Overexpression Of The AtSHI Transcript Factor Produces Dwarfed Ornamentals

Production of ornamental plants requires application of chemicals that modulate hormone levels in order to obtain uniform and high quality yields. Inhibitors of gibberellin biosynthesis can control elongation of growth, and synthetic anti-auxins, auxin transport inhibitors, and cytokinins can be used to increase branching. However, application of chemical growth regulators is a costly procedure, thus molecular plant breeding seems to be attractive to pursue in order to replace chemicals in the greenhouses. As a strategy to obtain dwarfed and compact plants, we have successfully used overexpression of the Arabidopsis thaliana Short Internodes gene (SHI) in Kalanchoë blossfeldiana and a range of commercial interspecific Kalanchoë lines. The major effect on morphology was more compact inflorescences, as a result of increased vegetative height. Although the effect of the AtSHI transgene copy number and expression levels varied in different lines, the whole range of transformed Kalanchoë lines showed compact phenotypes. Furthermore, none of the Kalanchoë SHI-lines exhibited alterations in leaf color or morphology. Using the same strategy in the woody species Poinsettia also resulted in dwarfed plants. The phylogeny of SHI transcription factor genes shows that this gene family is widely spread among plant species, but it is different from the dwarfing genes successfully introduced during the green revolution to produce semi-dwarf wheat and rice phenotypes.