Studies On Population Genetics And Domestication Of Myrica Rubra (Myricaceae)

Myrica rubra (Lour.) Sieb et Zucc, belonging to the family Myricaceae and the genus Myrica, also called Chinese Bayberry, is known as one of the famous Chinese specialty fruit,. M. rubra is widely distributed in11provinces and regions in south of China and this species is widely cultivated in Zhejiang, Jiangsu, Fujian, Chongqing provinces and so on. In this study, firstly, we reconstructed the phylogeny of the family Myricaceae based on nuclear ribosomal DNA ITS and cpDNA sequences psbA-trnH data. Secondly, we studied the genetic diversity and population genetic structure of M. rubra through sequencing chloroplast DNA fragment psbA-trnH and genotyping six nuclear microsatellite markers. Thirdly, based on phylogeography and population genetics theory, the distribution of this species and the relationship between wild populations were discussed. Finally, we discussed the relationships to cultivated populations and the domestication process of M. rubra based on SSR and cpDNApsbA-trnH data. There are4main conclusions of our research:1. Phylogeny of MyricaSamples including3genus of Myricaceae (three species of Myrica in China, one specie in Indonesia and two species in North America; one specie of Comptona in North America; the sequence of Canacomyrica downloaded from Genbank) were all surveyed by ITS fragments, Juglandacea and Fagaceae (sequences download from Genbank) as the outgroup.The molecular phylogenetic tree revealed that1) three genus of Myricaceae were divided into three lineages;2) Canacomyrica located in the the bottom of the phylogenetic tree with high bootstrap support;3) Comptona and Myrica are sister clade;4) two species of Myrica from North America (M. ceriferhera and M. gala) formed sister clade to East Asian Myrica.And then we used Comptona as outgroup, based on combined sequences (ITS and cpDNA psbA-trnH) to study on phylogeny of Myrica. The molecular phylogenetic tree showed that Myrica esculenta which is widely distributed in the Southeast Asia formed a good sister clade to other three Myrica that distributed in China only; but M. rubra, M. adenophora and M. nana clustered into one cladeand formed a Myrica species complex.2. The genetic diversity and population genetic structure of M. rubraStudy on cpDNA psbA-trnH. data, there are4haplotypes in the cultivated M. rubra and6haplotype in the wild populations. But there only one wide distribution haplotype HI in most of cultivated populations (92%)and haplotype diversity in cultivated populations is0.086much lower than that in wild populations (0.347), the nucleotide diversity in cultivated populations is0.00077and0.00279in wild populations,Genetic diversity in cultivated populations was lower than that of wild populations based on cpDNA psbA-trnH data. It reflects the strong influence by humen selection in the domestication process.The results of SSR marker showed that the level of genetic diversity in M. rubra populations is in the medium, but specific allele is rare. It suggests a human-mediated population expansion and gene flow event. And both of the cpDNA and SSR marker data showed that the differentiation between cultivated populations and wild populations is very low (Fst are2.9%and0.02%).3. Genetic diversity and phylogeography of wild M. rubraThe analysis of cpDNA psbA-trnH sequences showed that there are6haplotypes in wild populations, and haplotype H1in the central of the TCS figure, based on the coalescent theory, haplotype H2is the ancestor haplotype; H1is widely distributed into wild populations (82%); haplotype H3where is found in three populations; the other three haplotypes distributed in two or one populations.The distribution of haplotypes in the wild populations formed strong phylogeograghic pattern:those populations with only haplotype H1are distributed in the north of the Nanling mountains to the Eastern China, and the other haplotypes concentrated from the south the Nanling mountains to the southwest China. This phylogeograghic pattern may result form rapid expansion after the ice age. And the block of Nanling mountains to north and south airflow, made the climate is different between north of the Nanling and the south the Nanling in winter, haplotype H1may more suitable for the colder weather.4. The relationship among cultivated populationsThree groups were detected for all cultivated populations based on the results of STRUCTURE and UPGMA analysis of SSR data, different cultivated populations belong to different gene pool:7cultivated populations in green gene pool,10cultivated populations in blue gene pool,15cultivated populations in red gene pool. And the same name populations in different places have the same gene pool. Because clone can keep the stable of populations.We also found that the agronomy characteristics have no correlation with distribution of gene pool.5. Domestication of M. rubraThe results of cpDNA psbA-trnH sequences revealed92%cultivated populations have haplotype H1, indicating that H1played an important role in the domestication process. Two cultivated populations in Zhejiang (YYLZ and JBCQ) have the same haplotypes with Yunnan wild populations(MLP、ZJC), revealed a ancestor correlation, well we can’t exclude possibility that people bring those haplotypes from Yunnan yet.The analysis of nSSR markers showed us that all M. rubra populations can be classified into3gene pools, indicating that there are three times origin in M. rubra. Mainly in east of China, such as Zhejiang, Fujian and Jiangxi. Considering the result of cpDNA psbA-trnH sequences, nSSR markers and the habits when humen domesticat plants (such as nearby principle), we can conclude that the origin of the domestication about M. rubra is in different places and many times. And the the south of the Nanling mountains to the Southwest China is where the Myrica ancestral residence located, but the earliest domestication of M. rubra begin in the east of China such as Zhejiang ang Fujian province.