Protein Modification and Turnover
Farmer, Lisa , Fu, Hongyong , Vierstra, Richard .
The RAD23 Family of Ubiquitin-Like Proteins Regulates Plant Development and Abscisic Acid Signaling in Arabidopsis thaliana.
The Ubiquitin (Ub)/26S Proteasome System (UPS) preferentially degrades misfolded proteins and transient regulatory proteins in the cell, with the latter providing an important regulatory mechanism. Ub is covalently attached to target proteins by an E1-E2-E3 conjugation cascade, after which the resulting Ub conjugates are delivered to the 26S proteasome for breakdown. The identities of few proteasomal targets are known, and we know less about how they are delivered. Evidence suggests that RAD23 proteins help transport targets to the proteasome. They contain N-terminal Ub-like (UBL) and C-terminal Ub-associated (UBA) domains that allow them to accept Ub conjugates and “dock” with the proteasomal subunits RPN10 or RPN1 to relinquish their cargo. The Arabidopsis RAD23 family includes four highly conserved members for which genetic knockouts have revealed functions in appropriate root, shoot and reproductive organ development. Phenotypic variability among the rad23 mutants suggests that individual RAD23s have tissue-specific and/or target-specific functions. We are currently assembling a combinatorial library of rad23 mutants to uncover functional redundancy among the isoforms and to reveal their global importance to plant development. Biochemical analysis indicates that all four Arabidopsis RAD23 proteins associate with RPN10 and bind poly-Ub chains in vivo. These interactions probably regulate multiple signaling pathways in plants. For example, RPN10 regulates the levels of the ABA transcription factor ABI5, and we have evidence that ABI5 levels are affected in multiple rad23 mutants. Further analysis should reveal alternate functions of the RAD23 isoforms, as well as the identities of important developmental regulators that are recycled by the UPS.
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1 - University of Wisconsin, Genetics, 425 Henry Mall, Madison, WI, 53706, USA
2 - Institute of Plant and Microbial Biology, Academia Sinica, Taipei, Tai
Presentation Type: Plant Biology Abstract
Location: Exhibit Hall (Northeast, Southwest & Southeast)/Hilton
Date: Sunday, July 8th, 2007
Time: 8:00 AM