Bridging sugar metabolism and signaling with hormones in shoot branching regulation.

Shoot branching, a major determinant of plant architecture and productivity, has long been attributed to the coordinated action of auxin, cytokinins (CKs), and strigolactones (SLs). Recent work shows that sugars act not only as metabolic resources but also as early developmental signals that regulate axillary bud outgrowth, the initial step in shoot branching. Sugar availability can rapidly trigger bud outgrowth, often preceding major hormonal changes. Mechanistically, sugars antagonize auxin and SL signaling while acting synergistically with CKs. These effects involve sugar signaling pathways mediated by trehalose 6-phosphate (Tre6P) and HEXOKINASE1 (HXK1), as well as metabolic reprogramming of glycolysis, the tricarboxylic acid (TCA) cycle, and the oxidative pentose phosphate pathway (OPPP). The transcription factor BRANCHED1/TEOSINTE BRANCHED1 (BRC1/TB1) participates in this regulatory network by integrating specific sugar and hormonal inputs involved in the control of the transition between bud dormancy and bud outgrowth. Here, we synthesize current knowledge on the interplay between sugar metabolism, sugar signaling, and hormonal pathways in regulating bud fate and highlight key questions that will shape future research in this field.