The vegetative juvenile-to-adult transition (vegetative phase change) is a critical phase in plant development, the timing of which is controlled by the highly conserved age pathway, comprising the miR156/miR157-SPL module and the downstream miR172-AP2-like module, and is modulated by exogenous and endogenous cues. The phytohormones cytokinin (CK) and gibberellin (GA) have been described to both alter miR172 levels, most probably by regulating SPL activity. In this study, we establish an epistatic relation between CK and GA, in which CK action depends on GA, contrasting with the antagonistic nature described previously for CK-GA crosstalk. We show that CK positively affects GA biosynthesis during Arabidopsis vegetative development and depends on the GA biosynthetic enzymes GA3ox1 and GA3ox2 to modify the appearance of abaxial trichomes as well as leaf shape, both hallmarks of vegetative phase change. Downstream of CK, epidermal identity is regulated in dependence of SPL transcription factors, the GA signaling repressors GAI and RGA and the miR172-targets TOE1 and TOE2. Notably, genetic analysis revealed that GA regulates this process also CK-independently. Furthermore, our data from genetic analyses suggests that CK affects leaf shape through other GA signaling components and AP2-like transcription factors rather than SPLs. Hence, CK differentially regulates several aspects of vegetative phase change. The work contributes to the understanding of vegetative phase change regulation as well as phytohormone crosstalk in general.

• MeSH
• Arabidopsis * metabolism   genetics   growth & development   MeSH
• Cytokinins * metabolism   MeSH
• Gibberellins * metabolism   MeSH
• Plant Leaves metabolism   growth & development   MeSH
• MicroRNAs metabolism   genetics   MeSH
• Mixed Function Oxygenases metabolism   genetics   MeSH
• Arabidopsis Proteins metabolism   genetics   MeSH
• Gene Expression Regulation, Plant MeSH
• Plant Growth Regulators metabolism   MeSH
• Signal Transduction MeSH
• Transcription Factors metabolism   genetics   MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Cytokinins * MeSH
• GAI protein, Arabidopsis MeSH Browser
• Gibberellins * MeSH
• Nuclear Proteins MeSH
• MicroRNAs MeSH
• Mirn156 microRNA, Arabidopsis MeSH Browser
• Mixed Function Oxygenases MeSH
• Arabidopsis Proteins MeSH
• Plant Growth Regulators MeSH
• Repressor Proteins MeSH
• RGA protein, Arabidopsis MeSH Browser
• SPL protein, Arabidopsis MeSH Browser
• Transcription Factors MeSH

Common centaury (Centaurium eryhtraea Rafn) is a medicinal plant species with vigorous morphogenic potential in vitro. The process of spontaneous shoot regeneration in a solid root culture is characteristic for this plant species. In this context, the aim of this work was to investigate the dynamic changes of endogenous phytohormones and carbohydrates content in root explants at different time points (0, 2, 4, 7, 14, 21, 28, and 60 days) during spontaneous centaury morphogenesis in vitro. Detailed analysis of cytokinins (CKs) showed that trans-zeatin (tZ) was the major bioactive CK at all time points. The corresponding riboside, tZ9R, was also determined in the majority of the identified transport forms, at all time-points. Further analysis of endogenous auxin revealed a significant increase in endogenous indole-3-acetic acid (IAA) after 21 days, when a huge jump in the ratio of IAA/bioactive CKs was also observed. The maximum total soluble sugar content was measured after 14 days, while a significant decrease was determined after 21 days, when the first regenerated adventitious shoots appeared. This undoubtedly indicates an increased energy requirement prior to the actual regeneration of the shoots. The obtained results indicate that the period from day 14 to day 21 involves the most dramatic disturbances in endogenous bioactive CKs, IAA and carbohydrate balance, which are very important and valuable factors for the onset of shoot regeneration.

• Keywords
• auxin, centaury, cytokinin, morphogenesis, phytohormone, soluble sugars,
• Publication type
• Journal Article MeSH