Thesis presented October 30, 2014
Abstract :
The ULTRAPETALA1 (ULT1) factor is involved in several developmental processes during
Arabidopsis thaliana life cycle such as the homeostasis maintenance at aerial meristems and floral morphogenesis. In particular, ULT1 is critical to the restriction of the expression territory of
WUSCHEL, a central player in stem cell maintenance. ULT1 is also essential for the spatio-temporal activation of
AGAMOUS, a key floral developmental gene necessary to flower determinate growth. Nevertheless, the molecular mechanisms through which ULT1 functions haven't all been solved yet, including the nature of its protein partners assuring its binding specificity to DNA targets. The objectives of this thesis were (i) to identify new ULT1 interactors and (ii) to characterize the molecular and developmental function of one of them.
By genetic, molecular and biochemical approaches, we identified the ULT1 INTERACTING FACTOR 1 (UIF1) transcriptional repressor and characterized its function in the control of floral meristem activity in
Arabidopsis thaliana (Chapter I). In particular, UIF1 is able to specifically bind a promoter sequence in the
WUS gene. With this study we provide a mechanism for specific recognition of target genes by ULT1.
By a candidate gene approach, we identified novel ULT1 partners (Chapter II), which may explain (i) ULT1 effect on removal of chromatin repressive marks that maintain a locus in an inactive state (interaction with the demethylase RELATIVE OF EARLY FLOWERING 6); (ii) the ULT1 activating trithorax function (interaction with ARABIDOPSIS TRITHORAX LIKE I); and finally (iii) ULT1 role in the transcriptional initiation of target genes (interaction with the C-terminal domain of RNA Polymerase II). This dataset reveals a function for ULT1 at the interplay between chromatin de-repression and transcriptional initiation.