Analyses On The Type Of Copy And The Evolutionary Relationships And Suitability For Phylogeny Of ITS Of Cyanobacteria

16S rRNA-23S rRNA gene internal transcribed spacer (ITS) sequence ofcyanobacteria has been used to research identification and phylogeny of cyanobacteriadue to its high variability on length and base composition. At present the reports of thedistribution of different types of copy of ITS are not abundant as well as theevolutionary relationships among them. Moreover, it remains ill-defined whether ITSsequence is appropriate for studies at species level in cyanobacteria. In view of theabove reasons, the types and distribution of copy of ITS sequence for cyanobacteria, theevolutionary relationships among different types of copy, and the applicability forstudies at species level of ITS were studied.Twenty-four strains of cyanobacteria were identified by morphologicalidentification and molecular identification based on16S rRNA gene in our laboratory.The presence of PCR products of ITS sequence was detected by electrophoresis andsequencing after purified and TA cloning. By combining information of ITS of othergenuses from Genbank, the main results were summarized as follows:(1) There were atleast three types of copy of ITS in cyanobacteria, i.e., ITS-IA type (ITS contained boththe tRNAIleand tRNAAlacoding regions), ITS-I type (ITS contained only the tRNAIlecoding region), ITS-N type (ITS lacked tRNA coding region);(2)The copy of ITSsequence of Chroococcales strains was single type (i.e., ITS-IA or ITS-I type); The copyof ITS sequence of Osillatoriales strains was either single type (i.e., ITS-IA or ITS-Itype) or two types(i.e., ITS-IA and ITS-N type); The copy of ITS sequence ofNostocales strains was either single type (i.e., ITS-IA type) or two types(i.e., ITS-IAand ITS-N type); The copy of ITS sequence of Stigonematales strains was two types(i.e., ITS-IA and ITS-N type).The evolutionary relationships between ITS-IA and ITS-I type was analyzed. Theexperimental materials were four Phormidium strains from our laboratory and twelve Phormidium strains from Genbank which had single type of the copy of ITS sequence.The phylogenetic trees were obtained using Clustal X1.83and PAUP*4.0b4a software.The results showed that: All the phylogenetic trees showed ITS-IA and ITS-I type weredistributed in different groups respectively; ITS-IA type formed group I, while ITS-Itype formed group II; The node of group I appeared earlier than group II. These resultsindicate that ITS-I type is most likely evolved from a deletion of the tRNAAlacodingregion of its original ITS-IA type, and ITS-IA type should be the basic structure of ITSsequence of cyanobacteria.The suitability of ITS for studies at species level in cyanobacteria was analyzed.The experimental materials were the species strains of Anabaena and Arthrospiragenuses which had certain latin name. The results showed that: in the phylogenetic treesof Anabaena based on ITS, thirteen Anabaena strains distributed in five differentspecies were distinguished clearly at species level; but in the phylogenetic trees ofArthrospira based on ITS, thirteen Arthrospira strains distributed in four differentspecies were not distinguished clearly at species level. These results illustrate that ITSsequence is unable as a good tool for researching the phylogeny at species level for allgenuses of cyanophyta.