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Sugar availability suppresses the auxin-induced strigolactone pathway to promote bud outgrowth
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International audience. Apical dominance occurs when the growing shoot tip inhibits the outgrowth of axillarybuds. Apically-derived auxin in the nodal stem indirectly inhibits bud outgrowth via cytokininsand strigolactones. Recently, sugar deprivation was found to contribute to this phenomenon. Using rose and pea, we investigated whether sugar availability interacts with auxin in budoutgrowth control, and the role of cytokinins and strigolactones,in vitroandin planta. We show that sucrose antagonises auxin’s effect on bud outgrowth, in a dose-dependentand coupled manner. Sucrose also suppresses strigolactone inhibition of outgrowth and therms3strigolactone-perception mutant is less affected by reducing sucrose supply. However,sucrose does not interfere with the regulation of cytokinin levels by auxin and stimulates out-growth even with optimal cytokinin supply. These observations were assembled into a com-putational model in which sucrose represses bud response to strigolactones, largelyindependently of cytokinin levels. It quantitatively captures our observed dose-dependentsucrose-hormones effects on bud outgrowth and allows us to express outgrowth response tovarious combinations of auxin and sucrose levels as a simple quantitative law. This study places sugars in the bud outgrowth regulatory network and paves the way for abetter understanding of branching plasticity in response to environmental and genotypic factors.
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