Genetic Analysis And Fine Mapping Of A New Frego Bract Mutant In Cotton

Cotton bracts are usually in the form of pyramid-shaped coating flowers and cotton bolls.The bracts of the frego bract mutant were narrow,twisted,and rolled outwards,leaving the flowers and bolls fully exposed.The phenotype of frego bracts can improve the lint clarity of cotton varieties and reduce the occurrence of pests and diseases.We found a frego bract mutant that can be stably inherited in the transgenic offspring.The mutant showed that the bracts were narrow,twisted,and rolled outwards,leaving the flowers and bolls exposed.At the same time,the veins at the base of the leaf blade of the frego bract mutant merged,so that the leaf was shrunken.In this study,the newly discovered frego bract mutant of upland cotton was used for genetic analysis and fine mapping of candidate genes.The research results lay the foundation for further analysis of the formation mechanism of frego bract and breeding application.1.Genetic analysis and allelism test of frego bract mutants The genetic analysis of frego bract was carried out by constructing（TM-1×Frego bract mutant）F₂ segregating population.In F₂ population,there are 1205 plants with a phenotype similar to normal bract and 399plants with mutant phenotype similar to frego bract.The card square value is 0.1686,which is less than 3.84.Therefore,the segregation ratio of this trait is in line with the data of 3:1,indicating that the frego bract mutant is controlled by a recessive single gene.The allelic test of the frego bract mutant was carried out by constructing F₁ populations of（Frego bract mutant×T582）and（Frego bract mutant×PD695）,and all F₁ individual plants showed the phenotype of frego bract.The phenotype indicates that these three materials with frego bract are controlled by the same gene.2.Fine mapping of target gene in frego bract mutant of upland cotton.Based on the BSA-Seq technology,40 individuals with normal bract and 40 individuals with frego bract were selected from the（TM-1×Frego bract mutant）F₂ segregating population to construct two extreme mixed pools.Furthermore,the frego bract gene was initially located between0.11-11.89 Mb on A03 chromosome,and the physical distance was 11.78 Mb.According to the initial mapping results,the In Del primers were designed to identify the genotypes of individual plants with frego bract in the F₂ population,and then the number of exchanged individual plants was counted,and the gene of frego bract was further located between In Del-S9607 and In Del-S9875.The physical distance between In Del-S9607 and In Del-S9875 is 75Kb and contains 4 genes.Among them,there are two genes（GH＿A03G0233 and GH＿A03G0235）expressed in the bracts and leaves of TM-1,and the expression level of GH＿A03G0233 in the young bracts of the frego bract mutant was significantly lower than that of TM-1.GH＿A03G0233 encodes a CYP87A3-like protein,which belongs to the P450family and may be involved in the auxin.It is speculated that GH＿A03G0233 may be a candidate gene controlling frego bract phenotype.3.Transcriptome analysis of TM-1 and frego bract mutant.In the study,the RNA from the young bract of frego bract mutant and TM-1 was extracted and sequenced.A total of 1839differentially expressed genes were detected between the two parents.There are 1372 genes up-regulated and 467 genes down-regulated in frego bract mutant.Through the analysis of the KEGG metabolic pathway,both the up-regulation and down-regulation of differential genes are significantly enriched in plant hormone signal transduction and the biosynthesis of secondary metabolites.Among them,the plant signal transduction pathway is involved in more auxin-related genes.It is speculated that the frego bract related genes mediate the auxin signal transduction pathway and affect the development of bract.