High-temperature stress acclimation in plants

Research outline
My major research interest is how changes in the abiotic environment of a plant result in acclimation to the new environment. My work focuses on two important abiotic signals; high temperature-stress (heat), relevant in the context of climate change and low light intensities.
The primary goal is to unravel the molecular factors, mechanisms and genetic networks involved in sensing and transduction of these abiotic signals and how this information is translated in appropriate responses that allow survival and growth under changing environmental conditions. For this aim I focus on two independent lines of research using the model plant Arabidopsis thaliana. 

Several interesting BSc and MSc research internship topics are available on both projects. Please contact me for opportunities and more information.

Molecular and physiological regulation of heat-induced upward leaf movement (hyponastic growth)

Financed by NWO (Netherlands Organization for Scientific Research) Innovation Research Incentives Scheme VENI grant (Grant no. 863.11.008)

Collaborative project with the Plant Ecophysiology group, Utrecht University

Plants respond quickly and profoundly to changes in their abiotic environment. One of the most striking responses is upward leaf movement (hyponastic growth; see figure 1). 
This response is among others induced by high temperature-stress (heat) and low light in the model plant Arabidopsis thaliana and is a component of submergence escape. Upward oriented leaves capture less direct sunlight, resulting in reduced heat flux and facilitate better evaporative cooling. Hence, heat-induced leaf movement probably evolved as a mechanism to control leaf temperature.

Figure 1. Top: Typical hyponastic growth response to heat. Arabidopsis thalianaaccession Columbia-0 plants were kept in control conditions (left) or were subjected for 10 h to heat (transfer from 20oC to 38oC) (right). Note the painted dots used to facilitate image analysis to measure leaf angles.  Bottom: Simplified signaling network of hormonal control of hyponastic growth induced by different environmental signals.  Adapted from: Van Zanten et al., 2010, crit rev plant sci.

Previous work focussed on the hormonal, physiological and physical regulation of the hyponastic growth response which is now relatively well understood (see reference list below). However, the molecular networks and proteins that drive the response are still largely unknown, with the notable exception of the LRR-RLK protein ERECTA, which is a positive regulator of hyponastic growth. 
By combining quantitative genetic tools such as Genome-Wide Association mapping, next-generation sequencing, state-of-the-art growth-imaging technology and standard molecular and physiological techniques, we aim to identify and characterize molecular regulators of heat-induced hyponastic growth. This will result in a better understanding of the mechanistic basis of plant acclimation to increased temperatures. Secondly, we study natural variation in these genes to unravel how this affects adaptation and acclimation to local temperatures in natural Arabidopsis populations, collected throughout the Northern hemisphere.

Molecular mechanisms and function of heat and low light-induced changes in chromatin compaction

Collaborative project with Dr. Paul Fransz, Nuclear Organization Group, University of Amsterdam

Persistent high temperature and/or (low) light stress, but also developmental phase transitions such as flowering, seed maturation and germination, result in reversible changes in chromatin compaction.
We previously demonstrated that HISTONE DEACETYLASE 6 and photoreceptors such as PHYTOCHROMES B and CRYPTOCHROME 2 are important regulators of stress-mediated changes in chromatin organization. How environmental signals affect chromatin and for what functional reasons is a largely unexplored area. Aim of this project is to elucidate the molecular networks that control chromatin (de)compaction induced by heat and light signals and to understand how large scale chromatin reorganization contributes to physiological acclimation to changes in the environment of the plant.

Figure 2: Arabidopsis leaf cell nuclei exhibit a relatively simple chromatin organization. Essentially, highly condensed ‘heterochromatic’ domains (chromocenters (white spots); top left) containing compacted DNA associated with inactivated transposable elements, (peri)centromeric and other repeated sequences (top right) and less condensed gene-rich ‘euchromatin’. Heat and low light stress results in strong decondensation of chromatin, resulting in disappearance of chromocenters (bottom left) and dispersion of (peri)centromeric repeats (bottom right).