An update on strigolactone signaling in plants

Strigolactone signaling pathway is based on an F-box–mediated cascade reaction. The critical step in starting the signal transduction is perception of strigolactone molecule by receptor DWARF 14 (D14). The binding of hormone molecule by D14 results in conformational change of the receptor, which is required for interaction with other components of the strigolactone signaling pathway. At the same time, a conservative catalytic motif (Ser96, His246, Asp217) of D14 leads to the hydrolysis of strigolactone molecule. Thus, D14 acts as a dual-functional receptor, responsible for strigolactone perception and strigolactone molecule degradation. Further, the signal relay leads to the formation of SKP-CULLIN-F-BOX (SCF) complex and repressor degradation via 26S proteasome. Mutation in genes encoding the core components of strigolactone signaling pathway results in semidwarfism and greater number of lateral shoots and roots of plants. Additionally, the mutant's phenotype cannot be rescued by strigolactone treatment. Our knowledge about the genes encoding transcription factors (TFs), which regulate the plant's response to strigolactones, remains elusive. The role of only a few strigolactone-dependent TFs was experimentally confirmed, including BRANCHED1 (BRC1) protein. The BRC1 is well known to act locally in buds and regulates the shoot branching by inhibiting the axillary bud outgrowth. However, to describe how strigolactones regulate other aspects of plant development and plant response to stresses, it is necessary to characterize the new TFs which are involved in strigolactone signal transduction. This remains the biggest challenge that will allow us to understand how strigolactones act.