Genome-wide Identification Of Cotton Cell Wall-associated Receptor Kinase(WAK) And Analysis Of GhWAKL27 Function In Fiber Initiation

Cotton has evolved over millions of years to have a lot of long fibers in the ovule epidermis,which makes cotton fiber as an important raw material for global cotton production.With the development of cotton spinning technology and the demand of high quality fiber,it has the vital significance to explore the genes that regulate the development of cotton fiber and probe into the regulation mechanism of it to guide scientific and efficient breeding of cotton.The WAK(Cell wall-associated receptor kinase)gene family is an important type of plant cell receptor kinases involved in some physiological response processes such as defense against pathogenic bacteria,cell elongation,and metal ion stress.Therefore,it is speculated that the members of this gene family have positive regulatory effects on plant production increase,disease resistance and stress tolerance.However,there have been few reports on cotton at present.Previously,our research group focused on GhWAKL3(GhWAKL27)with a very significant correlation with lint percentage and lint index by means of high depth genome resequencing.Therefore,the genomic data of upland cotton were used to identify and analyze the members of the WAK gene family,and the gene function of GhWAKL27 was preliminarily verified.The main results are as follows:Seventy-four members of the WAK family,including 27 WAK genes and 47 WAKL genes,were identified in the upland cotton genome.Phylogenetic relationships with 27 members of the WAK family of Arabidopsis thaliana showed that they were divided into 6 classes.The results of chromosome distribution and collinearity analysis showed that WAK gene family members of upland cotton were mainly produced by segmental duplication.Functional analysis of cis-elements in the promoter region showed that members of the WAK gene family not only contain cis-elements that are responsive to hormones,biological or abiotic stress,but also contain HD-ZIP 1,a key transcription factor for plant growth.This accumulation of cis-related components of stress response indicates that the WAK family genes of upland cotton play an important role in growth and stress tolerance.The full-length CDS sequence of GhWAKL27 was 2931 bp,encoding 976 amino acids.The GhWAKL27 protein contains the GUB_WAK_bind,EGF_like and S_TKc domain.Transient expression of GhWAKL27 and green fluorescent protein fusion expression vector in tobacco indicated that GhWAKL27 was localized on the cell membrane.Overexpression of GhWAKL27 gene in Arabidopsis thaliana showed that the density of root hairs and the number of trichomes of transgenic lines were significantly higher than that of wild type,which proved that GhWAKL27 gene could promote the initiation of cotton fiber.In summary,the analysis results indicate that the WAK family gene of cotton may play an important role in the growth and development of cotton fiber and the response to biological or abiotic stress,and GhWAKL27 gene of upland cotton is involved in the regulation of cotton fiber initiation.This study provided key information for exploring WAK gene family members of upland cotton,laid a solid foundation for in-depth study on the function of GhWAKL27 in the development of cotton fiber,and also provided candidate genes for cotton production increase,disease resistance and stress tolerance breeding.