Morphological Characteristics, Expression Regulation And Gene Mapping Of A Floral Mutant Sis1-1 In Rice

Rice is an important food crop and a model monocot plant. So it has a great significance to carry out genetic research of rice floral organs. A rice floral organ mutant named sis 1-1 (spike-in-spikelet) was found from cultivar Minghui-63. The structures of three internal whorls in the typical sis1-1 spikelet are all degenerated, and the floral meristem differentiates into glume-like organs continuously, resulting in a spikelet-in-floret structure. Previously, SIS1-1 has been mapped on chromosome 8. This study aimed to observe the morphological characteristics of sis1-1,analyze the relationship between SIS1-1 and floral identity genes and fine map SIS1-1.The main results are as follows:(1) The sis1-1 has normal vegetative growth, inflorescence and flower bud development, but its floral organ is obviously abnormal. Observation of spikelet paraffin section and scanning electron microscopic displayed that the phenotype of lemma and palea in sisl-1 was normal. But the number of vascular bundle was increased which didn’t bring about close clogging of hull. At the same time, the lodicule, stamen and pistil in sis1-1 were degenerated. And the floral meristem in sisl-1 floral organ differentiates new hulls or spikelets consist of hulls continuously, resulting in a spikelet-in-floret structure. The results indicated that SIS1-1 participated in the development of rice floral and the determination of floral meristem.(2) Real-time fluorescence quantitative PCR results displayed that the expression level of three API-like genes was obviously up-regulated in sisl-1. B-class and C-class floral identity genes were down-regulated (especially the C-class gene). The expression level of OsMADS1/5/34 in SEP-like gene was up-regulated, while OsMADS7/8 was down-regulated. The results indicated that SIS 1-1 participated in the regulation of the identity genes in rice floral to determinate development of rice floral and determination of floral meristem.(3) The study used new mapping group to test the previous fine mapping result of SISl-1 and located it in the physical distance of～250kb between SSR21 and SSR24. There are 55 genes which have been annotated in the region, including some Non-MADS genes, such as AP2-like and zinc finger genes, which are probably related to the floral organ development. The sequencing analysis of the genes, which probably participated in the regulation of floral organ development, indicated that there was no sequence difference between wild-type and mutant. The result implied that SIS1-1 was probable a new kind of gene to regulate floral organ development and determination of floral meristem.