Universität zu Köln 

Prof. Dr. Martin Hülskamp

Botanisches Institut, Universität zu Köln
email: martin.huelskamp@uni-koeln.de
phone: +49-(0)221 470 2473
website

Sorting of mono-ubiquitylated transmembrane cargo into the inner vesicles of multivesicular bodies (MVB) for subsequent delivery to the vacuole/lysosome is mediated by the endosomal sorting complexes required for transport (ESCRT) system. Our results obtained in the first funding period indicate that the core sorting events involving the ESCRTI-III complexes have a high degree of conservation between plants, animals and yeast. In the next funding period we will focus on the analysis of three novel plant-specific genes that are involved in the first steps of ESCRT sorting. The chosen genes are functionally interrelated and may jointly regulate the initial steps of ESCRT sorting:

1. In yeast, the ubiquitin-binding affinity of ESCRT-I is enhanced by MVB12. A MVB12 homolog cannot be found in plants and might be functionally replaced by VPS23-3, a dicot-specific paralog of ELCH. We plan to explore how VPS23-3 affects ubiquitin binding properties and ultimately sorting efficiency of Arabidopsis ESCRT-I.

2. In yeast and mammals, the ESCRT-0 dimer is responsible for ESCRT recruitment to endosomes. In plants, ESCRT-0 homologs are not found. The Arabidopsis FYVE-2 protein is a good candidate to be involved in recruitment functions as it directly interacts with the ESCRT-I component ELCH and can bind the endosomal lipid phosphatidylinositol-3-phosphate. We will analyse the function of FYVE-2 in initial recruitment of ESCRT-I to the endosomal membrane.

3. ESCRT proteins have been reported to be themselves regulated by ubiquitylation. The E3 ligase EAL1 interacts directly with the plant ESCRT protein ELCH. In principle, EAL1 could regulate ESCRT trafficking by ubiquitylating the interacting ESCRT components or the ESCRT cargo. To distinguish these two possibilities we will analyse ubiquitylation of ELCH and determine the influence of EAL1 on vacuolar trafficking of soluble and transmembrane cargo.

Running time: 07/2003 – 06/2015

Recent publications:

Maier, A., Schrader, A., Kokkelink, L., Falke, C., Welter, B., Iniesto, E., Rubio, V., Uhrig, J.F., Hulskamp, M. and Hoecker, U. (2013). Light and the E3 ubiquitin ligase COP1/SPA control the protein stability of the MYB transcription factors PAP1 and PAP2 involved in anthocyanin accumulation in Arabidopsis. Plant J. 74, 638-51. PubMed

Herberth, S., Shahriari, M., Bruderek, M., Hessner, F., Muller, B., Hulskamp, M. and Schellmann, S. (2012). Artificial ubiquitylation is sufficient for sorting of a plasma membrane ATPase to the vacuolar lumen of Arabidopsis cells. Planta 236, 63-77. 

Shahriari, M., Richter, K., Keshavaiah, C., Sabovljevic, A., Huelskamp, M. and Schellmann, S. (2011). The Arabidopsis ESCRT protein-protein interaction network. Plant molecular biology 76, 85-96.

Shahriari, M., Keshavaiah, C., Scheuring, D., Sabovljevic, A., Pimpl, P., Häusler, R.E., Hülskamp, M., and Schellmann, S. (2010). The AAA-ATPase AtSKD1 contributes to vacuolar maintenance of A. thaliana. Plant J. 64, 71-85.

Shahriari, M., Hülskamp, M., and Schellmann, S. (2010). Seeds of Arabidopsis plants expressing dominant-negative AtSKD1 under control of the GL2 promoter show a transparent testa phenotype and a mucilage defect. Plant Signal Behav. 5, 71-85. Schellmann, S. and Pimpl, P. (2010). Coats of endosomal protein sorting: retromer and ESCRT. Curr. Opin. Plant Biol. 12, 670-676.

Saedler, R., Jakoby, M., Marin, B., Galiana-Jaime, E., and Hülskamp, M. (2009). The cell morphogenesis gene SPIRRIG in Arabidopsis encodes a WD/BEACH domain protein. Plant J. 59, 1080-1094.