Receptors, repressors, PINs: a playground for strigolactone signaling

Strigolactones, previously identified as active stimuli of seed germination in parasitic plants, are now recognized as a new group of plant hormones that are active in both shoots and roots. Here, we review recent insights into the concepts of strigolactones-signal transduction and their mode of action. Although strigolactones are sensed via a cell-specific reception system, at least some aspects of their activity are conducted in a non-cell-autonomous fashion. Strigolactones also affect trafficking and plasma-membrane localization of the auxin transporter PIN, thereby regulating auxin flux. We present a model for strigolactone-signal transduction that might also explain the integration of strigolactones into other hormone-signaling pathways via the regulation of PIN auxin transporters.