Transcription factor acting redundantly with MYB21 and MYB24 to control stamen filament elongation in the late developed flowers. Repressed at the transcript levels by DELLA proteins. Expressed specifically in flowers. No visible phenotype. Myb21 and myb57 double mutant has an intermediate sterility phenotype and petals that grew to a final height parallel to the pistil. Myb24 and myb57 double mutant has petals that grew to a final height parallel to the pistil. Myb21, myb24 and myb57 triple mutant has a strongly reduced fertility and an arrested growth of the petals that never grew out of the sepals.