Professor Hellmann's research is focusing on two main topics: the ubiquitin proteasome pathway and vitamin B6 biosynthesis.
Undergraduate Students: Interested students are
always welcome to do internships or BIO499 classes on selected
topics to gain practical experiences in laboratory work.
Graduate Students: I am currently accepting graduate students. Please feel free to contact me if you are interested in joining the lab.
In plants and most eukaryotes, the ubiquitin proteasome pathway has been proven to be crucial for many developmental and regulatory processes. The pathway is a response mediator of various different signals which are perceived by cellular receptors and transduced within the cell. E3 ubiquitin ligases are the key players in this pathway and facilitate transfer of the ubiquitin moiety to substrate proteins, which are usually transcription factors, thereby controlling stability and activity of these proteins and their downstream target genes. Cullin proteins are a common core subunit of many E3 ligase complexes. The group's main interest is in E3 ligases that contain cullins which have been demonstrated to participate in such important processes as embryo and organ development, phytohormone signal transduction, stress tolerance and light response. Ongoing goals in the group are 1) to unravel cellular and environmental conditions like phytohormones, heat stress, or light that lead to assembly of the different cullin based complexes within the cell, 2) to characterize organ and cell specific responses, 3) to identify substrate proteins that are degraded or modified by these E3 ligases, 4) to characterize signal transduction pathways activating the different cullin-based E3 ligases and 5) to functionally describe gain- and loss-of-function mutants affected in E3 ligase subunits or substrate proteins.
Vitamin B6, or pyridoxine, is an important compound that mediates more than 100 biochemical reactions. Plants, fungi, and some bacteria can synthesize this vitamin, however in humans and other mammals it must be taken up from nutrients. Several important functions of this vitamin include alleviating oxidative stress in fungus and UV-light and salt stress in higher plants. Professor Hellmann's group is interested in the final steps of vitamin B6 biosynthesis, which are catalyzed by two small protein families that assemble to higher-order protein complexes. Specifically, what mechanisms control activity of the protein complexes and how is this activity connected with stress tolerance in higher plants.
Mooney S, Leuendorf JE, Hendrickson C, Hellmann H. (2009) Vitamin B6: a long known compound of surprising complexity. Molecules 14:329-351.
Lytovchenko A, Beleggia R, Schauer N, Isaacson T, Leuendorf JE, Hellmann H, Rose JK, Fernie AR.(2009) Application of GC-MS for the detection of lipophilic compounds in diverse plant tissues.Plant Methods 5:4.
Weber H, Hellmann H. (2009) Arabidopsis thaliana BTB/ POZ-MATH proteins interact with members of the ERF/AP2 transcription factor family. FEBS J. 22: 6624 - 6635.
Leuendorf, J.E., Genau, A., Szewczyk, A, Mooney, S., Drewke, C., Leistner, E., Hellmann, H. (2008) The PDX1 family is structurally and functionally conserved between Arabidopsis thaliana and Ginkgo biloba. FEBS J. 275, 960-969.
Weber, H., Hano, P., Hellmann, H. (2007) The Charming Complexity of Cul3. Internat. J. Dev. Plant. 1, 178-184.
Bernhardt A., Lechner E., Hano P., Schade V., Dieterle M., Anders M., Dubin M.J., Benvenuto G., Bowler C., Genschik P., and Hellmann H. (2006) CUL4 associates with DDB1 and DET1 and its downregulation affects diverse aspects of development in Arabidopsis thaliana. Plant J. 47, 591-603.
Wagner S., Bernhardt A., Leuendorf J.E., Drewke C., Lytovchenko A., Mujahed N., Gurgui C., Frommer W.B., Leistner E., Fernie A.R., and Hellmann H. (2006) Analysis of the Arabidopsis rsr4-1/pdx1-3 mutant reveals the critical function of the PDX1 protein family in metabolism, development, and vitamin B6 biosynthesis. Plant Cell. 18, 1722-1735.
Ren C., Pan J., Peng W., Genschik P., Hobbie L., Hellmann H., Estelle M., Gao B., Peng J., Sun C., and Xie D. (2005) Point mutations in Arabidopsis Cullin1 reveal its essential role in jasmonate response Plant J. 42, 514-524.
Figueroa P., Gusmaroli G., Serino G., Habashi J., Ma L., Shen Y., Feng S., Bostick M., Callis J., Hellmann H., and Deng X.W. (2005) Arabidopsis Has Two Redundant Cullin3 Proteins That Are Essential for Embryo Development and That Interact with RBX1 and BTB Proteins to Form Multisubunit E3 Ubiquitin Ligase Complexes in Vivo. Plant Cell 17, 1180-1195.
Gingerich D.J., Gagne J.M., Salter D.W., Hellmann H., Estelle M., and Vierstra, R.D. (2005) Cullin 3A and B assemble with members of the broad complex/tramtrack/bric-A-brac (BTB). J Biol Chem. 280, 18810-18821.
Weber H., Bernhardt A., Dieterle M., Hano P., Mutlu A., Estelle M., Genschik P., and Hellmann H. (2005) Arabidopsis AtCUL3a and AtCUL3b form complexes with members of the BTB/POZ-MATH protein family. Plant Physiol. 137, 83-93.
Hellmann H., Hobbie L., Chapman A., Dharmasiri S., Dharmasiri N., del Pozo C., Reinhardt D., and Estelle M. (2003) Arabidopsis AXR6 encodes CUL1 implicating SCF E3 ligases in auxin regulation of embryogenesis. EMBO J. 22, 3314-3325.
Risseeuw E.P., Daskalchuk T.E., Banks T.W., Liu E., Cotelesage J., Hellmann H., Estelle M., Somers D.E., and Crosby W.L. (2003) Protein interaction analysis of SCF ubiquitin E3 ligase subunits from Arabidopsis (2003) Plant J. 34, 753-767.
Dharmasiri S., Dharmasiri N., Hellmann H., and Estelle M. (2003) The RUB/Nedd8 Conjugation Pathway is required for Early Development in Arabidopsis. EMBO J. 22, 1762-1770.
Gray W.M., Hellmann H., Dharmasiri S., and Estelle M. (2002) Role of the Arabidopsis RING-H2 protein RBX1 in RUB modification and SCF function. Plant Cell 14, 2137-2144.
del Pozo J.C., Dharmasiri S., Hellmann H., Walker L., Gray W.M., and Estelle M. (2002) AXR1-ECR1-dependent conjugation of RUB1 to the Arabidopsis Cullin AtCUL1 is required for auxin response. Plant Cell 14, 421-433.
Hellmann H. and Estelle M. (2002) Plant Development: Regulation by Protein Degradation. Science 297, 793-797.
Shen W.H., Parmentier Y., Hellmann H., Lechner E., Dong A., Masson J., Granier F., Lepiniec L., Estelle M., and Genschik P. (2002) Null Mutation of AtCUL1 Causes Arrest in Early Embryogenesis in Arabidopsis. Mol Biol Cell. 13, 1916-1928.
Deuschle K., Funck D., Hellmann H., Daschner K., Binder S., and Frommer W.B. (2001) A nuclear gene encoding mitochondrial Delta-pyrroline-5-carboxylate dehydrogenase and its potential role in protection from proline toxicity. Plant J. 27, 345-356.
Hellmann H., Funck D., Rentsch D., and Frommer W.B. (2000) Hypersensitivity of an Arabidopsis thaliana Sugar Signalling Mutant Towards Exogenous Proline Application. Plant Physiol. 123, 779-789.
Hellmann H., Barker L., Funck D., Frommer W.B. (2000) The Regulation of Assimilate Allocation and Transport. Aust. J. Plant. Physiol. 27, 583-594.
Barker L., Kühn C., Weise A., Schulz A., Gebhardt C., Hirner B., Hellmann H., Schulze W., Ward J.M., and Frommer W.B. (2000). SUT2, a Putative Sucrose Sensor in Sieve Elements. Plant Cell 12, 1153-1164.
Lalonde S., Boles E., Hellmann H., Ward J.M., and Frommer, W.B. (1999) A Dual Function of Plant Sugar Carriers in Transport and in Sugar Sensing? Plant Cell 11, 707-726.
Martin T., Hellmann H., Schmidt R., Willmitzer L., and Frommer W.B. (1997) Identification of Mutants in Metabolically Regulated Gene Expression. Plant J. 11, 53-62.