| The plant hormone auxin is involved in a variety of physiological and developmental processes. It is unique among plant hormones, since a directed polar transport of the growth regulator throughout the entire plant appears to be essential for auxin action in diverse growth responses. The most abundant natural occurring auxin is indole-3-acetic acid (IAA). The chemiosmotic model for polar IAA transport provides a working model for mechanisms ensuring directional distribution of the growth regulator. The most important aspect of this model is that the auxin efflux carrier is predominantly localised to one side of the cell, thereby ensuring polarity to IAA transport. The family of PINFORMED (PIN) proteins fulfils an essential role in the efflux of IAA. The PIN protein family of transmembrane domain (TMD) proteins, comprising eight family members, represents one of the most intensively studied in plants. Members of this protein family are involved in facilitating the efflux of the plant hormone auxin. Initial work on PIN1 and PIN2 provided first evidence for their involvement in polar IAA transport. In particular, the finding that PIN proteins exhibit an asymmetric intracellular distribution, together with the fact that they are transmembrane proteins, led to the assumption that PIN proteins might represent a component of the long-searched IAA efflux carrier complex. Subsequent functional analysis of these and additional members of the PIN family provided a conceptual framework, describing not only the role of individual PIN proteins in plant growth and development, but also their general correlation with local IAA gradients and their concerted impact on plant organogenesis. Taken together, it can be stated that PIN proteins represent a highly important function in plant growth and development. In the past decade a wealth of information about the function of representatives of the PIN protein family has been generated. However, from a biochemical point of view there is relatively little known about the PIN proteins. This is probably, in part, due to the fact that they are transmembrane proteins, which complicates biochemical analyses. A milestone for PIN research and for plant developmental biology in general would be to understand the structure function relationships of PIN proteins. Therefore the aims of the research proposed here are: 1.) Produce PIN proteoliposomes with purified PIN proteins to study the functional properties of PINs. 2.) Identify interactors of PIN proteins by co-immunoprecipitation (co-IP). 3.) Elucidate structure function relationships of PIN proteins by purification and the subsequent crystallization of representative PIN proteins. Through the collaboration between the Scheres and the Gros laboratories we are in the unique position to perform this research successfully. The neighbouring laboratory of Prof. Piet Gros, an established laboratory in the field of membrane protein crystallisation, provides essential know-how and expertise to this proposed research. With the information gathered in this research project we will be able to engineer PIN variants changing plant development beneficially and this thus represents a valuable contribution for plant science and future, applied biotechnological approaches in molecular breeding and crop improvement. |
