title: The Bryopsis hypnoides plastid genome: multimeric forms and complete nucleotide sequence.
abstract: BACKGROUND
  Bryopsis hypnoides Lamouroux is a siphonous green alga, and its extruded protoplasm can aggregate spontaneously in seawater and develop into mature individuals. The chloroplast of B. hypnoides is the biggest organelle in the cell and shows strong autonomy. To better understand this organelle, we sequenced and analyzed the chloroplast genome of this green alga.
  
  
  RESULTS
  A total of 111 functional genes, including 69 potential protein-coding genes, 5 ribosomal RNA genes, and 37 tRNA genes were identified. The genome size (153,429 bp), arrangement, and inverted-repeat (IR)-lacking structure of the B. hypnoides chloroplast DNA (cpDNA) closely resembles that of Chlorella vulgaris. Furthermore, our cytogenomic investigations using pulsed-field gel electrophoresis (PFGE) and southern blotting methods showed that the B. hypnoides cpDNA had multimeric forms, including monomer, dimer, trimer, tetramer, and even higher multimers, which is similar to the higher order organization observed previously for higher plant cpDNA. The relative amounts of the four multimeric cpDNA forms were estimated to be about 1, 1/2, 1/4, and 1/8 based on molecular hybridization analysis. Phylogenetic analyses based on a concatenated alignment of chloroplast protein sequences suggested that B. hypnoides is sister to all Chlorophyceae and this placement received moderate support.
  
  
  CONCLUSIONS
  All of the results suggest that the autonomy of the chloroplasts of B. hypnoides has little to do with the size and gene content of the cpDNA, and the IR-lacking structure of the chloroplasts indirectly demonstrated that the multimeric molecules might result from the random cleavage and fusion of replication intermediates instead of recombinational events.
authors.affiliation: Institute of Oceanology, The Chinese Academy of Sciences (IOCAS), Qingdao, China.
authors.forename: Fang
authors.initials: F
authors.lastname: Lü
authors.forename: Wei
authors.initials: W
authors.lastname: Xü
authors.forename: Chao
authors.initials: C
authors.lastname: Tian
authors.forename: Guangce
authors.initials: G
authors.lastname: Wang
authors.forename: Jiangfeng
authors.initials: J
authors.lastname: Niu
authors.forename: Guanghua
authors.initials: G
authors.lastname: Pan
authors.forename: Songnian
authors.initials: S
authors.lastname: Hu
mesh_terms: D001483:Base Sequence; D000460:Chlorophyta / Q000235:genetics* / Q000254:growth & development; D002874:Chromosome Mapping; D003593:Cytoplasm / Q000235:genetics; D040481:Genome Components / Q000235:genetics; D054627:Genome, Plastid; D018525:Germination / Q000235:genetics / Q000502:physiology; D008957:Models, Genetic; D015388:Organelles / Q000235:genetics / Q000378:metabolism; D010802:Phylogeny; D017422:Sequence Analysis, DNA / Q000379:methods