75 Integrating Membrane Transport with Male Gametophyte ... - TAIR

129 The Arabidopsis elch mutant reveals a link between an ESCRT-like pathway and cytokinesis
Christoph Spitzer, Swen Schellmann, Aneta Sabovljevic, Mojgan Shahriari, Channa Keshavaiah, Martin Hulskamp
Botanical Institute III, University of Cologne, Germany
Few years ago an alternative route to the proteasomal protein degradation pathway was discovered that specifically
targets proteins marked with a single ubiquitin to the endosomal multi-vesicular-body (MVB) and subsequently to the
vacuole (yeast)/lysosome (animals) where they are degraded by proteases. Vps23 and TSG101 respectively are key
components that recognize monoubiquitinated proteins and sort them through the ESCRT I-III complexes into the
multivesicular-body (MVB). After fusion of the MVB to the vacuole/lysosome the internal vesicles are accessible to
luminal proteases.
Here we report that the Arabidopsis ELCH gene encodes a Vps23/TSG101 homolog. ELCH binds monoubiquitin
in vitro and interacts in yeast two hybrid analysis with the putative plant homolog of Vps37 which is part of yeast and
mammalian ESCRT I complex. Whereas studies in yeast and mammals have focused mainly on sorting defects of plasma
membrane proteins we found that ELCH is important during cytokinesis in Arabidopsis. Cell division in plants depends
on vesicular transport, rearrangement of the endomembrane system and microtubule arrays. Accordingly we found that
ELCH interacts genetically with the kinesin like protein ZWICHEL/KCBP that has been shown to localise to microtubule
arrays like preprophase band and mitotic spindle in dividing cells. Compromising microtubule dynamics in elch mutant
background leads to a drastic enhancement of the otherwise subtle phenotype. In summary our data suggests that an
ESCRT-like pathway is conserved in Arabidopsis and plays an important role during cytokinesis.
This work is supported by SFB635.
130 Expression Patterns, Mutagenesis, and Protein Interactions of Arabidopsis thaliana DRG
Interaction Protein-2 (DRI-2)
Jennifer Kubic, Joel Stafstrom
Northern Illinois University, Department of Biological Sciences, DeKalb, IL 60115
GTP binding proteins (G protein) are vital to many cellular processes including signal transduction (Ras), translation
(eIF2, EF-Tu), cellular trafficking (ARF, SAR), cytoskeleton construction (Rho, Rop), and nuclear translocation (Ran).
G proteins are capable of acting as molecular switches in these processes: when they bind to GTP they are in the active
conformation; upon hydrolysis GTP and binding to GDP, they become inactive. The Developmentally Regulated GTP
binding protein (DRG) family is highly conserved. Amino acid identity among fungal, animal and plant DRG1s is about
71%, and AA identity of DRG2s is nearly as high. Arabidopsis DRG1 (At4g39520) and DRG2 (At1g17470) are about
57% identical. Arabidopsis DRG3 (At1g72660) is 95% identical to DRG2, suggesting a recent gene duplication. The
function of the DRGs remains unknown. Nevertheless, this high level of conservation and the important roles played
by other G proteins suggests an important physiological function for DRGs as well. The DRGs are closely related to
a family of bacterial G proteins called OBGs. Since OBGs are involved in ribosomal function and DNA replication,
similar activities may be regulated by DRGs. Proteins that interact are often involved in the same pathway. Based on
global yeast interaction experiments, both DRGs interact with the same protein, YDR152w. The apparent homologue
of this gene in Arabidopsis thaliana (At1g51730) is called DRG Interacting protein-2 (DRI-2). Analysis of expression
patterns, mutagenesis, and protein interaction partners of AtDRI-2 may provide clues to the function of an important
family of G proteins, the DRGs.