Plant Kelch phosphatases are Ser/Thr phosphatases involved in cell cycle regulation

Plant Kelch phosphatases are Ser/Thr phosphatases involved in cell cycle regulation | bioRxiv Skip to main content Home About Submit ALERTS / RSS Search for this keyword Advanced Search New Results Plant Kelch phosphatases are Ser/Thr phosphatases involved in cell cycle regulation View ORCID Profile Felix Rico-Resendiz , View ORCID Profile Oded Pri-Tal , View ORCID Profile Pierre Raia , View ORCID Profile Andrea Moretti , View ORCID Profile Houming Chen , View ORCID Profile Jun Yu , View ORCID Profile Larissa Broger , View ORCID Profile Christelle Fuchs , Ludwig A. Hothorn , View ORCID Profile Sylvain Loubéry , View ORCID Profile Michael Hothorn doi: https://doi.org/10.64898/2026.01.06.697939 Felix Rico-Resendiz 1 Structural Plant Biology Laboratory, Department of Plant Sciences, University of Geneva , 1211 Geneva, Switzerland Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Felix Rico-Resendiz Oded Pri-Tal 1 Structural Plant Biology Laboratory, Department of Plant Sciences, University of Geneva , 1211 Geneva, Switzerland Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Oded Pri-Tal Pierre Raia 1 Structural Plant Biology Laboratory, Department of Plant Sciences, University of Geneva , 1211 Geneva, Switzerland Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Pierre Raia Andrea Moretti 1 Structural Plant Biology Laboratory, Department of Plant Sciences, University of Geneva , 1211 Geneva, Switzerland Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Andrea Moretti Houming Chen 1 Structural Plant Biology Laboratory, Department of Plant Sciences, University of Geneva , 1211 Geneva, Switzerland Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Houming Chen Jun Yu 2 Department of Molecular and Cellular Biology, University of Geneva , 1211, Geneva, Switzerland Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Jun Yu Larissa Broger 1 Structural Plant Biology Laboratory, Department of Plant Sciences, University of Geneva , 1211 Geneva, Switzerland Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Larissa Broger Christelle Fuchs 3 Plant Imaging Unit, Department of Plant Sciences, University of Geneva , 1211 Geneva, Switzerland Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Christelle Fuchs Ludwig A. Hothorn 4 retired from Institute of Biostatistics, Leibniz University , 30419, Hannover, Germany Find this author on Google Scholar Find this author on PubMed Search for this author on this site Sylvain Loubéry 3 Plant Imaging Unit, Department of Plant Sciences, University of Geneva , 1211 Geneva, Switzerland Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Sylvain Loubéry Michael Hothorn 1 Structural Plant Biology Laboratory, Department of Plant Sciences, University of Geneva , 1211 Geneva, Switzerland Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Michael Hothorn For correspondence: michael.hothorn{at}unige.ch Abstract Full Text Info/History Metrics Preview PDF Abstract Brassinosteroids (BRs) are plant steroid hormones sensed by the membrane receptor kinase BRI1. Activation of BRI1 leads to the dephosphorylation of BZR1/BES1 transcription factors. Overexpression of the Kelch phosphatase BRI1 SUPPRESSOR 1 (BSU1) rescued the growth defects of bri1 mutants. Subsequent studies identified BSU1 as a protein tyrosine phosphatase, which promotes BR signaling by dephosphorylating a phosphotyrosine in the glycogen synthase kinase 3 BIN2. Crystal structures of the BSU1 phosphatase domain now reveal a high degree of structural similarity to protein phosphatase 1 (PP1), a eukaryotic serine/threonine phosphatase. Consistently, BSU1 efficiently dephosphorylated phosphothreonine– and phosphoserine-containing substrate peptides, but showed no detectable activity toward BIN2 and other phosphotyrosine substrates. A catalytically inactive BSU1 phosphatase domain suppresses the growth phenotypes of the Arabidopsis bri1-5 mutant and binds the BSU1 homologs BSL1-3. bsu1 and bsu1 bsl1 bsl2/3 loss-of-function mutants display wild-type-like BR responses, but exhibit stomatal patterning and fertility defects. Importantly, the PP1-like C-terminal tail of BSU1 is phosphorylated at Thr785 by a cyclin-dependent kinase complex. The phosphorylated tail binds to the BSU1 substrate-binding grooves, blocking access to the active site. Mutation of Thr785 to alanine activates BSU1, suggesting that Kelch phosphatases and PP1 share a common regulatory mechanism. Deletion of the Marchantia polymorpha Kelch phosphatase MpBSLM results in an undifferentiated cell mass phenotype, associated with the over-activation of a cell cycle reporter. Taken together, our experiments suggest that plant Kelch phosphatases act as PP1-like cell cycle regulators, rather than as tyrosine phosphatases in brassinosteroid signaling. (243 words) Significance Statement Brassinosteroid hormones initiate a well-characterized signaling pathways in plants. While the early signaling events at the plasma membrane have been thoroughly examined, the precise sequence of molecular events that comprise the cytoplasmic signaling cascade is less well-understood. Here, the molecular function of the Kelch protein phosphatase BSU1 is re-evaluated. Previous reports have indicated that BSU1 dephosphorylates the GSK3 kinase BIN2 on a central tyrosine residue. However, structural, quantitative enzyme kinetic, and genetic analyses now suggest that BSU1 is a PP1-like serine/threonine phosphatase involved in cell cycle control rather than a tyrosine phosphatase involved in BIN2 de-phosphorylation. The regulation of BSU1 by a cyclin-dependent kinase complex and the role of Kelch phosphatases in cell cycle progression in Marchantia polymorpha are experimentally characterized. (121 words) Competing Interest Statement The authors have declared no competing interest. Footnotes The manuscript has been revised taking into consideration the comments associated with the preprint on biorxiv. New data are shown in revised Fig. 1G, J, K and L, and SI Appendix Fig. S1. The results and disucssion sections have been revised accordingly. Funder Information Declared Swiss National Science Foundation , 310030_205201 Howard Hughes Medical Institute , 55008733 Copyright The copyright holder for this preprint is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under a CC-BY-NC-ND 4.0 International license . Back to top Previous Next Posted March 20, 2026. Download PDF Email Thank you for your interest in spreading the word about bioRxiv. NOTE: Your email address is requested solely to identify you as the sender of this article. Your Email * Your Name * Send To * Enter multiple addresses on separate lines or separate them with commas. 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Hothorn , Sylvain Loubéry , Michael Hothorn bioRxiv 2026.01.06.697939; doi: https://doi.org/10.64898/2026.01.06.697939 Share This Article: Copy Citation Tools Plant Kelch phosphatases are Ser/Thr phosphatases involved in cell cycle regulation Felix Rico-Resendiz , Oded Pri-Tal , Pierre Raia , Andrea Moretti , Houming Chen , Jun Yu , Larissa Broger , Christelle Fuchs , Ludwig A. Hothorn , Sylvain Loubéry , Michael Hothorn bioRxiv 2026.01.06.697939; doi: https://doi.org/10.64898/2026.01.06.697939 Citation Manager Formats BibTeX Bookends EasyBib EndNote (tagged) EndNote 8 (xml) Medlars Mendeley Papers RefWorks Tagged Ref Manager RIS Zotero Tweet Widget Facebook Like Google Plus One Subject Area Plant Biology Subject Areas All Articles Animal Behavior and Cognition (8164) Biochemistry (19027) Bioengineering (15171) Bioinformatics (45592) Biophysics (22958) Cancer Biology (20204) Cell Biology (27430) Clinical Trials (138) Developmental Biology (14199) Ecology (21485) Epidemiology (2067) Evolutionary Biology (25889) Genetics (16403) Genomics (23920) Immunology (19115) Microbiology (43383) Molecular Biology (18434) Neuroscience (95525) Paleontology (716) Pathology (3049) Pharmacology and Toxicology (5228) Physiology (8314) Plant Biology (16341) Scientific Communication and Education (2121) Synthetic Biology (4664) Systems Biology (10430) Zoology (2435)

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