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

383 The RAD23 Family of Ubiquitin-Like Proteins Regulates Plant Development and Abscisic
Acid Signalling in Arabidopsis thaliana
Lisa Farmer 1 , Hong-Yong Fu 2 , Richard Vierstra 1
1
Department of Genetics, University of Wisconsin-Madison, Madison, WI 53706, USA, 2 Institute of Plant and
Microbial Biology, Academia Sinica, Nankang, Taipei, Taiwan 11529
The Ubiquitin/26S Proteasome System (UPS) is the preferential mechanism by which transient regulatory or
misfolded proteins are discarded. Ubiquitin (Ub) is covalently attached to target proteins by a series of E1-E2-E3
enzymatic activities, and conjugates are delivered to the 26S proteasome, where they are unfolded and degraded. Ub
conjugation and proteolysis have been described, but less is known about the identities of specific targets and how they
are transported to the proteasome. Evidence suggests that RAD23 proteins are responsible for delivering targets to the
proteasome. RAD23s have N-terminal Ub-like (UBL) and C-terminal Ub-associated (UBA) domains that facilitate their
interactions with the proteasome and poly-Ub chains, respectively. We predict that these associations allow RAD23s to
accept ubiquitin conjugates and then “dock” with the proteasomal subunit RPN10 to relinquish their cargo. The Arabidopsis
RAD23 family includes four highly conserved members. By analysis of genetic knockouts in the four AtRAD23 genes,
we found that they are important for appropriate root, shoot and reproductive organ development in seedlings and mature
plants, respectively. The AtRAD23s preferentially bind Lys48-linked poly-ubiquitin chains, which are a signature for
degradation. They also interact with RPN10, which helps regulate the levels of hormone signaling factors such as the
ABA transcription factor ABI5. We have evidence that ABI5 levels are affected by multiple AtRAD23s. Further analysis
should reveal other functions of the AtRAD23s, as well as the identities of important developmental regulators that are
recycled by the UPS.
384 Characterization of Gal4-mediated driver lines
Karen Fitzsimmons, Melissa Curran, Robert Kranz
Washington University in St. Louis
Arabidopsis lines have been generated that contain three reporter genes (LUC, GFP, GUS) that are under the control
of Gal4, since the 5X UAS that binds Gal4 was cloned upstream of each reporter. A variety of Gal4 driver lines have been
identified based on tissue location of reporter expression. To express a gene ectopically, driver lines can be crossed with
responder lines, plants that have a gene of interest with 5X UAS. We have used the CAPRICE or CPC transcription factor
to test the driver/responder system. The CPC over expression phenotype (with a full 35S promoter) includes increased
root hairs and reduced trichomes. These multiple tissue-specific phenotypes make CPC an ideal transcription factor to
test. Several different Arabidopsis driver lines have been transformed with 5X UAS:CPC and phenotypes correlated
with expression. A quantitative analysis that correlates expression of the three reporters to phenotypic expression will
be presented.