Cytokinin-induced bud outgrowth depends on sugar metabolism and signalling

Abstract

Shoot branching is a key process of plant growth and development, finely controlled by cytokinin and sugars. However, cytokinin fails to induce bud outgrowth in the absence of sugar and so far nothing is known about its ability to antagonize auxin when sugar availability is limited. Here we demonstrate in rose that cytokinin requires sugars metabolism and signalling to promote bud outgrowth, to downregulate the expression of RhBRC1, a transcription factor that inhibits axillary bud growth, and to antagonise the inhibitory effect of auxin on bud outgrowth. Cytokinin regulation of bud sink strength was tightly associated to sugar metabolism, which was evidenced by the gene expression in sugar metabolism (e.g. glycolysis, the tricarboxylic acid and the oxidative phosphate pentose phosphate: OPPP), metabolomic approach and the quantification of total carbon and nitrogen in buds. Cytokinin supply is associated with a significant upregulation of OPPP and nitrogen accumulation. Meanwhile, sugar upregulated bud sensitivity to cytokinin, associating with a significant down-regulation of cytokinin signalling regulator RhARR1. These findings highlight the key role of sugars metabolism and signalling in the cytokinin-induced bud outgrowth and provide new insights into the importance of nutrient-hormone crosstalk in the regulation of shoot branching.

Keywords: ARR regulators; BRC1 regulation; Nutrient-hormone crosstalk; shoot branching; sink strength; sugar signalling.