Arabidopsis inositol polyphosphate kinases regulate COP9 signalosome functions in phosphate-homeostasis

Targeted protein degradation is essential for physiological development and adaptation to stress. Mammalian INOSITOL PENTAKISPHOSPHATE KINASE (IP5K) and INOSITOL HEXAKISPHOSPHATE KINASE 1 (IP6K1) pair modulates functions of Cullin RING Ubiquitin E3 ligases (CRLs) that execute targeted degradation of substrates. Coordinated activities of these kinases protect CRLs on a COP9 signalosome (CSN) platform and stimulates deneddylation-dependent disassembly to maintain continuity of its functions. In plants, CRL regulations on CSN by inositol phosphate (InsP) kinases are not known. Here, we show interactions of Arabidopsis thaliana INOSITOL PENTAKISPHOSPHATE 2-KINASE 1 (IPK1) and INOSITOL 1,3,4-TRISPHOSPHATE 5/6-KINASE 1 (ITPK1), counterparts of the above InsP-kinase pair, with CSN subunits and its positive influences on the dynamics of cullin deneddylation. We identify neddylation enhancements on CRLs as an early response to phosphate starvation and its orchestration by perturbed IPK1/ITPK1 activities. At a molecular level, specific kinetics of CSN5 deneddylase is affected by the above InsP-kinases. Overall, our data reveal conserved InsP-kinase involvements on CRL-CSN synergism in plants.