Terrestrial plants are sessile organisms and have to adapt to various different environmental stimuli by coordinating their growth and developmental processes accordingly. Because of these needs plants have evolved a high degree of developmental and morphological plasticity. In contrast to animals, most of the organs of adult plants are produced post-embryonically. Therefore, plants possess at the tip of the shoot and the root structures called meristems that harbor pluripotent stem cells from which most cells of the plant body derive. There are two main primary meristems, the shoot apical meristem (SAM), which generates all the above-ground tissues and organs, and the root apical meristem (RAM), which gives rise to the root system of the plant. The stem cells within meristems are maintained during the whole lifespan of the plant (which can be more than 1000 years for some trees) and give rise to all tissues and organs. The necessary longevity and continuous activity of these meristems can only be achieved if the stem cell pool is replenished, since cells are constantly lost from the meristem when organs are formed at the periphery.
Therefore, fundamental questions to solve are:
- What determines stem cell fate?
- How is stem cell fate and differentiation dynamically regulated?
Our research focuses on the regulation of the stem cells within the root apical meristem (RAM) of the small model plant Arabidopsis thaliana and Hordeum vulgare (barley). Plant roots are essential for overall plant development, growth and performance by providing anchorage in the soil and uptake of nutrients and water. Previous findings have shown that conserved mechanisms in SAM and RAM consisting of small peptides and receptor kinases are responsible for cell-to-cell communication within the meristems. The output of these signaling processes regulate the expression of stem cell promoting homeodomain transcription factors like WUSCHEL (WUS) in the SAM and WUSCHEL-RELATED HOMEOBOX5 (WOX5) in the RAM. These and other transcription factors play a major role in adjusting the cell fates also of surrounding cells. We are investigating how these transcription factors regulate stem cell fate dynamically by their potential movement, complex formation and localization. We use Arabidopsis thaliana, Hordeum vulgare and Nicotiana benthamiana plants, but also use human cell lines as model systems. We are using a combination of molecular biology, genetics and in vivo advanced fluorescence microscopy (e.g. fluorescence correlation spectroscopy (FCS), fluorescence recovery after photobleaching (FRAP), fluorescence resonance energy transfer (FRET) and fluorescent lifetime imaging (FLIM) and fluorescence anisotropy) to understand how these transcription factors control the necessary tight but also dynamic regulation from stem cell fate to differentiation.