While the master regulators of floral organ identity have been identified in multiple plant species, it remains poorly understood how the downstream transcriptional programs finally lead to the development of the different floral organs, and how evolutionary variations in these programs have yielded the astonishing floral architectural diversity existing in nature. The main objective of my PhD work was to start to address these fundamental questions by analysing floral development in Petunia x hybrida, chosen as model for its elaborate petal architecture combined with the availability of a powerful genetics toolkit. My PhD research was organized along three main lines (1) Unravelling the composition of the transcriptomes acting downstream of the homeotic gene functions in a floral organ specific manner. To achieve this, we employed an RNAseq strategy on young flowers from a unique collection of floral homeotic mutants, complemented with wild-type samples. (2) Providing a more detailed analysis for petal development, using a reverse genetics approach. 101 genes expressed during petal development were selected for functional analysis either by transposon mutagenesis or CRISPR-Cas9. (3) Investigating how tube and limb development of petunia petals depend on the cell-layer specific action of a MADS-box transcription factor. This will allow to define the contribution of the different cell-layers in petal development. Other side projects in link with flower development have also been developed in this manuscript (e.g. temperature dependent effects on petal development and transposase activity; cloning of a novel floral developmental mutant affecting petal and stamen development). All these results put together will be helpful to better understand floral organ development and architectural diversity.