dr.ir. R (Renze) Heidstra

A central question in biology is what determines the fate of a cell, tissue or even organ. Fate decisions taking place during embryogenesis are reiterated during the life of the plant to generate the adult architecture. Starting point in my studies on fate specification is the model plant Arabidopsis thaliana and its anatomically predictable embryonic patterning and simple root system.

Zygotic embryogenesis in many plants, including Arabidopsis thaliana, usually kicks off with the asymmetric division of the zygote, forming a smaller apical cell that generates the embryo proper and large basal cell initiating the suspensor. Natural zygotic poly-embryony originating from this normally quiescent suspensor is observed in several species but can also be experimentally induced, thereby presenting an intriguing example of reprogramming potential of cells during embryogenesis.

Mixed cell fate divisions, giving rise to daughter cells with characteristics of two tissue layers, are common in plants but near-absent in other organisms. We investigate how the SCHIZORIZA protein can influence several such occurrences during embryogenesis and root development. Specifically, the schizoriza mutant phenotype is characterized by root tissue fates moving inwards. Initial tissues are generated during embryogenesis indicating that SCHIZORIZA does not appear to represent a typical patterning gene. Instead, our results point to a novel control mechanism for plant cell fate stabilization. As SCHIZORIZA encodes a repressor heat-shock transcription factor, a related goal is to investigate whether and how its role in stress response is related to fate stability.  

Fate decisions are also instrumental during plant and tissue regeneration. However, phytohormone induced regenerative capacity varies widely between species and tissue types. This regenerative recalcitrance can be particularly distressing for the application of modern plant propagation and breeding techniques. Experiments in Arabidopsis demonstrated that during de novo shoot regeneration, cells are first persuaded to change fate towards root stem cell-like identity and subsequently are reprogrammed to acquire shoot fate. We apply our knowledge on root stem cell niche biology to induce stemness in relation to regeneration in phytohormone free conditions. PLETHORAs, SHORT ROOT / SCARECROW and WOX5 transcription factors involved in root stem cell niche specification are central in our rationale to induce regeneration.