Synergy in Rice Immunity:Exploring Strategies of Coordinated Disease Defense Through Receptor-Like Kinases and Receptor-Like Cytoplasmic Kinases

Receptor-like kinases(RLKs)and receptor-like cytoplasmic kinases(RLCKs)play an indispensable role in the perception and transmission of extracellular signals in plants.In rice,these kinases actively participate in immune responses against a variety of pathogens,including fungi,bacteria,and viruses.However,research on the specific response mechanisms and the spectrum of different kinase activities against various pathogens remains insufficient.This review provides an in-depth and comprehensive overview of the types and functions of RLKs and RLCKs involved in disease resistance,emphasizing the central role of certain RLKs and RLCKs in the plant immune system.These kinases can recognize specific molecular patterns of pathogens and rapidly initiate an immune response in rice.Furthermore,the activity and functional regulation of these key kinases are tightly controlled by various post-translational modifications,such as phosphorylation and ubiquitination.This meticulous regulation ensures that the rice immune system's response is both precise and timely,effectively balancing the intensity of the immune response and preventing potential issues caused by either hyperactivity or insufficiency.By synthesizing current research findings,this review not only broadens our understanding of the role of RLKs and RLCKs in plant immunity but also provides new perspectives and strategies for future research on disease resistance breeding in rice.Future studies are expected to delve deeper into the signaling networks and regulatory mechanisms of these kinases,exploring their potential in agricultural production to develop rice varieties with enhanced disease resistance.

The wheat receptor-like cytoplasmic kinase TaRLCK1B is required for host immune response to the necrotrophic pathogen Rhizoctonia cerealis

Receptor-like cytoplasmic kinases(RLCKs)represent a large family of proteins in plants.In Arabidopsis and rice,several RLCKs in subfamily VII(RLCKs-VII)have been implicated in pathogen-associated molecular pattern-triggered immunity and basal resistance against bacterial and fungal pathogens.However,little is known about roles of RLCKs-VII of the important crop common wheat(Triticum aestivum)in immune responses.Here,we isolated a RLCK-VII-encoding gene from wheat,designated as TaRLCK1B,and investigated its role in host immune response to infection of a necrotrophic fungus Rhizoctonia cerealis that is a major pathogen of sharp eyespot,a destructive disease of wheat.RNA-sequencing and RT-qPCR analyses showed that transcriptional level of TaRLCK1B was significantly higher in sharp eyespot-resistant wheat cultivars than in susceptible wheat cultivars.The gene transcription was rapidly and markedly elevated in the resistant wheat cultivars by R.cerealis infection.The TaRLCK1B protein was closely related to OsRLCK176,a rice resistance-related RLCKs-VII,with 84.03%identity.Virus-induced gene silencing plus wheat response to R.cerealis assay results indicated that silencing of TaRLCK1 impaired resistance to R.cerealis.Meantime,silencing of TaRLCK1 significantly elevated both the content of H2 O2(a major kind of reactive oxygen species,ROS)and the transcriptional level of the ROS-generating enzyme-encoding gene RBOH,but repressed the expression of the ROS-scavenging enzyme-encoding gene CAT1 at 18 hours after inoculation(hai)with R.cerealis.Taken together,these data suggested that TaRLCK1B was required for the early immune response of wheat to R.cerealis through modulating ROS signaling in wheat.

Screening of Extracellular Binding Proteins of Rice Receptor-like Kinase CR4 by the Yeast Two-hybrid

[Objective] The research aimed to find the extracellular binding proteins of CR4.[Method] The extracellular domain of OsCR4 was as the bait protein,and the yeast two-hybrid was used to screen cDNA library of seedling which was cultivated 14 d.[Result] A lot of proteins which included a peroxide B（D26484）,a methionine thioredoxin reductase（ABF96078）and an unknown function protein were gained.[Conclusion] It provided the theory basis for studying the signal transduction mechanism of CR4.

Cloning and Hybrid Identification of Banana Receptor-like Protein Kinase Gene

[Objective] This study aimed to clone and identify the banana fruit receptor-like protein kinase gene.[Method] The cDNA phage libraries of banana fruit were adopted as the experimental materials to screen positive phage libraries of banana receptor-like protein kinase gene;cloning and sequence analysis of the gene were conducted,and the banana receptor-like protein kinase gene was identified by using in situ hybridization method.[Result] In this study,a 1 698 bp long banana receptor-like protein kinase gene was cloned from banana fruit,encoding 563 amino acids.Southern hybridization result confirmed that the banana receptor-like protein kinase gene was a multiple-copy gene from banana genome.[Conclusion] The study laid the foundation for further investigating the functions of banana receptor-like protein kinase gene in fruit.

Cloning and Characterization of a Somatic Embryogenesis Receptor-Like Kinase Gene in Cotton (Gossypium hirsutum)

A novel gene, GhSERK1, was identified in cotton. It encoded a protein belonging to the somatic embryogenesis receptor- like kinase （SERK） family. The genomic sequence of GhSERK1 was 6 920 bp in length, containing a predicted transcriptional start site （TSS）. Its full-length cDNA was 2 502 bp, encoding a protein of 627 amino acids. Sequence analysis of GhSERK1 revealed high levels of similarity to other reported SERKs, as well as a conserved intron/exon structure that was unique to members of the SERK family. Expression analysis showed that GhSERK1 mRNA was present in all organs of cotton plants and at different developmental stages, but its transcripts were most abundant in reproductive organs. Compared with that of the male-fertile line, the level of GhSERK1 mRNA was lower in the anther of the male-sterile cotton line, in which the pollen development was defected. Taken together, these findings illustrated that the GhSERK1 play a critical role during the anther formation, and may also have a broad role in other aspects of plant development.

Receptor-like kinase OsASLRK regulates methylglyoxal response and content in rice

Receptor-like kinases(RLKs) are essential for plant abiotic stress responses. Methylglyoxal(MG) is a cellular metabolite that is often considered to be a stress signal molecule. However, limited information is available about the relationship between RLKs and MG. Here, we addressed the function of a receptor-like kinase, Os ASLRK, in the MG response and content in rice. A typical MG-responsive element(AAAAAAAA) exists in the promoter region of the OsASLRK gene. RTqPCR analysis indicated that the transcript level of OsASLRK was significantly increased by exogenous MG in a time-and dosage-dependent fashion. GUS staining also confirmed that the expression of Os ASLRK in rice root was enhanced by exogenous MG treatment. Genetic analysis suggested that the Osaslrk mutant displays increased sensitivity to MG and it showed higher endogenous MG content under exogenous MG treatments, while OsASLRK-overexpressing rice plants showed the opposite phenotypes. Diaminobenzidine(DAB) staining, scavenging enzyme activities and GSH content assays indicate that OsASLRK regulates MG sensitivity and content via the elevation of antioxidative enzyme activities and alleviation of membrane damage. Therefore, our results provide new evidence illustrating the roles that receptor-like kinase Os ASLRK plays in MG regulation in rice.

Down-regulation of transforming growth factor β1/activin receptor-like kinase 1 pathway gene expression by herbal compound 861 is related to deactivation of LX-2 cells

AIM: To investigate the effect of herbal compound 861 (Cpd861) on the transforming growth factor-β1 (TGFβ1)/ activin receptor-like kinase 1 (ALK1, type Ⅰ receptor) signaling-pathway-related gene expression in the LX-2 cell line, and the inhibitory mechanism of Cpd861 on the activation of LX-2 cells. METHODS: LX-2 cells were treated with TGFβ1 (5 ng/mL) Cpd861 (0.1 mg/mL), TGFβ1 (5 ng/mL) plus Cpd861 (5 ng/mL) for 24 h to investigate the effect of Cpd861 on the TGFβ1/ALK1 pathway. Real-time PCR was performed to examine the expression of α-SMA (α-smooth muscle actin), ALK1, Id1 (inhibitor of differentiation 1). Western blotting was carried out to measure the levels of α-SMA and phosphorylated Smad1, and immunocytochemical analysis for the expression of α-SMA. RESULTS: In LX-2 cells, TGFβ1/ALK1-pathway-related gene expression could be stimulated by TGFβ1, which led to excessive activation of the cells. Cpd861 decreased the activation of LX-2 cells by reducing the expression of α-SMA mRNA and protein expression. This effect was related to inhibition of the above TGFβ1/ALK1-pathway- related expression of genes such as Id1 and ALK1, and phosphorylation of Smad1 in LX-2 cells, even with TGFβ1 co-treatment for 24 h. CONCLUSION: Cpd861 can restrain the activation of LX-2 cells by inhibiting the TGFβ1/ALK1/Smad1 pathway.

Role of activin receptor-like kinase 1 in vascular development and cerebrovascular diseases

Activin receptor-like kinase 1(ALK1)is a transmembrane serine/threonine receptor kinase of the transforming growth factor beta(TGFβ)receptor superfamily.ALK1 is specifically expressed in vascular endothelial cells,and its dynamic changes are closely related to the proliferation of endothelial cells,the recruitment of pericytes to blood vessels,and functional differentiation during embryonic vascular development.The pathophysiology of many cerebrovascular diseases is today understood as a disorder of endothelial cell function and an imbalance in the proportion of vascular cells.Indeed,mutations in ALK1 and its co-receptor endoglin are major genetic risk factors for vascular arteriovenous malformation.Many studies have shown that ALK1 is closely related to the development of cerebral aneurysms,arteriovenous malformations,and cerebral atherosclerosis.In this review,we describe the various roles of ALK1 in the regulation of angiogenesis and in the maintenance of cerebral vascular homeostasis,and we discuss its relationship to functional dysregulation in cerebrovascular diseases.This review should provide new perspectives for basic research on cerebrovascular diseases and offer more effective targets and strategies for clinical diagnosis,treatment,and prevention.

Big Roles of Small Kinases:The Complex Functions of Receptor-Like Cytoplasmic Kinases in Plant Immunity and Development

Plants have evolved a large number of receptor-like cytoplasmic kinases （RLCKs） that often functionally and physically associate with receptor-like kinases （RLKs） to modulate plant growth, development and immune responses. Without any apparent extracellular domain, RLCKs relay intracellular signaling often via RLK complex-mediated transphosphorylation events. Recent advances have suggested essential roles of diverse RLCKs in concert with RLKs in regulating various cellular and physiological responses. We summarize here the complex roles of RLCKs in mediating plant immune responses and growth regulation, and discuss specific and overlapping functions of RLCKs in transducing diverse signaling pathways.

Regulation of plant responses to biotic and abiotic stress by receptor-like cytoplasmic kinases

As sessile organisms,plants have to cope with environmental change and numerous biotic and abiotic stress.Upon perceiving environmental cues and stress signals using different types of receptors,plant cells initiate immediate and complicated signaling to regulate cellular processes and respond to stress.Receptor-like cytoplasmic kinases(RLCKs)transduce signals from receptors to cellular components and play roles in diverse biological processes.Recent studies have revealed the hubbing roles of RLCKs in plant responses to biotic stress.Emerging evidence indicates the important regulatory roles of RLCKs in plant responses to abiotic stress,growth,and development.As a pivot of cellular signaling,the activity and stability of RLCKs are dynamically and tightly controlled.Here,we summarize the current understanding of how RLCKs regulate plant responses to biotic and abiotic stress.

OsCERK1-Mediated Chitin Perception and Immune Signaling Requires Receptor-like Cytoplasmic Kinase 185 to Activate an MAPK Cascade in Rice

Conserved pathogen-associated molecular patterns （PAMPs）, such as chitin, are perceived by pattem recognition receptors （PRRs） located at the host cell surface and trigger rapid activation of mitogen- activated protein kinase （MAPK） cascades, which are required for plant resistance to pathogens. However, the direct links from PAMP perception to MAPK activation in plants remain largely unknown. In this study, we found that the PRR-associated receptor-like cytoplasmic kinase Oryza sativa RLCK185 transmits immune signaling from the PAMP receptor OsCERK1 to an MAPK signaling cascade through interaction with an MAPK kinase kinase, OsMAPKKKε, which is the initial kinase of the MAPK cascade. OsRLCK185 interacts with and phosphorylates the C-terminal regulatory domain of OsMAPKKKε. Coexpression of phosphomi- metic OsR LCK185 and OsMAPKKKε activates MAPK3/6 phosphorylation in Nicotiana benthamiana leaves. Moreover, OsMAPKKKε interacts with and phosphorylates OsMKK4, a key MAPK kinase that transduces the chitin signal. Overexpression of OsMAPKKKε increases chitin-induced MAPK3/6 activation, whereas OsMAPKKKε knockdown compromises chitin-induced MAPK3/6 activation and resistance to rice blast fungus. Taken together, our results suggest the existence of a phospho-signaling pathway from cell surface chitin perception to intraceilular activation of an MAPK cascade in rice.

The receptor-like cytoplasmic kinase RIPK regulates broad-spectrum ROS signaling in multiple layers of plant immune system

Production of reactive oxygen species(ROS)via the activity of respiratory burst oxidase homologs(RBOHs)plays a vital role in multiple layers of the plant immune system,including pathogen-associated molecular pattern-triggered immunity(PTI),damage-associated molecular pattern-triggered immunity(DTI),effector-triggered immunity(ETI),and systemic acquired resistance(SAR).It is generally established that RBOHD is activated by different receptor-like cytoplasmic kinases(RLCKs)in response to various immune elicitors.In this study,we showed that RPM1-INDUCED PROTEIN KINASE(RIPK),an RLCK VII subfamily member,contributes to ROS production in multiple layers of plant immune system.The ripk mutants showed reduced ROS production in response to treatment with all examined immune elicitors that trigger PTI,DTI,ETI,and SAR.We found that RIPK can directly phosphorylate the N-terminal region of RBOHD in vitro,and the levels of phosphorylated S343/S347 residues of RBOHD are sigfniciantly lower in ripk mutants compared with the wild type upon treatment with all tested immune elicitors.We further demonstrated that phosphorylation of RIPK is required for its function in regulating RBOHD-mediated ROS production.Similar to rbohd,ripk mutants showed reduced stomatal closure and impaired SAR,and were susceptible to the necrotrophic bacterium Pectobacterium carotovorum.Collectively,our results indicate that RIPK regulates broad-spectrum RBOHD-mediated ROS signaling during PTI,DTI,ETI,and SAR,leading to subsequent RBOHD-dependent immune responses.

Identification, Expression and Functional Analysis of a Receptor-like Cytoplasmic Kinase, OsRLCK1, in Rice

Pollination involves a series of complex cellular interactions and signal transduction events. Numerous reports have suggested a central role for protein kinases in pollen germination and pollen tube growth and a large number of receptor-like kinases have been detected exclusively in pollen in higher plants. However, few are well characterized, especially for the receptor-like cytoplasmic kinases. Here we report a receptor-like kinase gene, OsRLCK1, which belongs to the receptor-like cytoplasmic kinase Ⅷ subfamily. Real-time quantitative polymerase chain reaction analysis and whole mount RNA in situ hybridization showed that OsRLCK1 is a pollen-specific gene and expressed only in the mature pollen. When expressed in the onion epidermal cells, the OsRLCK1-GFP fusion protein was diffused throughout the cell, indicating its cytoplasmic and nuclear localization. The Maltose Binding Protein-OsRLCK1 recombinant protein was found to be capable of autophosphorylation on threonine residue, showing that it encodes a functional kinase. These results suggest that OsRLCK1 is likely to play a role in a signaling pathway associated with pollen performance during pollination in rice.

Receptor-Like Kinases in Plant Innate Immunity

Plants employ a highly effective surveillance system to detect potential pathogens, which is critical for the success of land plants in an environment surrounded by numerous microbes. Recent efforts have led to the identification of a number of immune receptors and components of immune receptor complexes. It is now clear that receptor-like kinases （RLKs） and receptor-like proteins （RLPs） are key pattern-recognition receptors （PRRs） for microbe- and plant-derived molecular patterns that are associated with pathogen invasion. RLKs and RLPs involved in immune signaling belong to large gene families in plants and have undergone lineage specific expansion. Molecular evolution and population studies on phytopathogenic molecular signatures and their receptors have provided crucial insight into the co-evolution between plants and pathogens.

Genome-Wide Expression Pattern Analyses of the Arabidopsis Leucine-Rich Repeat Receptor-Like Kinases

Receptor-like protein kinases （RLKs） are a large group of transmembrane proteins playing critical roles in cell-cell and cell--environment communications. Based on extracellular domain structures, RLKs were classified into more than 21 subfamilies, among which leucine-rich repeat RLKs （LRR-RLKs） belong to the largest subfamily in plants such as Arabidopsis and rice. In Arabidopsis, there are approximately 223 LRR-RLKs, but only about 60 of which have been functionally described to date. To systematically investigate the roles of LRR-RLKs in regulating plant growth, development, and stress adaptations, we generated promoter：：GUS transgenic plants for all 223 LRR-RLK genes in Arabidopsis and analyzed their detailed expression patterns at various developmental stages. The results provide valuable resources for functionally elucidating this large and essential signaling protein subfamily.

Knights in Action： Lectin Receptor-Like Kinases in Plant Development and Stress Responses

The Receptor-Like Kinase （RLK） is a vast protein family with over 600 genes in Arabidopsis and 1100 in rice. The Lectin RLK （LecRLK） family is believed to play crucial roles in saccharide signaling as well as stress perception. All the LecRLKs possess three domains： an N-terminal lectin domain, an intermediate transmembrane domain, and a C-terminal kinase domain. On the basis of lectin domain variability, LecRLKs have been subgrouped into three subclasses： L-, G-, and C-type LecRLKs. While the previous studies on LecRLKs were dedicated to classification, comparative structural analysis and expression analysis by promoter-based studies, most of the recent studies on LecRLKs have laid special emphasis on the potential of this gene family in regulating biotic/abiotic stress and developmental pathways in plants, thus mak- ing the prospects of studying the LecRLK-mediated regulatory mechanism exceptionally promising. In this review, we have described in detail the LecRLK gene family with respect to a historical, evolutionary, and structural point of view. Furthermore, we have laid emphasis on the LecRLKs roles in development, stress conditions, and hormonal response. We have also discussed the exciting research prospects offered by the current knowledge on the LecRLK gene family. The multitude of the LecRLK gene family members and their functional diversity mark these genes as both interesting and worthy candidates for further analysis, especially in the field of crop improvement.

SERK Family Receptor-like Kinases Function as Co-receptors with PXY for Plant Vascular Development

In Arabidopsis, the CLAVATA3/EMBRYO SURROUNDING REGION-RELATED （CLE） peptides play important roles in regulating proliferation and differentiation of plant-specific stem cells. Although receptors of CLEs are reported to be leucine-rich repeat receptor kinases, the mechanisms underlying CLE-induced receptor activation remain largely unknown. Here we show that SOMATIC EMBRYOGENESIS RECEPTOR KINASEs （SERKs） serve as co-receptors in CLE41/TDIF-PXY signaling to regulate plant vascular development. TDIF induces interaction of its receptor PXY with SERKs in vitro and in vivo. Furthermore, the serk1-1 serk2-1 bakl-5 mutant plants are less sensitive to TDIF, phenocopying the pxy mutant with a compromised promotion of procambial cell proliferation. Crystal structure of the PXY-TDIF-SERK2 complex reveals that the last amino acid of TDIF conserved among CLEs and other evolutionary-related peptides is important for the interaction between SERK2 and PXY. Taken together, our current study identifies SERKs as signaling components of the TDIF-PXY pathway and suggests a conserved activation mechanism of CLE receptors.

Arabidopsis U-box E3 ubiquitin ligase PUB11 negatively regulates drought tolerance by degrading the receptor-like protein kinases LRR1 and KIN7

Both plant receptor-like protein kinases(RLKs)and ubiquitin-mediated proteolysis play crucial roles in plant responses to drought stress.However,the mechanism by which E3 ubiquitin ligases modulate RLKs is poorly understood.In this study,we showed that Arabidopsis PLANT U-BOX PROTEIN 11(PUB11),an E3 ubiquitin ligase,negatively regulates abscisic acid(ABA)-mediated drought responses.PUB11 interacts with and ubiquitinates two receptor-like protein kinases,LEUCINE RICH REPEAT PROTEIN 1(LRR1)and KINASE 7(KIN7),and mediates their degradation during plant responses to drought stress in vitro and in vivo.pub11 mutants were more tolerant,whereas Irr1 and kin7 mutants were more sensitive,to drought stress than the wild type.Genetic analyses show that the pub11 Irr1 kin7 triple mutant exhibited similar drought sensitivity as the Irr1 kin7 double mutant,placing PUB11 upstream of the two RLKs.Abscisic acid and drought treatment promoted the accumulation of PUB11,which likely accelerates LRR1 and KIN7 degradation.Together,our results reveal that PUB11 negatively regulates plant responses to drought stress by destabilizing the LRR1 and KIN7 RLKs.

Receptor-like kinases and receptor-like proteins： keys to pathogen recognition and defense signaling in plant innate immunity

Plants have evolved multiple layers of defense against various pathogens in the environment. Receptor-like kinases/proteins （RLKs/RLPs） are on the front lines of the battle between plants and pathogens since they are present at the plasma membrane and perceive signature molecules from either the invading pathogen or damaged plant tissue. With a few notable exceptions, most RLKs/RLPs are positive regulators of plant innate immunity. In this review, we summarize recently discovered RLKs/RLPs that are involved in plant defense responses against various classes of pathogens, We also describe what is currently known about the mechanisms of RLK-mediated initiation of signaling via protein-protein interactions and phosphorylation.

Notes from the Underground:Receptor-Like Kinases in Arabidopsis Root Development

During plant development, the frequency and context of cell division must be controlled, and cells must differentiate properly to perform their mature functions. In addition, stem cell niches need to be maintained as a reservoir for new cells. All of these processes require intercellular signaling, whether it is a cell relaying its position to other cells, or more mature cells signaling to the stem cell niche to regulate the rate of growth. Receptor-like kinases have emerged as a major component in these diverse roles, especially within the Arabidopsis root. In this review, the functions of receptor-like kinase signaling in regulating Arabidopsis root development will be examined in theareas of root apical meristem maintenance, regulation of epidermal cell fate, lateral root development and vascular differentiation.