OsROXY2 Regulates Stamen Number Through Interaction with OsbZIP47 in Rice

Precise regulation of floral primordia initiation is essential for normal flower development. However, the mechanisms regulating floral primordia initiation (PI) are complex and poorly understood. Herein, we identified a natural mutant in rice, stamen less (sl), which develops florets with reduced stamen number and no carpel due to defects in stamen and carpel PI. STAMENLESS (SL) encodes the CC-type glutaredoxin OsROXY2 and is involved in the regulation of stamen PI. OsROXY1, the closest homolog of OsROXY2, showed no function in stamen PI regulation. The osroxy1 single mutant showed normal reproductive development, while the floret phenotypes of osroxy1/2 double mutant were comparable to those of osroxy2 mutant. The TGA transcription factor OsbZIP47 showed a strong interaction with OsROXY2, and the two genes exhibited overlapping subcellular localizations and expression patterns during flower development. The number of stamens in the osbzip47 mutant was increased to seven (around 35%), indicating that OsbZIP47 is a negative regulator of stamen PI, in contrast to OsROXY2. Taken together, our results reveal that OsROXY2 regulates stamen number via interaction with OsbZIP47, indicating GRX-TGA-mediated floral organ number regulation mechanism is conserved in monocots and eudicots.