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 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.

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.

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.

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.

Characterization of a S-locus-related Receptor-like Kinase Cluster in Rice Chromosome 4

We have identified 14 S _locus glycoprotein (SLG)_related protein kinase genes in a 323 kb contig of rice (Oryza sativa L.) chromosome 4 and we detected the transcription pattern of this gene cluster by reverse transcription_polymerase reaction (RT_PCR). RT_PCR results revealed that nine putative genes were transcribed in rice and these genes had the different expression patterns: two genes are expressed predominantly in reproductive tissues while the other seven genes are expressed in both reproductive and vegetative tissues. Analysis of the predicted amino acid sequences demonstrated that the extracellular receptor domains are highly homologous to SLG of Brassica, whereas the cytoplasmic kinase domains contain conserved amino acids present in serine/threonine kinases.

OsSRK1,an Atypical S-Receptor-Like Kinase Positively Regulates Leaf Width and Salt Tolerance in Rice

Receptor-like kinases(RLKs)are important for plant growth,development and defense responses.The S-receptor protein kinases(SRKs),which represent an RLK subfamily,control the selfincompatibility among Brassica species.However,little information is available regarding SRK functions in rice.We identified a gene OsSRK1 encoding an atypical SRK.The transcript of OsSRK1 was induced by abscisic acid(ABA),salt and polyethylene glycol.OsSRK1 localized to the plasma membrane and cytoplasm.Leaf width was increased in OsSRK1-overexpression(OsSRK1-OX)transgenic rice plants,likely because of an increase in cell number per leaf.Furthermore,the expression levels of OsCYCA3-1 and OsCYCD2-1,which encode positive regulators of cell division,were up-regulated in leaf primordium of OsSRK1-OX rice plants relative to those in wild type.Meanwhile,the expression level of OsKRP1,which encodes cell cycle inhibitor,was down-regulated in the OsSRK1-OX plants.Therefore,it is deduced that OsSRK1 regulates leaf width by promoting cell division in the leaf primordium.Additionally,OsSRK1-OX plants exhibited enhanced ABA sensitivity and salt tolerance compared with wild type.These results suggest that OsSRK1 plays important roles in leaf development and salt responses in rice.

How many proteins interacting with symbiosis receptor-like kinase （SymRK） involved in nodulation？

Nodule formation is a tightly regulated process that integrates specific signal exchange and coordinated activation of developmental mechanisms to synchronize bacte-rial infection and organ development. Symbiosis receptor kinase （SymRK） is indispensable for symbiotic signal transduction of root nodule symbiosis （RNS） upon stimulation of root cells by microbial signaling molecules. But the protein turnover model of SymRK and the way for nodulation factor signals downstream transduction from SymRK are not clear. Over the past years, a number of proteins interacting with SymRK which required for root nodule symbiosis have been identified. Here we summarized structures and functions of these pro-teins, and concluded that major challenge would be revealing relations between them and the regulation mechanisms of SymRK in nodulation.

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.

Ubiquitination-mediated regulation of receptor-like kinases in symbiosis and immunity

Receptor-like kinases(RLKs)are plasma membrane(PM)proteins that monitor the extracellular environment and regulate various processes such as biotic interactions.Lysin motif(LysM)RLKs are a specific class of RLKs involved in the recognition of chitin-derived molecules produced by microorganisms(Buendia et al.,2018).Notably,the LysM-RLK heterocomplex LjNFR1/LjNFR5 recognizes lipochitooligosaccharides(LCOs,also called Nod factors)leading to root nodule symbiosis(RNS)in Lotus japonicus,whereas the heterocomplexes AtLYK5/AtCERK1 and OsCEBIP/OsCERK1 recognize chitooligosaccharides(COs)leading to defense responses in Arabidopsis thaliana and rice,respectively(Buendia et al.,2018).These receptors function as gatekeepers.Extracellular ligand binding activates the intracellular kinase activity of LjNFR1,AtCERK1,and OsCERK1,which mediate phosphorylation-dependent signaling cascades.Regulatory mechanisms are essential to tightly control RLK homeostasis and signaling,allowing cells to respond efficiently while preventing constitutive activation.The PM-resident pool of RLKs must be maintained for rapid response,while RLK endocytosis and ultimately degradation in lytic vacuoles is critical for both signaling and downregulation of the responses.In addition to its role in proteasome-dependent degradation,ubiquitination,a post-translational protein modification,has emerged as a key regulator of PM proteins by inducing their internalization and degradation in lytic vacuoles(Romero-Barrios and Vert,2018).

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.

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.

Global Analysis of Expression Profiles of Rice Receptor-Like Kinase Genes

The receptor-like kinases （RLKs） play critical roles in plant development and response to stress stimuli. By perceiving or sensing the extracellular signals, RLK activates the downstream signaling pathway through phosphorylating the specific targets. Up to now, only a few RLKs have been functionally identified, which are even fewer in rice （Oryza sativa L.）. We here report the systemic analysis of the expression profiles of rice RLK coding genes in different tissues, with the emphasis on seed development and in response to both abiotic stress and plant hormones. The results showed that most rice RLK genes are expressed in two or more tissues, of which the RLCK-RLKs have a higher, while WAK- and SD-RLKs have a lower, expression level in the vegetative tissues than other subfamily members. Interestingly, the constitutively highly expressed RLKs in rice and Arabidopsis are conserved, which is consistent with the previous hypothesis that RLKs existed before the differentiation of monocotyledon and dicotyledon plants. Nearly one-third of the detected rice RLKs are expressed during seed development, and the RLCK-RLK members possess a higher percentage during the endosperm de- velopment, suggesting a novel function of RLCK-RLK members in endosperm development. Further analysis revealed that many RLK genes expressed during seed development are also regulated by abiotic stresses （cold, salt, or drought） or hor- mones, indicating that RLKs may take part in the stress-related signaling pathways such as dehydration of endosperm. These results provide informative insights into the RLK studies and will be helpful to reveal the global regulatory network controlling rice seed development.

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.

Splicing of Receptor-Like Kinase-Encoding SNC4 and CERK1 is Regulated by Two Conserved Splicing Factors that Are Required for Plant Immunity

Plant immune receptors belonging to the receptor-like kinase （RLK） family play important roles in the recog- nition of microbial pathogens and activation of downstream defense responses. The Arabidopsis mutant snc4-1D con- tains a gain-of-function mutation in the RLK SNC4 （SUPPRESSOR OF NPRI-1, CONSTITUTIVE4）, which leads to constitutive activation of defense responses. Analysis of suppressor mutants of snc4-1D identified two conserved splicing factors, SUA （SUPPRESSOR OF ABI3-5） and RSN2 （REQUIRED FOR SNC4-1D 2）, that are required for the constitutive defense responses in snc4-1D. In sua and rsn2 mutants, SNC4 splicing is altered and the amount of 5NC4 transcripts is reduced. Further analysis showed that SUA and RSN2 are also required for the proper splicing of CERK1 （CHITIN ELICITOR RECEPTOR KINASE1）, which encodes another RLK that functions as a receptor for chitin. In sua and rsn2 mutants, induction of reactive oxygen species by chitin is reduced and the non-pathogenic bacteria Pseudomonas syringae pv. tomato DC3OOOhrcC grows to higher titers than in wild-type plants. Our study suggests that pre-mRNA splicing plays important roles in the regulation of plant immunity mediated by the RLKs SNC4 and CERK1.

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.

A G-type lectin receptor-like kinase regulates the perception of oomycete apoplastic expansin-like proteins

Phytophthora capsici is one of the most harmful pathogens in agriculture, which threatens the safe production of multiple crops and causes serious economic losses worldwide. Here, we identified a P. capsici expansin-like protein, Pc EXLX1, by liquid chromatography-tandem mass spectrometry from Nicotiana benthamiana apoplastic fluid infected with P. capsici. Clustered regularly interspaced short palindromic repeats/crispr associated protein9(CRISPR/Cas9)-mediated Pc EXLX1 knockout mutants exhibited significantly enhanced virulence,while the overexpression of Pc EXLX1 impaired the virulence. Prokaryotically expressed Pc EXLX1 activated multiple plant immune responses, which were BRI1-associated kinase 1(BAK1)-and suppressor of BIR1-1(SOBIR1)-dependent. Furthermore, overexpression of Pc EXLX1 homologs in N. benthamiana could also increase plant resistance to P. capsici. A G-type lectin receptor-like kinase from N. benthamiana, expansin-regulating kinase 1(ERK1), was shown to regulate the perception of Pc EXLX1 and positively mediate the plant resistance to P. capsici. These results reveal that the expansin-like protein, Pc EXLX1, is a novel apoplastic effector with plant immunity-inducing activity of oomycetes, perception of which is regulated by the receptor-like kinase, ERK1.

Receptor-Like Kinases:Key Regulators of Plant Development and Defense

Plants are multi-cellular organisms that live in diverse and fluctuating environments. Cell-cell and cell-environment com- munication are therefore critical to plant growth and develop- ment. In animals, transmembrane receptor protein tyrosine kinases play significant roles in cell-cell signaling. There was a great deal of surprise in the plant community, however, when the first receptor-like protein kinase （RLK） was isolated from maize by John C.