Prof. Thomas GrebDevelopmental Physiology
Radial growth of plant shoots and roots is essential for the formation of wood and of large plant bodies, and thus for the creation of biomass on earth. Our lab uses this process as an example to reveal principles of growth and cell fate regulation in multicellular organisms. Multi-cellularity is a fundamental concept of life on our planet. This concept of single cells taking over special functions in interaction with other cells in a multicellular body is striking and requires a very complex system of cell-to-cell communication. Elucidating comprehensive concepts of the development and function of multicellular systems is therefore challenging, but also essential to understand their functionality.
Radial growth of plant shoots and roots is based on the tissue-forming properties of a group of stem cells called the cambium, the activity of which leads to the production of secondary vascular tissue (xylem/"wood" and phloem/"bast"). Considering its function as a stem cell niche that is essential for the constant production of new tissues, as well as its dependence on environmental cues, the cambium represents an ideal model for addressing questions concerning the regulation of cell identity and how growth processes are aligned with endogenous and exogenous requirements. Given these attractive properties, our laboratory investigates radial plant growth in order to reveal general concepts of growth regulation in multicellular organisms at the interface between development and physiology.
(a) Cross section from the hypocotyl (i.e. the root-to-shoot junction) of a five week-old Arabidopsis thaliana plant. Hypocotyl diameter is at this stage about 2 mm. The picture on the right shows the magnified cambial zone. Figure taken from Chiang et al., 2019.
(b) Functional cambium domains and cell types. A layer of bifacial stem cells (in red) produces xylem and phloem tissues in opposite directions. These tissues contain different cell types specialized in transporting water (vessel elements) or sugars (sieve elements) throughout the plant body. Figure taken from Chiang et al., 2019.
(c) Activity patterns of promotors associated with distinct cambium domains.
(d) Recently revealed interactions between cambium regulators. Be aware that the role of the PEAR genes and their interaction with HD-ZIP III genes has only been characterized for cambium specification. The club-shaped symbol between ARF5/MP and WOX4 indicates that ARF5/MP keeps WOX4 activity at a certain level.
Shi D, et al. (2021) Tissue-specific transcriptome profiling of the Arabidopsis inflorescence stem reveals local cellular signatures. Plant Cell doi:10.1093/plcell/koaa019.
Chiang MH, et al. (2019) How to organize bidirectional tissue production? Curr Opin Plant Biol 51:15-21.
Miyashima S, et al. Helariutta Y (2019) Mobile PEAR transcription factors integrate positional cues to prime cambial growth. Nature 565:490–494.
Shi D, et al. (2019) Bifacial cambium stem cells generate xylem and phloem during radial plant growth. Development 146:dev171355.
Brackmann K, et al. (2018) Spatial specificity of auxin responses coordinates wood formation. Nat Commun 9(1):875.
Wallner ES, et al. (2017) Strigolactone and karrikin-independent SMXL proteins are central regulators of phloem formation. Curr Biol 27(8):1241–1247.