Genome-wide Identification Of SWEET Gene Family In Cotton And Cloning And Analysis Of GhSWEET1 Expression Patterns

Cotton is the important natural fiber plant in the world as well as an important economic crop in China.Cotton fiber is the main source of natural raw materials for textile industry.Cotton fiber sugar content is one of the important factors to determine the quality.Bolls and fibers mainly accumulating cellulose by carry out carbohydrate metabolism,and photosynthetic products are transported in the form of sucrose to the sink organ,providing energy to the growth and development of the sink organ.SWEET is a newly identified family of sugar transporters supporting import and efflux of sugars from cells.Also involved in plant growth and metabolic processes with many important physiological functions.First we measured the content of total soluble sugar in Gossypium hirsutum TM-1 varies with developmental time;Based on genome sequences of two diploid cotton species,Gossypium raimondii,SWEET gene families were analyzed at the genome-wide level;Researcted the expression patterns of GhSWEET1 in mature plants and seedlings under the induction of drought and cold stress were studied by fluorescence quantitative technique.The main results of this paper are as follows:1,Determination of total soluble sugar in 5,10,15,days of fiber,shell,petiole(para-leaf)and para-leaf in the same part of bolls of Gossypium hirsutum TM-1.The results showed that sugar content of fiber decreased first and then increased with the increase in the number of days;sugar content of para-leaf increased first and then decreased with the increase in the number of days;While the sugar content in the shell and petiole decreased with the increase of the number of days.2,Identification and evolutionary analysis of the whole genome family of SWEET gene associated with soluble sugar transport.The whole genome of SWEET gene was identified and analyzed by genome data of Gossypium raimondii of group D.The results showed that:(1)31 SWEET genes were identified and distributed unevenly or clustered among Gossypiumraimondii 11 chromosomes.All these SWEET proteins were divided into three subgroups.(2)Phylogenetic tree of the full-length proteins by the SWEET genes in Gossypium raimondii,Arabidopsis thaliana and Oryza sativa.All these SWEET proteins were divided into four subgroups: SWEET I,SWEET II,SWEET III,SWEET IV.Among them,SWEET I subfamily contains 13 Gossypium raimondii SWEET genes,7 Arabidopsis thaliana SWEET genes,9Oryza sativa SWEET genes.The SWEET II subfamily consists of 6 Gossypium raimondii SWEET genes,3 Arabidopsis thaliana SWEET genes and 6 Oryza sativa SWEET genes.Among the SWEET III subfamily,12 SWEET genes belong to Gossypium raimondii,6 from Arabidopsis thaliana,5 belong to Oryza sativa,While the SWEET IV subfamily had only two Oryza sativa SWEET genes in this study.In contrast,the number of SWEET genes in SWEET I and SWEET III subfamilies was higher in Gossypium raimondii than in Arabidopsis thaliana and Oryza sativa.Among the four different subfamilies,SWEET I and SWEET II of Gossypium raimondii are the subfamilies with maximum members.(3)Predicted transmembrane domain for 31 Gossypium raimondii SWEET proteins,the results showed that there were seven transmembrane domains comprised twenty two genes out of 31 including GrSWEET 1,2,3,4,5,11,12,13,15,16,17,18,20,21,22,23,25,26,27,28,30.However seven of them contained six transmembrane domains i.e.GrSWEET 9,10,14,19,24,29 and31.There are only two members GrSWEET6 and GrSWEET7 containing eight transmembrane domains.In addition to GrSWEET 6,7,9,19 with 4 introns,the remaining 27 SWEETs contained 5 introns.3,According to the published transcriptome data,the GhSWEET1 gene of Gossypium hirsutum TM-1 was selected as the target gene.The expression vector of GFP fused with the N terminal of GhSWEET1 was completed and transiently expressed in tobacco.The result showed that GhSWEET1 was located in cell membrane.GhSWEET1 gene specificity was analyzed by fluorescence quantitative technique.The results showed that the GhSWEET1 gene was expressed at 5 d,10 d and 15 d after flowering in Gossypium hirsutum TM-1.Wherein the expression level of the gene increased in the fiber and the shell with the increaseof the growth time;In the bracts,the change of the increase and decrease – increase with the increase of the fertility time;Decreased in the petiole with time;Increased gradually at 5 d and 10 d after flowering,and decreased significantly at 15 d.GhSWEET1 gene was expressed in the tissue of TM-1 seedling with the highest expression in true leaves,followed by cotyledons,stem,and root.The expression of GhSWEEET1 gene was analyzed by drought and cold stress of Gossypium hirsutum TM-1 seedlings.The results showed that the GhSWEEET1 gene was significantly up-regulated in the true leaves compared with the control,but at the different time intervals of the drought stress,the expression of the gene was "increase-decrease-increase" trend;In the roots,the GhSWEEET1 gene was significantly down-regulated by drought induction compared with the control,but in the different periods of treatment were "decrease-increase-decrease" trend;Compared with the control,the GhSWEEET1 gene was down-regulated in the true leaves of cotton at 3 h and 6 h after cold treatment under cold stress,significantly up-regulated expression at 9 h and 12 h after treatment,at the different time of cold stress,the overall trend was "decrease-increase-decrease".In this study,the content of total soluble sugar in the organs of Gossypium hirsutum TM-1 was determined,and the expression patterns of GhSWEEET1 in the corresponding cotton and cotton seedlings were analyzed,indicating that the gene can regulate the transport of sugar to regulate the growth and development of cotton;Analysis of differences in drought and cold stress after stress showed that the gene could regulate the resistance of cotton to drought and cold stress by adjusting the concentration of sugar in each tissue;Subcellular localization indicates that the gene is mainly present on the cell membrane.By the identification and evolution of SWEET gene family in Gossypium raimondii Which laid a foundation for the further study of the mechanism of the transporter SWEET in cotton growth and development.