Sugar availability suppresses the auxin-induced strigolactone pathway to promote bud outgrowth

O_LIApical dominance occurs when the growing shoot tip inhibits the outgrowth of axillary buds. Apically-derived auxin in the nodal stem indirectly inhibits bud outgrowth via cytokinins and strigolactones. Recently, sugar deprivation was found to contribute to this phenomenon.\nC_LIO_LIUsing rose and pea, we investigated whether sugar availability interacts with auxin in bud outgrowth control, and the role of cytokinins and strigolactones, in vitro and in planta.\nC_LIO_LIWe show that sucrose antagonizes auxins effect on bud outgrowth, in a dose-dependent and coupled manner. Sucrose also suppresses strigolactone-inhibition of outgrowth, and rms3 strigolactone-perception mutant is less affected by reducing sucrose supply; however, sucrose does not interfere with the regulation of cytokinin levels by auxin, and stimulates outgrowth even with optimal cytokinin supply. These observations were assembled into a computational model where sucrose represses bud response to strigolactones, largely independently of cytokinin levels. It quantitatively captures our observed dose-dependent sucrose-hormones effects on bud outgrowth, and allows us to express outgrowth response to various combinations of auxin and sucrose levels as a simple quantitative law.\nC_LIO_LIThis study places sugars in the bud outgrowth regulatory network, and paves the way for better understanding of branching plasticity in response to environmental and genotypic factors.\nC_LI