| The species of Porphyra (Bangiacea, Rhodophyta), distributed in the cold, temperate and subtropic intertide waters, are of economic importance in sea-weed farming industry. With the development of laver farming industry, those requirements for favorite lines and efficient farming techniques are more and more emphasized. However, the traditional seedling breeding of laver is mainly based on wild species without any selective breeding and genetic modification, which may deduce the adaptability to environment and resistance to disease, and may influence or even pollute the gene pool of natural species surrounded. Therefore, it's of significance to analyze the genetic variation, to detect the specific markers for lines and stains of Porphyra , so as to reveal their genetic background, based on which, the rational strategy for seedling production can be framed and the measures to protect the laver genetic resources can be taken. Random amplified polymorphic DNA (RAPD) and amplified fragment length polymorphism (AFLP) techniques were employed to investigate the genetic variation of 7 species of Porphyra : P. yezeonsis, P. haitanensis, P. katadae, P. ishigecola, P. suborbiculata, P. dentata, and P. crispata, which were distributed along the China coast. Eleven AFLP bands were selected as the specific markers to identify the different species. The obtained AFLP data were used to analyze the genetic flow among P. yezeonsis samples from the different waters in China and Japan. Primary study on the different morphorlogic type of P. haitanensis from wild and cultured samples were conducted through AFLP in order to detect the specific markers for the growth traits. AFLP technique is applied in the relevant studies on laver for the first time home and abroad, which fill the blanks of seaweed genetics and molecular biology in these fields. AFLP in genetic analysis for Porphyra A reaction system of AFLP were established to analyze the genetic structure of Porphyra, with a particular concern in the technique for extracting high quality genome DNA from laver to meet the requirement for AFLP analysis. Those factors effecting on AFLP were also discussed. Genetic variation and identification of seven species of Porphyra Applied both RAPD and AFLP techniques, high genetic variation in Porphyra species was detected. All the RAPD loci were polymorphic while the polymorphic loci proportion based on AFLP data was 98.79%. Neglecting the differences caused by sample numbers, the high genetic variance among species and populations differed faintly only with the primers used in RAPD and the primer pairs used in AFLP. High genetic variation suggested that the genetic resources of Porphyra be relatively rich and exist big potentialities in selective breeding and genetic modification. According to RAPD data, the minimum genetic distance were obtained between two P. yezoensis samples(Py no.4, 5), which was 0.2727, while the maximum (0.9273) were between P. dentata no.5 and P. ishgecola no.5. The intra-species genetic similarity was 0.5615, 0.5032, 0.4861, 0.4561, 0.4643, 0.5061 and 0.5377 respectively, with a mean value of 0.5021, accordingly, the mean intra-species genetic distance valued 0.4978.By analysis based on RAPD data, the UPGMA tree were divided into 6 RAPD branches. The samples of P. yezeonsis, P. katadae, P. haitanensis, and P. dentata made their own branch respectively, both the two P. crispata met with three P. ishigoecola; another two P.ishigoecola, one P. suborbiculata joined the branch of P. katadae; another two P. suborbiculata joined the branch of P. dentata and the last two P. suborbiculate made a small branch by themselves. While only three branches were gained in the Neighbor-joining tree, one of which included P. katadae, the second P. haitanensis, P. crispata and three P. suborbiculata samples, and the third the left samples. Because both UPGMA and Neighbor-joining cluster were gained from AFLP data showed that most of the branches were unsystematic, it's difficult to use AFLP data to demonstrate the difference among species. If the samples of the same species were considered as a whole, the genetic similarity among 7 laver species were ranged from 0.4184 to 0.5104, the minimum genetic distance among species was 0.4561, and the maximum was 0.5615. Generally, the inter-species genetic distance was a little higher than the mean value of that of intra-species, but the genetic distances between few species were lower than those between the different individuals from the same species. It could be concluded that the genetic variation be largely detected in the individuals within species. It is the fact that the species of Porphyra genus are morphologically different. But DNA variation among species sometimes was quite less than that occurred within species. This may be caused by 1) Ambiguity of mutation. The same mutations occurred in different species, which deduced the variance among species; 2) high resolution of DNA map enhanced the ambiguous mutation, and increased the genetic variation within species; and 3) the samples and primers were not typical enough to reveal all the genetic characters of laver genome. Eleven specific molecular markers selected from AFLP bands were usedto make up the DNA fingerprinting map, in order to identify the species of Porphyra. Generally speaking, RAPD technique is advisable to detect the genetic differentiation and to reveal the relationship between species. AFLP is relatively appropriate to detect the genetic variation and find out the specific gene markers within different individuals and lines of the same species. Genetic Variation and gene flow of Porphyra yezoensis Using AFLP, Porphyra yezoensis, one of the mainly cultured laver in China, was analyzed. The samples were collected from Kagoshima(Japan) , Qingdao, Nantong, Putuo and Naiji islands. Of 778 bands obtained by 16 AFLP primer pairs, 15 were monomorphic and the polymorphism was as high as 98.07%. Such high variance maybe caused by 1) the characteristic of sexual reproduction of this species; 2) gene exchanges among different wild species and cultivated seedlings. The AFLP data showed that the closest genetic distance were 0.180 between two Kagoshima samples, and the largest 0.393 was between one Kagoshima sample and one Nantong sample. The genetic distance of China samples showed positive correlation with geographic distance. The value between the index samples from Nanji and Putuo islands was only 0.244, and no distinct difference was found. Neighbor-joining and UPGMA cluster analysis indicated that samples from Kogoshima and Qingdao were highly similar, and the genetic distances among the samples of Nantong, Putuo and Nanji islands were low. Although Kagoshima locates almost the same latitude as that of Putuo islands, and near to Nantong and Putuo, the samples from Kagoshima shared fewer genetic similarity among those from Nangtong, Putuo and Nanji islands. The most possible explanation to this maybe that the action of sea currents enhances the gene flow of Porphyra inthese area. Distributed continuously along the coastline of China, P. yezoensis of Qingdao, Nantong, Putuo and Nanji islands can perform the gene flow from north to south by the aids of winter-spring sea currents in the East China sea. The gradual change of gene flow made the correlation between genetic distance and geographic distance positive. Meanwhile, segregated by Taiwan Current, Kuroshio and Tsushima Current, the gene exchange between Kagoshima and the east-south coastline of Chine are geographically isolated. Due to the closer distance between the continental shelf of the China coast and Korean Peninsular and the function of near-shore currents, little cycle currents, Huanghai Current and Tsushima Current, the laver capospores distributed in Qingdao can be carry from Qingdao to Kagoshima, which made the high similarities among samples of these two waters. High similarity among Porphyra yezoensis of Qingdao and Kagoshima implied the potential of obtaining high temperature resistant gene and disease resistant gene from the gene pool of the native species of China. Special marker for these samples were obtained also. Study on genetic variation of P. haitanensis through AFLP technique Porphyra haitanensis is an indigenous species Zhejiang and Fujian provinces, and is also the mainly cultured species in these two provinces. There exist two growth types: one was called as Jimao laver, with the trait of thin thallus and slow growth; another one was named as Mu-er laver with thick thallus and fast growth. In this study, AFLP technique was applied to detect the genetic variation in these two types of cultured samples and the wild samples from Putuo and Yushan islands, Nanji islands of Zhejiang. High genetic variation occurred in P. haitanensis. Among 528 loci recorded, 16 were unique, the ratio of polymorphic loci was 96.97%. The samples from the same location showed a close genetic distanceand jointed into each other early in clustering, which suggested that the environment factors might be the main effect on genetic variation in P. haitanensis. Similar cluster tree were obtained with UPGMA and Neighbor-joining methods, which further supported the reliability of the data. The wild samples from Zhejiang and Fujian provinces characterized by thin-thallus formed a basic AFLP branch. The cultivated thick-thallus samples i.e. Mu-er laver and the wild Fujian samples with thick-thallus made the other AFLP branch. The cluster of P. haitanensis basically reflected the differentiation of morphologic trait. The cultured Jimao laver (thin-thallus type) jointed into different AFLP groups at the outside, which indicated that it maybe on the process of genetic change and morphologic differentiation. Anyway as to the limitation of sample numbers, it was hard to perorate whether the two types means subspecies differentiation without any further research. Among those AFLP maps, ACC-CAA (100) and ACT-CAG (232) were commonly existed in thick-thallus type both wild and cultured, ACC-CAA (490) was shared by the thin-thallus type. These three bands may be used as the markers to detect the relative gene about the growth trait for selective breeding and genetic modification.
|
PDF Full Text Request