Phytohormones are signalling compounds that regulate crucial aspects of stress responses. Among these hormones, jasmonate (JA) is involved in biotic stress and abiotic stress responses. Plants perceive JA by the receptor CORONATINE INSENSITIVE1 (COI1) to induce JA signalling in the nucleus, consequently, conferring plant resistance to biotic stress conditions or tolerance to abiotic stress. In general, the cell biology of JA signalling remains poorly understood, and it is, for example, not investigated how the JA receptor COI1 or the receptor complex moves to the nucleus. While post translational modifications (PTMs), such as reversible phosphorylation, contribute extensively to protein stability and subcellular localization, the impact of PTMs on the receptor COI1 stability, activity and cellular localisation is still largely unknown. Recently, I identified a potential phosphatase IBR5 (INDOLE-3-BUTYRIC ACID RESPONSE 5) that directly interacts with Arabidopsis COI1 and mediates COI1 nuclear localisation, indicating that COI1 phosphorylation plays a crucial role in COI1 subcellular localisation and JA signalling. In this project, I will explore the regulation of COI1 protein nucleo-cytoplasmic partitioning through COI1 phosphorylation status mediated by IBR5 and an unknown kinase, using Arabidopsis as model plant. The identification of COI1 phosphosite(s) and regulatory kinase will shed novel light on COI1-mediated JA signalling.