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Plant development and growth are multifactorial processes regulated by a large number of endogenous signals and environmental cues. Besides other functions, the plant hormone cytokinin is a key morphogenic factor controlling cell division and differentiation, and thereby formation and growth rate of organs during the plant life cycle. The question, which plant developmental programs are under cytokinin control and which molecular mechanisms underlie cytokinin action in these processes, is in the focus of our work. Our multidisciplinary research is largely based on gene function discovery combining various molecular, genetic, biochemical and cellular approaches.

We are interested in metabolic regulation of cytokinin concentration in plant cells with a particular focus on catabolic and conjugation pathways mediated by specific enzymes.

Schematic model of cytokinin metabolism. Biosynthesis of cytokinins is initiated by adenosine phosphate-isopentenyltransferases (IPTs) to form iP-nucleotides which can be converted to the corresponding tZ-nucleotides by cytochrome P450 monooxygenases (CYP735As). Cytokinin nucleotides can be directly converted to active free bases by cytokinin nucleoside 5'-monophosphate phosphoribohydrolases (LOGs). Biologically active cytokinins are highlighted in blue, and can be inactivated by cytokinin oxidases/dehydrogenases (CKXs) and by conjugation to sugar moieties through glycosyltransferases (UGTs) (Werner & Schmülling 2009).

We aim to understand underlying mechanisms of cytokinin activity and to identify new genetic factors, which mediate or interact with the hormone activity. To this end, we for example carry out forward genetic screens, map the isolated genes and characterize them functionally.

Example of a forward genetic screen in Arabidopsis thaliana. Suppressor mutagenesis screen of cytokinin deficient Arabidopsis plants overexpressing a CKX gene and displaying complex phenotypic changes. Examples of growth rescue in different recessive and dominant second-site rock suppressor mutants (see e. g. Niemann et al. 2015; Bartrina et al. 2017).

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