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 Arabidopsis thaliana. 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.

• Keywords
• Arabidopsis, apical hook, auxin, differential cell growth,
• MeSH
• Arabidopsis * metabolism   growth & development   genetics   MeSH
• Indoleacetic Acids * metabolism   MeSH
• Arabidopsis Proteins * metabolism   genetics   MeSH
• Receptors for Activated C Kinase * metabolism   genetics   MeSH
• Gene Expression Regulation, Plant MeSH
• Plant Growth Regulators metabolism   MeSH
• Signal Transduction MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Indoleacetic Acids * MeSH
• Arabidopsis Proteins * MeSH
• RACK1 protein, Arabidopsis MeSH Browser
• Receptors for Activated C Kinase * MeSH
• Plant Growth Regulators MeSH