Nat Plants , IF:13.256 , 2021 May , V7 (5) : P619-632 doi: 10.1038/s41477-021-00917-x
Local brassinosteroid biosynthesis enables optimal root growth.
Department of Plant Biotechnology and Bioinformatics, Ghent University, Ghent, Belgium. nevuk@psb.vib-ugent.be.; Center for Plant Systems Biology, VIB, Ghent, Belgium. nevuk@psb.vib-ugent.be.; Department of Plant Biotechnology and Bioinformatics, Ghent University, Ghent, Belgium.; Center for Plant Systems Biology, VIB, Ghent, Belgium.; Department of Experimental Plant Biology, Faculty of Science, Charles University, Prague, Czech Republic.; College of Life Sciences, Wuhan University, Wuhan, China.; Laboratory of Growth Regulators, Institute of Experimental Botany, The Czech Academy of Sciences and Palacky University, Olomouc, Czech Republic.; Department of Plant Biotechnology and Bioinformatics, Ghent University, Ghent, Belgium. eurus@psb.vib-ugent.be.; Center for Plant Systems Biology, VIB, Ghent, Belgium. eurus@psb.vib-ugent.be.
Brassinosteroid (BR) hormones are indispensable for root growth and control both cell division and cell elongation through the establishment of an increasing signalling gradient along the longitudinal root axis. Because of their limited mobility, the importance of BR distribution in achieving a signalling maximum is largely overlooked. Expression pattern analysis of all known BR biosynthetic enzymes revealed that not all cells in the Arabidopsis thaliana root possess full biosynthetic machinery, and that completion of biosynthesis relies on cell-to-cell movement of hormone precursors. We demonstrate that BR biosynthesis is largely restricted to the root elongation zone, where it overlaps with BR signalling maxima. Moreover, optimal root growth requires hormone concentrations to be low in the meristem and high in the root elongation zone, attributable to increased biosynthesis. Our finding that spatiotemporal regulation of hormone synthesis results in local hormone accumulation provides a paradigm for hormone-driven organ growth in the absence of long-distance hormone transport in plants.
PMID: 34007032
Nat Commun , IF:12.121 , 2021 May , V12 (1) : P2842 doi: 10.1038/s41467-021-23112-0
The membrane-localized protein kinase MAP4K4/TOT3 regulates thermomorphogenesis.
Department of Plant Biotechnology and Bioinformatics, Ghent University, B-9052, Ghent, Belgium.; VIB Center for Plant Systems Biology, B-9052, Ghent, Belgium.; Department of Biomolecular Medicine, Ghent University, B-9000, Ghent, Belgium.; VIB Center for Medical Biotechnology, B-9000, Ghent, Belgium.; Molecular Plant Physiology, Institute of Environmental Biology, Utrecht University, 3584CH, Utrecht, The Netherlands.; Soybean & Nitrogen Fixation Research Unit, United States Department of Agriculture- Agricultural Research Service, Raleigh, NC, 27695, USA.; Department of Crop and Soil Sciences, North Carolina State University, Raleigh, NC, 27695, USA.; VIB Headquarters, 9052, Gent, Belgium.; Department of Crop Genetics, John Innes Centre, Norwich Research Park, NR4 7UH, UK.; Department of Biomolecular Medicine, Ghent University, B-9000, Ghent, Belgium. kris.gevaert@vib-ugent.be.; VIB Center for Medical Biotechnology, B-9000, Ghent, Belgium. kris.gevaert@vib-ugent.be.; Department of Plant Biotechnology and Bioinformatics, Ghent University, B-9052, Ghent, Belgium. ive.desmet@psb.vib-ugent.be.; VIB Center for Plant Systems Biology, B-9052, Ghent, Belgium. ive.desmet@psb.vib-ugent.be.
Plants respond to mild warm temperature conditions by increased elongation growth of organs to enhance cooling capacity, in a process called thermomorphogenesis. To this date, the regulation of thermomorphogenesis has been exclusively shown to intersect with light signalling pathways. To identify regulators of thermomorphogenesis that are conserved in flowering plants, we map changes in protein phosphorylation in both dicots and monocots exposed to warm temperature. We identify MITOGEN-ACTIVATED PROTEIN KINASE KINASE KINASE KINASE4 (MAP4K4)/TARGET OF TEMPERATURE3 (TOT3) as a regulator of thermomorphogenesis that impinges on brassinosteroid signalling in Arabidopsis thaliana. In addition, we show that TOT3 plays a role in thermal response in wheat, a monocot crop. Altogether, the conserved thermal regulation by TOT3 expands our knowledge of thermomorphogenesis beyond the well-studied pathways and can contribute to ensuring food security under a changing climate.
PMID: 33990595
Mol Plant , IF:12.084 , 2021 May doi: 10.1016/j.molp.2021.05.006
Chemical control of receptor kinase signaling by rapamycin-induced dimerization.
Department of Life Sciences, Korea University, Seoul, Korea.; Department of Bioenergy Science and Technology, Chonnam National University, Gwangju, Korea; Kumho Life Science Laboratory, Chonnam National University, Gwangju, Korea.; Department of Bioenergy Science and Technology, Chonnam National University, Gwangju, Korea.; Department of Life Sciences, Korea University, Seoul, Korea. Electronic address: ekoh@korea.ac.kr.; Department of Bioenergy Science and Technology, Chonnam National University, Gwangju, Korea; Kumho Life Science Laboratory, Chonnam National University, Gwangju, Korea; Department of Integrative Food, Bioscience and Biotechnology, Chonnam National University, Gwangju, Korea. Electronic address: ekoh@korea.ac.kr.
Membrane-localized leucine-rich repeat receptor kinases (LRR-RKs) sense diverse extracellular signals, and coordinate and specify cellular functions in plants. However, functional understanding and identification of the cellular signaling of most LRR-RKs remain a major challenge owing to their genetic redundancy, lack of ligand information, and subtle phenotypes of LRR-RK overexpression. Here, we report an engineered rapamycin-inducible dimerization (RiD) receptor system that triggers a receptor-specific LRR-RK signaling independent of their cognate ligands or endogenous receptors. Using the RiD-receptors, we demonstrated that the rapamycin-mediated association of chimeric cytosolic kinase domains from the BRI1/BAK1 receptor/co-receptor, but not the BRI1/BRI1 or BAK1/BAK1 homodimer, is sufficient to activate downstream brassinosteroid signaling and physiological responses and that the engineered RiD-FLS2/BAK1 activates flagellin-22-mediated immune signaling and responses. We also identified the potential function of an unknown orphan receptor in immune signaling and revealed the differential activities of SERK co-receptors of LRR-RKs. Our results demonstrated that the RiD method can serve as a synthetic biology tool for precise temporal manipulation of LRR-RK signaling and for understanding LRR-RK biology.
PMID: 33964457
Plant Cell , IF:9.618 , 2021 May doi: 10.1093/plcell/koab137
WRKY53 Integrates Classic Brassinosteroid Signaling and the Mitogen-Activated Protein Kinase Pathway to Regulate Rice Architecture and Seed Size.
Northeast Institute of Geography and Agroecology, Key Laboratory of Soybean Molecular Design Breeding, Chinese Academy of Sciences, Harbin 150081, China.; University of Chinese Academy of Sciences, Beijing 100049, China.; Ministry of Education Key Laboratory of Molecular and Cellular Biology, Hebei Key Laboratory of Molecular and Cellular Biology, College of Life Sciences, Hebei Normal University, Shijiazhuang 050024, China.; Key Laboratory of Saline-alkali Vegetation Ecology Restoration (Northeast Forestry University), Ministry of Education, Harbin 150040, China.; College of Life Science, Northeast Forestry University, Harbin 150040, China.; The Innovative Academy of Seed Design, Chinese Academy of Sciences, Beijing, China.
In rice (Oryza sativa) and other plants, plant architecture and seed size are closely related to yield. Brassinosteroid (BR) signaling and the mitogen-activated protein kinase (MAPK) pathway (MAPKKK10-MAPKK4-MAPK6) are two major regulatory pathways that control rice architecture and seed size. However, their possible relationship and crosstalk remain elusive. Here, we show that WRKY53 mediated the crosstalk between BR signaling and the MAPK pathway. Biochemical and genetic assays demonstrated that GSK2 phosphorylates WRKY53 and lowers its stability, indicating that WRKY53 is a substrate of GSK2 in BR signaling. WRKY53 interacted with BZR1; they function synergistically to regulate BR-related developmental processes. We also provide genetic evidence showing that WRKY53 functions in a common pathway with the MAPKKK10-MAPKK4-MAPK6 cascade in leaf angle and seed size control, suggesting that WRKY53 is a direct substrate of this pathway. Moreover, GSK2 phosphorylated MAPKK4 to suppress MAPK6 activity, suggesting that GSK2-mediated BR signaling might also regulated MAPK pathway. Together, our results revealed a critical role for WRKY53 and uncovered sophisticated levels of interplay between BR signaling and the MAPK pathway in regulating rice architecture and seed size.
PMID: 34003966
Plant J , IF:6.141 , 2021 May doi: 10.1111/tpj.15311
Boron deficiency-induced root growth inhibition is mediated by brassinosteroid signalling regulation in Arabidopsis.
National Key Laboratory of Crop Genetic Improvement, Huazhong Agricultural University, 430070, Wuhan, Hubei, P. R. China.; Microelement Research Center/Key Laboratory of Arable Land Conservation (Middle and Lower Reaches of Yangtze River), Ministry of Agriculture, Huazhong Agricultural University, 430070, Wuhan, Hubei, P. R. China.
Brassinosteroids (BRs) are pivotal phytohormones involved in dominating root development. Boron (B) is an essential micronutrient for plants, and root growth is rapidly inhibited under B-deficiency conditions. However, the mechanisms underlying this inhibition are still unclear. Here, we identified BR-related processes underlying B deficiency at the physiological, genetic, molecular/cell biological and transcriptomic levels and found strong evidence that B deficiency can affect BR biosynthesis and signalling, thereby altering root growth. RNA sequencing analysis revealed strong co-regulation between BR-regulated genes and B deficiency-responsive genes. We found that the BR receptor mutants bri1-119 and bri1-301 were more insensitive to decreased B supply, and the gain-of function mutants bes1-D and pBZR1-bzr1-D lines exhibited insensitivity to low-B stress. Under B-deficiency conditions, exogenous 24-epibrassinolide (eBL) rescued the inhibition of root growth, and application of the BR biosynthesis inhibitor BRZ exacerbated this inhibitory effect. The nuclear-localized signal of BES1 was reduced under low-B conditions compared with B-sufficiency conditions. We further found that B deficiency hindered the accumulation of brassinolide (BL) to downregulate BR signalling and modulate root elongation, which may occur through a reduction in BR6ox1 and BR6ox2 mRNA levels. Taken together, our results reveal a role of BR signalling in root elongation under B deficiency.
PMID: 33964043
J Exp Bot , IF:5.908 , 2021 May doi: 10.1093/jxb/erab192
A transcriptional hub integrating gibberellin-brassinosteroid signals to promote seed germination in Arabidopsis.
College of Forestry and Landscape Architecture, South China Agricultural University, Guangzhou, 510642, China.; Department of Plant and Soil Sciences, Kentucky Tobacco Research and Development Center, University of Kentucky; Lexington, KY 40546 USA.; Guangdong Provincial Key Laboratory of Biotechnology for Plant Development, School of Life Science, South China Normal University, Guangzhou 510631, China.
Seed germination is regulated by multiple phytohormones, including Gibberellins (GAs) and Brassinosteroids (BRs); however, the molecular mechanism underlying GA and BR co-induced seed germination is not well elucidated. We demonstrated that BRs induce seed germination through promoting testa and endosperm rupture in Arabidopsis. BRs promote cell elongation, rather than cell division, at the hypocotyl-radicle transition region of embryonic axis during endosperm rupture. Two key basic helix-loop-helix transcription factors (TFs) in the BR signaling pathway, HBI1 and BEE2, are involved in the regulation of endosperm rupture. Expression of HBI1 and BEE2 was induced in response to BR and GA treatment. In addition, HBI1 or BEE2 overexpressing Arabidopsis plants are less sensitive to the BR biosynthesis inhibitor, brassinazole, and the GA biosynthesis inhibitor, paclobutrazol. HBI1 and BEE2 promote endosperm rupture and seed germination by directly regulating the GA-Stimulated Arabidopsis 6 (GASA6) gene. Expression of GASA6 was altered in Arabidopsis overexpressing HBI1, BEE2, or SRDX-repressor forms of the two TFs. In addition, HBI1 interacts with BEE2 to synergistically activate GASA6 expression. Our findings define a new role for GASA6 in GA and BR signaling and reveal a regulatory module that controls GA and BR co-induced seed germination in Arabidopsis.
PMID: 33963401
PLoS Genet , IF:5.174 , 2021 May , V17 (5) : Pe1009540 doi: 10.1371/journal.pgen.1009540
Sugar inhibits brassinosteroid signaling by enhancing BIN2 phosphorylation of BZR1.
College of Life Sciences, Fujian Agriculture and Forestry University (FAFU), Fuzhou, China.; Department of Plant Biology, Carnegie Institution for Science, Stanford, California, United States of America.; Hebei Key Laboratory of Molecular and Cellular Biology, Key Laboratory of Molecular and Cellular Biology of Ministry of Education, College of Life Science, Hebei Normal University, Hebei Collaboration Innovation Center for Cell Signaling, Shijiazhuang, China.
Sugar, light, and hormones are major signals regulating plant growth and development, however, the interactions among these signals are not fully understood at the molecular level. Recent studies showed that sugar promotes hypocotyl elongation by activating the brassinosteroid (BR) signaling pathway after shifting Arabidopsis seedlings from light to extended darkness. Here, we show that sugar inhibits BR signaling in Arabidopsis seedlings grown under light. BR induction of hypocotyl elongation in seedlings grown under light is inhibited by increasing concentration of sucrose. The sugar inhibition of BR response is correlated with decreased effect of BR on the dephosphorylation of BZR1, the master transcription factor of the BR signaling pathway. This sugar effect is independent of the sugar sensors Hexokinase 1 (HXK1) and Target of Rapamycin (TOR), but requires the GSK3-like kinase Brassinosteroid-Insensitive 2 (BIN2), which is stabilized by sugar. Our study uncovers an inhibitory effect of sugar on BR signaling in plants grown under light, in contrast to its promotive effect in the dark. Such light-dependent sugar-BR crosstalk apparently contributes to optimal growth responses to photosynthate availability according to light-dark conditions.
PMID: 33989283
Mol Plant Pathol , IF:4.326 , 2021 May doi: 10.1111/mpp.13062
BRASSINOSTEROID-SIGNALLING KINASES 7 and 8 associate with the FLS2 immune receptor and are required for flg22-induced PTI responses.
School of Plant Sciences and Food Security, Tel-Aviv University, Tel-Aviv, Israel.
Pattern-triggered immunity (PTI) is typically initiated in plants by recognition of pathogen- or damage-associated molecular patterns (PAMP/DAMPs) by cell surface-localized pattern recognition receptors (PRRs). Here, we investigated the role in PTI of Arabidopsis thaliana brassinosteroid-signalling kinases 7 and 8 (BSK7 and BSK8), which are members of the receptor-like cytoplasmic kinase subfamily XII. BSK7 and BSK8 localized to the plant cell periphery and interacted in yeast and in planta with FLS2, but not with other PRRs. Consistent with a role in FLS2 signalling, bsk7 and bsk8 single and bsk7,8 double mutant plants were impaired in several immune responses induced by flg22, but not by other PAMP/DAMPs. These included resistance to Pseudomonas syringae and Botrytis cinerea, reactive oxygen species accumulation, callose deposition at the cell wall, and expression of the defence-related gene PR1, but not activation of MAP kinases and expression of the FRK1 and WRKY29 genes. bsk7, bsk8, and bsk7,8 plants also displayed enhanced susceptibility to P. syringae and B. cinerea. Finally, BSK7 and BSK8 variants mutated in their myristoylation site or in the ATP-binding site failed to complement defective phenotypes of the corresponding mutants, suggesting that localization to the cell periphery and kinase activity are critical for BSK7 and BSK8 functions. Together, these findings demonstrate that BSK7 and BSK8 play a role in PTI initiated by recognition of flg22 by interacting with the FLS2 immune receptor.
PMID: 33955635
Plant Signal Behav , IF:1.671 , 2021 May : P1926130 doi: 10.1080/15592324.2021.1926130
Endogenous level of abscisic acid down-regulated by brassinosteroids signaling via BZR1 to control the growth of Arabidopsis thaliana.
Department of Life Science, Chung-Ang University, Seoul, Republic of Korea.; Department of Plant Biology, Carnegie Institution for Science, Standford, USA.
The increased level of endogenous abscisic acid (ABA) in brassinosteroid (BR)-deficient mutants, such as det2 and cyp85a1 x cyp85a2, suggests that ABA synthesis is inhibited by endogenous BRs in Arabidopsis thaliana. Expression of the ABA biosynthesis gene ABA-deficient 2 (ABA2) was negatively regulated by exogenously applied BR but up-regulated by the application of brassinazole and in det2 and cyp85a1 x cyp85a2. In addition, ABA2 expression decreased in bzr1-1D, showing that ABA biosynthesis is inhibited by BR signaling via BZR1, intermediated by ABA2, in Arabidopsis. Four cis-element sequences (E-boxes 1-4) in the putative promoter region of ABA2 were identified as BZR1 binding sites. The electrophoretic mobility shift assay and chromatin immune precipitation analysis demonstrated that BZR1 directly binds to overlapped E-boxes (E-box 3/4) in the promoter region of ABA2. The level of endogenous ABA was decreased in bzr1-1D compared to wild-type, indicating that binding of BZR1 to the ABA2 promoter inhibits ABA synthesis in Arabidopsis. Compared to wild-type, aba2-1 exhibited severely reduced growth and development. The abnormalities in aba2-1 were rescued by the application of ABA, suggesting that ABA2 expression and ABA synthesis are necessary for the normal growth and development of A. thaliana. Finally, bzr1-KO x aba2-1 exhibited inhibitory growth of primary roots compared to bzr1-KO, verifying that ABA2 is a downstream target of BZR1 in the plant. Taken together, the level of endogenous ABA is down-regulated by BR signaling via BZR1, controlling the growth of A. thaliana.
PMID: 33980131