15th International Conference on Arabidopsis Research - TAIR

T03-005
The N-end rule pathway for protein degradation
Xiao-jun Yin(1), Marcus Garzon(1), Andrea Faust(1), Alexander Yephremov(1),
Andreas Bachmair(1)
1-Max Planck Institute for Plant Breeding Research, D-50829 Cologne Germany
The N-end rule pathway is a ubiquitin-dependent proteolysis pathway that
exists in all eukaryotes. The degradation signal contained in substrates of this
pathway is a bulky first amino acid residue. Recently, a role for this pathway
in senescence of plants was established (Yoshida et al. 2002, Plant J. 32,
129). In Drosophila, the pathway is involved in the fast cell death process of
apoptosis (Ditzel et al. 2003, Nat. Cell Biol. 5, 467). We have been characterizing
ubiquitin ligases of the N-end rule pathway. PRT1 (At3g24800), an
apparently plant-specific component, exclusively ubiquitylates proteins with
aromatic amino-terminal residues (Stary et al. 2003, Plant Physiol. 133,
1360). Another gene of Arabidopsis, At5g02310, is homologous to ScUBR1,
the ubiquitin ligase of the S. cerevisiae N-end rule pathway. At5g02310 is
annotated as the ECERIFERUM3 gene. However, we find that T-DNA insertion
mutants in this gene do not have the typical cer3 waxless phenotype. We are
currently analyzing the involvement of At5g02310 in the plant N-end rule
pathway, its possible contribution to the senescence process, and potential
reasons for the lack of the cer3 phenotype.
15 th <strong>International</strong> <strong>Conference</strong> on Arabidopsis Research 2004 · Berlin
T03-006
Comparative and functional genome analysis
corroborate the existence of ESCRT (endosomal
protein sorting complexes required for transport) in
Arabidopsis thaliana
Verena Winter(1), Sabine Müller(1), Marie-Theres Hauser(1)
1-Institute of Applied Genetics and Cell Biology, Department of Applied Plant Sciences and Plant
Biotechnology, BOKU - University of Natural Resources and Applied Life Sciences, Vienna
In contrast to the increasing attention on protein sorting via multi-vesicular
bodies (MVBs) in yeast and mammalian cells, knowledge in plants remains
limited and nothing is known about the ESCRT complexes -I, -II and -III which
are involved in cargo recognition, complex assembly, sorting, vesicle formation
and recycling of membrane proteins.
MVBs are recognized by their intralumenal vesicles/membranes and belong
to a subset of late prevacuolar endosomes. MVBs are crucial for the partitioning
of proteins either for degradation or recycling and are at the crossroad
of the biosynthetic and endocytic protein transport routes between the trans-
Golgi network (TGN), the vacuole and the plasmamembrane.
For instance in yeast and mammals some monoubiquitinated membranebound
proteins as cell surface receptors or the precursor of carboxypeptidase
S are targeted to the vacuole via the MVB pathway for degradation or activation,
respectively. Their sorting is executed by class E Vps proteins which assemble
into ESCRT complexes -I, -II, and -III, and the AAA-type ATPase Vps4.
Here we show that all class E VPS genes involved in MVB sorting are existing
in the Arabidopsis genome and present initial data about their function.
This project is supported by the Austrian Science Fund (FWF) project nos.
P16420-B12 to MTH
T03 Cell Biology