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. Questions we are asking are toward tissue patterning, cell fate specification and inter-cellular communication from the level of sub-cellular structures to whole organs.
In the first picture, you see 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 and one cross section contains 10,000 to 20,000 cells. By generating xylem and phloem cells in opposite directions, the cambium drives radial organ growth important for mechanical support of the plant body and for allowing enough water and sugars to be transported along xylem and phloem tissues, respectively.
In the second picture, functional cambium domains and cell types are shown. 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. Both pictures are taken from Chiang et al., 2019.
Shi D, et al. (2021) Tissue-specific transcriptome profiling of the Arabidopsis inflorescence stem reveals local cellular signatures. Plant Cell 33(2):200-223
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