Genome-wide Identification Of Fatty Acid Desaturase Gene Family In Gossypium Hirsutum L. And Their Expression Patterns

Fatty acids are the primary constituents of plant membrane phospholipids and seed storage triacylglycerols.Fatty acid desaturases(FADs),encoded by a large gene family,are the key enzymes that bring one or more carbon double bonds into hydrocarbon chains in different positions of fatty acids to produce unsaturased fatty acids,which play an un-alternative role in regulating plant growth and responding to variance in environmental signals.Gossypium hirsutum L.is the most important cultivated cotton species,accounting for about 90%of the world's total cotton production.It seems to be an interesting model system not only for the research of genome evolution,but also for studying the roles of polyploid in crop development and domestication with high research value.In addition,though cotton is a salt-tolerant pioneer crop,it would be easily harmed by the high soil salinity(>0.3%).Meanwhile,cotton is a thermophilic crop.Low temperature under 15? will lead to frost damage,which affecting the yield and quality.In this study,we did the genome-wide identification and gene structures on FAD gene family using bioinformatics and comparative genomics techniques,which based on the genomic database of G.hirsutum(AD1).And the expression patterns of the detected FAD genes in different varieties,organs and growth stages of G.hirsutum were conducted,as well as the expression patterns of FAD genes response to salt and cold stress regimes.This research work may provide some candidate genes and theoretical basis for modifying FAD profiles in order to improve the cottonseed oil content and abiotic resistance for cotton breeders.The main results were as follows:(1)39 full-length FAD genes had been identified in G.hirsutum.34 FAD genes were distributed on 22 chromosomes,and the rest of five genes were positioned on the scaffold sequences.These genes had been classified into four groups with conserved exon-intron structures in terms of the same subfamily.Total 13 segmental duplicated gene pairs were found,which might contribute to the expansion of GhFAD genes.(2)FAD genes in different varieties of G.hirsutum were expressed specifically.Most FAD genes of DF005 exhibited specifically high transcription in young leaves at the bud stage,developing ovules on 10DPA,20DPA and 30DPA,which might induced by the gens related to inhibition of gossypol synthesis,promoting its high expression to adapt to the external adverse environments.(3)FAD genes in different organs of G.hirsutum were expressed specifically.GhFAD2.1 A,GhFAD2.2,GhDSD1.2 A and GhFAD8.1 A in the roots of G.hirsutum TM-1 expressed significantly higher than that in other organs,suggesting the specific function in the process of development and growth of the roots.(4)FAD genes in different growth stages of G.hirsutum were expressed specifically.FAD genes were expressed highly in 30DPA ovules of different upland varieties,and most FAD2 subfamily members,such as GhFAD2.3A,GhFAD2.1D,GhFAD2.4A and GhFAD2.4D,showed high transcript abundance in the late lipid accumulation process with seed-specificity,which might have contributed to the synthesis of polyunsaturated fatty acids in the seeds of G.hirsutum.(5)FAD genes response to abiotic stress regimes were expressed specifically.GhFAD8.1D and GhADSSD exhibited specifically high transcript accumulation in tested tissues exposed to different levels of cold stress,which suggested that they might be required for salt tolerance.Meanwhile,GhFAD8.1A was likely to enhance the plant tolerance to cold stress according to the significant up-regulation after long periods of treatment.