ORIGINAL PAPER 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 Mariya Khodakovskaya Æ Radomira Van ˇ kova ´ Æ Jir ˇi Malbeck Æ Aizhen Li Æ Yi Li Æ Richard McAvoy Received: 31 December 2008 / Revised: 29 May 2009 / Accepted: 1 June 2009 / Published online: 17 June 2009 Ó Springer-Verlag 2009 Abstract The cytokinin biosynthesis gene, isopentenyl transferase (ipt), under the control of an 821 bp fragment of the LEACO1 gene promoter (from Lycopersicon esculen- tum) was introduced into Dendranthema 9 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 vegeta- tive and generative growth conditions. In general, trans- genic 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. Keywords ipt Gene Á Cytokinins Á Transgenic chrysanthemum Á LEACO1-promoter Á Branching Á Number of flower buds Introduction It is well known that growth and development of plants can be greatly affected by inducing variations in hormone concentrations. In ornamental horticulture, exogenously applied growth regulating chemicals are routinely used to enhance the aesthetic appearance of plants by increasing branching and/or reducing stem elongation. Although similar growth effects can be achieved through traditional breeding methods, molecular genetic modification (GM) can produce this phenotype by manipulating specific plant hormone levels. Thus, GM represents a tool that holds great potential for improving ornamental crops (Chandler 2003). Communicated by E. Guiderdoni. Electronic supplementary material The online version of this article (doi:10.1007/s00299-009-0735-x) contains supplementary material, which is available to authorized users. M. Khodakovskaya (&) Department of Applied Science, University of Arkansas at Little Rock, Little Rock, AR 72204, USA e-mail: mvkhodakovsk@ualr.edu; m_khod@yahoo.com A. Li Á Y. Li Á R. McAvoy Department of Plant Science, University of Connecticut, Storrs, CT 06269, USA M. Khodakovskaya Institute of Biology and Soil Science, Far-Eastern Branch, Russian Academy of Sciences, Vladivostok, Russian Federation R. Van ˇkova ´ Á J. Malbeck Institute of Experimental Botany, v.v.i., Academy of Sciences of the Czech Republic, Prague, Czech Republic 123 Plant Cell Rep (2009) 28:1351–1362 DOI 10.1007/s00299-009-0735-x