Strigolactones Regulate Sugar Allocation to Control Rice Tillering and Root Development via the OsSPL14‐OsSHR1‐OsSWEET16 Pathway

Strigolactones (SLs) are root-to-shoot phytohormones that regulate tillering (branching) and root development. Sugar, as an essential energy substance and signalling molecule, plays a fundamental role in the growth and development of plants. However, the molecular mechanisms by which SL directly regulates sugar allocation to control tillering and root development are still not fully understood. Here, we found that OsSHR1 operates directly downstream of OsSPL14 within the SL signalling pathway, facilitating root elongation while inhibiting tillering and crown root development. The expression of OsSHR1 is stimulated by OsSPL3/12/14 in vivo, and D53 can interact with these SPL proteins to suppress their transcriptional activities. Interestingly, we further demonstrate that OsSHR1 can directly bind to the promoters of OsSWEET2a/4/16, which encode sugar transporters that can control the allocation of sugar in plant growth and development. This binding facilitates the expression of sugar transporters, which in turn regulate sugar allocation and enable the plant's response to SLs. The results indicate that via the OsSPL14-OsSHR1-OsSWEET16 pathway, SLs orchestrate the distribution of sugars to ensure their effectiveness in stimulating root elongation while simultaneously suppressing tillering and crown root formation in rice.