FLOWER-LAYER

How cells coordinate their growth and division to generate organs with defined shapes is a long-standing question in biology. In plants, organs are formed by clonally-distinct cellular layers that remain independent throughout organ development. In the mean time, organ identity, shape and size are specified by master regulators. The main objective of the project is to understand how a master regulator can trigger organ development in all cellular layers in a coordinated manner, ensuring the robust acquisition of a proper identity, size and shape. We will tackle this question using Petunia hybrida flowers, whose petals are organized in a tube ending with colourful limbs. We obtained chimeric flowers in Petunia hybrida, originating from the layer-specific excision of a transposon inserted in the PhDEF gene, a MADS-box gene controlling petal development. These chimeras revealed that expression of PhDEF in the epidermis of the petal directs growth of the limbs, while its expression in the internal layers directs growth of the tube. This suggests that the tube and the limbs constitute two independent developmental modules, whose growth is controlled in a layer-specific fashion. Moreover, we obtained evidence for non-cell-autonomous effects between layers since PhDEF expression in the internal layers of the petal restores some petal epidermal features. The objective of this project is to characterize the layer-specific PhDEF regulatory netwok in the Petunia hybrida petal, in order to understand how PhDEF can direct tube or limb growth independently from specific cellular layers. For this, after a detailed characterization of the chimeric flowers we obtained, we will recreate these chimeras as transgenic plants. This will allow us to identify PhDEF target genes and interactors specifically for each cellular-layer, by a combination of cell sorting, RNA-Seq, ChIP-Seq and co-IP. We will also identify the non-autonomous targets of PhDEF induced in one layer by expression of PhDEF in another layer. Finally we will functionally characterize some key target genes, aiming to understand how they can direct tube or limb growth in a layer-specific fashion. Altogether this project should advance the field of plant developmental biology by addressing how a master regulator directs organ growth and identity in all cellular layers in a coordinated manner.