FERONIA receptor kinase as a cell surface-located regulator for RAC/ROP GTPase-mediated auxin signaling

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The plant hormone auxin controls both cell growth and cell division and also has a crucial role in determining overall morphology. The molecular-level details of auxin signal perception have been studied for decades. An auxin receptor complex located in the nucleus has been associated with many auxin-regulated processes. It is not clear, however, that this complex can explain the full range of auxin-regulated phenomena, especially those occurring along the cell membrane. Thus, the search for a cell surface-located auxin signaling mechanism continues. This project will extend previous work showing that auxin activates major signal mediators that function along the inner surface of the cell membrane called RAC/ROP GTPases. These important proteins may act as mediators activating surface-located responses. The current project will test whether the transmembrane protein FERONIA could be the missing link connecting extracellular auxin signals to this system. Specifically, this project will determine whether the extracellular domain of FERONIA directly interacts, alone or in a complex, with a low molecular weight extracellular matrix protein called LORELEI-like glucosylphosphatidylinositol-anchored protein1. Biochemical methods such as protein co-immunoprecipitation, pull-down assays and cell biological methods will be used to test for these interactions in plant cells and determine how auxin affects them. Direct auxin-binding studies will be used to test for receptor-ligand interactions between auxin and FERONIA or FERONIA complexes. These crucial experiments testing the potential of FERONIA as a cell surface auxin signaling apparatus will provide training for one graduate student and one postdoctoral fellow.