The Roles of Gibberellins and Cytokinins in Plant Phase Transitions

Plants undergo distinct phase transitions during their post-embryonic development and progresses from the juvenile to the adult and reproductive phases. These transitions are characterized by morphological and molecular changes and are differently influenced by gibberellins (GAs) and cytokinins (CKs). GAs are notably known to either induce or repress phase transition and flowering in diverse plant species. This GA-mediated modulation is ultimately related to the behavior of the DELLA transcriptional regulators. CKs influence phase transitions by promoting meristem cell divisions and flowering stimulation. Moreover, CKs and GAs can mutually repress each other or have complementary functions in processes such as branching and flowering. Therefore, the effects observed such as flower formation and vegetative growth is modulated by the co-regulation exerted by the cross-talk of both GA and CK pathways. We review the roles of GA and CK in phase transitions at the molecular level in model species such as Arabidopsis and the genes that are modulated by both GA and CK pathways. Additionally we point out perspectives of the conservation of these molecular pathways in tropical plants.