Salt Tolerance Evaluation And Genome Wide Analysis Of GST And ALDH Gene Families In AD Genome Cotton Species

Soil salinization is one of the main adverse environmental factors restricting crop growth and development.As the most important natural textile fiber crop in the world,cotton(Gossypium spp.)also is the pioneer crop in saline soils.However,high saline concentration will affect the physiology and metabolism of cotton,which ultimately inhibited cotton growth and development thus resulting in decreased yield.Different cotton species even different cultivar within a species show diverse salt tolerance ability.In addition to hyperosmotic stress and ionic toxicity on plants,high salinity in soil also cause the secondary injury to cottons which called oxidative damage induced by excessive reactive oxygen species(ROS)and aldehyde.Thus,the scavenge of ROS and aldehyde are very important to cotton growth under salinity.To evaluate genetic variation of salt tolerance among cotton species,17 diverse accessions of allopolyploid(AD-genome)and diploid(A-,D-genome)Gossypium were evaluated for a total of 29 morphological and physiological traits associated with salt tolerance.Furthermore,we use the genome sequences of allopolyploid cotton G.hirsutum and its two diploid cottons,G.raimondii and G.arboreum,to analyze the GST gene family and ALDH gene superfamily at genome-wide level.Their expression profiles under salt stress were also studied.The main results were as follows:1.Development of salt-tolerant genotypes is pivotal for the effective utilization of salinized land and to increase global crop productivity.Several cotton species comprise the most important source of textile fibers globally,and these are increasingly grown on marginal or increasingly saline agroecosystems.The allopolyploid cotton species also provide a model system for polyploid research,of relevance here because polyploidy was suggested to be associated with increased adaptation to stress.To evaluate genetic variation of salt tolerance among cotton species,17 diverse accessions of allotetraploid(AD-genome)and diploid(A-,D-genome)Gossypium were evaluated for a total of 29 morphological and physiological traits associated with salt tolerance.For most morphological and physiological traits,cotton accessions showed highly variable responses to two weeks of exposure to moderate(50 mM NaCl)and high(100 mM NaCl)hydroponic salinity treatments.Results showed that the most salt tolerant species were the NE Brazilian allopolyploid G.mustelinum,the D-genome diploid G.klotzschianum from the Galapagos Islands,following by the African/Asian,A-genome diploids.Generally,A-genome accessions outperformed D-genome cottons under salinity conditions.Allopolyploid accessions did not show significant differences from either diploid genomic group in salt tolerance,but they were more similar to one of the two progenitor lineages.2.A genome-wide survey of GST genes in G.hirsutum and its diploid progenitors,G.raimondii and G.arboreum,was carried out.Based on phylogenetic analyses,the GST gene family of all the three cotton species could be divided into eight classes,and the gene structures between the orthologues were highly conserved.The chromosomal localization analyses revealed that GST genes were unevenly distributed across the genome in both G.hirsutum and the diploid progenitors,G.raimondii and G.arboreum.Tandem duplication could be the major driver for the expansion of GST gene family in diploid cottons,whearaz whole genome duplication may explain the GST gene family expansion in allotetraploid G.hirsutum.Meanwhile,the expression analysis for the selected 40 GST genes in diploid cottons showed that they exhibited tissue-specific expression patterns and their expression were induced or repressed by salt stress.The expression patterns of orthologous GST gene in the two cotton species also differed,which might be caused by their adaptation to different surrounding environments.RNA-seq data of G.hirstum under salt treatment also indicated that most GhGSTs respond to salinity stress.3.A comprehensive whole-genomic study of ALDH gene superfamily was carried out for an allotetraploid cultivated cotton species,G.hirsutum,as well as in parallel relative to their diploid progenitors,G.arboreum and G.raimondii.Totally,30 and 58 ALDH gene sequences belong to 10 families were identified from diploid and allotetraploid cotton species,respectively.The total number of ALDH gene superfamily members in allotetraploid cottons were not the same as the sum of those in the two diploid progenitors,suggesting possible deletion,duplication or genome shuffling have occurred.Whole-genome duplication might be the major driver for the expansion of ALDH gene superfamily in G.hirsutum.The orthologs from the same subgenomes within two allotetraploid cottons tended to cluster together.In addition,the expression patterns of GhALDH genes were diverse across tissues.Most GhALDH genes were induced by salt stress in the leaf of upland cotton.In summary,the comprehensive analysis of GST was performed in G.raimondii and G.arboreum.ALDH genes were identified in G.hirsutum and G.barbadense as well as in parallel within their two progenitors through systematic genomics approach.The phylogenetic analysis suggested that both two gene families underwent expansion in Gossypium genomes.Expression patterns under salt treatment indicated that GST and ALDH genes participated in cotton response to salinity stress.The orthologous gene pairs between two diploid cottons shown different expression profiles implied that the function of these genes have been divergent during evolution.Our findings also demonstrate that allopolyploidy per se need not be associated with increased salinity stress tolerance and provide information relevant to utilization of the secondary Gossypium gene pool for breeding improved salt tolerance.