Extracellular pH sensing by plant cell-surface peptide-receptor complexes.

The extracellular pH is a vital regulator of various biological processes in plants. However, how plants perceive extracellular pH remains obscure. Here, we report that plant cell-surface peptide-receptor complexes can function as extracellular pH sensors. We found that pattern-triggered immunity (PTI) dramatically alkalinizes the acidic extracellular pH in root apical meristem (RAM) region, which is essential for root meristem growth factor 1 (RGF1)-mediated RAM growth. The extracellular alkalinization progressively inhibits the acidic-dependent interaction between RGF1 and its receptors (RGFRs) through the pH sensor sulfotyrosine. Conversely, extracellular alkalinization promotes the alkaline-dependent binding of plant elicitor peptides (Peps) to its receptors (PEPRs) through the pH sensor Glu/Asp, thereby promoting immunity. A domain swap between RGFR and PEPR switches the pH dependency of RAM growth. Thus, our results reveal a mechanism of extracellular pH sensing by plant peptide-receptor complexes and provide insights into the extracellular pH-mediated regulation of growth and immunity in the RAM.

A salt stress-activated GSO1-SOS2-SOS1 module protects the Arabidopsis root stem cell niche by enhancing sodium ion extrusion.

Soil salinity impairs plant growth reducing crop productivity. Toxic accumulation of sodium ions is counteracted by the Salt Overly Sensitive (SOS) pathway for Na+ extrusion, comprising the Na+ transporter SOS1, the kinase SOS2, and SOS3 as one of several Calcineurin-B-like (CBL) Ca2 + sensors. Here, we report that the receptor-like kinase GSO1/SGN3 activates SOS2, independently of SOS3 binding, by physical interaction and phosphorylation at Thr16. Loss of GSO1 function renders plants salt sensitive and GSO1 is both sufficient and required for activating the SOS2-SOS1 module in yeast and in planta. Salt stress causes the accumulation of GSO1 in two specific and spatially defined areas of the root tip: in the endodermis section undergoing Casparian strip (CS) formation, where it reinforces the CIF-GSO1-SGN1 axis for CS barrier formation; and in the meristem, where it creates the GSO1-SOS2-SOS1 axis for Na+ detoxification. Thus, GSO1 simultaneously prevents Na+ both from diffusing into the vasculature, and from poisoning unprotected stem cells in the meristem. By protecting the meristem, receptor-like kinase-conferred activation of the SOS2-SOS1 module allows root growth to be maintained in adverse environments.

The OsBDR1-MPK3 module negatively regulates blast resistance by suppressing the jasmonate signaling and terpenoid biosynthesis pathway.

Receptor-like kinases (RLKs) may initiate signaling pathways by perceiving and transmitting environmental signals to cellular machinery and play diverse roles in plant development and stress responses. The rice genome encodes more than one thousand RLKs, but only a small number have been characterized as receptors for phytohormones, polypeptides, elicitors, and effectors. Here, we screened the function of 11 RLKs in rice resistance to the blast fungus Magnaporthe oryzae (M. oryzae) and identified a negative regulator named BDR1 (Blast Disease Resistance 1). The expression of BDR1 was rapidly increased under M. oryzae infection, while silencing or knockout of BDR1 significantly enhanced M. oryzae resistance in two rice varieties. Protein interaction and kinase activity assays indicated that BDR1 directly interacted with and phosphorylated mitogen-activated kinase 3 (MPK3). Knockout of BDR1 compromised M. oryzae-induced MPK3 phosphorylation levels. Moreover, transcriptome analysis revealed that M. oryzae-elicited jasmonate (JA) signaling and terpenoid biosynthesis pathway were negatively regulated by BDR1 and MPK3. Mutation of JA biosynthetic (allene oxide cyclase (AOC)/signaling (MYC2) genes decreased rice resistance to M. oryzae. Besides diterpenoid, the monoterpene linalool and the sesquiterpene caryophyllene were identified as unique defensive compounds against M. oryzae, and their biosynthesis genes (TPS3 and TPS29) were transcriptionally regulated by JA signaling and suppressed by BDR1 and MPK3. These findings demonstrate the existence of a BDR1-MPK3 cascade that negatively mediates rice blast resistance by affecting JA-related defense responses.

BRCC3 Regulation of ALK2 in Vascular Smooth Muscle Cells: Implication in Pulmonary Hypertension.

BACKGROUND: An imbalance of antiproliferative BMP (bone morphogenetic protein) signaling and proliferative TGF-ß (transforming growth factor-ß) signaling is implicated in the development of pulmonary arterial hypertension (PAH). The posttranslational modification (eg, phosphorylation and ubiquitination) of TGF-ß family receptors, including BMPR2 (bone morphogenetic protein type 2 receptor)/ALK2 (activin receptor-like kinase-2) and TGF-ßR2/R1, and receptor-regulated Smads significantly affects their activity and thus regulates the target cell fate. BRCC3 modifies the activity and stability of its substrate proteins through K63-dependent deubiquitination. By modulating the posttranslational modifications of the BMP/TGF-ß-PPARγ pathway, BRCC3 may play a role in pulmonary vascular remodeling, hence the pathogenesis of PAH. METHODS: Bioinformatic analyses were used to explore the mechanism by which BRCC3 deubiquitinates ALK2. Cultured pulmonary artery smooth muscle cells (PASMCs), mouse models, and specimens from patients with idiopathic PAH were used to investigate the rebalance between BMP and TGF-ß signaling in regulating ALK2 phosphorylation and ubiquitination in the context of pulmonary hypertension. RESULTS: BRCC3 was significantly downregulated in PASMCs from patients with PAH and animals with experimental pulmonary hypertension. BRCC3, by de-ubiquitinating ALK2 at Lys-472 and Lys-475, activated receptor-regulated Smad1/5/9, which resulted in transcriptional activation of BMP-regulated PPARγ, p53, and Id1. Overexpression of BRCC3 also attenuated TGF-ß signaling by downregulating TGF-ß expression and inhibiting phosphorylation of Smad3. Experiments in vitro indicated that overexpression of BRCC3 or the de-ubiquitin-mimetic ALK2-K472/475R attenuated PASMC proliferation and migration and enhanced PASMC apoptosis. In SM22α-BRCC3-Tg mice, pulmonary hypertension was ameliorated because of activation of the ALK2-Smad1/5-PPARγ axis in PASMCs. In contrast, Brcc3-/- mice showed increased susceptibility of experimental pulmonary hypertension because of inhibition of the ALK2-Smad1/5 signaling. CONCLUSIONS: These results suggest a pivotal role of BRCC3 in sustaining pulmonary vascular homeostasis by maintaining the integrity of the BMP signaling (ie, the ALK2-Smad1/5-PPARγ axis) while suppressing TGF-ß signaling in PASMCs. Such rebalance of BMP/TGF-ß pathways is translationally important for PAH alleviation.

Arabidopsis root responses to salinity depend on pectin modification and cell wall sensing.

Owing to its detrimental effect on plant growth, salinity is an increasing worldwide problem for agriculture. To understand the molecular mechanisms activated in response to salt in Arabidopsis thaliana, we investigated the Catharanthus roseus receptor-like kinase 1-like family, which contains sensors that were previously shown to be involved in sensing the structural integrity of the cell walls. We found that herk1 the1-4 double mutants, lacking the function of HERKULES1 (HERK1) and combined with a gain-of-function allele of THESEUS1 (THE1), strongly respond to salt application, resulting in an intense activation of stress responses, similarly to plants lacking FERONIA (FER) function. We report that salt triggers pectin methyl esterase (PME) activation and show its requirement for the activation of several salt-dependent responses. Because chemical inhibition of PMEs alleviates these salt-induced responses, we hypothesize a model in which salt directly leads to cell wall modifications through the activation of PMEs. Responses to salt partly require the functionality of FER alone or HERK1/THE1 to attenuate salt effects, highlighting the complexity of the salt-sensing mechanisms that rely on cell wall integrity.

The CRK14 gene encoding a cysteine-rich receptor-like kinase is implicated in the regulation of global proliferative arrest in Arabidopsis thaliana.

Global proliferative arrest (GPA) is a phenomenon in monocarpic plants in which the activity of all aboveground meristems generally ceases in a nearly coordinated manner after the formation of a certain number of fruits. Despite the fact that GPA is a biologically and agriculturally important event, the underlying molecular mechanisms are not well understood. In this study, we attempted to elucidate the molecular mechanism of GPA regulation by identifying the gene responsible for the Arabidopsis mutant fireworks (fiw), causing an early GPA phenotype. Map-based cloning revealed that the fiw gene encodes CYSTEIN-RICH RECEPTOR-LIKE KINASE 14 (CRK14). Genetic analysis suggested that fiw is a missense, gain-of-function allele of CRK14. Since overexpression of the extracellular domain of CRK14 resulted in delayed GPA in the wild-type background, we concluded that CRK14 is involved in GPA regulation. Analysis of double mutants revealed that fiw acts downstream of or independently of the FRUITFULL-APETALA2 (AP2)/AP2-like pathway, which was previously reported as an age-dependent default pathway in GPA regulation. In addition, fiw is epistatic to clv with respect to GPA control. Furthermore, we found a negative effect on WUSCHEL expression in the fiw mutants. These results thus suggest the existence of a novel CRK14-dependent signaling pathway involved in GPA regulation.

Genetic analysis of resistance to bean leaf crumple virus identifies a candidate LRR-RLK gene.

Bean leaf crumple virus (BLCrV) is a novel begomovirus (family Geminiviridae, genus Begomovirus) infecting common bean (Phaseolus vulgaris L.), threatening bean production in Latin America. Genetic resistance is required to ensure yield stability and reduce the use of insecticides, yet the available resistance sources are limited. In this study, three common bean populations containing a total of 558 genotypes were evaluated in different yield and BLCrV resistance trials under natural infection in the field. A genome-wide association study identified the locus BLC7.1 on chromosome Pv07 at 3.31 Mbp, explaining 8 to 16% of the phenotypic variation for BLCrV resistance. In comparison, whole-genome regression models explained 51 to 78% of the variation and identified the same region on Pv07 to confer resistance. The most significantly associated markers were located within the gene model Phvul.007G040400, which encodes a leucine-rich repeat receptor-like kinase subfamily III member and is likely to be involved in the innate immune response against the virus. The allelic diversity within this gene revealed five different haplotype groups, one of which was significantly associated with BLCrV resistance. As the same genome region was previously reported to be associated with resistance against other geminiviruses affecting common bean, our study highlights the role of previous breeding efforts for virus resistance in the accumulation of positive alleles against newly emerging viruses. In addition, we provide novel diagnostic single-nucleotide polymorphism markers for marker-assisted selection to exploit BLC7.1 for breeding against geminivirus diseases in one of the most important food crops worldwide.

Large-scale analysis of the N-terminal regulatory elements of the kinase domain in plant Receptor-like kinase family.

BACKGROUND: The N-terminal regulatory element (NRE) of Receptor-like kinases (RLKs), consisting of the juxtamembrane segment in receptor kinases (RKs) and the N-terminal extension segment in RLCKs, is a crucial component that regulates the activities of these proteins. However, the features and functions of the NRE have remained largely unexplored. Herein, we comprehensively analyze 510,233 NRE sequences in RLKs from 528 plant species, using information theory and data mining techniques to unravel their common characteristics and diversity. We also use recombinant RKs to investigate the function of the NRE in vitro. RESULTS: Our findings indicate that the majority of NRE segments are around 40-80 amino acids in length and feature a serine-rich region and a 14-amino-acid consensus sequence, 'FSYEELEKAT[D/N]NF[S/D]', which contains a characteristic α-helix and ST motif that connects to the core kinase domain. This conserved signature sequence is capable of suppressing FERONIA's kinase activity. A motif discovery algorithm identifies 29 motifs with highly conserved phosphorylation sites in RK and RLCK classes, especially the motif 'VGPWKpTGLpSGQLQKAFVTGVP' in LRR-VI-2 class. Phosphorylation of an NRE motif in an LRR-VI-2 member, MDIS1, modulates the auto-phosphorylation of its co-receptor, MIK1, indicating the potential role of NRE as a 'kinase switch' in RLK activation. Furthermore, the characterization of phosphorylatable NRE motifs improves the accuracy of predicting phosphorylatable sites. CONCLUSIONS: Our study provides a comprehensive dataset to investigate NRE segments from individual RLKs and enhances our understanding of the underlying mechanisms of RLK signal transduction and kinase activation processes in plant adaptation.

An integrated docking and molecular dynamics simulation approach to discover potential inhibitors of activin receptor-like kinase 1.

Activin receptor-like kinase 1 (ALK1) is a transmembrane receptor involved in crucial signaling pathways associated with angiogenesis and vascular development. Inhibition of ALK1 signaling has emerged as a promising therapeutic strategy for various angiogenesis-related diseases, including cancer and hereditary hemorrhagic telangiectasia. This study aimed to investigate the potential of phytoconstituents as inhibitors of ALK1 using a combined approach of virtual screening and molecular dynamics (MDs) simulations. Phytoconstituents from the IMPPAT 2.0 database underwent virtual screening to identify potential inhibitors of ALK1. The compounds were initially filtered based on physicochemical parameters, following Lipinski's rules and the PAINS filter. Subsequently, compounds demonstrating high binding affinities in docking analysis were further analyzed. Additional assessments, including ADMET, PAINS, and PASS evaluations, were conducted to identify more potent hits. Through interaction analysis, a phytoconstituent, Candidine, exhibited appreciable affinity and specific interactions with the ALK1 active site. To validate the results, MD simulations and principal components analysis were performed. The MD simulations demonstrated that Candidine stabilized the ALK1 structure and reduced conformational fluctuations. In conclusion, Candidine shows promising potential as binding partners of ALK1. These findings provide a foundation for further exploration and development of Candidine as a lead molecule for therapeutic interventions targeting ALK1-associated diseases.

Receptor-like kinases and their signaling cascades for plant male fertility: loyal messengers.

Receptor-like kinases (RLKs) are evolved for plant cell-cell communications. The typical RLK protein contains an extracellular and hypervariable N-terminus to perceive various signals, a transmembrane domain to anchor into plasma membrane, and a cytoplasmic, highly conserved kinase domain to phosphorylate target proteins. To date, RLKs have manifested their significance in a myriad of biological processes during plant reproductive growth, especially in male fertility. This review first summarizes a recent update on RLKs and their interacting protein partners controlling anther and pollen development, pollen release from dehisced anther, and pollen function during pollination and fertilization. Then, regulatory networks of RLK signaling pathways are proposed. In addition, we predict RLKs in maize and rice genome, obtain homologs of well-studied RLKs from phylogeny of three subfamilies and then analyze their expression patterns in developing anthers of maize and rice to excavate potential RLKs regulating male fertility in crops. Finally, current challenges and future prospects regarding RLKs are discussed. This review will contribute to a better understanding of plant male fertility control by RLKs, creating potential male sterile lines, and inspiring innovative crop breeding methods.

LORE receptor homomerization is required for 3-hydroxydecanoic acid-induced immune signaling and determines the natural variation of immunosensitivity within the Arabidopsis genus.

The S-domain-type receptor-like kinase (SD-RLK) LIPOOLIGOSACCHARIDE-SPECIFIC REDUCED ELICITATION (LORE) from Arabidopsis thaliana is a pattern recognition receptor that senses medium-chain 3-hydroxy fatty acids, such as 3-hydroxydecanoic acid (3-OH-C10:0), to activate pattern-triggered immunity. Here, we show that LORE homomerization is required to activate 3-OH-C10:0-induced immune signaling. Fluorescence lifetime imaging in Nicotiana benthamiana demonstrates that AtLORE homomerizes via the extracellular and transmembrane domains. Co-expression of AtLORE truncations lacking the intracellular domain exerts a dominant negative effect on AtLORE signaling in both N. benthamiana and A. thaliana, highlighting that homomerization is essential for signaling. Screening for 3-OH-C10:0-induced reactive oxygen species production revealed natural variation within the Arabidopsis genus. Arabidopsis lyrata and Arabidopsis halleri do not respond to 3-OH-C10:0, although both possess a putative LORE ortholog. Both LORE orthologs have defective extracellular domains that bind 3-OH-C10:0 to a similar level as AtLORE, but lack the ability to homomerize. Thus, ligand binding is independent of LORE homomerization. Analysis of AtLORE and AlyrLORE chimera suggests that the loss of AlyrLORE homomerization is caused by several amino acid polymorphisms across the extracellular domain. Our findings shed light on the activation mechanism of LORE and the loss of 3-OH-C10:0 perception within the Arabidopsis genus.

Receptor-like kinases OsRLK902-1 and OsRLK902-2 form immune complexes with OsRLCK185 to regulate rice blast resistance.

Receptor-like kinases (RLKs) are major regulators of the plant immune response and play important roles in the perception and transmission of immune signals. RECEPTOR LIKE KINASE 902 (RLK902) is at the key node in leucine-rich repeat receptor-like kinase interaction networks and positively regulates resistance to the bacterial pathogen Pseudomonas syringae in Arabidopsis. However, the function of RLK902 in fungal disease resistance remains obscure. In this study, we found that the expression levels of OsRLK902-1 and OsRLK902-2, encoding two orthologues of RLK902 in rice, were induced by Magnaporthe oryzae, chitin, and flg22 treatment. osrlk902-1 and osrlk902-2 knockout mutants displayed enhanced susceptibility to M. oryzae. Interestingly, the osrlk902-1 rlk902-2 double mutant exhibited similar disease susceptibility, hydrogen peroxide production, and callose deposition to the two single mutants. Further investigation showed that OsRLK902-1 interacts with and stabilizes OsRLK902-2. The two OsRLKs form a complex with OsRLCK185, a key regulator in chitin-triggered immunity, and stabilize it. Taken together, our data demonstrate that OsRLK902-1 and OsRLK902-2, as well as OsRLCK185 function together in regulating disease resistance to M. oryzae in rice.

The cysteine-rich receptor-like kinase CRK10 targeted by Coniella diplodiella effector CdE1 contributes to white rot resistance in grapevine.

Grape white rot is a devastating fungal disease caused by Coniella diplodiella. The pathogen delivers effectors into the host cell that target crucial immune components to facilitate its infection. Here, we examined a secreted effector of C. diplodiella, known as CdE1, which has been found to inhibit Bax-triggered cell death in Nicotiana benthamiana plants. The expression of CdE1 was induced at 12-48 h after inoculation with C. diplodiella, and the transient overexpression of CdE1 led to increased susceptibility of grapevine to the fungus. Subsequent experiments revealed an interaction between CdE1 and Vitis davidii cysteine-rich receptor-like kinase 10 (VdCRK10) and suppression of VdCRK10-mediated immunity against C. diplodiella, partially by decreasing the accumulation of VdCRK10 protein. Furthermore, our investigation revealed that CRK10 expression was significantly higher and was up-regulated in the resistant wild grapevine V. davidii during C. diplodiella infection. The activity of the VdCRK10 promoter is induced by C. diplodiella and is higher than that of Vitis vitifera VvCRK10, indicating the involvement of transcriptional regulation in CRK10 gene expression. Taken together, our results highlight the potential of VdCRK10 as a resistant gene for enhancing white rot resistance in grapevine.

The wall-associated receptor-like kinase CsWAKL01, positively regulated by the transcription factor CsWRKY53, confers resistance to citrus bacterial canker via regulation of phytohormone signaling.

Citrus bacterial canker (CBC) is a disease that poses a major threat to global citrus production and is caused by infection with Xanthomonas citri subsp. citri (Xcc). Wall-associated receptor-like kinase (WAKL) proteins play an important role in shaping plant resistance to various bacterial and fungal pathogens. In a prior report, CsWAKL01 was identified as a candidate Xcc-inducible gene found to be upregulated in CBC-resistant citrus plants. However, the functional role of CsWAKL01 and the mechanisms whereby it may influence resistance to CBC have yet to be clarified. Here, CsWAKL01 was found to localize to the plasma membrane, and the overexpression of the corresponding gene in transgenic sweet oranges resulted in the pronounced enhancement of CBC resistance, whereas its knockdown had the opposite effect. Mechanistically, the ability of CsWAKL01 was linked to its ability to reprogram jasmonic acid, salicylic acid, and abscisic acid signaling activity. CsWRKY53 was further identified as a transcription factor capable of directly binding the CsWAKL01 promoter and inducing its transcriptional upregulation. CsWRKY53 silencing conferred greater CBC susceptibility to infected plants. Overall, these data support a model wherein CsWRKY53 functions as a positive regulator of CsWAKL01 to enhance resistance to CBC via the reprogramming of phytohormone signaling. Together these results offer new insight into the mechanisms whereby WAKLs shape phytopathogen resistance while underscoring the potential value of targeting the CsWRKY53-CsWAKL01 axis when seeking to breed CBC-resistant citrus plant varieties.

Elevated circulating BMP9 aggravates pulmonary angiogenesis in hepatopulmonary syndrome rats through ALK1-Endoglin-Smad1/5/9 signalling.

BACKGROUND: Bone morphogenetic protein 9 (BMP9) is a hepatokine that plays a pivotal role in the progression of liver diseases. Moreover, an increasing number of studies have shown that BMP9 is associated with hepatopulmonary syndrome (HPS), but its role in HPS is unclear. Here, we evaluated the influence of CBDL on BMP9 expression and investigated potential mechanisms of BMP9 signalling in HPS. METHODS: We profiled the circulating BMP9 levels in common bile duct ligation-induced HPS rat model, and then investigated the effects and mechanisms of HPS rat serum on pulmonary vascular endothelial dysfunction in rat model, as well as in primarily cultured rat pulmonary microvascular endothelial cells. RESULTS: Our data revealed that circulating BMP9 levels were significantly increased in the HPS rats compared to control group. Besides, the elevated BMP9 in HPS rat serum was not only crucial for promoting endothelial cell proliferation and tube formation through the activin receptor-like kinase1 (ALK1)-Endoglin-Smad1/5/9 pathway, but also important for accumulation of monocytes. Treatments with ALK1-Fc or silencing ALK1 expression to inhibit the BMP9 signalling pathway effectively eliminated these effects. In agreement with these observations, increased circulating BMP9 was associated with an increase in lung vessel density and accumulation of pro-angiogenic monocytes in the microvasculature in HPS rats. CONCLUSIONS: This study provided evidence that elevated circulating BMP9, secreted from the liver, promote pulmonary angiogenesis in HPS rats via ALK1-Endoglin-Smad1/5/9 pathway. In addition, BMP9-regulated pathways are also involved in accumulation of pro-angiogenic monocytes in the pulmonary microvasculature in HPS rats.

The receptor-like kinases BAM1 and BAM2 are required for root xylem patterning.

Xylem patterning in the root is established through the creation of opposing gradients of miRNAs and their targets, transcripts of the HD-ZIP III family of transcriptions factors, enabled by the cell-to-cell spread of the former. The miRNAs regulating xylem patterning, miR165/6, move through plasmodesmata, but how their trafficking is regulated remains elusive. Here, we describe that simultaneous mutation of the plasma membrane- and plasmodesmata-localized receptor-like kinases (RLKs) BARELY ANY MERISTEM (BAM) 1 and 2 or expression of the geminivirus-encoded BAM1/2-interactor C4 results in higher accumulation and broader distribution of the HD-ZIP III transcripts despite normal total accumulation of miR165/6, and ultimately causes defects in xylem patterning, which depend on the function of the aforementioned miRNA targets. Taken together, our results show that BAM1 and BAM2 are redundantly required for proper xylem patterning in the Arabidopsis root, by ensuring the proper distribution and accumulation of miR165/6-targeted transcripts.

[Genome-wide screening and bioinformatics analysis of Cannabis sativa LecRLK gene family].

Lectin receptor-like kinase(LecRLK) is a class of phytokinase with lectin conserved domain, which plays an important role in plant resistance to biological and abiotic stresses, as well as plant growth and development. Cannabis sativa is an important multi-purpose plant, widely used in food, textile, medicine, and other fields. Genome-wide screening and expression analysis of the LecRLK family of C. sativa were performed in this paper, so as to provide scientific reference for functional analysis of the LecRLK family of C. sativa. Based on BLAST and HMM methods, 93 LecRLKs were identified in the whole genome of C. sativa, including 69 G types, 23 L types, and one C types. Subsequently, a series of bioinformatics analyses were performed on the LecRLK family members, and the physicochemical properties of the protein of the LecRLK family members were initially revealed. The prediction of cis-acting elements of promoters in family members showed that family members were regulated by hormones and stress response. The expression analysis showed that some family members were highly expressed in the roots, which may participate in the process of stress resistance. Several members were highly expressed in female flowers and may be involved in female flower development. This study provides a theoretical basis for further study of LecRLK gene function. Meanwhile, the expression analysis screens candidate LecRLK members who may participate in the resistance of C. sativa, which provides a theoretical basis for the subsequent selection of C. sativa varieties against resistance.

OsSLA1 functions in leaf angle regulation by enhancing the interaction between OsBRI1 and OsBAK1 in rice.

Leaf angle is an important trait in plants. Here, we demonstrate that the leucine-rich repeat receptor-like kinase OsSLA1 plays an important role in leaf angle regulation in rice (Oryza sativa). OsSLA1 mutant plants exhibited a small leaf angle phenotype due to changes of adaxial cells in the lamina joint. GUS staining revealed that OsSLA1 was highly expressed in adaxial cells of the lamina joint. The OsSLA1 mutant plants were insensitive to exogenous epibrassinolide (eBL) and showed upregulated expression of DWARF and CPD, but downregulated expression of BU1, BUL1, and ILI1, indicating that brassinosteroid (BR) signal transduction was blocked. Fluorescence microscopy showed that OsSLA1 was localized to the plasma membrane and nearby periplasmic vesicles. Further study showed that OsSLA1 interacts with OsBRI1 and OsBAK1 via its intracellular domain and promotes the interaction between OsBRI1 and OsBAK1. In addition, phosphorylation experiments revealed that OsSLA1 does not possess kinase activity, but that it can be phosphorylated by OsBRI1 in vitro. Knockout of OsSLA1 in the context of d61 caused exacerbation of the mutant phenotype. These results demonstrate that OsSLA1 regulates leaf angle formation via positive regulation of BR signaling by enhancing the interaction of OsBRI1 with OsBAK1.

SymRK-dependent phosphorylation of Gα protein and its role in signaling during soybean (Glycine max) nodulation.

Heterotrimeric G proteins, comprised of Gα, Gß and Gγ subunits, influence signaling in most eukaryotes. In metazoans, G proteins are activated by G protein-coupled receptor (GPCR)-mediated GDP to GTP exchange on Gα; however, the role(s) of GPCRs in regulating plant G-protein signaling remains equivocal. Mounting evidence suggests the involvement of receptor-like kinases (RLKs) in regulating plant G-protein signaling, but their mechanistic details remain scarce. We have previously shown that during Glycine max (soybean) nodulation, the nod factor receptor 1 (NFR1) interacts with G-protein components and indirectly affects signaling. We explored the direct regulation of G-protein signaling by RLKs using protein-protein interactions, receptor-mediated in vitro phosphorylations and the effects of such phosphorylations on soybean nodule formation. Results presented in this study demonstrate a direct, phosphorylation-based regulation of Gα by symbiosis receptor kinase (SymRK). SymRKs interact with and phosphorylate Gα at multiple residues in vitro, including two in its active site, which abolishes GTP binding. Additionally, phospho-mimetic Gα fails to interact with Gßγ, potentially allowing for constitutive signaling by the freed Gßγ. These results uncover an unusual mechanism of G-protein cycle regulation in plants where the receptor-mediated phosphorylation of Gα not only affects its activity but also influences the availability of its signaling partners, thereby exerting a two-pronged check on signaling.

Liguleless narrow and narrow odd dwarf act in overlapping pathways to regulate maize development and metabolism.

Narrow odd dwarf (nod) and Liguleless narrow (Lgn) are pleiotropic maize mutants that both encode plasma membrane proteins, cause similar developmental patterning defects, and constitutively induce stress signaling pathways. To investigate how these mutants coordinate maize development and physiology, we screened for protein interactors of NOD by affinity purification. LGN was identified by this screen as a strong candidate interactor, and we confirmed the NOD-LGN molecular interaction through orthogonal experiments. We further demonstrated that LGN, a receptor-like kinase, can phosphorylate NOD in vitro, hinting that they could act in intersecting signal transduction pathways. To test this hypothesis, we generated Lgn-R;nod mutants in two backgrounds (B73 and A619), and found that these mutations enhance each other, causing more severe developmental defects than either single mutation on its own, with phenotypes including very narrow leaves, increased tillering, and failure of the main shoot. Transcriptomic and metabolomic analyses of the single and double mutants in the two genetic backgrounds revealed widespread induction of pathogen defense genes and a shift in resource allocation away from primary metabolism in favor of specialized metabolism. These effects were similar in each single mutant and heightened in the double mutant, leading us to conclude that NOD and LGN act cumulatively in overlapping signaling pathways to coordinate growth-defense tradeoffs in maize.