Decoding the role of phosphoinositides in phototropin signaling involved in chloroplast movements.

In angiosperms, light-dependent chloroplast movements are exclusively mediated by UVA/blue light receptors - phototropins. The two photoreceptors of Arabidopsis thaliana, phot1 and phot2, have overlapping roles in the control of these movements. Experiments performed in different plant species point to the participation of phosphoinositides in blue light-controlled chloroplast relocations. Here, we report a summary of recent findings presenting the involvement of phosphatidylinositol 4,5-bisphosphate as well as phosphatidylinositol 3- and 4-phosphates in weak blue light-mediated (accumulation) and strong blue light-mediated (avoidance) responses of chloroplasts. The blue light-activated alterations in phosphoinositide concentration are partly responsible for cytosolic Ca (2+) changes. Ca (2+) influx from apoplast does not seem to be involved in the mechanism of movement responses. In summary, interplay between phosphoinositides and intracellular Ca (2+) regulates chloroplast redistribution in response to blue light in higher plants.