Floral stem cell termination involves the direct regulation of AGAMOUS by PERIANTHIA

In Arabidopsis, the population of stem cells present in young flower buds is lost after the production of a fixed number of floral organs. The precisely timed repression of the stem cell identity gene WUSCHEL (WUS) by the floral homeotic protein AGAMOUS (AG) is a key part of this process. In this study, we report on the identification of a novel input into the process of floral stem cell regulation. We use genetics and chromatin immunoprecipitation assays to demonstrate that the bZIP transcription factor PERIANTHIA (PAN) plays a role in regulating stem cell fate by directly controlling AG expression and suggest that this activity is spatially restricted to the centermost region of the AG expression domain. These results suggest that the termination of floral stem cell fate is a multiply redundant process involving loci with unrelated floral patterning functions

My favourite flowering image: an Arabidopsis inflorescence expressing fluorescent reporters for the APETALA3 and SUPERMAN genes

When asked to provide a picture for the cover of the Flowering Newsletter, I picked this image of an Arabidopsis thaliana inflorescence expressing fluorescent reporters for two key regulators of flower development: APETALA3 (AP3), which promotes petal and stamen identity, and SUPERMAN (SUP), which encodes a transcriptional repressor that defines the boundary between stamens and pistil (Fig. 1). The choice was easy: it was an important breakthrough in my research on the role of SUP in the separation of stamens in whorl 3 and carpels in whorl 4; and among the images of flowers I have taken with a confocal microscope, it is also one my favourites aesthetically. The image won awards at the 2015 Nikon Small World and FASEB BioArt competitions and is published in Prunet et al. (2017)

CRABS CLAW Acts as a Bifunctional Transcription Factor in Flower Development

One of the crucial steps in the life cycle of angiosperms is the development of carpels. They are the most complex plant organs, harbor the seeds, and, after fertilization, develop into fruits and are thus an important ecological and economic trait. CRABS CLAW (CRC), a YABBY protein and putative transcription factor, is one of the major carpel developmental regulators in A. thaliana that includes a C2C2 zinc finger and a domain with similarities to an HMG box. CRC is involved in the regulation of processes such as carpel fusion and growth, floral meristem termination, and nectary formation. While its genetic interactions with other carpel development regulators are well described, its biochemical properties and molecular way of action remain unclear. We combined Bimolecular Fluorescence Complementation, Yeast Two-Hybrid, and Yeast One-Hybrid analyzes to shed light on the molecular biology of CRC. Our results showed that CRC dimerizes, also with other YABBY proteins, via the YABBY domain, and that its DNA binding is mainly cooperative and is mediated by the YABBY domain. Further, we identified that CRC is involved in floral meristem termination via transcriptional repression while it acts as a transcriptional activator in nectary development and carpel fusion and growth control. This work increases our understanding on how YABBY transcription factors interact with other proteins and how they regulate their targets