About this Research Topic
Cytokinins represent a group of growth regulators controlling a wide spectrum of plant developmental and adaptive responses. In the last decade, we have witnessed tremendous progress in the understanding of many aspects of cytokinin biology.
The genes controlling cytokinin biosynthesis and metabolism, including the formation of active bases from cytokinin ribotides as well as cytokinin inactivation via glucosylation or degradation, were identified and the substrate specificity of some of the encoded proteins was determined. Additional research has uncovered the cytokinin sensors and the entire downstream signaling pathway and the majority of the cytokinin-controlled genes are now known. Employing knock-out mutants of individual members of the multistep phosphorelay allowed the identification of the role of cytokinins in the control of key developmental processes, including cell division and cell differentiation, cell type and organ specification, positioning of apical meristem organizing centers, sink formation, chloroplast biogenesis, and tropisms. Development of novel MS-based protocols for the quantification of individual cytokinin metabolites made it possible to study cytokinin distribution not only on the organ but also on cellular and even subcellular levels. Supplementing these techniques, proteins involved in active cytokinin transport were identified. Several mechanisms mediating the crosstalk of cytokinins with other hormones were described. Finally, the roles of cytokinins in (a)biotic stress responses and epigenetic regulation are emerging, promising to pave new roads for cytokinin research in crop breeding.
In spite of the dramatic improvement of knowledge in the aforementioned aspects of cytokinin research, there are still many twisted roads and niches that remain to be explored, as well as previously established dogmas to be challenged using steadily developing technologies. A good example could be a recent finding on the ability of activation in planta of N-glucosides, previously thought to be permanently inactivated cytokinin forms.
This Research Topic aims to provide a platform to consolidate recent knowledge, as well as to publish novel findings and propose new directions that will shape the future of cytokinin research. Within the Research Topic, we welcome Original Research, Review and Methods falling under (but not limited to) the following categories:
• Cytokinin biosynthesis and metabolism
• Cytokinin signaling and gene regulation
• Cytokinins and plant proteome
• Control of cytokinin distribution (both on the tissue/organ level as well as intracellular partitioning)
• Cytokinins in plant development
• Cytokinins in (a)biotic stress response and epigenetic regulations
• Crosstalk of cytokinins with other hormones or signals
• Applied aspects of cytokinin research
• Evolution of the cytokinin signaling system
Keywords: Cytokinin biosynthesis and metabolism, Cytokinin sensors, Signaling pathway, Developmental processes, Cytokinin active transport, Cytokinin distribution, Hormone crosstalk
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