Peptide-mediated cell-to-cell signaling has crucial roles in coordination and definition of cellular functions in plants. Peptide-receptor matching is important for understanding the mechanisms underlying peptide-mediated signaling. Here we report the structure-guided identification of root meristem growth factor (RGF) receptors important for plant development. An assay based on a signature ligand recognition motif (Arg-x-Arg) conserved in a subfamily of leucine-rich repeat receptor kinases (LRR-RKs) identified the functionally uncharacterized LRR-RK At4g26540 as a receptor of RGF1 (RGFR1). We further solved the crystal structure of RGF1 in complex with the LRR domain of RGFR1 at a resolution of 2.6 Å, which reveals that the Arg-x-Gly-Gly (RxGG) motif is responsible for specific recognition of the sulfate group of RGF1 by RGFR1. Based on the RxGG motif, we identified additional four RGFRs. Participation of the five RGFRs in RGF-induced signaling is supported by biochemical and genetic data. We also offer evidence showing that SERKs function as co-receptors for RGFs. Taken together, our study identifies RGF receptors and co-receptors that can link RGF signals with their downstream components and provides a proof of principle for structure-based matching of LRR-RKs with their peptide ligands.
SUMMARY Abscission is a developmental process that enables plants to shed unwanted organs. In Arabidopsis, the floral organ abscission is regulated by a signaling pathway consisting of the peptide ligand IDA, the receptor-like kinases (RLKs) HAE and HSL2, and a downstream MAP kinase (MAPK) cascade. However, little is known about the molecular link between ligand-receptor pairs and intracellular signaling. Here, we report that the SERK family RLKs function redundantly in regulating floral organ abscission downstream of IDA and upstream of the MAPK cascade. IDA induces heterodimerization of HAE/HSL2 and SERKs, which transphosphorylate each other. The SERK3 residues mediating its interaction with the immune receptor FLS2 and the brassinosteroid receptor BRI1 are also required for IDA-induced HAE/HSL2-SERK3 interaction, suggesting SERKs serve as co-receptors of HAE/HSL2 in perceiving IDA. Thus, our study reveals the signaling activation mechanism in floral organ abscission by IDA-induced HAE/HSL2-SERK complex formation accompanied by transphosphorylation.
The endogenous peptides AtPep1-8 in Arabidopsis mature from the conserved C-terminal portions of their precursor proteins PROPEP1-8, respectively. The two homologous leucine-rich repeat-receptor kinases (LRR-RKs) PEPR1 and PEPR2 act as receptors of AtPeps. AtPep binding leads to stable association of PEPR1,2 with the shared receptor LRR-RK BAK1, eliciting immune responses similar to those induced by pathogens. Here we report a crystal structure of the extracellular LRR domain of PEPR1 (PEPR1LRR) in complex with AtPep1. The structure reveals that AtPep1 adopts a fully extended conformation and binds to the inner surface of the superhelical PEPR1LRR. Biochemical assays showed that AtPep1 is capable of inducing PEPR1LRR-BAK1LRR heterodimerization. The conserved C-terminal portion of AtPep1 dominates AtPep1 binding to PEPR1LRR, with the last amino acid of AtPep1 Asn23 forming extensive interactions with PEPR1LRR. Deletion of the last residue of AtPep1 significantly compromised AtPep1 interaction with PEPR1LRR. Together, our data reveal a conserved structural mechanism of AtPep1 recognition by PEPR1, providing significant insight into prediction of recognition of other peptides by their cognate LRR-RKs.
The mechanisms by which organisms adapt to variable environments are a fundamental question in evolutionary biology and are important to protect important species in response to a changing climate. An interesting candidate to study this question is the honey bee Apis cerana, a keystone pollinator with a wide distribution throughout a large variety of climates, that exhibits rapid dispersal. Here, we resequenced the genome of 180 A. cerana individuals from 18 populations throughout China. Using a population genomics approach, we observed considerable genetic variation in A. cerana. Patterns of genetic differentiation indicate high divergence at the subspecies level, and physical barriers rather than distance are the driving force for population divergence. Estimations of divergence time suggested that the main branches diverged between 300 and 500 Ka. Analyses of the population history revealed a substantial influence of the Earth’s climate on the effective population size of A. cerana, as increased population sizes were observed during warmer periods. Further analyses identified candidate genes under natural selection that are potentially related to honey bee cognition, temperature adaptation, and olfactory. Based on our results, A. cerana may have great potential in response to climate change. Our study provides fundamental knowledge of the evolution and adaptation of A. cerana.
Microalgae (Nannochloropsis sp., NS), with high contents of eicosapentaenoic acid (EPA) and crude protein, may be one of the important n-3 polyunsaturated fatty acid (PUFA) sources and potential protein feed ingredient. The purposes of this study were to enrich yolk with n-3 PUFA by dietary EPA-rich NS supplementation and to evaluate whether it is feasible to partly substitute for soybean meal in laying hens diet. A total of 360 37-wk-old healthy Lohmann Brown laying hens, with similar laying rate and body weight, were randomly allotted to 5 groups (6 replicates, 12 birds/replicate) and fed 5 experimental diets (0, 1, 2, 4, and 8% NS) for 4 wk. The hen performance and egg quality (except yolk color) were not affected (P > 0.05) by the NS supplemental diets. Yolk color score was increased as NS supplementation in diets (P < 0.001), and peaked on about the seventh day in all NS supplemental groups. The concentration of total n-3 PUFA was increased (P < 0.001), while total n-6 PUFA and n-6/n-3 ratio were decreased (P < 0.001) in yolk with increasing NS levels in diets. The 8% NS group had highest docosahexaenoic acid (DHA) and total n-3 PUFA levels, reaching 111.6 mg DHA and 148.6 mg total n-3 PUFA per egg. Maximum DHA, total n-3 PUFA, very long-chain (LC-) n-3 PUFA, and LC-PUFA levels were all observed at day 13 of NS supplementation. In conclusion, dietary NS supplementation enriched yolk with n-3 PUFA (especially DHA) and enhanced yolk color score without adverse effects on performance and egg quality, and indicated the practical feasibility of partial replacement for soybean meal in laying hens diet.
Andrographolide, the main active component extracted from Andrographis paniculata (Burm.f.) Wall. ex Nees, exerts anti-inflammatory effects; however, the principal molecular mechanisms remain unclear. The objective of this study was to investigate the molecular mechanisms of Andrographolide in modifying lipopolysaccharide- (LPS-) induced signaling pathway in RAW264.7 cells. An in vitro model of inflammation was induced by LPS in mouse RAW264.7 cells in the presence of Andrographolide. The concentration and expression levels of proinflammatory cytokines were determined by an enzyme-linked immunosorbent assay (ELISA) and quantitative real-time polymerase chain reaction (qRT-PCR), respectively. The nuclear level of NF-κB was measured by an electrophoretic mobility shift assay (EMSA). The expression levels of NF-κB, p38, ERK, and JNK were determined by western blot. Andrographolide dose-dependently inhibited the release and mRNA expression of TNF-α, IL-6, and IL-1β in LPS-stimulated RAW264.7 cells. The nuclear level of p65 protein was decreased in Andrographolide treatment group. Western blot analysis showed that Andrographolide suppressed LPS-induced NF-κB activation and the phosphorylation of IkBa, ERK1/2, JNK, and p38. These results suggest that Andrographolide exerts an anti-inflammatory effect by inhibiting the activation of NF-κB/MAPK signaling pathway and the induction of proinflammatory cytokines.
Brassinosteroids (BRs) are a class of polyhydroxylated steroidal phytohormones in plants with similar structures to animals’ steroid hormones. Brassinosteroids regulate a wide range of physiological processes including plant growth, development and immunity. Brassinosteroid signalling and its integration with other signalling pathways have been investigated thoroughly at the molecular level.
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