PIN polarity control by Arabidopsis WAV3-type proteins

Plants are characterized by directed growth and show a defined polarity in the formation and differentiation of organs, such as roots or shoots. Such polarity in growth occurs in response to environmental parameters in order to enable optimal adaptation to highly variable environmental conditions. Directional growth of plants is regulated by different growth factors. The plant hormone auxin plays a central role and is involved in a wide range of plant development processes. This diversity is made possible by controlled, local variations in intracellular auxin concentration, which in turn is influenced by the directional transport of the hormone throughout the entire plant body. PIN-FORMED auxin transport proteins are responsible for the directional transport of the hormone and adopt an asymmetric, polar distribution at the cellular plasma membrane, which ultimately defines the direction of auxin transport. To gain a deeper understanding of the mechanisms that influence the distribution of PIN-FORMED proteins and variations therein, we try to understand the function of the WAV3 proteins in the model plant Arabidopsis. WAV3 itself shows a polar distribution at the plasma membrane and controls the polar distribution of the PIN-FORMED proteins. Variability in WAV3 expression as well as the subcellular distribution and enzymatic activity of WAV3, all could play a role. In this project we attempt to define and functionally characterize the WAV3 protein domains and their relevance for PIN-FORMED polarity control. For this purpose, a wide variety of mutated versions of WAV3 as well as chimeric protein fusions composed of domains of WAV3 and of related proteins are tested for their functionality. In addition, we want to analyze the mechanisms of subcellular polar distribution of WAV3, by using cell biology, pharmacological and genetic methods. With these approaches, a potential function of WAV3 as a positional marker in the control of PIN-FORMED polarity shall be tested. Ultimately, we will identify cellular factors that interact with WAV3, employing innovative state-of-the-art labeling techniques. The resulting characterization of the WAV3 interactome should contribute significantly to an understanding of molecular mechanisms that mediate polar PIN-FORMED distribution and adaptability in higher plants.