Intra-individual Variability Of RDNA In Camellia L. And The Spatial Genetic Structure Of C. Changii C.X.Ye

This thesis including two different researches, one is intra-individual variability of rDNA in Camellia L.; the other is the genetic diversity of C. changii. C. X.Ye. To be specific, the thesis consists of three parts:the intragenomic variability of the internal transcribed spacer of rDNA (ITS) in C. hongkongensis Seemann, the polymorphism of26S rDNA in Camellia L., and genetic diversity and spatial genetic structure of C. changii.1) We amplified, cloned and sequenced the ITS region of C. hongkongensis, and obtained74sequences in total from an individual. We found that the ITS region exhibited high polymorphism within individual, and76%of the sequences were pseudogenes. We believed that pseudogenes might be an important reason for the polymorphism, besides the functional genes also existed a high degree of polymorphism. Phylogenetic analysis showed that some pseudogenes might originate independently from functional genes at different times. However, more than half of the pseudogenes have originated from a common ancestor. They have the longest history and have now differentiated into at least5types of pseudogenes after repeatedly gene duplication, and sequences in each type were very similar to each other. The results indicated that these pseudogenes had gone through duplication events recently. Besides, we were successed in using the pseudogenes as a molecular marker to identify species. And it indicates that these pseudogenes may be a useful marker to identify species. The result implied that we should be more cautious when we construct the phylogeny of Camellia using ITS sequences.2) We amplified, cloned, and sequenced the3’end region of26S rDNA from10Camellia species and4species of Theaceae(Tutcheria, Stewatia, Schima, Ternstroemia), and we got552sequences in all. We found that the sequences obtained in any individual were highly polymorphic and there were a large number of pseudogenes of26S rDNA existed in Camellia and Tutcheria. The proportion of pseudogenes was100%in Camellia and Tutcheria, while much lower in the other outgroups. The result indicated that rDNA repeats in Camellia and Tutcheria showed higher polymorphic than those in other species. However, the fact that all the rDNA sequences cloned directly from total DNA digested by restriction enzymes were functional genes demonstrates that the abundance of functional genes is far higher than that of pseudogenes in Camellia genome. The bias in PCR amplification made26S rDNA pseudogenes to be amplified predominantly. The results of phylogenetic analysis showed that various types of pseudogenes could be found in all the species of Camellia and Tutcheria and that these pseudogenes may have been existed in genomes for a long time and some of them can even be traced back to the original of Theaceae. In all the13Camellia species detected, we found the recent duplication of pseudogenes common, and it suggests that these pseudogenes may in the exercise of certain functions. Also, the study found that although there were different types of pseudogenes in C. piquetiana, they didn’t form any relilable clades with pseudogenes from other species. The similar phenomenon was also found in the outgroup species Tutcheria hirta, and these results indicated that C. piquetiana was either an ancient species, or an independent genus.3) Camellia changii is an endemic species in China (Guangdong province) and the entire species consists of only one population with about1000individuals. We collected almost all the individuals of the population (697) and did the ecology surveys. We amplified all the individuals using9pairs of SSR primers, aiming to analyze the genetic diversity and spatial genetic structure. The results showed that the population exhibited high genetic diversity and strong gene flow. And the isolation caused by river and dams didn’t make significant differentiation between subpopulations which may related to the extent pollen dispersal. The result of STRUCTURE showed there were two different sources for the population and the PCA analysis divided the population into three groups, but the differentiation is not strong which may be due to the impact of gene flow. The population had a significant spatial structure which may be related to the restricted seed dispersal. Our results indicated that the barrier effect of the dam on the gene flow is not obvious, but to some extent, limited the spread of seed flow. In addition, the estimated effective population size is176, suggesting that, the population size shouldn’t be less than176otherwise may lead to severe inbreeding depression.