APETALA2 antagonizes the transcriptional activity of AGAMOUS in regulating floral stem cells in Arabidopsis thaliana

Summary

• APETALA2 ( AP2 ) is best known for its function in the outer two floral whorls, where it specifies the identities of sepals and petals by restricting the expression of AGAMOUS ( AG ) to the inner two whorls in Arabidopsis thaliana. Here, we describe a role of AP2 in promoting the maintenance of floral stem cell fate, not by repressing AG transcription, but by antagonizing AG activity in the center of the flower.

• We performed a genetic screen with ag‐10 plants, which exhibit a weak floral determinacy defect, and isolated a mutant with a strong floral determinacy defect. This mutant was found to harbor another mutation in AG and was named ag‐11. We performed a genetic screen in the ag‐11 background to isolate mutations that suppress the floral determinacy defect. Two suppressor mutants were found to harbor mutations in AP2 .

• While AG is known to shut down the expression of the stem cell maintenance gene WUSCHEL ( WUS ) to terminate floral stem cell fate, AP2 promotes the expression of WUS .

• AP2 does not repress the transcription of AG in the inner two whorls, but instead counteracts AG activity.