A Complexity Science Approach to Plant Tissue Regeneration

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Tissue regeneration in multi-cellular organisms is a topic of great interest both from a basic scientific point of view and from an applied one. In the attempt to shed new light on the fundamental nature of the mechanisms underlying tissue regeneration, this project intends to test experimentally a quite technical but intriguing hypothesis on the way cellular divisions are organized during regeneration.The experimental case studied is that of a plant's root that completely regenerates its tip when this is excised by mechanical means, and a multi-disciplinary approach combining live imaging and advanced statistical analysis is followed.From the experimental point of view, the main challenge is to develop a type of microscope that allows very frequent observations of the internal organisation of a regenerating root, without of course killing the root. The idea is to be able to collect data about when and where cell divisions occur during the tissue re-growth and reorganization, and this can be achieved through a non-invasive technique that detects fluorescent proteins in the sample. The trick is to genetically engineer a fluorescent protein that is expressed in a cell only at the moment of its division, and this has been done, already.The initial part of this project is dedicated to the optimisation of a microscope - starting from existing prototypes - specifically redesigned to image for many days a regenerating root, quite often and at cellular resolution. Time-lapse sequences will be then systematically collected with this instrument, to capture in great details the regeneration of the root tip.The more advanced part of the project is aimed at the statistical analysis of such data, to test the hypothesis that the dynamics of cellular divisions guiding root regeneration shares common features with a wide class of complex phenomena found in physics and biology, as different from each other as sand piles, earthquakes, flying birds or neural networks. This class is sometimes called Self-Organizing Critical (SOC) systems, and is characterized by the ideas that (i) global patterns emerge simply from interactions among all the system's elements and without the need of a central director (self-organization) and that (ii) the system exhibits a spontaneous convergence towards a special (critical) state. At the critical state the system is said to be scale-free, which means that there is no typical length or duration in the underlying dynamics. Moreover, at the critical state some statistical distributions that describe the system's dynamics take a universal shape (power law distributions). It is a bit technical, but it turns out that these statistical distributions can be measured from the data collected with the microscope used in this project, and therefore it becomes possible to test whether a regenerating root behaves like a SOC system or not. We will then be able to test more in details the causal link between cellular interactions and global tissue behavior by developing a mathematical model designed to give a simplified representation of all the key characteristics of the system. This will be based on previous experience gained by applied mathematicians in the field of complexity science, where SOC and similar phenomena are studied in great details.Finally, it is understood that any major improvement of our understanding on how a root can regenerate its tip after a major injury opens the possibility to enhance growth and resistance of plants of economic interests in harsh conditions. Moreover, any new insight in natural mechanisms leading to tissue repair and regeneration is of major interest for the biomedical and biotech community.