Confocal projection showing polar localisation of the auxin efflux carrier PIN1 fused to GFP. At organ inception PIN1 polarities are directed away from adjacent organ sites and towards the new site.
Using A. thaliana as a model, the Heisler group seeks to understand patterning in plant development and how it is established and regulated.
Previous and current research
In addition to providing us with the air we breathe, the food we eat and much of the energy and materials we use, plants exhibit a unique beauty associated with their strikingly symmetrical patterns of development. Multicellularity also evolved independently in plants giving us an opportunity to compare and contrast the developmental strategies used in different kingdoms.
Lateral organ formation in the model plant species Arabidopsis thaliana provides an ideal system for investigating such questions, since organ formation involves the coordination of cell polarity, gene expression and morphogenesis. Our recent work reveals that patterns of cell polarity control both morphogenesis at the cellular level as well as at the tissue level. This integration occurs through the co-alignment of microtubule arrays with the polar localisation patterns of the auxin efflux carrier PIN1. The microtubule cytoskeleton regulates growth direction at the cellular level, while PIN1 works to concentrate the hormone auxin at the tissue level to localise growth. Our data so far suggests a role for mechanical stresses in orienting these factors and we are further investigating this possibility. Interestingly, we have also found that the patterns of cell polarity associated with organogenesis correlate spatially with particular patterns of gene expression normally associated with the dorsal and ventral cell types of lateral organs. This raises the question of whether these expression domains play a causal role in organising cell polarity patterns and, in turn, whether these polarity patterns influence dorsiventral gene expression. This rich interplay is one of our prime focuses.
Future projects and goals
Our ERC-funded project focuses on the establishment and function of dorsiventral boundaries. Previously we developed confocalbased methods for imaging growing plant tissues, enabling us to obtain dynamic high-resolution data for protein localisation and gene expression (making full use of the different GFP spectral variants). By incorporating such data directly into mathematical models we aim to develop an explicit understanding of the complexity underlying patterning processes associated with dorsiventral cell type specification. Our main questions include: How do dorsiventral gene expression boundaries regulate organ morphogenesis and positioning – for example cell polarity patterns? How are dorsiventral gene expression boundaries established and regulated?
Like animals, plants can also re-pattern their tissues in response to wounding. Wounding also causes dramatic changes to dorsiventral patterning, although the mechanisms by which this occurs remain unknown. Our recent results show that cell polarity patterns respond dramatically to wounds, suggesting this cellular response may play an important role in tissue reorganisation. We aim to investigate this possibility using two-photon induced ablation and DSLM microscopy.