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

Zhigang Huang,Rae Eden Yumul,Chenjiang You,Langtao Xiao,Ting Shi,Xigang Liu,Binglian Zheng,Xuemei Chen,Zhihong Gao

doi:10.1111/nph.14151

Abstract

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.

Highlights

The angiosperm flower is an innovation that supports sexual reproduction and consists of four types of floral organ: sepal, petal, stamen and carpel
Ag-10 flowers have a full complement of floral organs (Fig. 1b)
Most ag-10 flowers are normal in terms of floral determinacy; < 10% of ag-10 flowers have bulged gynoecia with additional floral organs inside, a manifestation of compromised floral determinacy (Ji et al, 2011)

Summary

Introduction

The angiosperm flower is an innovation that supports sexual reproduction and consists of four types of floral organ: sepal, petal, stamen and carpel. Like the shoot apical meristem (SAM), floral meristems harbor stem cells in the central zone and descendants of the stem cells that give rise to organ primordia in the peripheral zone. In both the SAM and floral meristems, a small number of cells that express the WUSCHEL (WUS) gene lie underneath the stem cells (Mayer et al, 1998; Schoof et al, 2000). Failure to terminate the floral stem cells results in additional floral organs or even flowers internal to the fourth whorl Many genes, such as AGAMOUS (AG), CRABS CLAW (CRC), KNUCKLES (KNU), ULTRAPETALA1 (ULT1), CURLY LEAF (CLF), AUXIN RESPONSE FACTOR3 (ARF3), POWERDRESS (PWR)

Methods

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Discussion

Conclusion