Systems biology of cambium differentiation in Arabidopsis thaliana L.
Bioinformatics and Theoretical Biology
Final Report Abstract
As a fundamental principle, growth and development of multicellular organisms is based on the activity of stem cell systems. The dualisms of stem cell proliferation on the one side and fate determination of immediate descendants on the other side lays at the core of this principle. Bidirectional stem cell niches are in this sense unique because they depend on a strict spatial organization and a flexible fate determination based on positional cues. Interestingly, similar patterns in regulatory circuits of bifacial stem cell niches are found in the plant and animal kingdom where for instance radial plant growth and the expansion of the fish retina, respectively, involves the production of two tissue by a common stem cell niche. Radial plant growth is conducted by lateral meristems organized in cylindrical domains at the periphery of shoots and roots. The most prominent lateral meristem is the cambium which is embedded in and produce two distinct vascular tissues in opposite directions by periclinal cell divisions: the xylem (wood) and the phloem (bast). These tissues are important for longdistance transport of water and nutrients in case of the xylem and of sugars and a multitude of signalling molecules in the case of the phloem. Ultimately, cambium activity leads to the thickening of stems and roots. Based on its tightly controlled bidirectionality of tissue production and bipartite organization, the cambium is used as one paradigm for bifacial stem cell niches found across different kingdoms of life. The role of cambium-dependent tissue production as an essential sink for atmospheric CO2 contributes to the importance of revealing its molecular regulation. By joining forces of the groups of Victoria Mironova (Radboud University, The Netherlands) and Thomas Greb (Heidelberg University, Germany) within this project, the decisionmaking process within cambium-derived cells was systematically characterized. Combining expertise from the two groups allowed both mathematical and molecular investigation of gene regulatory networks resulting in the identification of three interacting factors sufficient to instruct continuous bidirectional production of xylem and phloem cells. The project also allowed assigning roles of the cytokinin and the auxin signaling pathways to two of these factors which are, in turn, balanced by the transcription factor WUSCHEL-RELATED HOMEOBOX4 (WOX4) as a third factor. By furthermore identifying downstream targets of WOX4, we established molecular representatives of factors described by the mathematical model. In conclusion, this study provided a mechanism of cell fate decision making in vascular cambium stem cells.
Publications
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Tissue-specific transcriptome profiling of the Arabidopsis inflorescence stem reveals local cellular signatures. The Plant Cell, 33(2), 200-223.
Shi, Dongbo; Jouannet, Virginie; Agustí, Javier; Kaul, Verena; Levitsky, Victor; Sanchez, Pablo; Mironova, Victoria V. & Greb, Thomas
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Cell Fate Decisions Within the Vascular Cambium–Initiating Wood and Bast Formation. Frontiers in Plant Science, 13.
Haas, Aylin S.; Shi, Dongbo & Greb, Thomas
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Control of cambium initiation and activity in Arabidopsis by the transcriptional regulator AHL15. Current Biology, 32(8), 1764-1775.e3.
Rahimi, Arezoo; Karami, Omid; Lestari, Angga Dwituti; de Werk, Tobias; Amakorová, Petra; Shi, Dongbo; Novák, Ondřej; Greb, Thomas & Offringa, Remko
