Adenosine monophosphate enhances callus regeneration competence for de novo plant organogenesis

Plant tissue culture involves callus formation and de novo shoot regeneration. First, explants from differentiated tissues are used to generate a pluripotent cell mass, called callus, on auxin-rich callus-inducing medium (CIM), followed by shoot regeneration on cytokinin-rich shoot-inducing medium (SIM). Callus results from division of pericycle-like cells ( Atta et al., 2009 Atta R. Laurens L. Boucheron-Dubuisson E. et al. Pluripotency of Arabidopsis xylem pericycle underlies shoot regeneration from root and hypocotyl explants grown in vitro. Plant J. 2009; 57: 626-644 Crossref PubMed Scopus (319) Google Scholar ; Sugimoto et al., 2010 Sugimoto K. Jiao Y. Meyerowitz E.M. Arabidopsis regeneration from multiple tissues occurs via a root development pathway. Dev. Cell. 2010; 18: 463-471 Abstract Full Text Full Text PDF PubMed Scopus (439) Google Scholar ); its cellular identity resembles that of lateral root primordia ( Atta et al., 2009 Atta R. Laurens L. Boucheron-Dubuisson E. et al. Pluripotency of Arabidopsis xylem pericycle underlies shoot regeneration from root and hypocotyl explants grown in vitro. Plant J. 2009; 57: 626-644 Crossref PubMed Scopus (319) Google Scholar ; Sugimoto et al., 2010 Sugimoto K. Jiao Y. Meyerowitz E.M. Arabidopsis regeneration from multiple tissues occurs via a root development pathway. Dev. Cell. 2010; 18: 463-471 Abstract Full Text Full Text PDF PubMed Scopus (439) Google Scholar ). Callus acquires cellular pluripotency by forming root stem cell niches on CIM ( Sugimoto et al., 2010 Sugimoto K. Jiao Y. Meyerowitz E.M. Arabidopsis regeneration from multiple tissues occurs via a root development pathway. Dev. Cell. 2010; 18: 463-471 Abstract Full Text Full Text PDF PubMed Scopus (439) Google Scholar ), consistent with the upregulation of root primordium and meristem identity genes, such as LATERAL ORGAN BOUNDARIES-DOMAINs (LBDs) and PLETHORAs (PLTs) during callus formation ( Sugimoto et al., 2010 Sugimoto K. Jiao Y. Meyerowitz E.M. Arabidopsis regeneration from multiple tissues occurs via a root development pathway. Dev. Cell. 2010; 18: 463-471 Abstract Full Text Full Text PDF PubMed Scopus (439) Google Scholar ; Fan et al., 2012 Fan M. Xu C. Xu K. Hu Y. LATERAL ORGAN BOUNDARIES DOMAIN transcription factors direct callus formation in Arabidopsis regeneration. Cell Res. 2012; 22: 1169-1180 Crossref PubMed Scopus (261) Google Scholar ; Kareem et al., 2015 Kareem A. Durgaprasad K. Sugimoto K. et al. PLETHORA genes control regeneration by a two-step mechanism. Curr. Biol. 2015; 25: 1017-1030 Abstract Full Text Full Text PDF PubMed Scopus (181) Google Scholar ). After acquiring regeneration competence, calli are transferred to SIM to initiate shoot organogenesis. Cytokinin-responsive type-B ARABIDOPSIS RESPONSE REGULATORs (ARRs) and WUSCHEL (WUS) genes specify shoot stem cell niches in callus and enable shoot outgrowth ( Meng et al., 2017 Meng W.J. Cheng Z.J. Sang Y.L. Zhang M.M. Rong X.F. Wang Z.W. Tang Y.Y. Zhang X.S. Type-B ARABIDOPSIS RESPONSE REGULATORs specify the shoot stem cell niche by dual regulation of WUSCHEL. Plant Cell. 2017; 29: 1357-1372 Crossref PubMed Scopus (178) Google Scholar ).