Hanjo A. Hellmann

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Sugars are ubiquitous and critical components for general metabolism. These primary products from photosynthesis affect most, if not all, processes in plant cells by providing skeletons for organic compounds and storing energy for chemical reactions. Sugars also serve as critical signaling molecules in relation to both cellular metabolic status and biotic(More)
In leaves, sucrose uptake kinetics involve high- and low-affinity components. A family of low- and high-affinity sucrose transporters (SUT) was identified. SUT1 serves as a high-affinity transporter essential for phloem loading and long-distance transport in solanaceous species. SUT4 is a low-affinity transporter with an expression pattern overlapping that(More)
Ubiquitin E3 ligases are a diverse family of protein complexes that mediate the ubiquitination and subsequent proteolytic turnover of proteins in a highly specific manner. Among the several classes of ubiquitin E3 ligases, the Skp1-Cullin-F-box (SCF) class is generally comprised of three 'core' subunits: Skp1 and Cullin, plus at least one F-box protein(More)
Delta1-pyrroline-5-carboxylate (P5C), an intermediate in biosynthesis and degradation of proline (Pro), is assumed to play a role in cell death in plants and animals. Toxicity of external Pro and P5C supply to Arabidopsis suggested that P5C dehydrogenase (P5CDH; EC plays a crucial role in this process by degrading the toxic Pro catabolism(More)
Selective modification of proteins by ubiquitination is directed by diverse families of ubiquitin-protein ligases (or E3s). A large collection of E3s use Cullins (CULs) as scaffolds to form multisubunit E3 complexes in which the CUL binds a target recognition subcomplex and the RBX1 docking protein, which delivers the activated ubiquitin moiety. Arabidopsis(More)
Cullin-based E3 ubiquitin ligases play important roles in the regulation of diverse developmental processes and environmental responses in eukaryotic organisms. Recently, it was shown in Schizosaccharomyces pombe, Caenorhabditis elegans, and mammals that Cullin3 (CUL3) directly associates with RBX1 and BTB domain proteins in vivo to form a new family of E3(More)
The AXR6 gene is required for auxin signaling in the Arabidopsis embryo and during postembryonic development. One of the effects of auxin is to stimulate degradation of the Aux/IAA auxin response proteins through the action of the ubiquitin protein ligase SCF(TIR1). Here we show that AXR6 encodes the SCF subunit CUL1. The axr6 mutations affect the ability(More)
Sucrose is the main transported form of assimilates, but, significantly, it also regulates a variety of processes such as photosynthesis and carbon or nitrogen storage. The effects of high sucrose levels are mediated directly by modulation of gene expression. The regulation of storage protein accumulation, here patatin from potato tubers, was used as a(More)
In transgenic Arabidopsis a patatin class I promoter from potato is regulated by sugars and proline (Pro), thus integrating signals derived from carbon and nitrogen metabolism. In both cases a signaling cascade involving protein phosphatases is involved in induction. Other endogenous genes are also regulated by both Pro and carbohydrates. Chalcone synthase(More)
Mutations in the AXR1 gene result in a reduction in auxin response and diverse defects in auxin-regulated growth and development. In a previous study, we showed that AXR1 forms a heterodimer with the ECR1 protein. This enzyme activates the ubiquitin-related protein RUB1 in vitro. Furthermore, we showed that the Skp1-Cul1/Cdc53-F-box (SCF) subunit AtCUL1 is(More)