Evolution of AGC1 kinase-mediated polarity modules in early land plant development

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Animal and plant cells establish polar regions on their plasma membranes to control cell division and cell differentiation. In animals, the regulation of polar PAR proteins is well understood and an important model for the study of numerous differentiation processes. There are no PAR orthologues in plants but we have evidence that so-called AGC1 kinases, such as D6PK or PAX from Arabidopsis thaliana, are needed for the formation of various polarity processes in higher plants. AGC1 kinases appear for the first time in mosses and liverworts, and we therefore postulate that they play a role in important evolutionary changes in the transition to terrestrial life. A very well understood function of the AGC1 kinases is the activation of the PIN auxin transporters, which localize - independently of AGC1 kinases - in the plasma membrane. In higher plants, the polarity of the PIN proteins is regulated by so-called AGC3 kinases, which, however, are absent from early land plants. We therefore want to investigate whether PIN proteins from early land plants can already respond to AGC3 signaling and whether AGC1 kinases may play the role of AGC3 kinases in early land plants. With these studies, we will be able to make an important contribution to the understanding of molecular adaptations in early land plants.