Abstract: 【Objective】The abnormal floral organ number mutant of rice was used to study the molecular mechanisms of floral organ development, and to identify the related genes of floral organ in rice. 【Method】In present study, a rice mutant, abnormal floral organ number1 (afon1) was isolated from an indica cultivar Zhenong 34 M2 population by mutagenesis with ethyl methane sulfonate (EMS). At flowering stage, five panicles from afon1 and Zhenong 34 were randomly selected to observe the morphological phenotype, cytological features and pollen fertility by histology analysis and scanning electron microscopy, respectively. At mature stage, ten plants from afon1 and Zhenong 34 were randomly chosen for measuring the main agronomic traits, such as plant height, number of tillering, panicle length, number of floret per panicle, number of filled grain per panicle and 1 000-grain weight. One hundred plump seeds were selected for calculating the germination potential and germination rate of the mutant afon1 and wild type. The F2 population from crossing of afon1 with WT Zhenong 34 and Zhenongda 104 were used for genetic analysis and gene mapping, respectively. Then, the DNA sequencing was conducted, the model of AFON1 protein was built and the space structure for AFON1 protein was analyzed. Moreover, the expression of candidate gene and floral organ number associated genes were detected by real-time PCR. 【Result】Compared with the wild type, the floral organ number of 59.64% spikelet was abnormal in mutant afon1, which most of them had a glume-like organ on the side of the leman and there were 2-4 rounds of floral organ number increased at the same time in others. Furthermore, the plant height and 1 000-grain weight of afon1 were visibly higher, while the seed setting rate was significantly reduced. The results of the genetic analysis showed that the phenotype of F1 population from the crossing of afon1 with Zhenong 34 was normal and the segregation ratio of wild-type and mutant phenotype plants from F2 population fitted a ratio of 3﹕1, which revealed that the mutant trait of afon1 was controlled by a single recessive nuclear gene. The afon1 was further mapped on the arm of chromosome 1 between InDel markers 1M5 and 1M18 with a physical distance of 73 kb, where there were 6 annotated genes. The sequencing results between the mutant afon1 and the wild type illustrated that there was a single base-pair substitution of T (565th) to A on the exon of LOC_Os01g67430 resulting in the mutation of Trp (189th) to Arg. Protein sequencing and structure analysis revealed that there was a Lipase_3 domain and the mutation in the region changed the space structure of AFON1 obviously. The real-time PCR result showed that the expression of LOC_Os01g67430 in young panicle increased significantly, while the expression had no obvious difference in root, stem and leaf. Additionally, the expression of floral organ number related genes FON1 and FON2/4 was obviously increased in floral organ at young panicle developmental stage. 【Conclusion】The LOC_Os01g67430 was speculated as the gene afon1 regulating the number of floral organ by influencing the expression of corresponding genes which determined the number of floral organ.

Key words: rice, abnormal floral organ number1 (afon1), gene mapping, expression analysis