SlBPC1 regulates fruit elongation by directly repressing SlOFP2/SlOFP21 and SUN expression in tomato.

Fruit shape is an important agronomical trait that influences consumer preference. Despite the dramatic variations in fruit shape among tomato germplasms, the underlying genes and regulatory mechanisms remain poorly understood. Here, we found that knockout of the transcription factor SlBPC1 leads to elongated fruits, resulting from altered cell division patterns during ovary development. Further studies revealed that SlBPC1 regulates fruit shape by repressing its target genes SlOFP21 and SUN. Overexpression of SlOFP21 resulted in the formation of elongated fruits with an increased fruit shape index. Moreover, SlBPC1 also represses the expression of SlOFP2, a homolog of SlOFP21. Consistently, overexpression of SlOFP2 also led to elongated fruits in tomato. SlOFP2 and SlOFP21 were found to interact with fruit elongation activator SlTRM5 and repressors SlTRM17/20a and SlTRM19. Together, our results revealed an SlBPC1-SlOFP2/SlOFP21/SUN regulatory module that provides new insights and molecular tools for the genetic improvement of fruit shape traits in tomato breeding programs.