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

Article Article scientifique Article Plant Kelch phosphatases are Ser/Thr phosphatases involved in cell cycle regulation eng 2026-05-20 2026-05-26 author Rico Resendiz Félix Edgardo 0000-0003-0260-7298 Structural Plant Biology Laboratory, Department of Plant Sciences, University of Geneva, Geneva 1211, Switzerland. 962981 Département des sciences végétales (BIVEG) author Pri Tal Oded Yaacov Structural Plant Biology Laboratory, Department of Plant Sciences, University of Geneva, Geneva 1211, Switzerland. 957911 author Raia Pierre 0000-0003-3469-1922 Structural Plant Biology Laboratory, Department of Plant Sciences, University of Geneva, Geneva 1211, Switzerland. 930734 Département des sciences végétales (BIVEG) author Moretti Andréa Structural Plant Biology Laboratory, Department of Plant Sciences, University of Geneva, Geneva 1211, Switzerland. 882215 author Chen Houming 0009-0007-8828-2549 Structural Plant Biology Laboratory, Department of Plant Sciences, University of Geneva, Geneva 1211, Switzerland. 404343 Département des sciences végétales (BIVEG) author Yu Jun Department of Molecular and Cellular Biology, University of Geneva, Geneva 1211, Switzerland. 924631 Département de biologie moléculaire et cellulaire (MOCEL) author Broger Larissa Structural Plant Biology Laboratory, Department of Plant Sciences, University of Geneva, Geneva 1211, Switzerland. 95643 Département des sciences végétales (BIVEG) author Fuchs Christelle 0000-0001-8181-2294 Plant Imaging Unit, Department of Plant Sciences, University of Geneva, Geneva 1211, Switzerland. 823460 Département des sciences végétales (BIVEG) author Hothorn Ludwig A Institute of Biostatistics, Leibniz University, Hannover 30419, Germany. author Loubery Sylvain Philippe 0000-0001-7061-9456 Plant Imaging Unit, Department of Plant Sciences, University of Geneva, Geneva 1211, Switzerland. 669207 Département des sciences végétales (BIVEG) author Hothorn Michael 0000-0002-3597-5698 Structural Plant Biology Laboratory, Department of Plant Sciences, University of Geneva, Geneva 1211, Switzerland. 826130 Département des sciences végétales (BIVEG) e2600591123 10.1073/pnas.2600591123 42166246 0027-8424 PMC13214054 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 overactivation 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 BR signaling. Marchantia polymorpha Brassinosteroid Cell cycle Protein crystallography Protein phosphatase Arabidopsis / enzymology Arabidopsis / genetics Arabidopsis Proteins / metabolism Arabidopsis Proteins / genetics Arabidopsis Proteins / chemistry Cell Cycle / physiology Phosphorylation Signal Transduction Phosphoprotein Phosphatases / metabolism Phosphoprotein Phosphatases / genetics Phosphoprotein Phosphatases / chemistry Gene Expression Regulation, Plant Protein Kinases / metabolism Protein Kinases / genetics Brassinosteroids / metabolism Mutation Dewey 580 HHMI (HHMI) 55008733 Swiss National Science Foundation Structural and functional investigation of plant membrane receptor kinases and their cytoplasmic signaling cascades 205201 CH 45 Département des sciences végétales 163 false 830 Groupe Hothorn Proceedings of the National Academy of Sciences of the United States of America 123 21 0caed12b-ba7d-4c5b-8aeb-11d9aee895d6 Article (Published version) Public rico-resendiz-et-al-2026-plant-kelc.pdf 5105703 application/pdf CC BY-NC-ND-4.0 b59aee641e85c2d3f70c54106fa06213ae172eb5b81d78f9bca7470342b6c117 openAccess Faculté des sciences / Section de biologie / Département des sciences végétales

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Plant Kelch phosphatases are Ser/Thr phosphatases involved in cell cycle regulation	Proceedings of the National Academy of Sciences of the United States of America	2026	3	33
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