Plant Growth Regulation
Research focus
Plants show remarkable developmental and regenerative plasticity through the sustained activity of stem cells in meristems. Under certain conditions, pluripotency can even be reestablished in cells that have already entered differentiation pathways, and this ability is an important prerequisite for plant biotechnological applications.
Using Arabidopsis as a model, we characterize genetic factors that either promote or restrict stem cell fate in different developmental contexts. In parallel, we design chemical tools capable of reprogramming differentiated cells back into stem cells. This regeneration boosters are used to optimize regeneration dependent breeding approaches such as genome editing in tissue-culture recalcitrant crop species.
Research Topic 1: Characterization of the AMP1 regulatory pathway
Mutation of the putative carboxypeptidase ALTERED MERISTEM PROGRAM1 (AMP1) causes a set of hypertrophic phenotypes, indicating a defect in the suppression of pluripotency. However, the biochemical function of this enzyme and the corresponding substrates are not known. We use genetic and biochemical approaches to identify additional components of this pathway. This let to the identification of CYP78A oxidases that act together with AMP1and its paralog LAMP1 to promote differentiation in the embryo and the shoot meristem (Huang et al., 2015; Poretska et al., 2020). Moreover, our studies revealed RAP2.6L (Yang et al., 2018) and the HD-ZIP III class of transcription factors (Yang et al., 2018; Yang et al., 2024) downstream of AMP1 function in the control pluripotency. Currently we work on further genetic candidates acting together with AMP1 to mediate cell fate maintenance in a non-cell autonomous manner.
Research Topic 2: Chemical activation of HD-ZIPIII transcription factors
We perform phenotype based as well as reporter-based small molecule screens to isolate regeneration promoting compounds which can be used to enhance organogenesis in tissue culture. One of these approaches let to the identification of Hyperphyllin (Poretska et al., 2016). This compound mimics amp1mutant phenotypes including ectopic stem cell pool formation in the shoot meristem and also provoke transcriptomic changes highly similar to a defect in AMP1 function. Using ZPR3 expression as a read out we also screened for chemicals directly inducing HD-ZIPIII activity. In this screen we identified ZIC2, which not only activated HD-ZIPIII transcription but also significantly promoted de novo shoot regeneration in tissue culture. ZIC2’s effect on HD-ZIP III expression and regeneration is based on its ability to limit polar auxin transport. Furthermore, we could show that chemical modulation of auxin efflux can enhance de novo shoot formation in the regeneration recalcitrant species sunflower (Yang et al., 2022). Additional ZIC compounds are currently under investigation.
Contact
Dr. Tobias Sieberer
Research Group Plant Growth Regulation
TUM School of Life Sciences
Technical University of Munich
Liesel-Beckmann-Strasse 1
85354 Freising
Germany
Email: tobias.sieberer(at)tum.de
Publications
Lautenbach J, Abbas Q, Brajkovic S, Sieberer T, Neumuller M, Kuster B, Poppenberger B (2025) Unraveling the proteomic landscape of red-fleshed apples to identify regulators of anthocyanin accumulation.
J Proteomics 319: 105470.
Yang S, Poretska O, Poppenberger B, Sieberer T (2024) ALTERED MERISTEM PROGRAM1 sustains cellular differentiation by limiting HD-ZIP III transcription factor gene expression.
Plant Physiol. 196: 291–308
Yang S, de Haan M, Mayer J, Janacek DP, Hammes UZ, Poppenberger B, Sieberer T (2022) A novel chemical inhibitor of polar auxin transport promotes shoot regeneration by local enhancement of HD-ZIP III transcription.
New Phytol. 235: 1111–1128
Shuai H, Chen T, Wlk T, Rozhon W, Pimenta Lange MJ, Sieberer T, Lange T, Poppenberger B (2022) SlCESTA Is a Brassinosteroid-Regulated bHLH Transcription Factor of Tomato That Promotes Chilling Tolerance and Fruit Growth When Over-Expressed.
Front Plant Sci. 13: 930805
Adedeji-Badmus AN, Schramm S, Gigl M, Iwebema W, Albertos P, Dawid C, Sieberer T, Poppenberger B(2022) Species-Specific Variation in Abscisic Acid Homeostasis and Responses Impacts Important Traits in Crassocephalum Orphan Crops.
Front Plant Sci. 13: 923421
Albertos P, Dundar G, Schenk P, Carrera S, Cavelius P, Sieberer T, Poppenberger B (2022) Transcription factor BES1 interacts with HSFA1 to promote heat stress resistance of plants.
EMBO J.: e108664
Poretska O, Yang S, Pitorre D, Poppenberger B, Sieberer T (2020) AMP1 and CYP78A5/7 act through a common pathway to govern cell fate maintenance in Arabidopsis thaliana.
PLoS Genet. 16: e1009043
Yang S, Poretska O, Sieberer T (2018) ALTERED MERISTEM PROGRAM1 Restricts Shoot Meristem Proliferation and Regeneration by Limiting HD-ZIP III-Mediated Expression of RAP2.6L.
Plant Physiol. 177: 1580-94
Poretska O, Yang S, Pitorre D, Rozhon W, Zwerger K, Uribe MC, May S, McCourt P, Poppenberger B, Sieberer T (2016) The Small Molecule Hyperphyllin Enhances Leaf Formation Rate and Mimics Shoot Meristem Integrity Defects Associated with AMP1 Deficiency.
Plant Physiol. 171: 1277-90
Huang W, Pitorre D, Poretska O, Marizzi C, Winter N, Poppenberger B, Sieberer T (2015) ALTERED MERISTEM PROGRAM1 suppresses ectopic stem cell niche formation in the shoot apical meristem in a largely cytokinin-independent manner.
Plant Physiol. 167: 1471-86
Unterholzner SJ, Rozhon W, Papacek M, Ciomas J, Lange T, Kugler KG, Mayer KF, Sieberer T, Poppenberger B (2015) Brassinosteroids Are Master Regulators of Gibberellin Biosynthesis in Arabidopsis.
Plant Cell 27: 2261-72
Khan M, Rozhon W, Unterholzner SJ, Chen T, Eremina M, Wurzinger B, Bachmair A, Teige M, Sieberer T, Isono E, Poppenberger B (2014) Interplay between phosphorylation and SUMOylation events determines CESTA protein fate in brassinosteroid signalling.
Nature Commun. 5: 4687
Rozhon W, Wang W, Berthiller F, Mayerhofer J, Chen T, Petutschnig E, Sieberer T, Poppenberger B, Jonak C (2014) Bikinin-like inhibitors targeting GSK3/Shaggy-like kinases: characterisation of novel compounds and elucidation of their catabolism in planta.
BMC Plant Biol. 14: 172
Agusti J, Herold S, Schwarz M, Sanchez P, Ljung K, Dun EA, Brewer PB, Beveridge CA, Sieberer T, Sehr EM, Greb T (2011) Strigolactone signaling is required for auxin-dependent stimulation of secondary growth in plants.
Proc Natl Acad Sci U S A 108: 20242-47
Poppenberger B, Rozhon W, Khan M, Husar S, Adam G, Luschnig C, Fujioka S, Sieberer T (2011) CESTA, a positive regulator of brassinosteroid biosynthesis.
EMBO J 30: 1149-61
Crawford S, Shinohara N, Sieberer T, Williamson L, George G, Hepworth J, Muller D, Domagalska MA, Leyser O (2010) Strigolactones enhance competition between shoot branches by dampening auxin transport.
Development 137: 2905–13
Anzola JM, Sieberer T, Ortbauer M, Butt H, Korbei B, Weinhofer I, Mullner AE, Luschnig C (2010) Putative Arabidopsis transcriptional adaptor protein (PROPORZ1) is required to modulate histone acetylation in response to auxin.
Proc Natl Acad Sci U S A 107: 10308–13
Abas L, Benjamins R, Malenica N, Paciorek T, Wisniewska J, Moulinier-Anzola JC, Sieberer T, Friml J, Luschnig C (2006) Intracellular trafficking and proteolysis of the Arabidopsis auxin-efflux facilitator PIN2 are involved in root gravitropism.
Nat Cell Biol. 8: 249–56
Bennett T, Sieberer T, Willett B, Booker J, Luschnig C, Leyser O (2006) The Arabidopsis MAX pathway controls shoot branching by regulating auxin transport.
Curr Biol. 16: 553–63
Sieberer T, Leyser O (2006) Plant science. Auxin transport, but in which direction?
Science 312: 858-60
Booker J, Sieberer T, Wright W, Williamson L, Willett B, Stirnberg P, Turnbull C, Srinivasan M, Goddard P, Leyser O (2005) MAX1 encodes a cytochrome P450 family member that acts downstream of MAX3/4 to produce a carotenoid-derived branch-inhibiting hormone.
Dev Cell 8: 443–49
Poppenberger B, Berthiller F, Lucyshyn D, Sieberer T, Schuhmacher R, Krska R, Kuchler K, Glossl J, Luschnig C, Adam G (2003) Detoxification of the Fusarium mycotoxin deoxynivalenol by a UDP-glucosyltransferase from Arabidopsis thaliana.
J Biol Chem. 278: 47905–14
Sieberer T, Hauser MT, Seifert GJ, Luschnig C (2003) PROPORZ1, a putative Arabidopsis transcriptional adaptor protein, mediates auxin and cytokinin signals in the control of cell proliferation.
Curr Biol. 13: 837–42
Sieberer T, Seifert GJ, Hauser MT, Grisafi P, Fink GR, Luschnig C (2000) Post-transcriptional control of the Arabidopsis auxin efflux carrier EIR1 requires AXR1.
Curr Biol. 10: 1595–98