Characterization of the Arabidopsis thaliana Auxin F-Box Family Members AFB4 and AFB5

Abstract

Ubiquitination is a three-step pathway that links a chain of small molecules, UBQ, onto a substrate protein. UBQ serves as a signal that the tagged protein is to be targeted for degradation by the 26S proteasome. This ubiquitin-mediated protein degradation system is highly conserved throughout eukaryotic cells, including the model plant Arabidopsis thaliana. In Arabidopsis many growth and developmental process are influenced by the plant hormone auxin. Transcription factors involved in auxin response have been shown to be targets for ubiquitination and subsequent degradation. Recent work has identified a family of auxin receptors, TIR1, AFB1, AFB2 and AFB3, are key components of this process. This work is focused on the characterization of two additional members of this family AFB4 and AFB5. Using a combination of molecular biology, genetics and biochemistry I have begun the characterization of these two proteins plant development and their possible function as auxin receptors. While both proteins are clearly involved in auxin response, AFB4 has a more pleiotropic role in all aspects of the plant life cycle. This work also shows that AFB5, and AFB4 to a lesser extent, can mediate a receptor-like interaction in the presence of the synthetic auxin picloram, leaving open the question of whether or not they participate as auxin receptors in the plant to the same level as the other four family members.