Strigolactone signalling: standing on the shoulders of DWARFs

• Strigolactones (SLs) have important endogenous signalling roles in plants.
• The core components of a higher plant SL signalling pathway have been identified.
• It evolved by elaboration, duplication and subfunctionalisation of a simpler system.
• Immediate likely targets are transcription and/or auxin transporter endocytosis.
• The D53 protein may be key to linking the known pathway to these targets.

Strigolactones are an ancient and major class of endogenous plant growth regulators. Although only recently identified, rapid progress has been made in understanding strigolactone biology, including the identification of a signalling pathway involving DWARF14 α/β-fold proteins, the SCFMAX2 ubiquitin ligase and SMAX1-LIKE (SMXL) family of chaperonin-like proteins. Several rapid effects of strigolactone signalling have also been identified, including endocytosis of the PIN-FORMED1 (PIN1) auxin efflux carrier and transcript accumulation of the BRANCHED1 (BRC1) transcription factor. Here we assess our current knowledge of strigolactone signalling, and discuss how increased understanding of the cell biology of the system can help to resolve some of the current uncertainties in the field.