The miR167-ARF8 module coordinates stamen-pistil development and fruit set in tomato

Auxin is an important regulator of reproductive development. The families of the AUXIN RESPONSE FACTOR (ARF) genes, important components of the auxin signal, have expanded in flowering plants. Tomato (Solanum lycopersicum) has two copies of ARF8, which are negatively regulated by miR167. Here, we investigated the involvement of this expanded SlmiR167-SlARF8 module in flower development. Mutants were generated in 5 SlmiR167 and 2 SlARF8 genes, and flower development and fruit set were characterized in mutant combinations. We show that the SlmiR167-SlARF8 module regulates flower-organ development and fruit set. The two SlARF8 paralogs are found to have both overlapping and distinct roles. They additively affect stigma position by oppositely affecting stamen and pistil growth, while SlARF8B has evolved a unique role in the inhibition of anther dehiscence. Loss of SlARF8B in the Slmir167a background uncovers a unique reproductive syndrome of fast, early, fertilization-independent fruit set and increased yield under cold stress, mediated by the deregulation of SlARF8A. These results demonstrate how gene duplication within the miR167-ARF8 module enables fine-tuning of auxin signaling to achieve coordinated, robust reproductive development, with implications for the control of fruit set in tomato.