Abstract
JAGGED (JAG) and DROOPING LEAF (DL) are two key regulators of floral organ pattern in rice, but how they work together in establishing reproductive organs and terminating FM remains to be determined. Here, we have analyzed the coordination mechanism in detail. While the floral meristem (FM) determinacy is severely compromised in null-allele jag and dl spikelets, jag dl exhibits a complete loss of FM determinacy, with a large bouquet composed of lemma-like organs sprouting from the center of spikelets replacing the stamen and pistil, indicating that they synergistically determine sexual organ identity and FM termination. Protein-protein interactions revealed that JAG binds to SUPERWOMAN1 (SPW1)/OsMADS16 and DL, forming two heterodimers, JAG-SPW1 and JAG-DL. Expression analysis revealed that JAG binds to the promoters of both DL and SPW1 and directly activates SPW1, while SPW1 and DL do not directly inhibit each other. However, JAG-SPW1 inhibits DL transcription, while JAG-DL inhibits SPW1 transcription, indicating that JAG may mediate the transcription antagonism through these two heterodimers to limit the transcription of DL in stamen and SPW1 in pistil, which is crucial for sexual organ origination in the appropriate location. Meanwhile, JAG and DL can directly inhibit OSH1 and OSH15, individually or synergistically, which is essential for timely termination of FM. These findings reveal the unique synergistic manner of JAG and DL in rice reproductive organ generation, providing insights into the regulatory mechanisms of floral morphogenesis in plants.