RACK1A positively regulates opening of the apical hook in via suppression of its auxin response gradient.

Qian Ma, Sijia Liu, Siamsa M Doyle, Sara Raggi, Barbora Pařízková, Deepak Kumar Barange, Hemamshu Ratnakaram, Edward G Wilkinson, Isidro Crespo Garcia, Joakim Bygdell, Gunnar Wingsle, Dirk Roeland Boer, Lucia C Strader, Fredrik Almqvist, Ondřej Novák, Stéphanie Robert

Journal: Proceedings of the National Academy of Sciences of the United States of America 2025;122(30):e2407224122

PMID: 40690664

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Abstract

Apical hook development is an ideal model for studying differential growth in plants and is controlled by complex phytohormonal crosstalk, with auxin being the major player. Here, we identified a bioactive small molecule that decelerates apical hook opening in . Our genetic studies suggest that this molecule enhances or maintains the auxin maximum found in the inner hook side and requires certain auxin signaling components to modulate apical hook opening. Using biochemical approaches, we then revealed the WD40 repeat scaffold protein RECEPTOR FOR ACTIVATED C KINASE 1A (RACK1A) as a direct target of this compound. We present data in support of RACK1A playing a positive role in apical hook opening by activating specific auxin signaling mechanisms and negatively regulating the differential auxin response gradient across the hook, thereby adjusting differential cell growth, an essential process for organ structure and function in plants.

Address: Umeå Plant Science Centre, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences, Umeå SE-901 83, Sweden.; Laboratory of Growth Regulators, Faculty of Science of Palacký University & Institute of Experimental Botany of the Czech Academy of Sciences, Olomouc CZ-783 71, Czech Republic.; Umeå Plant Science Centre, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences, Umeå SE-901 83, Sweden.; Department of Chemistry, Umeå University, Umeå SE-901 87, Sweden.; Department of Biology, Duke University, Durham, NC 27008.; BL13-XALOC Beamline, Experiments Division, ALBA Synchrotron, Cerdanyola del Vallès, Barcelona 08290, Spain.; Computational Life Science Cluster, Department of Chemistry, Umeå University, Umeå SE-901 87, Sweden.; Department of Chemistry, Umeå University, Umeå SE-901 87, Sweden.; Umeå Plant Science Centre, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences, Umeå SE-901 83, Sweden.; Laboratory of Growth Regulators, Faculty of Science of Palacký University & Institute of Experimental Botany of the Czech Academy of Sciences, Olomouc CZ-783 71, Czech Republic.

DOI: 10.1073/pnas.2407224122

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MeSH Terms: Arabidopsis, Arabidopsis Proteins, Indoleacetic Acids, Receptors for Activated C Kinase, Signal Transduction, Gene Expression Regulation, Plant, Plant Growth Regulators