BRI1 Research Articles

The pathogen-induced peptide CEP14 is perceived by the receptor-like kinase CEPR2 to promote systemic disease resistance in Arabidopsis.

Secreted plant peptides that trigger cellular signaling are crucial for plant growth, development, and adaptive responses to environmental stresses. In Arabidopsis (Arabidopsis thaliana), the C-TERMINALLY ENCODED PEPTIDE (CEP) family is a class of secreted signaling peptides that is phylogenetically divided into two groups: group I (CEP1-CEP12) and group II (CEP13-CEP15). Several group I CEP peptides regulate root architecture and nitrogen starvation responses, whereas the biological activity and roles of group II CEPs remain unknown. Here, we report that a group II CEP peptide, CEP14, functions as a pathogen-induced elicitor of Arabidopsis immunity. In response to infection by the bacterial pathogen Pseudomonas syringae, CEP14 expression was highly induced via the salicylic acid pathway in Arabidopsis leaves and roots. In the absence of pathogen attack, treatment of Arabidopsis plants with synthetic CEP14 peptides was sufficient to trigger immune responses. Genetic and biochemical analyses demonstrated that the receptor-like kinase CEP RECEPTOR 2 (CEPR2) perceives CEP14 to trigger plant immunity. The SOMATIC EMBRYOGENESIS RECEPTOR KINASES (SERKs) BRASSINOSTEROID INSENSITIVE 1-ASSOCIATED RECEPTOR KINASE 1 (BAK1) and SERK4 also participated in CEP14 perception by forming CEP14-induced complexes with CEPR2. Overexpression of CEP14 largely enhanced Arabidopsis resistance to P. syringae, while CEP14 or CEPR2 mutation significantly attenuated Arabidopsis systemic resistance to P. syringae. Taken together, our data reveal that the pathogen-induced CEP14 peptide, which is perceived by the CEPR2-BAK1/SERK4 receptor complexes, acts as an endogenous elicitor to promote systemic disease resistance in Arabidopsis.

The HAT1 transcription factor regulates photomorphogenesis and skotomorphogenesis via phytohormone levels.

Plants dynamically modulate their growth and development to acclimate to the fluctuating light environment via a complex phytohormone network. However, the dynamic molecular regulatory mechanisms underlying how plants regulate phytohormones during skotomorphogenesis and photomorphogenesis are largely unknown. Here, we identified a HD-ZIP II transcription factor, HOMEODOMAIN ARABIDOPSIS THALIANA1 (HAT1), as a key node that modulates the dose effects of brassinosteroids (BR) and auxin on hypocotyl growth during skotomorphogenesis and photomorphogenesis. Compared with the wild-type (Col-0), both HAT1 loss of function and its overexpression led to disrupted photomorphogenic and skotomorphogenic hypocotyl growth. HAT1 overexpression (HAT1OX) plants displayed longer hypocotyls in the light but shorter hypocotyls in darkness, whereas the triple mutant hat1hat2hat3 showed the opposite phenotype. Furthermore, we found that CONSTITUTIVE PHOTOMORPHOGENIC 1 (COP1) interacted with dephosphorylated HAT1 and facilitated the degradation of HAT1 by ubiquitination in darkness, while HAT1 was phosphorylated and stabilized by BRASSINOSTEROID INSENSITIVE2 (BIN2) in the light. Interestingly, we observed distinct dose-dependent effects of BR and auxin on hypocotyl elongation under varying light conditions and that HAT1 functioned as a key node in this process. The shorter hypocotyl of HAT1OX in darkness was due to the inhibition of BR biosynthetic gene BRASSINOSTEROID-6-OXIDASE2 (BR6OX2) expression to reduce BRs content, while brassinolide (BL) treatment alleviated this growth repression. In the light, HAT1 inhibited BR biosynthesis but enhanced auxin signaling by directly repressing IAA3/SHORT HYPOCOTYL 2 (SHY2) expression. Our findings uncover a dual function of HAT1 in regulating BR biosynthesis and auxin signaling that is crucial for ensuring proper skotomorphogenic and photomorphogenic growth.

A receptor for dual ligands governs plant immunity and hormone response and is targeted by a nematode effector

In this study, we show that the potato (Solanum tuberosum) pattern recognition receptor (PRR) NEMATODE-INDUCED LEUCINE-RICH REPEAT (LRR)-RLK1 (StNILR1) functions as a dual receptor, recognizing both nematode-associated molecular pattern ascaroside #18 (Ascr18) and plant hormone brassinosteroid (BR) to activate two different physiological outputs: pattern-triggered immunity (PTI) and BR response. Ascr18/BR-StNILR1 signaling requires the coreceptor potato BRASSINOSTEROID INSENSITIVE 1-ASSOCIATED RECEPTOR KINASE 1 (StBAK1) and perception of either ligand strengthens StNILR1 interaction with StBAK1 in plant cells. Significantly, the parasitically successful potato cyst nematode (Globodera pallida) utilizes the effector RHA1B, which is a functional ubiquitin ligase, to target StNILR1 for ubiquitination-mediated proteasome-dependent degradation, thereby countering Ascr18/BR-StNILR1-mediated PTI in potato and facilitating nematode parasitism. These findings broaden our understanding of PRR specificity and reveal a nematode parasitic mechanism that targets a PTI signaling pathway.

Natural variation in maize ZmLecRK1 fine-tunes co-receptor interactions to boost immunity

Pattern recognition receptors (PRRs) are integral to plant immunity, functioning as the first line of defense against pathogens. Among these, receptor kinases (RKs) play a critical role in recognizing external signals and initiating immune responses. Recent studies by Li et al. (2024) have identified the G-type lectin receptor kinase ZmLecRK1 in maize as essential for resistance to Pythium aphanidermatum and other fungal pathogens. A key finding is that a resistant variant of ZmLecRK1, which carries an alanine at position 404, has emerged in maize, while the ancestral form, with a serine at this position, is conserved across most grasses. This amino acid substitution significantly influences the interaction with the co-receptor BRASSINOSTEROID INSENSITIVE 1-ASSOCIATED RECEPTOR KINASE 1 (BAK1), enhancing immune complex formation and subsequent defense signaling. This work underscores the importance of genetic variation in enhancing disease resistance, offering potential strategies for crop improvement through targeted genetic modification.

CNGC20 plays dual roles in regulating plant growth and immunity in Brassica napus

Inflorescence architecture is determined by inflorescence length, branch angles and the density of siliques, which affects planting density, lodging resistance and mechanical operation in rapeseed. However, the molecular mechanisms controlling inflorescence architecture are poorly understood, restricting the progress of breeding varieties with ideal plant architecture in oilseed rape. In this study, we have identified and characterized a rapeseed inflorescence development mutant, reduced inflorescence length (ril), which exhibits determinate and shortened inflorescences, reduced plant height, compact branches, and increased silique density. Through BSA-seq and map-based cloning, we find that RIL encodes a cyclic nucleotide-gated channel 20 (BnaA01.CNGC20). A substitution of proline at the 304th position to leucine (P304L) was identified in the conserved transmembrane domain of BnaA01.CNGC20. This P304L substitution neither affects the subcellular localization and self-assembly of BnaA01.CNGC20, nor disrupts the interactions with BRASSINOSTEROID INSENSITIVE 1-associated receptor kinase 1 (BAK1), which interacts with CNGC20 and phosphorylates it to regulate Ca2+ channel stability. However, the P304L substitution increases channel activity and Ca2+ influx, which in turn induces immune responses such as cell death, H2O2 accumulation, upregulation of pathogenesis-related genes, and pattern-triggered immunity. The enhanced immunity improves the resistance to Leptosphaeria biglobosa and Sclerotinia sclerotiorum. Transcriptome analysis further revealed that CNGC20 plays dual roles in regulating plant growth and immunity via the brassinosteroid and auxin signaling pathways. The findings in this study provide deeper insights into the intricate relationship between cytosolic Ca2+ level and plant development and immunity, as well as the trade-off between immunity and the performance of yield-related traits in the heterozygous plants (+/ril), which may serve as a guide for balancing yield and disease resistance in oilseed rape breeding.

The brassinosteroid receptor gene BRI1 safeguards cell-autonomous brassinosteroid signaling across tissues.

Brassinosteroid signaling is essential for plant growth as exemplified by the dwarf phenotype of loss-of-function mutants in BRASSINOSTEROID INSENSITIVE 1 (BRI1), a ubiquitously expressed Arabidopsis brassinosteroid receptor gene. Complementation of brassinosteroid-blind receptor mutants by BRI1 expression with various tissue-specific promoters implied that local brassinosteroid signaling may instruct growth non-cell autonomously. Here, we performed such rescues with a panel of receptor variants and promoters, in combination with tissue-specific transgene knockouts. Our experiments demonstrate that brassinosteroid receptor expression in several tissues is necessary but not sufficient for rescue. Moreover, complementation with tissue-specific promoters requires the genuine BRI1 gene body sequence, which confers ubiquitous expression of trace receptor amounts that are sufficient to promote brassinosteroid-dependent root growth. Our data, therefore, argue for a largely cell-autonomous action of brassinosteroid receptors.

Phosphorylation of the transcription factor SlBIML1 by SlBIN2 kinases delays flowering in tomato.

Brassinosteroids (BRs) are well known for their important role in the regulation of plant growth and development. Plants with deficiency in BR signaling show delayed plant development and exhibit late flowering phenotypes. However, the precise mechanisms involved in this process require investigation. In this study, we cloned homologs of BRASSINOSTEROID INSENSITIVE 2 (SlBIN2), the GSK3-like protein kinase in tomato (Solanum lycopersicum). We characterized growth-related processes and phenotypic changes in the transgenic lines and found that SlBIN2s transgenic lines have delayed development and slow growing phenotypes. SlBIN2s work redundantly to negatively regulate BR signaling in tomato. Furthermore, the transcription factor SlBIN2.1-INTERACTING MYB-LIKE 1 (SlBIML1) was identified as a downstream substrate of SlBIN2s that SlBIN2s interact with and phosphorylate to synergistically regulate tomato developmental processes. Specifically, SlBIN2s modulated protein stability of SlBIML1 by phosphorylating multiple amino acid residues, including the sites Thr266 and Thr280. This study reveals a branch of the BR signaling pathway that regulates the vegetative growth phase and delays floral transition in tomato without the feedback affecting BR signaling. This information enriches our understanding of the downstream transduction pathway of BR signaling and provides potential targets for adjusting tomato flowering time.

YELLOW, SERRATED LEAF is essential for cotyledon vein patterning in Arabidopsis.

Venation develops complex patterns within the leaves of angiosperms, and the mechanism of leaf vein patterning remains poorly understood. Here, we report a spontaneous mutant that exhibits yellow serrated leaves and defective cotyledon vein patterning. We mapped and cloned the relevant gene YELLOW, SERRATED LEAF (YSL), a previously unreported gene in plants. YSL interacts with VH1-interacting kinase (VIK), a protein that functions in cotyledon venation development. VIK is a vascular-specific adaptor protein kinase that interacts with another vascular developmental protein, VASCULAR HIGHWAY1 (VH1)/BRASSINOSTEROID INSENSITIVE 1-LIKE 2 (BRL2), which is a receptor-like kinase of the BRASSINOSTEROID INSENSITIVE 1 (BRI1) family. Mutation of YSL affects the auxin response and the expression of auxin-related genes in Arabidopsis (Arabidopsis thaliana). Our results reveal that YSL affects cotyledon vein patterning by interacting with VIK in Arabidopsis.

The brassinosteroid receptor StBRI1 promotes tuber development by enhancing plasma membrane H+-ATPase activity in potato.

The brassinosteroid (BR) receptor BRASSINOSTEROID-INSENSITIVE 1 (BRI1) plays a critical role in plant growth and development. Although much is known about how BR signaling regulates growth and development in many crop species, the role of StBRI1 in regulating potato (Solanum tuberosum) tuber development is not well understood. To address this question, a series of comprehensive genetic and biochemical methods were applied in this investigation. It was determined that StBRI1 and Solanum tuberosum PLASMA MEMBRANE (PM) PROTON ATPASE2 (PHA2), a PM-localized proton ATPase, play important roles in potato tuber development. The individual overexpression of StBRI1 and PHA2 led to a 22% and 25% increase in tuber yield per plant, respectively. Consistent with the genetic evidence, in vivo interaction analysis using double transgenic lines and PM H+-ATPase activity assays indicated that StBRI1 interacts with the C-terminus of PHA2, which restrains the intramolecular interaction of the PHA2 C-terminus with the PHA2 central loop to attenuate autoinhibition of PM H+-ATPase activity, resulting in increased PHA2 activity. Furthermore, the extent of PM H+-ATPase autoinhibition involving phosphorylation-dependent mechanisms corresponds to phosphorylation of the penultimate Thr residue (Thr-951) in PHA2. These results suggest that StBRI1 phosphorylates PHA2 and enhances its activity, which subsequently promotes tuber development. Altogether, our results uncover a BR-StBRI1-PHA2 module that regulates tuber development and suggest a prospective strategy for improving tuberous crop growth and increasing yield via the cell surface-based BR signaling pathway.

A computational analysis revealed BES1 transcription factor and β-amylase as crosstalk elements in Upland cotton species (Gossypium sp.)

Cotton is a resilient and multipurpose crop, meeting major of the world’s textile needs while also yielding byproducts like edible oil and animal feed. Starch plays a crucial role in cotton fabric production. It enhances fabric strength by forming a protective film around cotton fibers, making them more resistant to wear and tear. BES1 (brassinosteroid insensitive 1) is a key regulator in brassinosteroid signaling. It controls thousands of target genes involved in development processes. Interestingly, two β-amylase proteins (BAM7 and BAM8) are part of the BES1 family, despite their primary function as β-amylases. β-Amylase (BAM) and BES1 are two gene families with functional and regulatory roles in controlling shoot growth and development by mediating brassinosteroid effects. They share similar domains and participate in various biological processes, tolerance and responses to stresses like salt and drought. In a computational analysis comparing Arabidopsis and Gossypium species, BAM and BES1 were characterized. BES1 genes were grouped into four clusters based on the comparison of the two species. Two clusters corresponded to BAM7 and BAM8, while the other two clusters were associated with BES1. The conserved nucleotide domain sequence is GCTGGATGG. Short tandem repeats include TG and TTG, which can serve as molecular markers. BES1 is specifically linked to cellulose and fiber production and holds promise as a candidate for plant selection and breeding in Gossypium (cotton).

Phenotypic and transcriptomics characterization uncovers genes underlying tuber yield traits and gene expression marker development in potato under aeroponics.

Transcriptome analysis in potato varieties revealed genes associated with tuber yield-related traits and developed gene expression markers. This study aimed to identify genes involved in high tuber yield and its component traits in test potato varieties (Kufri Frysona, Kufri Khyati, and Kufri Mohan) compared to control (Kufri Sutlej). The aeroponic evaluation showed significant differences in yield-related traits in the varieties. Total RNA sequencing was performed using tuber and leaf tissues on the Illumina platform. The high-quality reads (QV > 25) mapping with the reference potato genomes revealed statistically significant (P < 0.05) differentially expressed genes (DEGs) into two categories: up-regulated (> 2 Log2 fold change) and down-regulated (< -2 Log2 fold change). DEGs were characterized by Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. Collectively, we identified genes participating in sugar metabolism, stress response, transcription factors, phytohormones, kinase proteins, and other genes greatly affecting tuber yield and its related traits. A few selected genes were UDP-glucose glucosyltransferase, glutathion S-transferase, GDSL esterase/lipase, transcription factors (MYB, WRKY, bHLH63, and BURP), phytohormones (auxin-induced protein X10A, and GA20 oxidase), kinase proteins (Kunitz-type tuber invertase inhibitor, BRASSINOSTEROID INSENSITIVE 1-associated receptor kinase 1) and laccase. Based on the selected 17 peptide sequences representing 13 genes, a phylogeny tree and motifs were analyzed. Real time-quantitative polymerase chain reaction (RT-qPCR) analysis was used to validate the RNA-seq results. RT-qPCR based gene expression markers were developed for the genes such as 101kDa heat shock protein, catechol oxidase B chloroplastic, cysteine protease inhibitor 1, Kunitz-type tuber invertase inhibitor, and laccase to identify high yielding potato genotypes. Thus, our study paved the path for potential genes associated with tuber yield traits in potato under aeroponics.

Leveraging coevolutionary insights and AI-based structural modeling to unravel receptor–peptide ligand-binding mechanisms

Secreted signaling peptides are central regulators of growth, development, and stress responses, but specific steps in the evolution of these peptides and their receptors are not well understood. Also, the molecular mechanisms of peptide-receptor binding are only known for a few examples, primarily owing to the limited availability of protein structural determination capabilities to few laboratories worldwide. Plants have evolved a multitude of secreted signaling peptides and corresponding transmembrane receptors. Stress-responsive SERINE RICH ENDOGENOUS PEPTIDES (SCOOPs) were recently identified. Bioactive SCOOPs are proteolytically processed by subtilases and are perceived by the leucine-rich repeat receptor kinase MALE DISCOVERER 1-INTERACTING RECEPTOR-LIKE KINASE 2 (MIK2) in the model plant Arabidopsis thaliana. How SCOOPs and MIK2 have (co)evolved, and how SCOOPs bind to MIK2 are unknown. Using in silico analysis of 350 plant genomes and subsequent functional testing, we revealed the conservation of MIK2 as SCOOP receptor within the plant order Brassicales. We then leveraged AI-based structural modeling and comparative genomics to identify two conserved putative SCOOP-MIK2 binding pockets across Brassicales MIK2 homologues predicted to interact with the "SxS" motif of otherwise sequence-divergent SCOOPs. Mutagenesis of both predicted binding pockets compromised SCOOP binding to MIK2, SCOOP-induced complex formation between MIK2 and its coreceptor BRASSINOSTEROID INSENSITIVE 1-ASSOCIATED KINASE 1, and SCOOP-induced reactive oxygen species production, thus, confirming our in silico predictions. Collectively, in addition to revealing the elusive SCOOP-MIK2 binding mechanism, our analytic pipeline combining phylogenomics, AI-based structural predictions, and experimental biochemical and physiological validation provides a blueprint for the elucidation of peptide ligand-receptor perception mechanisms.

ATBS1-INTERACTING FACTOR 2 Positively Regulates Freezing Tolerance via INDUCER OF CBF EXPRESSION 1/C-REPEAT BINDING FACTOR-Induced Cold Acclimation Pathway.

The INDUCER OF CBF EXPRESSION 1/C-REPEAT BINDING FACTOR (ICE1/CBF) pathway plays a crucial role in plant responses to cold stress, impacting growth and development. Here, we demonstrated that ATBS1-INTERACTING FACTOR 2 (AIF2), a non-DNA-binding basic helix-loop-helix transcription factor, positively regulates freezing tolerance through the ICE1/CBF-induced cold tolerance pathway in Arabidopsis. Cold stress transcriptionally upregulated AIF2 expression and induced AIF2 phosphorylation, thereby stabilizing the AIF2 protein during early stages of cold acclimation. The AIF2 loss-of-function mutant, aif2-1, exhibited heightened sensitivity to freezing before and after cold acclimation. In contrast, ectopic expression of AIF2, but not the C-terminal-deleted AIF2 variant, restored freezing tolerance. AIF2 enhanced ICE1 stability during cold acclimation and promoted the transcriptional expression of CBFs and downstream cold-responsive genes, ultimately enhancing plant tolerance to freezing stress. MITOGEN-ACTIVATED PROTEIN KINASES 3 and 6 (MPK3/6), known negative regulators of freezing tolerance, interacted with and phosphorylated AIF2, subjecting it to protein degradation. Furthermore, transient co-expression of MPK3/6 with AIF2 and ICE1 downregulated AIF2/ICE1-induced transactivation of CBF2 expression. AIF2 interacted preferentially with BRASSINOSTEROID-INSENSITIVE 2 (BIN2) and MPK3/6 during the early and later stages of cold acclimation, respectively, thereby differentially regulating AIF2 activity in a cold acclimation time-dependent manner. Moreover, AIF2 acted additively in a gain-of-function mutant of BRASSINAZOLE-RESISTANT 1 (BZR1; bzr1-1D) and a triple knockout mutant of BIN2 and its homologs (bin2bil1bil2) to induce CBFs-mediated freezing tolerance. This suggests that cold-induced AIF2 coordinates freezing tolerance along with BZR1 and BIN2, key positive and negative components, respectively, of brassinosteroid signaling pathways.

Post-translational Regulation of BRI1-EMS Suppressor 1 and Brassinazole-Resistant 1.

Brassinosteroid-insensitive 1 (BRI1)-EMS suppressor 1 (BES1) and Brassinazole-resistant 1 (BZR1) are two highly similar master transcription factors of the brassinosteroid (BR) signaling pathway that regulates a variety of plant growth and development processes as well as stress responses. Previous genetic and biochemical analyses have established a complex regulatory network to control the two transcription factors. This network includes coordination with other transcription factors and interactors, multiple post-translational modifications (PTMs) and differential subcellular localizations. In this review, we systematically detail the functions and regulatory mechanisms of various PTMs: phosphorylation/dephosphorylation, ubiquitination/deubiquitination, SUMOylation/deSUMOylation and oxidation/reduction, in regulating the subcellular localization, protein stability and the transcriptional activity of BES1/BZR1. We also discuss the current knowledge about the BES1/BZR1 interactors mediating the dynamic nucleocytoplasmic shuttling of BES1 and BZR1.

SERK3A and SERK3B could be S-nitrosylated and enhance the salt resistance in tomato seedlings

Salinity hinders plant growth and development, resulting in reduced crop yields and diminished crop quality. Nitric oxide (NO) and brassinolides (BR) are plant growth regulators that coordinate a plethora of plant physiological responses. Nonetheless, the way in which these factors interact to affect salt tolerance is not well understood. BR is perceived by the BR receptor BRASSINOSTEROID INSENSITIVE 1 (BRI1) and its co-receptor BRI1-associated kinase 1 (BAK1) to form the receptor complex, eventually inducing BR-regulated responses. To response stress, a wide range of NO-mediated protein modifications is undergone in eukaryotic cells. Here, we showed that BR participated in NO-enhanced salt tolerance of tomato seedlings (Solanum lycopersicum cv. Micro-Tom) and NO may activate BR signaling under salt stress, which was related to NO-mediated S-nitrosylation. Further, in vitro and in vivo results suggested that BAK1 (SERK3A and SERK3B) was S-nitrosylated, which was inhibited under salt condition and enhanced by NO. Accordingly, knockdown of SERK3A and SERK3B reduced the S-nitrosylation of BAK1 and resulted in a compromised BR response, thereby abolishing NO-induced salt tolerance. Besides, we provided evidence for the interaction between BRI1 and SERK3A/SERK3B. Meanwhile, NO enhanced BRI1-SERK3A/SERK3B interaction. These results imply that NO-mediated S-nitrosylation of BAK1 enhances the interaction BRI1-BAK1, facilitating BR response and subsequently improving salt tolerance in tomato. Our findings illustrate a mechanism by which redox signaling and BR signaling coordinate plant growth in response to abiotic stress.

MiR394 modulates brassinosteroid signaling to regulate hypocotyl elongation in Arabidopsis.

The interplay between microRNAs (miRNAs) and phytohormones allows plants to integrate multiple internal and external signals to optimize their survival of different environmental conditions. Here, we report that miR394 and its target gene LEAF CURLING RESPONSIVENESS (LCR), which are transcriptionally responsive to BR, participate in BR signaling to regulate hypocotyl elongation in Arabidopsis thaliana. Phenotypic analysis of various transgenic and mutant lines revealed that miR394 negatively regulates BR signaling during hypocotyl elongation, whereas LCR positively regulates this process. Genetically, miR394 functions upstream of BRASSINOSTEROID INSENSITIVE2 (BIN2), BRASSINAZOLEs RESISTANT1 (BZR1), and BRI1-EMS-SUPPRESSOR1 (BES1), but interacts with BRASSINOSTEROID INSENSITIVE1 (BRI1) and BRI1 SUPRESSOR PROTEIN (BSU1). RNA-sequencing analysis suggested that miR394 inhibits BR signaling through BIN2, as miR394 regulates a significant number of genes in common with BIN2. Additionally, miR394 increases the accumulation of BIN2 but decreases the accumulation of BZR1 and BES1, which are phosphorylated by BIN2. MiR394 also represses the transcription of PACLOBUTRAZOL RESISTANCE1/5/6 and EXPANSIN8, key genes that regulate hypocotyl elongation and are targets of BZR1/BES1. These findings reveal a new role for a miRNA in BR signaling in Arabidopsis.

Bona Fide Plant Steroid Receptors are Innovated in Seed Plants and Angiosperms through Successive Whole-Genome Duplication Events.

Whole-genome duplication (WGD) events are widespread in plants and animals, thus their long-term evolutionary contribution has long been speculated, yet a specific contribution is difficult to verify. Here, we show that ɛ-WGD and ζ-WGD contribute to the origin and evolution of bona fide brassinosteroid (BR) signaling through the innovation of active BR biosynthetic enzymes and active BR receptors from their respective ancestors. We found that BR receptors BRI1 (BR INSENSITIVE 1) and BRL1/3 (BRI1-LIKES 1/3) derived by ɛ-WGD and ζ-WGD, which occurred in the common ancestor of angiosperms and seed plants, respectively, while orphan BR receptor BRL2 first appeared in stomatophytes. Additionally, CYP85A enzymes synthesizing the bioactive BRs derived from a common ancestor of seed plants, while its sister enzymes CYP90 synthesizing BR precursors presented in all land plants, implying possible ligand-receptor coevolution. Consistently, the island domains (IDs) responsible for BR perception in BR receptors were most divergent among different receptor branches, supporting ligand-driven evolution. As a result, BRI1 was the most diversified BR receptor in angiosperms. Importantly, relative to the BR biosynthetic DET2 gene presented in all land plants, BRL2, BRL1/3 and BRI1 had high expression in vascular plants ferns, gymnosperms and angiosperms, respectively. Notably, BRI1 is the most diversified BR receptor with the most abundant expression in angiosperms, suggesting potential positive selection. Therefore, WGDs initiate a neofunctionalization process diverged by ligand-perception and transcriptional expression, which might optimize both BR biosynthetic enzymes and BR receptors, likely contributing to the evolution of land plants, especially seed plants and angiosperms.

Effector Cs02526 from Ciboria shiraiana induces cell death and modulates plant immunity.

Sclerotinia disease is one of the most devastating fungal diseases worldwide, as it reduces the yields of many economically important crops. Pathogen-secreted effectors play crucial roles in infection processes. However, key effectors of Ciboria shiraiana, the pathogen primarily responsible for sclerotinia disease in mulberry (Morus spp.), remain poorly understood. In this study, we identified and functionally characterized the effector Cs02526 in C. shiraiana and found that Cs02526 could induce cell death in a variety of plants. Moreover, Cs02526-induced cell death was mediated by the central immune regulator brassinosteroid insensitive 1-associated receptor kinase 1, dependent on a 67-amino acid fragment. Notably, Cs02526 homologs were widely distributed in hemibiotrophic and necrotrophic phytopathogenic fungi, but the homologs failed to induce cell death in plants. Pretreatment of plants with recombinant Cs02526 protein enhanced resistance against both C. shiraiana and Sclerotinia sclerotiorum. Furthermore, the pathogenicity of C. shiraiana was diminished upon spraying plants with synthetic dsRNA-Cs02526. In conclusion, our findings highlight the cell death-inducing effector Cs02526 as a potential target for future biological control strategies against plant diseases.

Allosteric activation of the co-receptor BAK1 by the EFR receptor kinase initiates immune signaling.

Transmembrane signaling by plant receptor kinases (RKs) has long been thought to involve reciprocal trans-phosphorylation of their intracellular kinase domains. The fact that many of these are pseudokinase domains, however, suggests that additional mechanisms must govern RK signaling activation. Non-catalytic (pseudo)kinase signaling mechanisms have been described in metazoans, but information is scarce for plants. Recently, a non-catalytic function was reported for the leucine-rich repeat (LRR)-RK subfamily XIIa member EFR (ELONGATION FACTOR TU RECEPTOR) and phosphorylation-dependent conformational changes were proposed to regulate signaling of RKs with non-RD kinase domains. Here, using EFR as a model, we describe a non-catalytic activation mechanism for LRR-RKs with non-RD kinase domains. EFR is an active kinase, but a kinase-dead variant retains the ability to enhance catalytic activity of its co-receptor kinase BAK1/SERK3 (BRASSINOSTEROID INSENSITIVE 1-ASSOCIATED KINASE 1/SOMATIC EMBRYOGENESIS RECEPTOR KINASE 3). Applying hydrogen-deuterium exchange mass spectrometry (HDX-MS) analysis and designing homology-based intragenic suppressor mutations, we provide evidence that the EFR kinase domain must adopt its active conformation in order to activate BAK1 allosterically, likely by supporting αC-helix positioning in BAK1. Our results suggest a conformational toggle model for signaling, in which BAK1 first phosphorylates EFR in the activation loop to stabilize its active conformation, allowing EFR in turn to allosterically activate BAK1.

Identifying receptor-like kinases that enable Caulobacter RHG1 to promote plant growth in Arabidopsis thaliana

ABSTRACT Plants express an array of receptor-like kinases (RLKs) to control development and communicate with their environment. Many RLKs are uncharacterized and some of them are expected to regulate plant responses to plant growth-promoting rhizobacteria (PGPR). Despite documented effects induced by Caulobacter RHG1, the underlying signaling pathways and the involved RLKs remain uncharted. Through a targeted RLK mutant screening, we aimed to decipher the receptors that steer the Caulobacter RHG1-induced growth promotion in Arabidopsis thaliana. We identified four RLKs that are pivotal in the RHG1-Arabidopsis interaction, including the coreceptors SOMATIC EMBRYOGENESIS RECEPTOR-LIKE KINASE 1 (SERK1) and BRASSINOSTEROID INSENSITIVE 1-ASSOCIATED KINASE 1 (BAK1/SERK3), which act redundantly in the RHG1-Arabidopsis interaction, possibly by interplaying with the unknown RLK AT3G28040 and the immunity-related ELONGATION FACTOR-TU RECEPTOR (EFR). These results shed new light on the molecular dynamics orchestrating plant responses to PGPR, and concurrently contribute a crucial piece to the intricate puzzle of RLK interactions. Key policy highlights Four RLKs; BAK1, SERK1, EFR, and AT3G28040 (RRHG) are involved in the RHG1-Arabidopsis interaction. BAK1 and SERK1, two well-described co-receptors, act redundantly and play a pivotal role in the RHG1-driven growth promotion, possibly by interplaying with the unknown RLK AT3G28040 and the immunity-related RLK EFR. Most known development – and immunity-related RLKs barely influence RHG1-driven plant growth promotion in Arabidopsis.