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Plants, unlike animals, are unique in their developmental plasticity that allows them to undergo postembryonic de novo organogenesis – create new organs postembryonicly. This requires the presence of regulators that trigger and mediate specific spatiotemporal changes in developmental programs. The phytohormones auxin and cytokinins have been known as the principal regulators of plant development for more than six decades. In de novo organogenesis, auxin is the principal morphogen required to induce new organ onset, while cytokinins modulate the type of organogenic response. In in vitro regeneration, auxin activates root formation while cytokinins mediate early loss of the root identity, morphological changes, and initiation of shoot development. Exogenous but also endogenous cytokinins influence both the initiation of newly formed organs as well as the pace of organ developmental sequence. The process of de novo shoot apical meristem establishment is accompanied by strong activation of AHK4-mediated cytokinin signalling, induction of shoot-specific homeodomain regulator WUSCHEL and upregulation of endogenous isopentenyladenine-type cytokinins. Moreover, AHK4-controlled cytokinin signalling negatively regulates root stem cell organizer WUSCHEL RELATED HOMEOBOX 5 in the root quiescent centre thus probably suppressing root identity. It seems that endogenous cytokinin biosynthesis and AHK4-mediated cytokinin signalling play an important role in the control of de novo induced organ identity. Currently, we study particular cytokinin signalling pathways and the impact of cytokinin metabolism leading to organ identity specification during regeneration.
