Enhancement of flowering and branching phenotype in chrysanthemum by expression of ipt under the control of a 0.821 kb fragment of the LEACO1 gene promoter.

The cytokinin biosynthesis gene, isopentenyl transferase (ipt), under the control of an 821 bp fragment of the LEACO1 gene promoter (from Lycopersicon esculentum) was introduced into Dendranthema x grandiflorium 'Iridon' (chrysanthemum). LEACO1(0.821kb)-ipt transgenic lines grown in the vegetative state, exhibited a range of phenotypic changes including increased branching and reduced internode lengths. LEACO1(0.821kb)-ipt transgenic lines grown in the generative state, exhibited increased flower bud count that ranged from 3.8- to 6.7-times the number produced by wild-type plants. Dramatic increases in flower number were associated with a delay of flower bud development and a decrease in flower bud diameter. RT-PCR analysis indicated differences in ipt gene expression between individual transgenic lines that exhibited a range of phenotypes. Within an individual transgenic line, RT-PCR analysis revealed changes in ipt gene expression at different stages of generative shoot development. Expression of ipt in transgenic lines correlated well with high concentrations of the sum total to bioactive cytokinins plus the glucosides and phosphate derivatives of these species, under both vegetative and generative growth conditions. In general, transgenic lines accumulated higher concentrations of both storage-form cytokinins (O-glucosides) and deactivated-form cytokinins (N-glucosides) in generative shoots of than in vegetative shoots. Based on the range of phenotypes observed in various transgenic chrysanthemum lines, we conclude that the LEACO1 (0.821kb) -ipt gene appears to have great potential for use in ornamental crop improvement.