Study On Differences Of Gene Evolution In Liriodendron Based On Chs And Adh Sequences

There are only two relic species in the genus Liriodendron of the Magnoliaceae family:Liriodendron chinense and L.tulipifera. Interspecies differences in Liriodendron are obvious inthe geographical distributions, ecological habitats and biological characteristics. Interspecifichybridization between these two species could produce fertile seeds, indicating that genes can beexchanged across species. To explore evolutionary divergence between these two species, it isnecessary to detect interspecific genetic differentiation, or differences in gene evolution.In plants, Chs and Adh are two key genes in the processes of flavonoid metabolism andshort-chain alcohol metabolism respectively. Both genes play crucial roles in plant growth,flower color development, and resistance to stress, and they were frequently used as target genesin plant systematic evolution research. In this paper, Chs and Adh genes were cloned from theflower buds of L. tulipifera by RACE technology. Their evolutionary differences between speciesas well as among populations were compared. The aim of this paper is to analyze interspecificgenetic differentiation in Liriodendron. The results are as follows:1. The full-length sequence of three genes (two Chs and one Adh) in L. tulipifera wereobtained by RACE technology. The cDNA length of Chs1, Chs2, and Adh genes were875bp,1457bp, and1163bp respectively, encoding233,394, and268amino acids respectively.2. The sequences of Chs and Adh genes were highly homologous between L.chinense andL.tulipifera. Most of interspecies sequence differences were reflected in single nucleotidemutation, except for Adh intron6where sequence difference between these two species was up to80bp..3. The tissue differential expression of Chs genes were obvious in Liriodendron. The Chs1gene expressed only in L.tulipifera and Chs2gene expressed only in L.chinense, while inL.chinense×tulipifera, both genes expressed.4. The evolutionary rate of Chs1was distint between two species, it was higher inL.chinense than that in L.tulipifera, but no significant differences were found within species. Theevolutionary rate of Chs2exonII had no obvious differences between species as well as amongprovenances of L.tulipifera. However, significant differences were found among provenances ofL.chinense for the synonymous substitution, although no significant difference fornon-synonymous substitutions.5. The evolutionary rates for two Chs genes were distint between species as well as amongprovenances.6. For Adh exon, there were significant differences between two species for synonymoussubstitution ratio, while no significant difference for non-synonymous substitutions. However,the relative evolutionary rate of Adh exon was significantly different among provenances. InL.chinense, the evolutionary rate of Adh exon and intron had no significant differences among provenances.7. The evolutionary rate among three genes was significantly different in Liriodendron. Theevolutionary rates of Chs1, Chs2exon2and Adh exon were significant different between speciesas well as among provenances. Chs2exon2had the largest selection pressure, followed by Adhexon, while Chs1had the smallest selection pressure.