| As the main food crop in the world,rice is vulnerable to cold damage at different growth stages,which leads to the decline of yield and quality of rice.Therefore,it has great significance to study the cold tolerance of rice and to excavate the genes related to cold tolerance.The cold tolerance of rice is a quantitative trait controlled by multiple genes,which makes it more difficult to excavate the genes related to cold tolerance.In recent years,with the development and application of molecular marker technology,they have gradually become an important means of cold tolerance gene mining in rice.At the same time,with the continuous upgrading of high-throughput sequencing methods,many high-density molecular linkage maps of rice have been established by using high-throughput sequencing methods such as simplified genome sequencing,and a lot of progresses have been made in QTLs for traits such as low temperature resistance,salt resistance,and drought resistance.Brassinolide(BRs)is a new plant hormone,which can improve the cold tolerance of rice.This study used140 backcross recombinant inbred lines group derived from the cross of SN 265 with good agronomic characters and dongxiang wild rice with good cold resistance.We identified the cold resistance of all meterials by investigating the seedling shoot length,seedling root length,seedling dry weight,and seedling wet weight under cold stress and cold stress with BRs spraying in seedling stage of rice.Combining with the SNP data from simplified genome sequencing,we performed the QTL mapping related to the cold tolerance in rice.This study will establish a theoretical basis for breeding rice materials with cold tolerance and identifying the gene related to the cold tolerance in rice.The specific research results are as follows:(1)Classification related to cold tolerance was conducted according to the phenotypic data of seedling shoot length,seedling root length,seedling dry weight and seedling wet weight.In the phenotypic data of seedling shoot length,the seedling shoot length of all lines under cold stress and BRs+cold stress was generally concentrated in the range of 20-30 cm.In the range of 25-30 cm in seedling shoot length,there were 22 lines more under BRs+cold stress than those under cold stress alone.In the phenotypic data of seedling dry weight,the weight of all lines under cold stress alone and BRs+cold stress was generally concentrated in0.02-0.03 g,there were 15 more lines under BRs+cold stress than those under cold stress alone.In the phenotypic data of seedling wet weight,the weightof all lines under cold stress alone and BRs+cold stress was generally concentrated in 0.1-0.2 g.In the range of 0.15-0.2 g,there were 12 more lines under BRs+cold stress than those under cold stress alone.These results indicated that BRs could improve the cold tolerance in seedling stage of rice.(2)140 lines of the recombinant group of self-interbreeding groups were sequenced by simplified genome sequencing.1145 polymorphic markers were screened to establish a genetic map by the genetic classification of SNP with loss rate of 200% and minimum isoele5%.Its feature is: there are 1145 makerings on 12 chromosomes.The least numbers of themarkers with 77 sites distributed on chromosome 7,whereas the most numbers of the markers with 177 sites distributed on chromosome 4.The total genetic distance of the chromosomes is31883.3 c M and the total physical distance is 394.1 Mbp.The genetic distance of each mark is between 1.9-146.3 c M.(3)Using the complete interval mapping method in the IciMapping4.2 software,the Lod threshold is set to 3 for QTL positioning analysis.114 QTL sites were mapped according to the data of 4 traits.27 QTL sites were mapped under cold stress alone,and the maximum of Lod values was 8.4626 and the maximum of the phenotype contribution was 18.2439%.Whereas,87 QTL sites were mapped under BRs+cold stress,and the maximum of lod value was 11.4737 and the maximum phenotype contributed was 15.0490%.In the case of cold stress alone,there were 3 QTL sites related to the seedling shoot length,2 QTL sites related to the seedling root length,19 QTL sites related to the dry weight,and 3 QTL sites related to the fresh weight.For BRs+cold stress,there are 6 QTL sites related to the seedling shoot length,31 QTL sites related to the seedling root length,30 QTL sites related to the seedling root length,and 20 QTL sites related to the fresh weight.Overall,the number of QTL sites mapped under BRs+cold stress was more than those under cold stress alone.In addition,the intervals of some QTL sites with different treatment from same trait or different trait were overlapped even coincident perfectly.(4)According to the QTL mapping results of the four traits,4 kinds cold-resistant genes were annotated in the physical region of the target interval,namely MYB,WRKY,ERF and LIC genes.LIC genes are cold-resistant genes associated with BRs pathways and are only commented under BRs+cold stress.These can lay the foundation for further research on the specific function and regulatory relationship of cold tolerance genes in BRs pathway. |
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