Identification of RACK1A as a component of the auxin-ethylene crosstalk regulating apical hook development inArabidopsis thaliana

Abstract

Apical hook development is an ideal model for studying differential growth in plants, and is controlled by complex hormonal crosstalk, with auxin and ethylene being the major players. 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 and ethylene 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 negatively regulating the differential auxin response gradient across the hook via specific auxin and ethylene signaling mechanisms and thereby adjusting differential cell growth, an essential process for organ structure and function in plants. We have thus identified a role for RACK1A and auxin-ethylene crosstalk in negatively regulating differential cell growth to promote apical hook opening.