Effects of the plant growth regulators on expression of MdTFL1 promoter fused β-glucuronidase (GUS) reporter gene in apple (Malus spp.) tissues in vitro

Apple has a relatively long juvenile growth period, taking approximately 8 years to reach the flowering stage. This period has impeded breeding programs. Since MdTFL1 (an ortholog of TERMINAL FLOWER1) is strongly related to juvenility/vegetative and flower initiation in apple, its studies will provide insight into relationship between phytohormones and juvenile/vegetative growth and flower bud formation. In this study, we monitored expression of the MdTFL1 promoter-β-glucuronidase (GUS) fusion construct in apple tissues in vitro, to determine which plant growth regulators affect its expression. Expression of MdTFL1 was induced strongly throughout newly generated young shoots of cytokinin-treated plants and in apices of shoots on medium containing cytokinin+auxin. These results suggest that cytokinin may induce MdTFL1 expression to maintain the juvenile form at the base of plant, and that cytokinin and auxin determine whether the shoot apical meristem will transit from the vegetative to the reproductive state.