Identification Of TPX2 Gene Family In Upland Cotton And Its Functional Analysis In Cotton Fiber Development

Cotton is a significant source of textile industry.Microtubules as a part of cytoskeleton are of great importance to fiber development.Microtubule-associated proteins(MAPs)which can specifically bind to the microtubule cytoskeleton regulate the dynamic assembly processes and structure to affect their function.The Xklp2(TPX2)proteins are a class of MAPs,which play a key role in plant growth and development by regulating the dynamic changes of microtubules(MTs).However,the connections between TPX2 proteins and tubulins are still unknown in cotton.Meanwhile,fiber cells which are single cell without cell division are significant models to study cell elongation and cell wall and cellulose biosynthesis.Therefore,a genome-wide analysis of TPX2 family was performed in the Gossypium hirsutum.We identified 41 GhTPX2 sequences in the assembled G.hirsutum genome by a series of bioinformatic methods.All these members have the TPX2 domain.Generally,this gene family was phylogenetically grouped into six subfamilies.The number of members of WDLB subgroup(clade 4)was the largest and the MAP20 subgroup(clade 1)was the least.41 G.hirsutum TPX2 genes were distributed across 21 chromosomes.We performed a transcriptome analysis of TPX2 gene family in upland cotton.A heatmap of TPX2 gene family showed that homologous pairs,GhWDLA2/7 and GhWDLA4/9,had great differences between two upland cotton lines 69307 with longer and stronger cotton fiber and 69362 with shorter and weaker cotton fiber at 20 days post anthesis(DPA).The ovules were treated with oryzalin,a specific microtubule depolymerization agent.The relative data indicated that these four genes were down-regulated under oryzalin,a specific microtuble depolymerization agent.Subcellular localization suggested that GhWDLA2 and GhWDLA7 were localized to the microtubule cytoskeleton,and GhWDLA4 and GhWDLA9 were localized in the nucleus.We further detected the relationships between GhWDLA2,GhWDLA7 and tubulin genes which were specifically expressed in cotton.The results of Y2 H indicated that GhWDLA7 could interact with GhTUA2.These results lay the foundation for further function study of TPX2 gene family.