Molecular Evolution And Taxonomy Analysis Of Plant Isoflavone Metabolism Pathway

Since the beginning of the eighteenth century,French naturalist Lamarck first established the theory of biological evolution,the biological evolution had gone through "use-forward and disuse-back" theory,"natural selection" theory and "a modern comprehensive theory"(the new Darwinism) periods.Discovery of DNA as the genetic material and the double helix structure of DNA signed life sciences had gone into molecular era.Molecular biology researches not only added new important evidences into biological evolution but also brought new challenges.Japanese geneticist Motoo Kimura brought up the neutral theory,an important opinion in the theory is that evolution is not affected by natural selection in molecular level,but follows a way that mutations randomly occur in certain rate,which is neither good nor bad to an organism.Besides, most of mutations at the molecular level is neutral or near neutral on which natural selection has not any effect.And these mutations rely on random drift,which therefore lead changes at molecular level or intraspecific variation.Isoflavones,as secondary metabolites produced primarily from leguminous plants play important effects on stress resistance,anti-pest,as well as human health.Isoflavones are synthesized from p-coumaric acid coenzyme A and malonyl coenzyme A,metabolic product of amino acid phenylalanine and tyrosine metabolite in the plant through a series of catalysis of Chalcone synthase(CHS),Chalcone isomerase(CHI) and Isoflavone synthase (IFS).Full-length cDNA sequences of Chalcone synthase(CHS),Chalcone isomerase (CHI) and Isoflavone synthase(IFS) were gained throught RT-PCR in this paper.Three key regulatory enzymes were studied for the molecular evolution and the relationships with the systematic classification research with the use of cluster analysis method, combined with data from gene database.Results are shown as follow:(1) Full-length cDNA sequences of Chalcone synthase(CHS),Chalcone isomerase (CHI) and Isoflavone synthase(IFS) were gained throught RT-PCR and the results show more than 98%homology through comparison with published species of plants,which provided groundwork for the further research of plant isoflavone metabolic pathway. (2) Researches of these three key regulatory enzymes at nucleic acid level and protein level through the method of Cluster Analysis had shown:Similarity relationship and the evolution level of the same enzyme differ at nucleic acid level and protein level; Relationship and the evolution level of the different step enzyme are not coordinated either. The amino acid sequences are more suitability for molecular evolution of metabolic enzymes.(3) Molecular evolution relationship in isoflavone metabolic pathway is different with other traditional evolution relationship in plant according to the results above. Morphological structure obscures the relevance of plant metabolism,particularly the differences in secondary metabolites,and plant secondary metabolites have a lot of relevance with the natural environment.Findings in the characteristics of metabolic pathways in substrate metabolism and the branches of metabolic pathway have a certain impact on the status of clustering and classification relationship.The above-mentioned research results not only provide new ideas on the overall study of molecular evolution and systematics through plant secondary metabolic pathway but also have practical effect on development and researches of bioactives of isoflavone secondary metabolites.