| Cotton is a natural fiber crop,which is the most important fiber source of textile industry and plays a pivotal role in our national economy.It has been the main goal of cotton breeding to improve the yield of cotton.Cotton lint percentage is one of the important factors that constitute the yield of cotton,and it is a complex quantitative character that is regulated by many factors.Wall-associated kinases(WAKs),a subfamily of receptor like kinases(RLKs),are directly involved in plant cell elongation and response to biotic and abiotic stresses.At present,more and more plants have completed the whole genome sequencing,especially the genome sequencing of several species of Gossypium,which provides solid data support for the study of the origin and evolution of green plant WAK gene through comparative genomics,especially the evolution and biological function of Gossypium WAK genes.In this study,genomic data from different lineages of green plants were used to reveal the origin and evolutionary patterns of WAK gene families in green plants based on phylogenetic analysis.The genome-wide identification of WAK gene family was conducted in cotton,and its functional role in the development of cotton fiber was explored.The main research results are as follows:(1)A total of 1061 WAK genes were identified in 37 species of green plants by homology search and domain prediction,but no WAK gene was identified in chlorophytes and charophytes.WAK gene first appeared in bryophytes,suggesting that WAK gene family may have emerged during the transition from aquatic plants to land plants.Phylogenetic analysis showed that WAK formed specific clades in monocots and eudicots,indicating that gene duplication events that occurred after eudicot and monocot separation or gene loss events after branch formation.The analysis of cis-acting elements and expression patterns of monocotyledonous plant model plants rice and dicotyledonous model plants Arabidopsis indicated the functional diversity of WAK gene in monocots and eudicots,implying that they may be involved in multiple organ development,and participate in diverse signaling pathways in response to different plant phytohormones or stresses.A large number of species-specific expansions of WAK gene were found in angiosperms by duplication and loss analysis,leading to an increase in the number of genes.(2)Genome-wide identification of WAK gene family was performed using the genome data of two diploid Gossypium arboreum and G.raimondii,as well as the allotetraploid G.hirsutum,and 58,66 and 99 WAK genes were identified respectively.Synteny analysis showed that segmental and tandem duplications led to the expansion of WAK gene family in cotton.Ka/Ks ratios analysis indicated that the family was exposed to purifying selection pressure during evolution.The structures of the Gh WAK genes and encoded proteins suggested the functions of WAKs in cotton were conserved.Analysis of cis-acting elements in the promoter region suggests that WAK gene may be involved in plant growth and development and stress response in cotton.A closely linked WAK gene cluster with seven genes was identified on chromosome Dt02.The WAK gene cluster existed in diploid cotton species and five allotetraploid cotton species,including cultivated and wild species,and its relative position was highly conserved.It is speculated that the WAK gene cluster may play an important role in the growth and development of cotton.(3)The SNP number and correlation analysis of seven WAK genes in the gene cluster showed that Gh WAKL39 was highly correlated with lint percentage.q RT-PCR showed Gh WAKL39 was highly expressed in fiber initiation and development stages,and the expression level of Gh WAKL39 in fiber initiation stage of xuzhou142 was significantly higher than that of xuzhou142 lintless-fuzzless mutant(xuzhou142-fl),suggesting that Gh WAKL39 may be involved in regulating fiber development of cotton.The protein encoded by Gh WAKL39 gene was determined to be located on the cell membrane by subcellular localization experiments.The ectopic expression of Gh WAKL39 in Arabidopsis significantly increased the root hair,stem hair and trichomes.Knockout of Gh WAKL39 in cotton hindered fiber initiation and elongation,and reduced lint percentage.In contrast,overexpression of Gh WAKL39 in cotton promoted fiber initiation and elongation,and increased lint percentage.Gh SUT6,a sucrose transporter,was identified to interact with Gh WAKL39.Moreover,the root hair,stem hair and trichomes of Arabidopsis were also significantly increased with ectopic expression of Gh SUT6.Overexpression of Gh SUT6 in cotton also promoted fiber initiation and elongation,and increased lint percentage.The interaction mechanism analysis showed that Gh WAKL39 could enhance the sucrose transport activity of Gh SUT6.In conclusion,we found the origin and evolution of WAK gene family in green plants,and the evolutionary trajectory during polyploidization of cotton.The function of WAK genes is diversified,and they may be involved in plant growth and development,various hormone and abiotic stress responses,and may participate in regulating cotton fiber development.In addition,Gh WAKL39 may promote fiber initiation and elongation by activating the sucrose transport activity of sucrose transporter Gh SUT6,thereby improving lint percentage. |
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