CHIMERIC FLORAL ORGANS 1, encoding a grass-specific MADS-box protein, is required for regulates floral organ identity in rice
Xianchun Sang^1,#, Yunfeng Li^1,#, Zengke Luo^1,#, Deyong Ren¹, Likui Fang¹, Nan Wang¹, Fangming Zhao¹ , Yinghua Ling¹ , Zhenglin Yang¹, Yongsheng Liu², Guanghua He^1, *

¹Rice Research Institute, Southwest University, Chongqing 400715, China.
²Ministry of Education Key Laboratory for Southwest Bio-resource and Eco-environment, College of Life Science and State Key Laboratory of Hydraulics and Mountain River Engineering, Sichuan University, Chengdu 610064, China.
^#These authors contributed equally to this paper.
^*Corresponding author: Guanghua He, e-mail: hegh1968@yahoo.com.cn

Abstract
The control of floral organ identity by homeotic MADS-box genes is well established in eudicots. However grasses have highly specialized outer floral organs, the identities of the genes that regulate the highly specialized outer floral organs of grasses remain unclear. In the present study, we characterized a MIKC-type MADS-box gene, CHIMERIC FLORAL ORGANS (CFO1), which plays a key role in regulation of floral organ identity in rice (Oryza sativa). The cfo1 mutant displayed defective marginal regions of the palea, chimeric floral organs, and ectopic floral organs. Map-based cloning demonstrated that CFO1 encoded the OsMADS32 protein. Phylogenetic analysis revealed that CFO1/OsMADS32 belonged to a monocot-specific clade in the MIKC-type MADS-box gene family. The expression domains of CFO1 were mainly restricted to the marginal region of the palea and inner floral organs. The floral-organ-identity gene DROOPING LEAF (DL) was expressed ectopically in all defective organs of cfo1 flowers. Double-mutant analysis revealed that loss of DL function mitigated some of the defects of floral organs in cfo1 flowers. We propose that the CFO1 gene plays a pivotal role in maintaining floral organ identity through negative regulation of DL expression.