Identification And Functional Analysis Of Horizontally Transferred Genes In Soybean(Glycine Max) And Barrel Medic (Medicago Truncatula)

Horizontal gene transfer（HGT）is also known as lateral gene transfer（LGT）,the process that exchange of genetic material between species or organelles,which have reproductive isolation.HGT events,the main mechanism for the evolution,which is an universial phenomenon in prokaryotes having important effects in pathogenicity and drug resistance.However,HGT is less studied in eukaryotes.This is due to the existence of nucleus and cell differentiation between germ cells and body cells,which may lead to the low probability.The reasearch on HGT in eukaroytes is conducive to understanding the biological function of exogenous genetic material in receptor species,and plays an important role in the evolution of eukaryotes.Leguminous plants as the main grain and oil crops,has important economic significance.The study of HGT in leguminous can deepen the level of gene transfer as a source of genetic variation in understanding,while we found that leguminous plants through horizontal gene transfer of the gene to provide candidate genes for genome research of leguminous plant,but also can find functions and roles of transferred gens in legumes.Therefore,in this paper,the whole genome sequences of soybean and barrel medic were used as material.Candidate genes were screened using protein sequences and non redundant protein databases of sequenced genomes by similarity comparison method.These candidate genes were further identified by phylogenetic analysis and then we can obtain horizontally transferred genes in soybean and barrel medic.In order to investigate the origin and characteristics of horizontally transferred genes,the GC content bias and the donor source of these genes and evolutionary characteristics were analyzed.Through the analysis of domain structure,the expression of horizontally transferred genes,the analysis of co-expression network and KEGG,functions of genes were predicted.The main results are as follows:1)Three soybean horizontally transferred genes,XP₀06595841,XP₀06591171 and NP₀01239970,were identified.The donors of the three genes were Bacillcus pseudaliphilus,Zootermopsis nevadensis and Halymorpha halys.GC content analysis showed that the GC content of the 3 transferred genes was between 0.35～0.41,tended to the average value of the GC content in the soybean genome,which was consistent with the evolutionary characteristics of HGT.Genes transfer into legumes is preceded by the differentiation of the Phaseoleae ancestors.Phylogenetic analysis showed that only NP₀01239970.1 gene was positively selected.The expression analyses indicated that XP₀06591171 and NP₀01239970 were highly expressed in pod,leaf and stem,and XP₀06595841 was expressed in pod,leaf,stem,sam and flower,implying their specific expressions.XP₀06595841 belongs to the second GRP protein family,involved in the responses of plants to environmental stress,co-expression and KEGG analysis showed that genes involved in cell metabolism,response to plant hormones and involved in plant signal transduction pathway;XP₀06591171 has a conserved structure of MCPVI,which acts as a protein cofactor and catalyzes enzyme activity.It is mainly involved in lipid metabolism and carbohydrate metabolism in co-expression and KEGG analyses;NP₀01239970 is a transmembrane protein belonging to the predic_Ig_block protein family,co-expression and KEGG showed influence in cell differentiation,eell metabolism,the development of multicellular organisms,lipid metabolism and signal transduction pathway,transport processes involving RNA.2)Six barrel medic horizontally transferred genes were XP 013448061,XP 013466591,XP₀13455044,XP₀13455718,XP₀13454200 and XP₀13454201.The donor and characterization of horizontally transferred genes were studied:XP₀13448061,XP₀13466591,XP₀13455044 were derived from fungi,XP₀13455718 came from bacteria,XP₀13454200 and XP₀13454201 were derived from animals;The GC contents of genes between 0.3～0.55 which tends to the average GC content of genome.Phylogenetic analysis showed that XP₀13455718 and XP₀13466591 have experienced positive selection.The trend of expression analysis showed that XP₀13455044 maiuly expressed in the bud and seed pods,XP₀13466591 has a higher expression in flowers,XP₀13448061 has higher expression in bud and seedpod,XP₀13455718 has higher expression in blade,bud and seed pod,XP₀13454201 and XP₀13454200 expressed in seedpod,almost no expression in other tissues,with the expression of specific.XP₀13455044 is the S13 ribosomal subunit,involved in ribosome pathway;co-expression and KEGG analysis showed that the XP₀13455718 is signal anchor,KEGG is mainly involved in plant photosynthesis,XP₀13448061 has truB domain which is associeted with RNA modification,co-expression and KEGG analysis showed that the encoded protein was mainly involved in signal transduction and disease resistance in the form of enzyme;XP₀13466591 nucleosome H5 is associated with nucleosome assembly,co-expression of KEGG analysis involved in the translocation and synthesis of RNA and its transcription and translation processes.Through the identification of horizontally transferred genes of soybean and barrel medic in this paper,after transfering into the receptor,theses genes integrated with receptor genome,Plays an important role in receptor.Therefore,this paper explores the fanctions of horizontally transferred genes in plants and provides reference for horizontal gene transfer bet,Areen plant and non-plant species.