Analysis of functional PI-pools and the interaction network of PI4P 5-kinases
PIs have regulatory effects on the physiology of eukyaryotic organisms, including plants. The effects of PIs on plant metabolism are manifold. One possibility how diverse and sometimes even contrapuntal effects of PIs can be orchestrated is presented by the notion of independent functional “pools” of PIs. Such PI-pools with distinct physiological functions could be distinguished by the nature of their associated fatty acids. Current work is directed towards elucidating whether certain molecular species of PIs can be assigned to particular physiological functions. Besides the direct biochemical analysis of PIs in plant material this task also involves the characterization of enzymes of PI biosynthesis regarding their preferences for substrate lipids with characteristic fatty acid patterns.
The various regulatory effects of PIs on physiological processe in plant cells are strictly regulated. For instance, we have observed that the formation of PtdIns(4,5)P2 by certain PI4P 5-kinase isoforms will influence different processes than PtdIns(4,5)P2 formed by other isoforms. These observations suggest channeled function of PtdIns(4,5)P2 that is presented only to certain partner proteins instead of freely diffusing within the membrane. Our experiments indicate that specific interactions of PI4P 5-kinases with PtdIns(4,5)P2-controlled target proteins underlie the observed channeling effects. Our current research is aimed at identifying proteins interacting with PI4P 5-kinases and at testing the physiological relevance of the interactions.