Study On The Mechanism Of Exogenous IAA On Cotton Fiber Initiation And Differentiation And Its Application

Cotton is the most important fiber crop in the world.Cotton fibers are trichomes derived from individual epidermal cells on the outer integument of the ovules.Fiber development undergoes four distinctive,but overlopping stages:initiation,elongation,secondary wall thickening and maturation.The initiation is the first step which plays a crucial effect on the number of fibers and lint yield.Multiple phytohormones participate in the regulation to the development of cotton fiber.Among them,the study of auxin is most comprehensive.Previous studies have shown that auxin can regulate the differentiation of epidermal cells of ovules,but the mechanism is still not clear.In this study,exogenous IAA and water were taken to treat the cotton cultivar TM-1,and the latter was served as the control.Also,scanning electron microscopy was used to observe the differentiation of ovule epidermal cells.Then contents of IAA,GA3 and ABA in the ovule were measured and fiber quality was also measured.Furthermore,ovules of-3 DPA(Days post anthesis),0 DPA and 3 DPA were provided from the two samples which were used to construct the library and sequencing.Expression levels of some miRNAs and their target genes were subsequently analyzed by qRT-PCR.Main results were as follows:1.Scanning electron microscopy(SEM)showed that the number of fiber initiation was significantly different between the treated and the control,which indicated that auxin could induce the differentiation of ovule epidemal cells.After measuring the lint percentage and cotton fiber quality,it was found that auxin could significantly improve the lint percentage and cotton fiber quality,therein the micronaire were promoted from B level to A level.2.After exogenous IAA spraying,the contents of endogenous IAA,GA3 and ABA were all changed in the fiber initial period of cotton ovule.For instance,when compared with the control,the content of IAA in the treated was improved on 2 DPA and 5 DPA,and the difference reached a very significant level;it also improved on 0 DPA and 3 DPA,and the difference reached a significant level.The content of GA3 was improved on 3 DPA,while the content of ABA was decreased on the-1 DPA and 0 DPA,and they all reached significant difference levels.3.Taken upland cotton genome sequences which published by Nanjing Agricultural University for reference sequences,a total of 142 miRNAs were identified in this study.Therein,58 miRNAs belong to 50 miRNA families which had conserved sequence to miRNAs of other plant species,and 84 were novel miRNAs.A total of 56 miRNAs were differentially expressed between the two samples.Among them,11 conserved and 23 novel miRNAs were differentially expressed between the-3 DPA ovules of two samples,10 conserved and 6 novel miRNAs were differentially expressed between the 0 DPA ovules of two samples,and 10 conserved and 14 novel miRNAs were differentially expressed between the ovules of two samples.Novel miRNAs account for 66.9%of the total differentially expressed miRNAs number,indicating that novel miRNAs might play an important role in the process of auxin regulating the fiber initial development.Therefore,studying the function of novel miRNAs was of great significance.4.6 differentially expressed miRNAs and their target genes were validated by qRT-PCR in cotton ovules at the fiber initiation phase.Results suggested that the expression of most miRNAs were negative correlation with their targets,demonstrating that these miRNAs might negatively control their targets and then regulate the fiber initial development.