Arranged marriage in lipid signalling? The limited choices of P td I ns(4,5) P 2 in finding the right partner

Abstract Inositol‐containing phospholipids (phosphoinositides, PI s) control numerous cellular processes in eukaryotic cells. For plants, a key involvement of PI s has been demonstrated in the regulation of membrane trafficking, cytoskeletal dynamics and in processes mediating the adaptation to changing environmental conditions. Phosphatidylinositol‐4,5‐bisphosphate ( P td I ns(4,5) P 2 ) mediates its cellular functions via binding to various alternative target proteins. Such downstream targets of P td I ns(4,5) P 2 are characterised by the possession of specific lipid‐binding domains, and binding of the P td I ns(4,5) P 2 ligand exerts effects on their activity or localisation. The large number of potential alternative binding partners – and associated cellular processes – raises the question how alternative or even contrapuntal effects of P td I ns(4,5) P 2 are orchestrated to enable cellular function. This article aims to provide an overview of recent insights and new views on how distinct functional pools of P td I ns(4,5) P 2 are generated and maintained. The emerging picture suggests that P td I ns(4,5) P 2 species containing different fatty acids influence the lateral mobility of the lipids in the membrane, possibly enabling specific interactions of P td I ns(4,5) P 2 pools with certain downstream targets. P td I ns(4,5) P 2 pools with certain functions might also be defined by protein–protein interactions of PI 4P 5‐kinases, which pass P td I ns(4,5) P 2 only to certain downstream partners. Individually or in combination, P td I ns(4,5) P 2 species and specific protein–protein interactions of PI 4 P 5‐kinases might contribute to the channelling of P td I ns(4,5) P 2 signals towards specific functional effects. The dynamic nature of PI ‐dependent signalling complexes with specific functions is an added challenge for future studies of plant PI signalling.