Sucrose promotes etiolated stem branching through activation of cytokinin accumulation followed by vacuolar invertase activity

The potato (Solanum tuberosum L.) tuber is a swollen stem. Sprouts growing from the tuber nodes represent dormancy release and loss of apical dominance. We recently identified sucrose as a key player in triggering potato stem branching. To decipher the mechanisms by which sucrose induces stem branching, we investigated the nature of the inducing molecule and the involvement of vacuolar invertase (VInv) and the plant hormone cytokinin (CK) in this process. Sucrose was more efficient at enhancing lateral bud burst and elongation than either of its hexose moieties (glucose and fructose), or a slowly metabolizable analog of sucrose (palatinose). Sucrose feeding induced expression of the sucrose transporter gene SUT2, followed by enhanced expression and activity of VInv in the lateral bud prior to its burst. We observed a reduction in the number of branches on stems of VInv-RNA interference lines during sucrose feeding, suggesting that sucrose breakdown is needed for lateral bud burst. Sucrose feeding led to increased CK content in the lateral bud base prior to bud burst. Inhibition of CK synthesis or perception inhibited the sucrose-induced bud burst, suggesting that sucrose induces stem branching through CK. Together, our results indicate that sucrose is transported to the bud, where it promotes bud burst by inducing CK accumulation and VInv activity.