Control of ROP function by membrane lipids during plant exocytosis and endocytosis
Final Report Abstract
Phosphoinositides (PIs) are key players in plant development and physiology, serving as landmarks to recruit proteins and influence the inner charge distribution of the plasma membrane. This project was intended to delineate molecular targets of PIs that contribute to the control of endocytosis or exocytosis, and/or of cytoskeletal dynamics. As output, we identified proteins in the machineries for membrane trafficking and cytoskeletal control which interact with PIs and/or with enzymes of PI-metabolism, and we elucidated functional consequences of these interactions. PIs, such as phosphatidylinositol 4,5-bisphosphate (PIP2), can control more than one alternative process, and it is a major question in eukaryotic cell biology what principles lend specificity to PIP2 effects. Based on data from this project, we can report new observations on this important aspect from experiments on the polar tip growth of pollen tube cells, which requires strict coordination of cytoskeletal dynamics, exocytosis and endocytosis, and which employs PIP2 as a regulatory factor. Based on our previous observation that overproduction of PIP2 by certain isoenzymes of PI4P 5-kinase in pollen tube cells perturbs cell morphology differentially in an isoform-specific manner, our data revealed that alternative PIP2-dependent effects on either actin-dynamics or on secretion/endocytosis are based on asymmetric lateral plasma membrane-distribution of PI4P 5-kinase isoforms, e.g., in membrane nanodomains. The observation that nanodomain-associated PIP2 specifically influenced actin-dynamics is consistent with reports by others describing actinregulatory factors, such as ROPs or their GEFs, associated with plasma membrane nanodomains in plants. However, it is unclear why the regulation of actin-dynamics in plant cells occurs at the plasma membrane, or even how actin filaments interact with the plasma membrane to aid membrane-proximal vesicle trafficking. Here we identified so far enigmatic myosins of the plant-specific class VIII as proteins that bind anionic membrane phospholipids as well as actin, thereby mediating actin-plasma membrane attachment. Moreover, we identified class VIII myosins as regulators of PIP2 production in membrane nanodomains and revealed a novel interaction of the class VIII myosin, ATM2, with endocytotic adaptor complexes (AP-2 complexes), linking the PIP2-dependent stabilization of actin-filaments at the plasama membrane with the initiation of clathrin-mediated endocytosis. In this context, we furthermore characterized the contribution of lipid- and especially PIP2-binding features of AP-2 subunits to the functionality of the AP-2 complex during endocytis.
Publications
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Plasma membrane nano-organization specifies phosphoinositide effects on Rho-GTPases and actin dynamics in tobacco pollen tubes. The Plant Cell, 33(3), 642-670.
Fratini, Marta; Krishnamoorthy, Praveen; Stenzel, Irene; Riechmann, Mara; Matzner, Monique; Bacia, Kirsten; Heilmann, Mareike & Heilmann, Ingo
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Swap, Combine and Substitute to Unravel Specific Functions of Arabidopsis PI4P 5-kinases. Plant and Cell Physiology, 63(5), 576-579.
Heilmann, Ingo
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The pollen-specific class VIII-myosin ATM2 from Arabidopsis thaliana associates with the plasma membrane through a polybasic region binding anionic phospholipids. Biochimie, 203, 65-76.
Kastner, Christoph; Wagner, Vera C.; Fratini, Marta; Dobritzsch, Dirk; Fuszard, Matthew; Heilmann, Mareike & Heilmann, Ingo
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Association of the Arabidopsis oleoyl Δ12‐desaturase FAD2 with pre‐cis‐Golgi stacks at endoplasmic reticulum‐Golgi‐exit sites. The Plant Journal, 117(1), 242-263.
Launhardt, Larissa; Uhlenberg, Johanna; Stellmach, Hagen; Schomburg, Marie; Hause, Bettina; Heilmann, Ingo & Heilmann, Mareike
