Characterization of Osmads6-5, a null allele, reveals that OsMADS6 is a critical regulator for early flower development in rice (Oryza sativa L.) Yuanlin Duan • Zhuo Xing • Zhijuan Diao • Wenying Xu • Shengping Li • Xiaoqiu Du • Guangheng Wu • Chuanlei Wang • Tao Lan • Zheng Meng • Huaqing Liu • Feng Wang • Weiren Wu • Yongbiao Xue Received: 10 March 2012 / Accepted: 16 August 2012 / Published online: 30 August 2012 Ó Springer Science+Business Media B.V. 2012 Abstract AGL6-clade genes are a subfamily of MADS- box genes and preferentially expressed in floral organs. OsMADS6 and OsMADS17 are two AGL6-like genes in rice. OsMADS17 has been shown to play a minor role in floral development and appears to result from a duplication of OsMADS6. OsMADS6 was initially named as MFO1 for mosaic floral organs based on its moderate mutant pheno- types. So far, four moderate or weak mutant alleles of OsMADS6 have been described, providing valuable insights into its role in flower development. Here, we report a null allele of OsMADS6 (Osmads6-5), which exhibited a strong mutant phenotype in spikelet without affecting vegetative traits, causing all floral organs except lemma homeotically transformed into lemma-like organs (LLOs) as well as an indeterminate floral meristem, thus resulting in a mutant floret consisting of reiterating whorls of lemma and LLOs. In consistently, over-expression of OsMADS6 led to additional lodicule-, stamen- and carpel-like organs. Expression analysis showed that OsMADS6 controls the formation of the incipient primordia of lodicule, stamen and carpel via regulating the expression of class B, C and SEP-like MADS-box genes. Taken together, our results revealed that OsMADS6 acts as a critical regulator for early flower development in rice and provide novel insights into the molecular mechanism of OsMADS6. Keywords Rice Á Osmads6-5 Á Null allele Á Floral meristem determinacy Á Floral organ identity Abbreviations Os Oryza sativa AGL Agamous-like MFO Mosaic floral organ SEP Sepallata FT Flowering time Yuanlin Duan and Zhuo Xing contributed equally to this work. Electronic supplementary material The online version of this article (doi:10.1007/s11103-012-9958-2) contains supplementary material, which is available to authorized users. Y. Duan Á Z. Diao Á S. Li Á G. Wu Á C. Wang Á T. Lan Á W. Wu Key Laboratory of Ministry of Education for Genetics, Breeding and Multiple Utilization of Crops, Fujian Agricultural & Forestry University, Fuzhou 350002, China Y. Duan Á T. Lan Á W. Wu (&) Fujian Provincial Key Laboratory of Marker-Assisted Breeding of Rice, Fujian Agriculture and Forestry University, Fuzhou 350002, Fujian, China e-mail: wuwr@fjau.edu.cn Z. Xing Á W. Xu Á Y. Xue (&) Laboratory of Molecular and Developmental Biology, Institute of Genetics & Developmental Biology, Chinese Academy of Sciences and National Center for Plant Gene Research, Beijing 100101, China e-mail: ybxue@genetics.ac.cn Z. Xing Graduate University of Chinese Academy of Sciences, Beijing 100049, China X. Du Á Z. Meng Laboratory of Photosynthesis and Environmental Molecular Physiology, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China H. Liu Á F. Wang Academy of Agricultural Science, Fuzhou 350000, Fujian Province, China 123 Plant Mol Biol (2012) 80:429–442 DOI 10.1007/s11103-012-9958-2