Item

Abstract

The genome of Arabidopsis thaliana encodes more than 26,000 proteins, many of which are completely uncharacterized. Analysis of the function of these genes is one of the major challenges in the field. Given the large number of genes, application of genomic techniques such as expression profiling is a good way to pre-select genes of interest to a particular pathway. Based on expression profiling of flowering time mutants (1), a small gene family with four members in Arabidopsis was chosen for further investigation. Expression of these genes in the apical region changes throughout the transition from vegetative to reproductive development. RNA in situ analysis demonstrates that the UGF genes are extensively regulated throughout development. This is further confirmed by transcriptional fusion of 2.5kb of the region upstream of the UGF coding sequences to the β-glucuronidase (GUS) reporter in planta. All UGFs are detected strongly in the vasculature, including the pro-vasculature, but individual UGFs are present in specific domains that overlap only partially. To gain insight into the function of the UGF gene family during Arabidopsis development we have carried out extensive yeast-2-hybrid screens and have identified potentially interacting proteins. Most of the proteins found encode for putative transcription factors, but we also found two proteins containing BTP/POZ/MATH domains. Among the transcription factors identified were VOZ1 and VOZ2, two proteins supposedly involved in vasculature development. Interaction with these and other transcription factors hints at a role of the UGF proteins in transcription control. This possibility is investigated in a yeast-transactivation assay using a binding site in the regulatory region of a confirmed VOZ target, AtAVP1 (2), as a reporter. BTP/POZ/MATH containing proteins on the other hand participate in Cullin-3a/b-mediated ubiquitination (3-6), suggesting, that the UGF proteins themselves are regulated by protein degradation. UGF expression overlaps at least partially with the expression of the VOZ and BTP/POZ/MATH proteins identified in the Y2H screens, indicating that those interactions might take place in planta as well.