A FUL-SHP-AP2 module regulates fruit development in petunia

Fruit development is a key angiosperm innovation for seed dispersal, yet it remains unclear whether a conserved gene regulatory network operates during early fruit development. We investigated Petunia x hybrida homologs of FRUITFULL (FUL), SHATTERPROOF (SHP), and APETALA 2 (AP2), transcription factors repeatedly linked to fruit development/ripening. As a model species close to tomato, but producing dry dehiscent fruits like Arabidopsis, petunia is ideal for investigating conserved regulatory mechanisms in early fruit patterning. We used reverse genetics to dissect the roles of the petunia FUL, SHP and AP2 homologs in pericarp development. We found that the three petunia FUL-like genes redundantly regulate endocarp formation, likely via auxin/brassinosteroid signalling and cell-wall modification. Interestingly, FBP6 (SHP-like) has an opposite effect on endocarp cell morphology, suggesting antagonistic interactions. Mutants in the AP2-like ROB genes show the most severe pericarp patterning defects, with failure of dehiscence in rob1/2/3 mutants. ROB factors repress FUL-like activity and, along with FBP6, oppositely regulate auxin/brassinosteroid signalling genes. Our findings uncover a conserved module of antagonistically acting transcription factors (AP2, FUL, SHP co-orthologs) that regulates early pericarp patterning via hormonal signalling, providing a framework for comparative fruit development studies across angiosperms.