Gene Mapping Of Li₃ And N₂ And MicroRNA Analysis Of Cotton Lintless Mutant

Upland cotton is the most important cultivar of allotetraploid cotton and the main natural raw material in textile industry.Cotton fiber is formed by single cells protruding outward from the surface of cotton seed.The first protrusion forms lint,and the second protrusion forms fuzz.Cotton fiber mutants are of great value in revealing the genetic law of cotton fiber initiation and development.In this study,three F2 populations were constructed using Xinxiangxiaoji,XinFLM,XinWX,respectively.The lint control gene li3 and fuzz control gene n2 were located by SSR molecular markers.Six small RNA libraries were constructed from ovule of Xinxiangxiaoji（WT）and its XinFLM mutant on the flowering day,and high-throughput sequencing was performed.The main results of this study are as follows:1.In this experiment,F2 isolated population of intra-species（land-land）hybridization was constructed,2000 pairs of SSR primers were randomly selected from chromosome 26,and 63 pairs of polymorphic primers were screened.We used these SSR markers for F2 population to construct linkage maps using JoinMap 4.0 software.Finally,a linkage map of 83.7 cM was constructed,and the n2 gene was located within the genetic interval of 18 cM,4.3 cM from SSR marker D12₁926 on one side and 13.7 cM from D12₂082 on the other side.The gene li3 was located between SSR labeled SWU17386 and D12₂494,with a genetic interval of 8.0 cM with a genetic distance of 0.7 cM and 7.3 cM,respectively.2.In this study,combined with high-throughput sequencing technology and bioinformatics analysis method,small RNA sequencing was performed on ovule of 0 DPA in Xinxiangxiaoji and its XinFLM mutant.A total of 459 miRNAs were found,including 301 conserved miRNAs and 158 newly predicted miRNAs.Thirteen differentially expressed miRNAs were obtained and their target genes were predicted and analyzed.According to the bioinformatics analysis of the target genes,the predicted target genes focus on the transcription factors encoding HD-ZIP,GRAS and AP2 families,and their functions were focus on the transcriptional and post-transcriptional regulatory stages.GO annotation for target genes was revealed that they were involved in biological processes such as cell differentiation,anther development and flower organ development.In this study,the initial locus of li3 and n2 genes regulating fiber initiation and development were obtained by screening polymorphic SSR molecular markers in the constructed land-land hybrid F2 population.In addition,small RNA sequencing showed that miRNA negatively regulated target transcription factors and hormone-related genes to affect the initiation and development of fiber.The results of this experiment laid a foundation for fine localization and cloning of fuzz gene n2,and provided a theoretical basis for revealing the molecular biological mechanism of cotton fiber.