Studies On Population Genetic Diversity And Molecular Evolution Of Thellungiella Salsuginea

Thellungiella salsuginea (salt cress ), belonging to Thellungiella of Cruciferae, is an annual herb. It is a close relative of Arabidopsis. Studies showed that 300mM NaCl was a salinity threshold for salt cress growth which decreased the survival rate by 50% relative to the medium without salt, 100~150mM NaCl was the optimum growth salinity for salt cress. As we know, a model plant would be needed that had desirable traits, i.e. small size, short life cycle, self-pollination, and high seed number, and favorable genetic traits such as self-fertilization, a small genome, efficient transformation, and mutagenesis. T. salsuginea is one of the halophytes who meets all of these criteria.This study mainly includes: We have studied the morphology and micromorphology of seven populations of T. salsuginea from China and one population from North America, which indicated some morphology difference and a certain population differentiation among the populations of T. salsuginea. We have studied the genetic diversity of the populations by means of SSR and RAPD, which can prepare for the genetic mapping. We also discussed the evolution process of molecular phylogenetics of T. salsuginea based on plastosome gene and chloroplast gene.The results were as follows:1.Study on morphology and micromorphology showed that there were some differences among T. salsuginea populations on leaf-shape index, stomatal density and stomatal morpha characteristics. The outline of the seed coat cell is hexagon or irregular polygon and the seed coat cell breaks out forming many muri and lumina, but there is certain difference among the populations. The eight populations have fairly similar in pollen shape(prolate-spheroidal or subprolate-spheroidal) in equatorial view.The result of morphology T. salsuginea showed that there was a certain differentiation among the eight populations, especially great differentiation during North America population, Xinjiang population, Henan population, Jiangsu population and Henan population, but little differentiation among Jiangsu population, Henan population, Hebei population, Dongying population and Qihe population.2. The genetic diversity of T. salsuginea populations was investigated by RAPD. 23 primers were chosen for amplification among populations because they showed strong, reproducible amplification and distinct polymorphisms from over 400 arbitrary primers. A total of 138 DNA fragments were amplified from 220bp to 2020bp, among which 108 were polymorphics, and constituted 78.26%. The average number of DNA bands produced by each primer was 6. Genetic distance and DNA molecular dendrogram was worked out by popgene1.31 and NTSYS-PC software. The result showed that T. salsuginea possessed a higher genetic diversity.3. SSR was also used to study the genetic diversity of T. salsugin populations. 21 pairs of primers were chosen for amplification from 50 pairs, which account for 42%. The result showed that the variety of the number of alleles and allele frequency is distinct. The locus nga126 has the highest effective number of alleles(3.6395),and nga151 has the lowest(1.3740). The allele frequency changes from 0.0125 to 0.8375. The percentage of polymorphic loci is 100%, which showed that T. salsuginea possessed a higher genetic diversity. Genetic distance and DNA molecular dendrogram was worked out by popgene1.31 and NTSYS-PC software.The result of the two kinds of molecular markers showed that Xinjiang population and North America population were distinct with other populations. Dongying population was almost the same to Qihe population, so we could look the two populations as one. The genetic distance accorded with the distribution approximately. In summary, T. salsuginea was rich in genetic diversity. Different environment caused the differentiation of T. salsuginea populations4. The several chloroplast gene sequences from T. salsuginea populations were to be nearly completely same and did not have the difference. The reason of this kind of phenomenon possibly is that chloroplast gene is relative quite conservative, moreover chloroplast DNA has the independence evolution route and it is not completely consistent with the nuclear gene.This study included these main innovation spots thereinafter:1. Laboratory collected T. salsuginea germplasm resources coming from China for the first time.2. Morphology and micromorphology of T. salsuginea of eight populations from China and North America were studied for the first time. Result showed that there was certain difference among populations and eight populations have certain differentiation.3. We have studied the genetic diversity of the populations by means of SSR and RAPD for the first time. The result of the two kinds of molecular markers showed that Xinjiang population and North America population were distinct with other populations from coastal area of east China.4. We have discussed the evolution process of molecular phylogenetics of T. salsuginea based on plastosome gene and chloroplast gene for the first time.