Functional Analysis Of MIXTA Transcription Factor GhMYB106 In Cotton Fiber Initiation

Cotton is one of the most important cash crops in the world,and cotton fiber is one of the most important products of cotton.Fiber,one of the longest cells in the plant kingdom,is formed by protrusion and elongation of epidermal cells in cotton ovules,which has become a classic model for studying cell fate determination and cell elongation.The development of cotton fiber is a complicated and programmed biological process.Studies have shown that transcription factors(TFs),as important factors regulating RNA transcription in eukaryotes,play important roles in the development of cotton fibers.In this study,a MIXTA TF GhMYB106,which is highly expressed in the ovules of upland cotton Xu142 but hardly expressed in the ovules of Xu142 fl without fiber was screened,and its function and gene regulatory network were analyzed.The main research results are as follows:The expression profile analysis of upland cotton TM-1 showed that GhMYB106 was highly expressed in ovules of 0 DPA(day post anthesis)and 1 DPA.The expression levels of GhMYB106 in Xu142 and Xu142 fl were significantly different,and the expression of GhMYB106 in the ovules of Xu142 fl was completely inhibited.In transgenic cotton explant Jin668 GhMYB106 was highly expressed at-0.5 DPA,0 DPA,and 1 DPA ovule and after 1DPA the expression level was lower.GhMYB106 is highly homologous to At MYB106 of Arabidopsis thaliana.GhMYB106,GhMYB25,and GhMYB25-like are all R2R3-MYB TFs,belonging to the 9 subgroup branch 2(Sg9-2).Besides,GhMYB106 is most closely related to GhMYB25 in cotton.GhMYB106 was accurately knocked out by CRISPR/Cas9 technology in Jin668.The trichome formation of stem and petiole was inhibited in knockout lines.And the fiber initiation and early elongation was delayed,resulting in that the mature fiber is significantly shorter and the quality is significantly reduced.In GhMYB106 overexpression lines driven by the Ca MV 35 S promoter,the number of trichomes is increased to a certain extent.RNAseq was performed with the 0 DPA ovules and stems of three GhMYB106 knockout lines,wild-type(Jin668),and negative control(Null),and 443 differentially expressed genes(DEGs)were obtained for 0 DPA ovule and 862 DEGs were obtained for stem epidermis.Among these DEGs,genes related to fiber initiation and trichome formation have been identified,including auxin response factor SAUR50(Ghir＿D05G026100),ethylene synthesis gene ACO(Ghir＿D05G017800),cell fate determination and trichome formation related gene GhMYB109(Ghir＿A05G037220),SPL8(Ghir＿A07G015770),and so on.Through screening the TFs library of related fiber initiation by yeast two-hybrid,six interacting proteins including C2H2 TF Gh RBE,ethylene response factor Gh ERF7 and HD-ZIP TFs Gh HDG2,Gh HD-1,Gh PDF2 and Gh HOX3 were obtained.These genes were preferentially expressed at the fiber initiation stage,which was consistent with the expression profile of GhMYB106.These proteins may form a complex with GhMYB106 to regulate the initiation of fibers.