The protein-protein interaction network of plant PI4P 5-kinases controlling polar tip growth

The channeling of signaling molecules is not well understood. In previous work, we have described various  effects of the regulatory phospholipid, phosphatidylinositol-4,5-bisphosphate (PtdIns(4,5)P2), on polar tip growth in plant cells, such as pollen tubes or root hairs. Based on our data, two types of PI4P 5-kinases can be distinguished that produce PtdIns(4,5)P2 with roles in controlling actin dynamics or in controlling apical secretion, respectively. We hypothesize that the two types of PI4P 5-kinases generate PtdIns(4,5)P2 that is channelled toward specific downstream targets to enable their exclusive regulatory effects. The comparison of PI4P 5-kinase isoforms with divergent function has resulted in the identification of variable protein regions whose reciprocal swapping between isoforms conferred the capabilities to act in the context of controlling actin-dynamics or of apical secretion on the respective other isoforms. These protein domains appear ideal adaptors to enable specific protein-protein interactions of PI4P 5-kinases that could recruit the enzymes into different signaling contexts. Therefore, we hypothesize further that the different isoforms of PI4P 5-kinases are recruited to functional plasma membrane domains by interacting with specific protein partners via their variable domains. Thus, the protein-protein interaction network of PI4P 5-kinases might be at the base of the channeling effect observed and their specific recruitment will define the functional output of the PtdIns(4,5)P2-pool generated by a given PI4P 5-kinase.