Proper gibberellin localization in vascular tissue is required to control auxin-dependent leaf development and bud outgrowth in hybrid aspen

Bioactive gibberellins (GAs) are involved in many developmental aspects in the life cycle of plants, acting either directly or through interaction with other hormones. One way to study the role of GA in specific mechanisms is to modify the levels of bioactive GA in specific tissues. We increased GA catabolism in different parts of the vascular tissue by overexpressing two different GA 2-oxidase genes that encode oxidases with affinity for C-20- or C-19-GA. We show that, irrespective of their localization in the vascular tissue, the expression of different members of this gene family leads to similar modifications in the primary and secondary growth of the stem of hybrid aspen. We also show that the precise localization of bioactive GA downregulation is important for the proper control of other developmental aspects, namely leaf shape and bud dormancy. Expression under the control of one of the studied promoters significantly affected both the shape of the leaves and the number of sylleptic branches. These phenotypic defects were correlated with alterations in the levels and repartitioning of auxins. We conclude that a precise localization of bioactive GA in the vasculature of the apex is necessary for the normal development of the plant through the effect of GAs on auxin transport.