| Cinnamomum camphora,a member of the Lauraceae family,is an evergreen broad-leaf tree which has significant economic and ecological value.Monoterpenoids are the main essential oil component of camphor tree.The MEP pathway is an important regulatory node in the biosynthesis process of monoterpenoids.1-deoxy-D-xylulose-5-phosphate synthase(DXS),1-deoxy-D-xylulose-5-phosphate reductoisomerase(DXR),1-hydroxy-2-methyl-2-(E)-butenyl-4-pyrophosphate reductase(HDR)are key enzymes in the MEP pathway.However,few studies were reported on relative enzymes at present.In this study,the essential oil components in different chemical types of camphor tree leaves were compared.Besides,the evolutionary history and expression patterns of DXS,DXR and HDR in camphor tree were also explored.The functions of these genes were preliminarily identified.This study will not only enrich the understanding of the molecular mechanism of essential oil synthesis of camphor tree,but also provide theoretical support for the study of camphor tree elite breeding and business model optimization.The main results of this study are as follows:1)Analysis of essential oil components of camphor tree leaves.A total of 89 compounds were detected from the essential oils extracted from five chemical types of camphor tree leaves.Except for nerolidol-type,the content of monoterpenoids in the essential oils of the other four types was all higher than 90%,which verified that the monoterpenoids were the dominating component in essential oil of camphor tree.2)Identification and evolutionary analysis of DXS,DXR and HDR genes in camphor tree.The DXS,DXR and HDR genes was identified in the C.camphora leaf transcriptome data,and the number is 5,1 and 2,respectively.The coding regions of these gene were successfully cloned by PCR to be consistent with the sequence in the transcriptome.Conserved domains were found in the proteins encoded by the three gene families.Phylogenetic analysis indicated that these genes were highly conserved,suggesting that they might undergo the strong negative selection during the evolution.3)Expression pattern analysis of DXS,DXR and HDR genes in camphor tree.Tissue-specific expression analysis showed that CcDXS,CcDXR and CcHDR were constitutively expressed in five organs,e.g.roots,stems,leaves,flowers and fruits.Among them,the transcript levels of CcDXS1-4 were the highest in flowers and the lowest in rhizomes;CcDXR expression was significantly abundant in flowers,followed by leaves,and the expression level in flowers was about 4 times as much in leaves;CcHDR was expressed the highest in leaves.The experimental results indicated that tissue-specific expressed diversification may exist during the evolution of these genes.4)The effects of plant hormones on the expression of DXS,DXR and HDR genes in camphor tree.Under the treatment of methyl linoleate(MeJA),the expression of CcDXS1 reached the peak both at 12 h and 24 h,and the expression levels were 30.8 times and 47.6 times of the control,respectively.Both CcDXS2 and CcDXS2 reached the peak at 24 h.However,the increase of CcDXS4 expression was not obvious,indicating the function of the paralogs gene may be divergent;under the treatment of gibberellin(GA3),the expression levels of CcDXS1-4,CcDXR and CcHDR increased to various degrees;under the treatment of indoleacetic acid(IAA),the expression of the gene did not show a clear upward trend.On the contrary,the expression level decreased significantly at some points.Although different plant hormones have different degrees of influence on the expression of the above three types of genes,their regulatory pathways may not be the same and further studies are needed in the future. |
PDF Full Text Request