Brassinosteroid Insensitive 1-associated Receptor Kinase Research Articles

Regulation of sugar transporter activity for antibacterial defense in Arabidopsis.

Microbial pathogens strategically acquire metabolites from their hosts during infection. Here we show that the host can intervene to prevent such metabolite loss to pathogens. Phosphorylation-dependent regulation of sugar transport protein 13 (STP13) is required for antibacterial defense in the plant Arabidopsis thaliana STP13 physically associates with the flagellin receptor flagellin-sensitive 2 (FLS2) and its co-receptor BRASSINOSTEROID INSENSITIVE 1-associated receptor kinase 1 (BAK1). BAK1 phosphorylates STP13 at threonine 485, which enhances its monosaccharide uptake activity to compete with bacteria for extracellular sugars. Limiting the availability of extracellular sugar deprives bacteria of an energy source and restricts virulence factor delivery. Our results reveal that control of sugar uptake, managed by regulation of a host sugar transporter, is a defense strategy deployed against microbial infection. Competition for sugar thus shapes host-pathogen interactions.

Specific control of Arabidopsis BAK1/SERK4-regulated cell death by protein glycosylation.

Precise control of cell death is essential for the survival of all organisms. Arabidopsis thaliana BRASSINOSTEROID INSENSITIVE 1-associated receptor kinase 1 (BAK1) and somatic embryogenesis receptor kinase 4 (SERK4) redundantly and negatively regulate cell death through elusive mechanisms. By deploying a genetic screen for suppressors of cell death triggered by virus-induced gene silencing of BAK1/SERK4 on Arabidopsis knockout collections, we identified STT3a, a protein involved in N-glycosylation modification, as an important regulator of bak1/serk4 cell death. Systematic investigation of glycosylation pathway and endoplasmic reticulum (ER) quality control (ERQC) components revealed distinct and overlapping mechanisms of cell death regulated by BAK1/SERK4 and their interacting protein BIR1. Genome-wide transcriptional analysis revealed the activation of members of cysteine-rich receptor-like kinase (CRK) genes in the bak1/serk4 mutant. Ectopic expression of CRK4 induced STT3a/N-glycosylation-dependent cell death in Arabidopsis and Nicotiana benthamiana. Therefore, N-glycosylation and specific ERQC components are essential to activate bak1/serk4 cell death, and CRK4 is likely to be among client proteins of protein glycosylation involved in BAK1/SERK4-regulated cell death.

Endophytic colonization of barley (Hordeum vulgare) roots by the nematophagous fungus Pochonia chlamydosporia reveals plant growth promotion and a general defense and stress transcriptomic response.

Plant crop yields are negatively conditioned by a large set of biotic and abiotic factors. An alternative to mitigate these adverse effects is the use of fungal biological control agents and endophytes. The egg-parasitic fungus Pochonia chlamydosporia has been traditionally studied because of its potential as a biological control agent of plant-parasitic nematodes. This fungus can also act as an endophyte in monocot and dicot plants, and has been shown to promote plant growth in different agronomic crops. An Affymetrix 22K Barley GeneChip was used in this work to analyze the barley root transcriptomic response to P. chlamydosporia root colonization. Functional gene ontology (GO) and gene set enrichment analyses showed that genes involved in stress response were enriched in the barley transcriptome under endophytism. An 87.5% of the probesets identified within the abiotic stress response group encoded heat shock proteins. Additionally, we found in our transcriptomic analysis an up-regulation of genes implicated in the biosynthesis of plant hormones, such as auxin, ethylene and jasmonic acid. Along with these, we detected induction of brassinosteroid insensitive 1-associated receptor kinase 1 (BR1) and other genes related to effector-triggered immunity (ETI) and pattern-triggered immunity (PTI). Our study supports at the molecular level the growth-promoting effect observed in plants endophytically colonized by P. chlamydosporia, which opens the door to further studies addressing the capacity of this fungus to mitigate the negative effects of biotic and abiotic factors on plant crops.

An Overdose of the Arabidopsis Coreceptor BRASSINOSTEROID INSENSITIVE1-ASSOCIATED RECEPTOR KINASE1 or Its Ectodomain Causes Autoimmunity in a SUPPRESSOR OF BIR1-1-Dependent Manner.

The membrane-bound Brassinosteroid insensitive1-associated receptor kinase1 (BAK1) is a common coreceptor in plants and regulates distinct cellular programs ranging from growth and development to defense against pathogens. BAK1 functions through binding to ligand-stimulated transmembrane receptors and activating their kinase domains via transphosphorylation. In the absence of microbes, BAK1 activity may be suppressed by different mechanisms, like interaction with the regulatory BIR (for BAK1-interacting receptor-like kinase) proteins. Here, we demonstrated that BAK1 overexpression in Arabidopsis (Arabidopsis thaliana) could cause detrimental effects on plant development, including growth arrest, leaf necrosis, and reduced seed production. Further analysis using an inducible expression system showed that BAK1 accumulation quickly stimulated immune responses, even under axenic conditions, and led to increased resistance to pathogenic Pseudomonas syringae pv tomato DC3000. Intriguingly, our study also revealed that the plasma membrane-associated BAK1 ectodomain was sufficient to induce autoimmunity, indicating a novel mode of action for BAK1 in immunity control. We postulate that an excess of BAK1 or its ectodomain could trigger immune receptor activation in the absence of microbes through unbalancing regulatory interactions, including those with BIRs. Consistently, mutation of suppressor of BIR1-1, which encodes an emerging positive regulator of transmembrane receptors in plants, suppressed the effects of BAK1 overexpression. In conclusion, our findings unravel a new role for the BAK1 ectodomain in the tight regulation of Arabidopsis immune receptors necessary to avoid inappropriate activation of immunity.

ArabidopsisRECEPTOR-LIKE PROTEIN30 and Receptor-Like Kinase SUPPRESSOR OF BIR1-1/EVERSHED Mediate Innate Immunity to Necrotrophic Fungi

Effective plant defense strategies rely in part on the perception of non-self determinants, so-called microbe-associated molecular patterns (MAMPs), by transmembrane pattern recognition receptors leading to MAMP-triggered immunity. Plant resistance against necrotrophic pathogens with a broad host range is complex and yet not well understood. Particularly, it is unclear if resistance to necrotrophs involves pattern recognition receptors. Here, we partially purified a novel proteinaceous elicitor called sclerotinia culture filtrate elicitor1 (SCFE1) from the necrotrophic fungal pathogen Sclerotinia sclerotiorum that induces typical MAMP-triggered immune responses in Arabidopsis thaliana. Analysis of natural genetic variation revealed five Arabidopsis accessions (Mt-0, Lov-1, Lov-5, Br-0, and Sq-1) that are fully insensitive to the SCFE1-containing fraction. We used a forward genetics approach and mapped the locus determining SCFE1 sensitivity to receptor-like protein30 (RLP30). We also show that SCFE1-triggered immune responses engage a signaling pathway dependent on the regulatory receptor-like kinases brassinosteroid insensitive1-associated receptor kinase1 (BAK1) and Suppressor of BIR1-1/evershed (SOBIR1/EVR). Mutants of RLP30, BAK1, and SOBIR1 are more susceptible to S. sclerotiorum and the related fungus Botrytis cinerea. The presence of an elicitor in S. sclerotiorum evoking MAMP-triggered immune responses and sensed by RLP30/SOBIR1/BAK1 demonstrates the relevance of MAMP-triggered immunity in resistance to necrotrophic fungi.

Profiling the differentially expressed genes in two rice varieties during rapid grain-filling stages

Grain filling is an important agronomic trait, which directly affects the final yield of rice. Partially filled and empty rice grains are among the factors that limit the yield of MR219, one of the highest yielding rice varieties in Malaysia. In this study, the NSF 20 K rice oligonucleotide array, which contains 20,000 70-mer oligonucleotide probes, was used for direct comparison of the transcriptomes of MR219 and MR84 (a rice variety that has higher percentage of filled grains compared to MR219), during rapid grain-filling period at 5 and 10 days after fertilization (DAF). A total of 155 and 233 genes were differentially expressed in MR219 compared to MR84 at 5 and 10 DAF, respectively; and 9 of these expression ratios were tested using quantitative real-time RT PCR. Among the differentially expressed genes identified were those encoding hexokinase, various sugar transporters, GSDL-like lipase/acylhydrolase, brassinosteroid-insensitive 1-associated receptor kinase 1 precursor and homeobox protein GLABRA2, which were analyzed by real-time RT PCR in this study. The differences demonstrated by these genes in their transcript levels and profiles, between the two rice varieties understudied at different stages of grain filling may contribute to the formulation of hypotheses toward the understanding of poor percentage of filled grains in MR219.

Contrasting cDNA-AFLP profiles between crown and leaf tissues of cold-acclimated wheat plants indicate differing regulatory circuitries for low temperature tolerance

Low-temperature (LT) tolerance in winter wheat (Triticum aestivum L.) is an economically important but complex trait. Four selected wheat genotypes, a winter hardy cultivar, Norstar, a tender spring cultivar, Manitou and two near-isogenic lines with Vrn-A1 (spring Norstar) and vrn-A1 (winter Manitou) alleles of Manitou and Norstar were cold-acclimated at 6°C and crown and leaf tissues were collected at 0, 2, 14, 21, 35, 42, 56 and 70days of cold acclimation. cDNA-AFLP profiling was used to determine temporal expression profiles of transcripts during cold-acclimation in crown and leaf tissues, separately to determine if LT regulatory circuitries in crown and leaf tissues could be delineated using this approach. Screening 64 primer combinations identified 4,074 and 2,757 differentially expressed transcript-derived fragments (TDFs) out of which 38 and 16% were up-regulated as compared to 3 and 6% that were down-regulated in crown and leaf tissues, respectively. DNA sequencing of TDFs revealed sequences common to both tissues including genes coding for DEAD-box RNA helicase, choline-phosphate cytidylyltransferase and delta-1-pyrroline carboxylate synthetase. TDF specific to crown tissues included genes coding for phospahtidylinositol kinase, auxin response factor protein and brassinosteroid insensitive 1-associated receptor kinase. In leaf, genes such as methylene tetrahydrofolate reductase, NADH-cytochrome b5 reductase and malate dehydrogenase were identified. However, 30 and 14% of the DNA sequences from the crown and leaf tissues, respectively, were hypothetical or unknown proteins. Cluster analysis of up-, down-regulated and unique TDFs, DNA sequence and real-time PCR validation, infer that mechanisms operating in crown and leaf tissue in response to LT are differently regulated and warrant further studies.

COE1, an LRR-RLK responsible for commissural vein pattern formation in rice

Leaf veins have a complex network pattern. Formation of this vein pattern has been widely studied as a model of tissue pattern formation in plants. To understand the molecular mechanism governing the vascular patterning process, we isolated the rice mutant, commissural vein excessive1 (coe1). The coe1 mutants had short commissural vein (CV) intervals and produced clustered CVs. Application of 1-N-naphthylphthalamic acid and brefeldin A decreased CV intervals, and application of 1-naphthaleneacetic acid increased CV intervals in wild-type rice; however, coe1 mutants were insensitive to these chemicals. COE1 encodes a leucine-rich repeat receptor-like kinase, whose amino acid sequence is similar to that of brassinosteroid-insensitive 1-associated receptor kinase 1 (BAK1), and which is localized at the plasma membrane. Because of the sequence similarity of COE1 to BAK1, we also examined the involvement of brassinosteroids in CV formation. Brassinolide, an active brassinosteroid, decreased the CV intervals of wild-type rice, and brassinazole, an inhibitor of brassinosteroid biosynthesis, increased the CV intervals of wild-type rice, but coe1 mutants showed insensitivity to these chemicals. These results suggest that auxin and brassinosteroids regulate CV intervals in opposite directions, and COE1 may regulate CV intervals downstream of auxin and brassinosteroid signals.

Regulation of Cell Death and Innate Immunity by Two Receptor-like Kinases in Arabidopsis

Upon recognition of bacterial flagellin, the plant receptor FLS2 heterodimerizes with brassinosteroid insensitive 1-associated receptor kinase 1 (BAK1) and activates plant defense responses. Because constitutive activation of defense responses is detrimental, plant resistance signaling pathways must be negatively controlled, although the mechanisms involved are unclear. We identified Arabidopsis BIR1 as a BAK1-interacting receptor-like kinase. Knocking out BIR1 leads to extensive cell death, activation of constitutive defense responses, and impairment in the activation of MPK4, a negative regulator of plant resistance (R) protein signaling, by flagellin. sobir1-1, a mutant obtained in a screen for suppressors of the bir1-1 phenotype, rescued cell death observed in bir1-1. SOBIR1 encodes another receptor-like kinase whose overexpression activates cell death and defense responses. Our data suggest that BIR1 negatively regulates multiple plant resistance signaling pathways, one of which is the SOBIR1-dependent pathway identified here.

Structural Characterization and Expression Analysis of the SERK/SERL Gene Family in Rice (Oryza sativa)

Somatic embryogenesis (SE) is the developmental restructuring of somatic cells towards the embryogenic pathway and forms the basis of cellular totipotency in angiosperms. With the availability of full-length cDNA sequences from Knowledge-based Oryza Molecular Biological Encylopedia (KOME), we identified the leucine-rich repeat receptor-like kinase (LRR-RLK) genes from rice (Oryza sativa), which also encompasses genes involved in regulating somatic embryogenesis. Eight out of eleven of the rice SERK and SERL (SERK-like) genes have the TIGR annotation as (putative) brassinosteroid insensitive 1-associated receptor kinase (precursor). Real-time polymerase chain reaction analysis was undertaken to quantify transcript levels of these 11 genes. Most of these genes were upregulated by brassinosteroids although only a few of these displayed auxin induction. The expression profile of these genes is nearly uniform in the zygotic embryogenic tissue, but the expression pattern is more complex in the somatic embryogenic tissue. It is likely that OsSERKs and OsSERLs may be involved in somatic embryogenesis and also perform a role in morphogenesis and various other plant developmental processes. Functional validation of these somatic embryogenesis receptor-like kinase genes may help in elucidating their precise functions in regulating various facets of plant development.

Characterization of a sugarcane (Saccharum spp.) gene homolog to the brassinosteroid insensitive1-associated receptor kinase 1 that is associated to sugar content

The present article reports on the characterization of ScBAK1, a leucine-rich repeat receptor-like kinase from sugarcane (Saccharum spp.), expressed predominantly in bundle-sheath cells of the mature leaf and potentially involved in cellular signaling cascades mediated by high levels of sugar in this organ. In this report, it was shown that the ScBAK1 sequence was similar to the brassinosteroid insensitive1-associated receptor kinase1 (BAK1). The putative cytoplasmatic domain of ScBAK1 contains all the amino acids characteristic of protein kinases, and the extracellular domain contains five leucine-rich repeats and a putative leucine zipper. Transcripts of ScBAK1 were almost undetectable in sugarcane roots or in any other sink tissue, but accumulated abundantly in the mature leaves. The ScBAK1 expression was higher in the higher sugar content individuals from a population segregating for sugar content throughout the growing season. In situ hybridization in sugarcane leaves showed that the ScBAK1 mRNA accumulated at much higher levels in bundle-sheath cells than in mesophyll cells. In addition, using biolistic bombardment of onion epidermal cells, it was shown that ScBAK1-GFP fusions were localized in the plasma membrane as predicted for a receptor kinase. All together, the present data indicate that ScBAK1 might be a receptor involved in the regulation of specific processes in bundle-sheath cells and in sucrose synthesis in mature sugarcane leaves.

Cell Signalling: The Merry Lives of BAK1

Plant receptor-like kinases characterised by leucine-rich repeats have been shown to play dual roles in seemingly unrelated biological processes, inviting comparison with TOLL-like receptors of animals.

BAK1 for Pathogen Response

BAK1 (brassinosteroid insensitive 1-associated receptor kinase 1) is best known and is named for its role as a leucine-rich repeat receptor-like kinase (LRR-RLK) involved in brassinosteroid signaling in Arabidopsis thaliana . Chinchilla et al . report that BAK1 also contributes to the response to pathogen-associated molecular patterns (PAMPs), such as those triggered by bacterial flagellin or elongation factor Tu (EF-Tu). Heese et al . identified BAK1 as a coimmunoprecipitation partner for Arabipdosis FLS2. Chinchilla et al . identified plants with insertions in the bak1 gene in a screen for genes that encode LRR-RLKs that produce plants with decreased sensitivity to the PAMP flagellin peptide flg22 (the growth of seedlings was not inhibited by flg22). The insertional mutant plants also showed decreased responsiveness to brassinosteroids; however, the defect in brassinosteroid signaling was not the cause of the defective PAMP response. Even when brassinosteroid signaling was restored by high concentrations of exogenous brassinolide, the bak1 mutant seedlings failed to exhibit growth inhibition in response to flg22. Both groups reported that stimulation of mitogen-activated protein kinase activity and the oxidative burst that are characteristic of the wild-type response to flg22 were diminished in bak1 mutant plants. Both groups also determined that BAK1 was not specific to the flagellin PAMP but appeared to play a role in triggering responses to various PAMPs. Heese et al . identified the Nicotiana benthamiana homolog of BAK1 and found that knockdown of the protein in this plant allowed enhanced growth of bacteria on the plants. Thus, BAK1 appears to be a promiscuous LRR-RLK, partnering with various ligand-binding receptors to trigger ligand-specific responses. D. Chinchilla, C. Zipfel, S. Robatzek, B. Kemmerling, T. Nürnberger, J. D. G. Jones, G. Felix, T. Boller, A flagellin-induced complex of the receptor FLS2 and BAK1 initiates plant defence. Nature 448 , 497-500 (2007). [PubMed] A. Heese, D. R. Hann, S. Gimenez-Ibanez, A. M. E. Jones, K. He, J. Li, J. I. Schroeder, S. C. Peck, J. P. Rathjen, The receptor-like kinase SERK3/BAK1 is a central regulator of innate immunity in plants. Proc. Natl. Acad. Sci. U.S.A. 104 , 12217-12222 (2007). [Abstract] [Full Text]