Scientists have identified cucumber auxin regulatory factor 3 (CsARF3), which plays a key role in seedling (carpel) development and flower sex determination.1[3] Knocking out the CsARF3 gene resulted in a phenotype with exclusively male flowers (androecious).[Conversely, overexpression of CsARF3 increased the number of female flowers.1[1] CsARF3 promotes female-biasedness by directly stimulating the expression of the meristem (stem cell-maintaining) gene CsSTM and repressing the activity of the gynoecial gene CsWIP1.[1][3] Auxin and ethylene have a reciprocal link in sex determination: ethylene at the beginning of flower development promotes seedling formation via auxin, while auxin signaling in the seedling then increases ethylene synthesis to inhibit stamen development.[1][3] This mechanism elucidates the interaction of auxin and ethylene in unisexual flower formation in cucumber.