Kirsten ten Tusscher
- Patterning and decision making in plant development and adaptation
Multicellular life has evolved independently in plants, animals and fungi with substantially different outcomes. In plants, developmental patterning continues throughout the entire lifespan of the plant, perpetually extending the body plan with new branches and organs. Each time a new lateral root, leaf bud or branch is formed the de novo formation of a stem cell niche needed to fuel the organs growth occurs, implying a high level of self-organization in plant developmental patterning. Additionally, rather than being fully steoretypical, the numbers, sizes, shapes, functional properties and orientations of new organs are fine tuned in response to environmental conditions as well as overall plant status. This requires the integration, weighting and prioritization of a multitude of environmental and internal plant signals enabling the plant to decide when, where and what to best invest its resources in.
Developmental patterning and decision making typically involve biological processes playing out at vastly differing temporal and spatial scales, ranging from the millisecond-to-minute scale movement of a transcription factor into the nucleus, via the minute-to-hour scale redistribution of auxin patterns, to the hour-to-day scale slow responses to long term nutrient starvation. In our group we use multi-scale modeling approaches, integrating these various biological processes and their interactions, to decipher the mechanisms underlying developmental patterning and decision making. We develop these models in parallel to experimental approaches, either in our own group or those of collaborators, to firmly ground our models as well as validate assumptions and test predictions. Using this approach we focus on questions such as:
How do plants determine when and where to form new lateral roots?
In the earliest step of lateral root formation, called priming, subset of root cells receive the competence for future lateral root formation. Whether or not they will subsequently develop into a lateral root will depend on environmental conditions. Priming is characterized by enigmatic oscillations in auxin levels which through growth become translated into stable peaks of high auxin signalling activity endowing the cells with lateral root competency. The nature of the priming signal and how it leads to lateral root competency is highly debated, yet its understanding is critical to decipher how lateral root spacing can be engineered.
How do plant roots sense a gradient of salt and are able to turn away from it?
Plant roots seem able to sense a salt gradient that results in 10% or less difference in salt concentrations between the left and right side of the root. Furthermore, a root does not have a central information processing center like a brain. So, with these small differences and no central processor, how then do the different sides of the root decide on which side most salt is perceived and hence where growth should turn away from? Understanding these processes may contribute to the development of salinity resistant crops, important in the light of world-wide increasing agricultural soil salinization.
How can plants preferentially invest in root growth in nutrient rich patches?
In split root experiments, the root half where most nutrients are present shows enhanced growth relative to roots only experiencing high nutrient levels while the root half where least nutrients are present shows reduced growth compared to roots only experiencing low nutrient levels. This implies that rather than simply opportunistically responding to local nutrient levels the root halves communicate, with the unlucky half somehow telling the lucky half to work harder and the lucky half somehow telling the unlucky half to stop bothering. Furthermore, the extent to which this happens depends on how much the plant is in need of that nutrient, suggesting additional integration of plant level nutrient signals. Understanding of these complex growth decision making networks may enable the breeding of less fertilizer dependent crops, capable of fending for themselves under conditions of scarce, heterogeneously distributed nutrients.