The invention relates to a method to change an annual plant into a perennial plant, to change a monocarpic plant into a polycarpic plant, to change a herbaceous plant into a woody plant, to increase branching in a plant, to keep plant cells in a juvenile state, to prevent flowering in a plant and/or to increase the ploidy level in a plant or plant cell, characterised in that a protein selected from the AHL15 clade of AHL proteins or an ortholog of such a protein is introduced into said plant or plant cell. The AHL15 clade consists of the proteins AHL15, AHL16, AHL17, AHL18, AHL19, AHL20, AHL21, AHL22, AHL23, AHL24, AHL25, AHL26, AH27, AHL28, AHL29.
