Fruit morphogenesis is a complex process that is only partly understood. Ripoll et al. show in Arabidopsis thaliana that microRNA172 (miR172) targets and inhibits the transcriptional repressor APETALA2, thereby facilitating normal fruit valve growth. In turn, the MADS-domain transcription factor FRUITFULL (FUL), which is a master regulator of fruit morphogenesis, as well as the transcription factors AUXIN RESPONSE FACTOR 6 (ARF6) and ARF8 bind to the promoter of the MIR172C gene and positively regulate miR172. As is the case with mutations in FUL, plants with combined mutations in ARF6 and ARF8 have defects in valve growth. Moreover, the effects of FUL, ARF6 and ARF8 binding (or lack thereof) on miR172 expression and valve growth are additive, and the authors found that FUL physically interacts with ARF6 and ARF8. Thus, miR172 is an essential regulator of fruit growth, linking auxin signalling to fruit morphogenesis.