Major goal of the proposed project is to understand how protein kinases identified recently in 26S proteasome-associated SCF ubiquitin ligase complexes control the stability of essential regulatory factors, and thereby major developmental and hormonal signaling pathways in plants. In collaboration with the host institute, we have found that all thus far known subunits of glucose/sucrose and stress regulated SnRK protein kinases are present in an SCF ligase complex that controls the stability of IAA/AUX transcription factors, which regulate cellular responses to the plant hormone auxin. Using biochemical and immunological methods, we aim to characterize the SnRK protein kinase-SCF-proteasome complexes by i) studying their interaction with IAA/AUX and other substrate proteins and ii) identifying their yet unknown regulatory subunits using MALDI-Q-TOF mass spectrometry. Our preliminary data show that, in addition to SnRK, the proteasome associated SCF ubiquitin ligases can also interact through theirSkp1 subunits with other signaling protein kinases. Therefore, we aim to use a systematic proteomics approach based on epitopetagging of multiple SCF-subunits to biochemically characterize their associated protein kinase partners and to link their function to defined developmental and hormonal signaling pathways using a functional genomics approach, which is based on the identification of insertional mutations in genes encoding components of these regulatory complexes. The proposed research project is based on an interdisciplinary approach, which includes a wide scale of modern proteomics technologies, extending from protein immunoaffinity labeling, immunoaffinity chromatography, protein interaction studies, massspectrometry and immunocytology to molecular genetic approaches using transgenic plant and cell cultures, sequenced-based mutant screening approaches and advanced classical genetic studies. The applicant brings into the host laboratory specific expertise in protein biochemistry and analytics and is offered with an extensive training in molecular genetic technologies. This interdisciplinary combination of expertise is required for successful combination of proteomics with functional genomics approaches and expected to lead to a better understanding how conserved eukaryotic protein kinases control the SCF-mediated ubiquitination and proteasomal degradation of essential regulatory factors in major signaling pathways of plants.