OsLUGL is involved in the regulating auxin level and OsARFs expression in rice (Oryza sativa L.)

•Mutation of OsLUGL can cause uncharacteristic floret and abnormal seed in rice.•OsLUGL-OsSEU-OsAP1-OsSEP3 functions together as a transcription co-regulator to regulate A/B/C/D/E genes expression during floral development.•OsAP1 and OsSEP3 regulate OsGH3-8 expression through binding to promoter of OsGH3-8.•The altered of OsGH3-8 can lead to a change of IAA content, which further effect the expressions of OsARFs.•OsLUGL involved in regulating of floral development through auxin related process. Specification of floral organ identity is critical for floral morphology and inflorescence architecture. Floral organ identity in plants is controlled by floral homeotic A/B/C/D/E-class genes. Although multiple genes regulate floral organogenesis, our understanding of the regulatory network remains fragmentary. Here, we characterized a rice floral organ gene KAIKOUXIAO (KKX), mutation of which produces an uncharacteristic open hull, abnormal seed and semi-sterility. KKX encodes a putative LEUNIG-like (LUGL) transcriptional regulator OsLUGL. OsLUGL is preferentially expressed in young panicles and its protein can interact with OsSEU, which functions were reported as an adaptor for LEUNIG. OsLUGL-OsSEU functions together as a transcriptional co-regulatory complex to control organ identity. SEP3 (such as OsMADS8) and AP1 (such as OsMADS18) serve as the DNA-binding partner of OsLUGL-OsSEU complex. Further studies indicated that OsMADS8 and OsMADS18 could bind to the promoter of OsGH3-8. The altered expression of OsGH3-8 might cause the increased auxin level and the decreased expression of OsARFs. Overall, our results demonstrate a possible pathway whereby OsLUGL-OsSEU-OsAP1-OsSEP3 complex as a transcriptional co-regulator by targeting the promoter of OsGH3-8, then affecting auxin level, OsARFs expression and thereby influencing floral development. These findings provide a valuable insight into the molecular functions of OsLUGL in rice floral development.