Identification And Fine Mapping Of Thermo-sensitive Mutant Osv15 In Rice

Rice can achieve biomass accumulation through photosynthesis,and leaf color is a key factor affecting the process.Therefore,it is important to use rice leaf color mutant to explore rice photosynthesis and leaf color development.In this study,the thermo-sensitive mutant osv15 obtained from rice cultivar Nipponbare（abbreviated as Nip）mutagenized by irradiation was used as research materials.The phenotypic characterization and map-based cloning of osv15 were conducted,and the main results were as follows:1.osv15 was a thermo-sensitive mutant,and it exhibited etiolation at 22℃.With the increase of temperature,color of the leaf was turning green.Agronomic traits showed that compared with the wild type,the seed setting rate and 1000-grain weight decreased by 12.5%and 11%,and the number of tilers and productive Panicles decreased by 44.7%and 52.9%,respectively.2.The chlorophyll content and photosynthetic rate were determined under different temperatures（22℃,24℃,26℃,28℃,30℃）.The results showed that the total chlorophyll content of osv15 was 10%,16.8%,17.8%,24.3%and 68%of the wild type,respectively.The vaule ofΦPSⅡ,qP were increased as the rise of the temperature,eventually reaching the wild-type level at 30℃.3.The chloroplast structure of the mutant was abnormal,in which the thylakoid was arranged chaotically,and there were more osmiophile,at 22℃.However at high temperature（30℃）,the chloroplasts developed wel,with more normal thylako ids,and less osmiophiles.4.The combination of osv15 crossed with Nip and Kasalath were used for Genetic Analysis.The results showed that the leaf color of F₁ were normal,and the separation ratio of normal green seedlings to yelow seedlings of F₂ were nearly3:1,which revealed that the mutant phenotype of osv15 was controlled by a single recessive gene.5.For Genetic mapping of osv15,F₂ population was constructed by crossing the mutant with Kasalath,and mutant individuals seeding were selected to futher map the mutant gene.The gene was located in the 84 kb region of chromosome 6,between molecular markers S4 and S5.6.The Candidate genes was predicted,the target region was analyzed with RGAP（http://rice.plantbiology.msu.edu/）.We found that there were 23 ORFs.Sequencinganalysisof these 23 ORFs in this regionshowed that Os06g02380,encoding a putative chaperonin 60 beta precursor,showed a single base deletion in osv15,appeared as a candidate gene involved in the chloroplast development.