ABSTRACT
Mutual interactions of the phytohormones, cytokinins and auxin determine root or shoot identity during postembryonic de novo organogenesis in plants. However, our understanding of the role of hormonal metabolism and perception during early stages of cell fate reprogramming is still elusive. Here we show that auxin activates root formation, whereas cytokinins mediate early loss of the root identity, primordia disorganisation and initiation of shoot development. Exogenous and endogenous cytokinins influence the initiation of newly formed organs, as well as the pace of organ development. The process of de novo shoot apical meristem establishment is accompanied by accumulation of endogenous cytokinins, differential regulation of genes for individual cytokinin receptors, strong activation of AHK4-mediated signalling and induction of the shoot-specific homeodomain regulator WUSCHEL. The last is associated with upregulation of isopentenyladenine-type cytokinins, revealing higher shoot-forming potential when compared with trans-zeatin. Moreover, AHK4-controlled cytokinin signalling negatively regulates the root stem cell organiser WUSCHEL RELATED HOMEOBOX 5 in the root quiescent centre. We propose an important role for endogenous cytokinin biosynthesis and AHK4-mediated cytokinin signalling in the control of de novo-induced organ identity.
Footnotes
Author contributions
Conceptualization: M.P., J.H.; Methodology: M.P., D.H., T. Kakimoto, M.G.H., O.N.; Formal analysis: M.P., M.G., T. Konecny, L.P., D.H., T. Kakimoto, M.G.H., O.N.; Investigation: M.P., J.H.; Resources: M.P., T. Kakimoto, J.H.; Data curation: M.P., M.G., T. Konecny, L.P., D.H., O.N.; Writing - original draft: M.P., J.H.; Writing - review & editing: M.P., J.H.; Visualization: M.P.; Supervision: M.P., O.N., J.H.; Project administration: M.P.; Funding acquisition: M.P., O.N., J.H., T. Kakimoto.
Funding
This work was supported by the Grantová Agentura České Republiky [GP14-30004P to M.P. and T. Konecny, and 13-25280S to J.H.], the Ministerstvo Školství, Mládeže a Tělovýchovy [CEITEC 2020 (LQ1601) to M.P., M.M. and J.H.; LH14104 to M.P. and J.H.; National Program for Sustainability I, LO1204 to L.P. and O.N.; LM2015062 Czech-BioImaging], the EU Seventh Framework Programme [286154 – SYLICA to M.P.] and a Japan Society for the Promotion of Science grant [25113006 to T. Kakimoto].
