The homeotic gene PhDEF regulates production of volatiles in petunia flowers by activating EOBI and EOBII

In petunia (Petunia × hybrida), MADS-box homeotic genes dictate floral organ identity. For instance, DEFICIENS (PhDEF), GLOBOSA1, and GLOBOSA2 (PhGLO1/2) are responsible for petal and stamen identity. However, whether homeotic genes, particularly PhDEF, have a function at the later stages of flower development remains elusive. In petunia flowers, scent production initiates at anthesis, when the flower is ready for pollination, and is triggered by activation of EMISSION OF BENZENOIDS I (EOBI) and EOBII, MYB transcriptional regulators of scent-related genes. Here, we revealed the role of PhDEF in mature flowers, showing that it activates scent production. PhDEF suppression using a transient viral system in petunia flowers led to a significant reduction in volatile emission and pool levels, and in the transcript levels of scent-related transcriptional regulators and enzymes. Promoter activity assays demonstrated that PhDEF activates EOBI, EOBII, and the phenylpropanoid biosynthesis genes L-PHENYLALANINE AMMONIA LYASE and PHENYLACETALDEHYDE SYNTHASE. Our findings underscore the importance of PhDEF in petunia flower development from initiation to maturation and in coordinating petal specification and the establishment of showy pollination-related traits.