic/prevention purposes. Additionally,the review article identifies potential areas for future investigation that would enhance our understanding of the role of poly P in C. jejuni and other bacteria,which ultimately would facilitate design of effective therapeutic/preventive strategies to reduce not only the burden of C. jejuni-caused foodborne infections but also of other bacterial infections in humans.

Rice sl-MH-1 mutant induces cell death and confers blast resistance via the synergistic roles of signaling systems

Serotonin is ubiquitous across all forms of life and functions in responses to biotic and abiotic stresses.In rice,the conversion of tryptamine to serotonin is catalyzed by Sekiguchi lesion(SL).Previous studies have identified an sl mutation(a null mutation of SL)in several rice varieties and confirmed its increase of resistance and cell death.However,a systematic understanding of the reprogrammed cellular processes causing cell death and resistance is lacking.We performed a multi-omics analysis to clarify the fundamental mechanisms at the protein,gene transcript,and metabolite levels.We found that cell death and Magnaporthe oryzae(M.oryzae)infection of the sl-MH-1 mutant activated plant hormone signal transduction involving salicylic acid(SA),jasmonic acid(JA),and abscisic acid(ABA)in multiple regulatory layers.We characterized the dynamic changes of several key hormone levels during disease progression and under the cell death conditions and showed that SA and JA positively regulated rice cell death and disease resistance.SL-overexpressing lines confirmed that the sl-MH-1 mutant positively regulated rice resistance to M.oryzae.Our studies shed light on cell death and facilitate further mechanistic dissection of programmed cell death in rice.

Probiotic yeasts: Anti-inflammatory potential of various non-pathogenic strains in experimental colitis in mice

AIM: To evaluate the in vitro immunomodulation capacity of various non-pathogenic yeast strains and to investigate the ability of some of these food grade yeasts to prevent experimental colitis in mice.METHODS: In vitro immunomodulation was assessed by measuring cytokines [interleukin (IL)-12p70,IL-10,tumor necrosis factor and interferon γ] released by human peripheral blood mononuclear cells after 24 h stimulation with 6 live yeast strains (Saccharomyces ssp.) and with bacterial reference strains.A murine model of acute 2-4-6-trinitrobenzene sulfonic acid (TNBS)-colitis was next used to evaluate the distinct prophylactic protective capacities of three yeast strains compared with the performance of prednisolone treatment.RESULTS: The six yeast strains all showed similar non-discriminating anti-inflammatory potential when tested on immunocompetent cells in vitro .However,although they exhibited similar colonization patterns in vivo ,some yeast strains showed significant anti-inflammatory activities in the TNBS-induced colitis model,whereas others had weaker or no preventive effect at all,as evidenced by colitis markers (body-weight loss,macroscopic and histological scores,myeloperoxidase activities and blood inflammatory markers).CONCLUSION: A careful selection of strains is required among the biodiversity of yeasts for specific clinical studies,including applications in inflammatory bowel disease and other therapeutic uses.

Phytochemical Screening and Toxicity Assessment of Imperata cylindrica (L.) P. Beauv. (Poaceae) Raw Extracts with Brine Shrimp (Artemia salina) Lethality Assay

Background: Herbal medicinal preparations are used as dietary supplements for disease prevention and as alternative/complementary medicine. The growing interest in herbal medicine raises the question of its safety and efficacy. Numerous recorded cases of intoxication and toxicological studies reveal that medicinal plants can be toxic, which hinders their safe use. Plant intoxications related to a variety of factors include plant organs and many extraction solvents. Little toxicological data on medicinal plants is available. The need to investigate is important for safe use. Imperata cylindrica, a poaceae, is one of the medicinal plants for which few toxicological data are available. Materials & Methods: To expand toxicological data, water, 70% ethanol, and 30% acetone extracts of the leaves and roots, obtained by maceration and reflux methods, were used for phytochemicals molecules qualitative detection and toxicity test by the brine shrimp lethality assay. Results: The qualitative analysis of the different extracts revealed the presence of alkaloids, polyphenolic compounds, saponins, and polyterpenoids. The toxicity endpoint was lethal concentration 50 (LC50). The leaves’ extracts LC50 was between 489.78 μg/mL and 1066.6 μg/mL. As for the root extracts, the LC50 was between 341.98 μg/mL and 1530 μg/mL. Discussion: The different compounds’ presence justifies the use of Imperata cylindrica as a medicinal plant. According to Clarkson classification the root extracts are moderately toxic (LC50: 168.47 μg/mL), and leaf extracts are weakly toxic (LC50: 527.25 μg/mL). The extrapolation made in relation to the Gosselin, Smith, and Hodge scale, allows us to characterize the Imperata cylindrica root and leaf extracts as non-toxic to humans by oral route. Conclusion: This result can be a base for more precise toxicological studies.

Perception of unrelated microbe-associated molecular patterns triggers conserved yet variable physiological and transcriptional changes in Brassica rapa ssp.pekinensis

Pattern-triggered immunity(PTI)includes the different transcriptional and physiological responses that enable plants to ward off microbial invasion.Surface-localized pattern-recognition receptors(PRRs)recognize conserved microbeassociated molecular patterns(MAMPs)and initiate a branched signaling cascade that culminate in an effective restriction of pathogen growth.In the model species Arabidopsis thaliana,early PTI events triggered by different PRRs are broadly conserved although their nature or intensity is dependent on the origin and features of the detected MAMP.In order to provide a functional basis for disease resistance in leafy vegetable crops,we surveyed the conservation of PTI events in Brassica rapa ssp.pekinensis.We identified the PRR homologs present in B.rapa genome and found that only one of the two copies of the bacterial Elongation factor-Tu receptor(EFR)might function.We also characterized the extent and unexpected specificity of the transcriptional changes occurring when B.rapa seedlings are treated with two unrelated MAMPs,the bacterial flagellin flg22 peptide and the fungal cell wall component chitin.Finally,using a MAMP-induced protection assay,we could show that bacterial and fungal MAMPs elicit a robust immunity in B.rapa,despite significant differences in the kinetic and amplitude of the early signaling events.Our data support the relevance of PTI for crop protection and highlight specific functional target for disease resistance breeding in Brassica crops.

Phytochemical Characterization of Three Plants and Their Antisickling Activity in the Management of Sickle Cell Disease

Natural plant products have been used by the population of the south-eastern part of Côte d’Ivoire in the management of sickle cell anemia. This study was aimed at investigating the antisickling activity of the hydro-ethanolic extract of a combination of the leaves of J. secunda, J. gossypiifolia and P. nigrescens. These three plants species were used in the Ivorian traditional herbal medicine. Preliminary phytochemistry was carried out using standard methods. As for the sickling reversal test, the Hb SS blood sickling was induced with 2% sodium metabisulfite. After 120 minutes of incubation, the plant extract was added. Every 30 minutes for a period of 120 minutes, a drop of the prepared solution was observed at (40×) magnification and the percentage of reversion calculated. The phytochemical analysis revealed the presence of Alkaloids, Flavonoids, Polyphenols, Catechic Tannins, Sterols and Polyterpenes. The results of the reversal test showed that the percentage of sickling reversal effect of the combination of the plants (75.00 ± 4.33b,c) was highly superior than the negative control (10.17 ± 0.55d) but was significantly (p < 0.05) the same as the percentage of the individual plant (J. secunda: 83.50 ± 2.33a;J. gossypiifolia: 78.00 ± 3.67b,c and P. nigrescens: 77.83 ± 2.89b,c) and the positive control (80.66 ± 2.22a,b). From the results, the extracts J. secunda, J. gossypiifolia and P. nigrescens have shown to be therapeutically beneficial to the population. Their use is also justified in the management of sickle cell disease in the south-eastern part of Côte d’Ivoire.

Factors Associated with PCV13 Vaccine Hesitancy in Parents under an Innovative Immunization Strategy:a Cross-Sectional Study—Weifang City,Shandong Province,China,2021

Summary What is already known on this topic?Pneumococcal diseases(PDs)are serious threats to child health.Although vaccination is one of the most effective ways to prevent these diseases,the pneumococcal vaccination coverage rate is still relatively low in China.What is added by this report?This study investigated the factors associated with 13-valent pneumococcal conjugate vaccine(PCV13)vaccine hesitancy in parents under an innovative immunization strategy.

The actin motor protein OsMYA1 associates with OsExo70H1 and contributes to rice secretory defense by modulating OsSyp121 distribution

Magnaporthe oryzae(M.oryzae)is a devastating hemibiotrophic pathogen.Its biotrophic invasive hyphae(IH)are enclosed in the extrainvasive hyphal membrane produced by plant cells,thus generating a front line of the battlefield between the pathogen and the host plants.In plants,defense-related complexes such as proteins,callose-rich materials and vesicles,are directionally secreted to this interface to confer defense responses,but the underlying molecular mechanism is poorly understood.In this study,we found that a Myosin gene,Myosin A1(OsMYA1),contributed to rice defense.The OsMYA1 knockout mutant exhibited decreased resistance to M.oryzae infection.OsMYA1 localizes to the actin cytoskeleton and surrounds the IH of M.oryzae.OsMYA1 interacts with an exocyst subunit,OsExo70H1,and regulates its accumulation at the plasma membrane(PM)and pathogen–plant interface.Furthermore,OsExo70H1 interacted with the rice syntaxin of the plants121 protein(OsSyp121),and the distribution of OsSyp121 to the PM or the pathogen–plant interface was disrupted in both the OsMYA1 and OsExo70H1 mutants.Overall,these results not only reveal a new function of OsMYA1 in rice blast resistance,but also uncover a molecular mechanism by which plants regulate defense against M.oryzae by OsMYA1-initiated vesicle secretory pathway,which originates from the actin cytoskeleton to the PM.

Guardian of the rice:Unveiling OsSSP1 for broad-spectrum disease resistance

Plants are continuously exposed to numerous biotic stresses throughout their growth.Through arms race-driven coevolution with pathogens,plants have developed sophisticated immune systems,including pathogen-associated molecular pattern(PAMP)-triggered immunity(PTI)and effector-triggered immunity(ETI).PTI is initiated by the binding of danger signals to extracellular membrane-localized receptors calledpattern recognition receptors(PRRs).PTI triggers responses,including reactive oxygen species(ROS)bursts and the expression of defenseassociated genes.However,pathogens adapted to PTl secrete virulence proteins,effectors,to aid colonization,and ETl is then triggered by the recognition of these effectors by resistance proteins with a nucleotide-binding domain leucinerich repeat receptor(NLR).To circumvent this immune response,pathogens secrete various effectors into the host intracellular region and induce effector-triggered susceptibility(Zhou and Zhang.,2020).Currently,research on plant immunity has been primarily focused on plasma membrane and cytoplasmlocalized proteins,including oligomeric NLRs,resistosomes,and the secretion mechanisms of cytoplasmic effectors.

A plasma membrane nucleotide-binding leucinerich repeat receptor mediates the recognition of the Ralstonia pseudosolanacearum effector RipY in Nicotiana benthamiana

Bacterial wilt disease caused by several Ralstonia species is one of the most destructive diseases in Solanaceae crops.Only a few functional resistance genes against bacterial wilt have been cloned to date.Here,we showthat the broadly conserved typeⅢsecreted effector RipY is recognized by the Nicotiana benthamiana immune system,leading to cell death induction,induction of defense-related gene expression,and restriction of bacterial pathogen growth.Using a multiplexed virus-induced gene-silencing-based N.benthamiana nucleotide-binding and leucine-rich repeat receptor(NbNLR)library,we identified a coiled-coil(CC)nucleotide-binding and leucine-rich repeat receptor(CNL)required for recognition of RipY,which we named RESISTANCE TO RALSTONIA SOLANACEARUM RIPY(RRS-Y).Genetic complementation assays in RRS-Y-silenced plants and stable rrs-y knockout mutants demonstrated that RRS-Y is sufficient to activate RipY-induced cell death andRipY-induced immunity to Ralstonia pseudosolanacearum.RRS-Y function is dependent on the phosphate-binding loop motif of the nucleotide-binding domain but independent of the characterized signaling components ENHANCED DISEASE SUSCEPTIBILITY 1,ACTIVATED DISEASE RESISTANCE 1,and N REQUIREMENT GENE 1 and the NLR helpers NB-LRR REQUIRED FOR HR-ASSOCIATED CELL DEATH-2,-3,and-4 in N.benthamiana.We further show that RRS-Y localization at the plasma membrane is mediated by two cysteine residues in the CC domain and is required for RipY recognition.RRSY also broadly recognizes RipY homologs across Ralstonia species.Lastly,we show that the C-terminal region of RipY is indispensable for RRS-Y activation.Together,our findings provide an additional effector/receptor pair system to deepen our understanding of CNL activation in plants.

The Phytophthora nucleolar effector Pi23226 targets host ribosome biogenesis to induce necrotrophic cell death

Pathogen effectors target diverse subcellular organelles to manipulate the plant immune system.Although the nucleolus has emerged as a stress marker and several effectors are localized in the nucleolus,the roles of nucleolar-targeted effectors remain elusive.In this study,we showed that Phytophthora infestans infection of Nicotiana benthamiana results in nucleolar inflation during the transition from the biotrophic to the necrotrophic phase.Multiple P.infestans effectors were localized in the nucleolus:Pi23226 induced cell death in N.benthamiana and nucleolar inflation similar to that observed in the necrotrophic stage of infection,whereas its homolog Pi23015 and a deletion mutant(Pi23226DC)did not induce cell death or affect nucleolar size.RNA immunoprecipitation and individual-nucleotide-resolution UV crosslinking and immunoprecipitation sequencing analysis indicated that Pi23226 bound to the 30 end of 25S rRNA precursors,resulting in accumulation of unprocessed 27S pre-rRNAs.The nucleolar stress marker NAC082 was strongly upregulated under Pi23226-expressing conditions.Pi23226 subsequently inhibited global protein translation in host cells by interacting with ribosomes.Pi23226 enhanced P.infestans pathogenicity,indicating that Pi23226-induced ribosome malfunction and cell death were beneficial for pathogenesis in the host.Our results provide evidence for the molecular mechanism underlying RNA-binding effector activity in host ribosome biogenesis and lead to new insights into the nucleolar action of effectors in pathogenesis.

Plant immune signaling: Advancing on two frontiers

Plants have evolved multiple defense strategies to cope with pathogens, among which plant immune signaling that relies on cell-surface localized and intracellular receptors takes fundamental roles. Exciting breakthroughs were made recently on the signaling mechanisms of pattern recognition receptors(PRRs) and intracellular nucleotide-binding site(NBS) and leucine-rich repeat(LRR)domain receptors(NLRs). This review summarizes the current view of PRRs activation, emphasizing the most recent discoveries about PRRs’ dynamic regulation and signaling mechanisms directly leading to downstream molecular events including mitogen-activated protein kinase(MAPK) activation and calcium(Ca2+) burst. Plants also have evolved intracellular NLRs to perceive the presence of specific pathogen effectors and trigger more robust immune responses. We also discuss the current understanding of the mechanisms of NLR activation, which has been greatly advanced by recent breakthroughs including structures of the first full-length plant NLR complex, findings of NLR sensor-helper pairs and novel biochemical activity of Toll/interleukin-1 receptor(TIR) domain.

Antagonism of Transcription Factor MYC2 by EDS1/PAD4 Complexes Bolsters Salicylic Acid Defense in Arabidopsis Effector-Triggered Immunity

In plant immunity, pathogen-activated intracellular nucleotide binding/leucine rich repeat （NLR） receptors mobilize disease resistance pathways, but the downstream signaling mechanisms remain obscure. Enhanced disease susceptibility 1 （EDS1） controls transcriptional reprogramming in resistance triggered by Toll-lnterleukinl-Receptor domain （TIR）-family NLRs （TNLs）. Transcriptional induction of the salicylic acid （SA） hormone defense sector provides one crucial barrier against biotrophic pathogens. Here, we present genetic and molecular evidence that in Arabidopsis an EDS1 complex with its partner PAD4 inhibits MYC2, a master regulator of SA-antagonizing jasmonic acid （JA） hormone pathways. In the TNL immune response, EDSl/PAD4 interference with MYC2 boosts the SA defense sector independently of EDS1-induced SA synthesis, thereby effectively blocking actions of a potent bacterial JA mimic, coronatine （COR）. We show that antagonism of MYC2 occurs after COR has been sensed inside the nucleus but before or coincident with MYC2 binding to a target promoter, pANAC019. The stable interaction of PAD4 with MYC2 in planta is competed by EDS1-PAD4 complexes. However, suppression of MYC2-promoted genes requires EDS1 together with PAD4, pointing to an essential EDS1-PAD4 heterodimer activity in MYC2 inhibition. Taken together, these results uncover an immune receptor signaling circuit that intersects with hormone pathway crosstalk to reduce bacterial pathogen growth.

RECEPTOR-LIKE KINASE 902 Associates with and Phosphorylates BRASSINOSTEROID-SIGNALING KINASE1 to Regulate Plant Immunity

Plants employ receptor-like kinases (RLKs)and receptor-like proteins for rapid recognition of invading pathogens,and RLKs then transmit signals to receptor-like cytoplasmic kinases (RLCKs)to activate immune responses.RLKs are under fine regulation mediated by subcellular trafficking,which contributes to proper activation of plant immunity.In this study,we show that Arabidopsisthaliana RECEPTOR-LIKE KINASE 902 (RLK902)plays important roles in resistance to the bacterial pathogen Pseudomonas syringae, but not to the fungal powdery mildew pathogen Golovinomyces cichoracearum.RLK902 localizes at the plasma membrane and associates with ENHANCED DISEASE RESISTANCE 4 (EDR4),a protein involved in clathrin-mediated trafficking pathways.EDR4 and CLATHRIN HEAVY CHAIN 2 (CHC2)regulate the subcellular trafficking and accumulation of RLK902 protein.Furthermore,we found that RLKg02 directly associates with the RLCK BRASSINOSTEROID-SIGNALING KINASE1 (BSK1),a key component of plant immunity,but not with other members of the FLAGELLIN SENSING 2 immune complex.RLK902 phosphorylates BSK1,and its Ser-230 is a key phosphorylation site critical for RLK902-mediated defense signaling. Taken together,our data indicate that EDR4 regulates plant immunity by modulating the subcellular trafficking and protein accumulation of RLK902,and that RLK902 transmits immune signals by phosphorylating BSK1.

The RECEPTOR-LIKE PROTEIN53 immune complex associates with LLG1 to positively regulate plant immunity

Pattern recognition receptors(PRRs)sense ligands in pattern-triggered immunity(PTI).Plant PRRs include numerous receptor-like proteins(RLPs),but many RLPs remain functionally uncharacterized.Here,we examine an Arabidopsis thaliana RLP,RLP53,which positively regulates immune signaling.Our forward genetic screen for suppressors of enhanced disease resistance1(edr1)identified a point mutation in RLP53 that fully suppresses disease resistance and mildewinduced cell death in edr1 mutants.The rlp53 mutants showed enhanced susceptibility to virulent pathogens,including fungi,oomycetes,and bacteria,indicating that RLP53 is important for plant immunity.The ectodomain of RLP53 contains leucine-rich repeat(LRR)motifs.RLP53 constitutively associates with the LRR receptorlike kinase SUPPRESSOR OF BRASSINOSTEROIDINSENSITIVE1-ASSOCIATEDKINASE(BAK1)-INTERACTINGRECEPTORKINASE1(SOBIR1)and interacts with the co-receptor BAK1 in a pathogen-induced manner.The double mutation sobir1-12 bak1-5 suppresses edr1-mediated disease resistance,suggesting that EDR1 negatively regulates PTI modulated by the RLP53–SOBIR1–BAK1 complex.Moreover,the glycosylphosphatidylinositol(GPI)-anchored protein LORELEI-LIKE GPI-ANCHORED PROTEIN1(LLG1)interacts with RLP53 and mediates RLP53 accumulation in the plasma membrane.We thus uncovered the role of a novel RLP and its associated immune complex in plant defense responses and revealed a potential new mechanism underlying regulation of RLP immune function by a GPI-anchored protein.