植物特征性基因的分子进化及其在系统发育中的应用

The techniques of molecular biology have been applied to many areas of life.sciences such as plant phylogeny and evolution. This project has been focused on.the studies of the evolution of some genes that are specific to plants or eukaryotic.organisms, and tried to use these genes to study the phylogeny of certain plant groups..I. CHS gene family.CHS gene is specific to plants. It encodes chalcone synthase which is a key.enzyme in flavonoids synthesis. CHS plays an important role in plant floral coloring,.stress tolerance, disease resistance, root nodulation, and so on. CHS genes are in the.form of gene family in most plant species. This project sequenced CHS genes from.about 73 angiosperm, gymnosperm, liverworts species and analyzed about more than.200 CHS gene sequences. It is found that CHS genes are very active in angiosperm.plants. The event of duplication/loss is very frequent. Some duplication event is.proceeded the differentiation of the family and some is after the differentiation..Lardizabalaceae is a good example. The CHS genes in Lardizabalaceae.differentiated into two groups, one with a single gene from each species studied and.one with the rest of genes. The latter has sub-groups, and the sub-grouping does not.follow any rule. It is obvious that the duplication/loss of CHS gene has been very.frequent in this family and the “gain and/or loss” of paralogous gene is different in.different sublineages. Therefore, this kind of gene can not be used to construct the.phylogeny of angiosperms at the family or generic level. But this kind gene would.be a good model for molecular evolution studies. Studies on the molecular evolution.of CHS genes from Dendranthema and Ipomoea found that the members in the gene.family have diverged into two main classes: one experienced negative selection with.relatively low substitution rate and another experienced positive selection with.relatively high substitute rate. The one with low evolution rate might maintain the.original function, but the one with high rate might have some new functions..Before this project is carried out, only few CHS genes were reported from.gymnosperms. We have sequenced CHS genes of many species from gymnosperms,.especially from Pinaceae and Cupressaceae. Our studies showed that the copy.number of CHS gene is quite few low in gymnosperms comparing with angiosperms,.which is supported by Southern blotting data. The family relationships in the.phylogenetic tree based on the CHS genes is close to that in the trees constructed by.国家自然科学基金资助项目结题报告.10.other genes that are frequently used for phylogenetic studies. Pinaceae and.Cupressaceae are clustered as a monophyletic group respectively. It seems that CHS.gene can be used as a marker for construction the phylogeny of gymnosperm plants at.family level. Studies on molecular evolution indicate that there is different selective.pressure between CHS genes of Pinaceae and Cupressaceae. There is no positive.selection detected in the CHS genes of Pinaceae. In Cupressaceae, CHS genes are.sub-divided into two groups, TC1 and TC2. No positive selection detected in TC1,.either. Positive selection has been detected in TC2 which also has relatively high.rate of substitution. The studies on the phylogeny and evolution of CHS genes from.gymnosperms have paved ways to a complete picture of molecular evolution of this.gene in seed plants..It is recorded that CHS gene exits in mosses and vascular plants. Up to now,.CHS genes are only reported from ferns and seed plants. There has no record of this.gene in mosses or liverworts. We have cloned a gene fragment about 1kb, for the.first time, from Lunularia cruciata, a species of liverworts. Its nucleic acid sequence.and deduced amino acid sequence are very similar to that CHS gene. The most.important is that it has the same active sites at those of identified CHS genes. We at.least have obtained a CHS-like gene. Now we are trying to clone the complete gene.from Lunularia cruciata for further function and evolution st

查尔酮合酶（CHS）基因家族是植物特有的一类DNA序列，本项目将对水稻CHS基因家族成员进行序列分析，对第伦桃亚纲及被子植物中代表性物种的CHS基因进行PCR扩增和测序，分析此基因家族的进化规律；并在此基础上进行第伦桃亚纲和被子植物的系统发育重建；寻找新的适用于植物系统进化研究的分子标识；促进我国的分子进化方面的研究。

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