Genetic Characteristics Of Rate-limiting Enzymes For Terpenoids Synthesis Pathway And Transcriptional Regulation In Tobacco

Terpenoids are widely existing in nature,which have a wide range of physiological functions and play an indispensable role in plant growth and development.MEP(2-C-Methyl-D-erythritol-4-phosphate)is the main channel of plant terpenoids material in the synthesis.In this way,DXS(1?deoxy?D?xylulose 5?phosphate synthases)gene is the key enzyme in the synthesis pathway,responsible for regulating the rate of the synthesis in plants.Terpenoids are important components of tobacco aroma compounds.Therefore,the study on DXS gene can increase the regulation of the terpenoid synthesis in MEP pathway,as well as improve the main components of aroma substances and the quality of tobacco.Therefore,based on the known information of the public data,this study analyzed the characteristics and evolution mode of DXS gene of 9 species.Meanwhile,according to the transcriptome data in tobacco,the expression pattern of DXS gene in tobacco was studied,which played an important role in the synthesis of terpenoids in tobacco and the improvement of tobacco quality.The results of the study on the characteristics of DXS gene are as follows:(1)The characteristics of the genome and each element in the genome show diversity.Among them,the average length of exon and CDS fluctuates within a small range,but the characteristics of other elements are still quite different.Therefore,the characteristics of each element in 9 species selected in this study are diverse due to different genomes.(2)By using the DXS gene in Arabidopsis as the reference sequences,29 DXS genes were obtained in 9 plant species,and each species contained 2 ~ 4 DXS genes.(3)The phylogenetic tree construction and phylogenetic analysis of all DXS genes showed that the whole DXS family members were divided into three evolutionary branches.Both of the first branch and the second branch have 11 members,the third branch has 7 members.DXS members of tobacco were distributed in all three branches,and DXS members of tobacco in all branches were closely related to other Solanaceae crops.(4)In 9 species,the physical properties of all DXS genes were highly conserved.The number of amino acid residues of the identified family members was mostly within the range of 700 ~ 730,most of the isoelectric points were in the range of 6 ~ 7,and the molecular weight of the protein was ranged in 63148.46 ~ 79505.87 Da.Some of the members may deviate from the above range partly,which may be caused by the variation of gene sequence,resulting in sequence diversity.(5)Combined with the special structural domains and conserved motifs of DXS family,the analysis of sequence composition characteristics of DXS family in this study indicated that 29 members all contained 8 motifs.Tobacco NtDXS3 did not contain motif3,and NtDXS1 did not contain motif2,which may be caused by gene loss in the process of evolution.Three special domains of DXS family,DXP_Synthase_N,TPP_PYR_DXS_TK_like and Transketolase_C,exist in all members.This high degree of conservation indicates that these sequences play an irreplaceable role in the growth and development of plants.(6)The genetic structure of DXS showed that genes on the location of the different components,the number and length in the same clade DXS members of the present high degree of similarity and conservation,the whole length of the gene in the same branch show similarity,the number of introns are same in some degree,some contain nine introns may be lost.(7)Molecular evolution analysis of DXS gene by PAML showed that all DXS genes showed strong purification and selection during natural selection.The number of synonymous substitutions among family members is more than that of non-synonymous substitutions.In most cases,the gene functionalization and the protein structure remains unchanged.The regulation results of DXS gene in tobacco on the synthesis pathway of terpenoids were as follows: DXS genes in tobacco had the highest expression level in the shootapex and the lowest expression level in the root,which may be related to the primary metabolism of photosynthetic organisms.This study analyzed the expression level of DXS genes in tobacco under low temperature stress,and the results showed that the expression level of all DXS genes decreased under low temperature,mainly due to the influence of low temperature on the rate of photosynthesis,resulting in the downregulation of DXS genes.