Sucrose-induced bud outgrowth in Chrysanthemum morifolium involves changes of auxin transport and gene expression

• Sucrose is transported to buds and promotes bud outgrowth in the sucrose treatment of two-node chrysanthemum segments. • Sucrose-mediated bud growth may be related to the auxin export pathway. • The transport of sucrose may have “apical dominance” in chrysanthemum. In plants, auxin and sucrose are the major factors controlling bud outgrowth. Here, we established an effective culturing system using two-node stems to study sucrose-induced bud outgrowth in C hrysanthemum morifolium . Treatment of plant segments with 20 mM sucrose in the dark promoted the growth of the upper bud. No growth was observed for the bottom bud in the 20 mM sucrose treatment nor in the upper and bottom buds in the 0 mM sucrose treatment. Transcriptomics and real-time PCR analysis revealed that sucrose induced the expression of auxin transport carrier genes ( CmPIN1 and CmAUX1 ) and inhibitory auxin signaling genes ( CmIAA3, CmIAA14 , and CmIAA16 ) and down-regulated the expression of the auxin response factor gene CmARF2 in the upper bud. Endogenous auxin levels of the upper buds were significantly reduced, suggesting that auxin transport was enhanced under sucrose treatment. Furthermore, the radioactivity assay of 14 C-labeled sucrose demonstrated that sucrose was indeed transported to the growing upper bud. The administration of TIBA (auxin transport inhibitor) or IAA together with 20 mM sucrose weakened the promoting effect of sucrose on the outgrowth of the upper bud. Auxin-related gene expression analysis and auxin content measurements revealed that the expression of CmPIN1 and CmAUX1 was down-regulated, the auxin content increased, and the expression of CmIAA3, CmIAA14, CmIAA16 , and CmARF2 was altered in the upper bud in the TIBA and IAA treatment. In conclusion, sucrose promoted bud outgrowth, possibly through an auxin pathway-dependent mechanism.