Study On The Genetic Relationship Of 5 Samples Of Arthrospira By RAPD Technique And ITS Sequence

As a group of photosynthetic autotrophic prokaryote, Arthrospira has a bright prospect for exploitation because it contains abundant nutritional ingredients and physiological active materials. World Health Organization and Food and Agriculture Organization call it"the best health care products and foods in the 21st century". Since Greach discovered A. platensis in Chad Lake in 1940, the research about Arthrospira has been paid much attention.In 1996, three species of Arthrospira were found in the alkaline lake of Erdos Plateau by Professor Qiao et al., which filled the gaps in the germplasm resource of Arthrospira in our country. In recent years, many studies about Arthrospira of Erdos Plateau which is mainly on morphology anatomic structure and physiological biochemical character has been reported. But there is little report on genetic diversity, evolution and genetic relationship. In 2008, Tai Lihua using RAPD technique analyzed two species of A. platensis from different environment, and Li Lin using AFLP analyzed four samples of Arthrospira about genetic diversity and genetic relationship.In this paper, to enrich and consummate the basic investigation of Arthrospira which is meaningful to protect and utilize the genetic diversity of Arthrospira germplasm resource in Erdos Plateau, the technique of RAPD molecular marker and 16S-23S rRNA internally transcribed spacer (ITS) were used to analyze the genetic diversity of A₁, A₂, A₃, A₄ and A₅.The genome DNA of 5 samples of Arthrospira is analyzed with random amplified polymorphic DNA (RAPD) technique. With the 114 random primers, 32 primers revealed their obvious polymorphisms and 681 clear bandings whose sizes are between 200bp～4000bp can be gained. 674 bands of them are polymorphism, and each primer can obtain 21.28 polymorphic bandings averagely. The specific band is 276 for A₁, 273 for A₂, 175 for A₃, 185 for A₄, and 220 for A₅. According to the more band number the high evolutionary level, conjecture the low to high evolutionary level is: A₃-A₄-A₅-A₂-A₁. But the result of A₃ is different from Li Lin using AFLP analyzed four samples of Arthrospira about evolutionary level. Therefore, it needs further investigation. The average genetic distance of five samples is between 0.3581 and 0.7935, among which the shortest genetic distance is 0.3581 between sample A₄ and A₅ and the longest is 0.7935 between sample A₂ and A₅. It means that there were some genetic differences among samples. The cluster analysis based on UPMGA and the data of genetic distance results demonstrated that the introduced samples A₄ and A₅ have the closest genetic relationship, and A₁ and A₂ have a relatively farther genetic relationship, but the genetic relationship among A₃,A₄ and A₅ is closer, the A. platensis A₁ from Erdos Plateau and A₄ from Chad is farther.Compared with the five sequences of ITS, the results show that five sequences comprise 472～477 nucleotides, in which contain two tRNA genes, tRNAIle and tRNAAla. The GC contents of ITS are 47.88%～48.01%, and the similarities of nucleotide sequences range from 91.5% to 100%. The genetic distance of five samples is between 0.000 and 0.091, among which the shortest genetic distance are between A₄ and A₅, A₂ and A₃, and the longest genetic distance are between A₁ and A₄ which came from two different provenances. The cluster analysis results demonstrated that the genetic relationship between A₁ and A₄, A₄ and A₅ are identical with the result of RAPD, which means genetic relationship of interspecies is closer than intraspecies. The author presumes that the different environments and geographical isolation are the primary reasons for the result.The RAPD result shows that A₁ and A₂ have a closer genetic relationship, but farther than A₃, which is different from the result of ITS. The reason may be that there are limitations only using ITS sequence to inspect genetic relationship between samples whose length about 540bp, however the amplification fragment of RAPD mainly distributes 200～4000bp, exceeding ITS sequence. Different molecular marker reveal different genetic locus, so analytic results exist distinction.