<i>SUPERMAN</i> prevents class B gene expression and promotes stem cell termination in the fourth whorl of <i>Arabidopsis thaliana</i> flowers.

Abstract

The molecular and genetic networks underlying the determination of floral organ identity are well studied, but much less is known about how the flower is partitioned into four developmentally distinct whorls. The <i>SUPERMAN</i> gene is required for proper specification of the boundary between stamens in whorl 3 and carpels in whorl 4, as <i>superman</i> mutants exhibit supernumerary stamens but usually lack carpels. However, it has remained unclear whether extra stamens in <i>superman</i> mutants originate from an organ identity change in whorl 4 or the overproliferation of whorl 3. Using live confocal imaging, we show that the extra stamens in <i>superman</i> mutants arise from cells in whorl 4, which change their fate from female to male, while floral stem cells proliferate longer, allowing for the production of additional stamens.