• ALGAE
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• 제17권1호
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• pp.53-58
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• 2002

The transition of plant life from aquatic algae to land to land plants was one of the major events in the history of life. However, in hypothesizing the exact evolutionary path of the transition, limited shared phenotypic characters in aquatic algae and land plants (embryophytes) have been a major hinderance. Chloroplast genomes contain characters useful in tracing evolutionary histories. Embryophyte chloroplast genomes are distinguished from algal cpDNAs by having over 20 group Ⅱ introns, some of which were gained during the transition from algae to embryophytes (Manhart and Palmer 1990; Lew and Manhart 1993;Lee and Manhart 2002). Here we examine a gene cluster that, in land plants, contains psbB, psbT, psbH, petB and petD with introns found in petB and petD (petB.i and petD.i). In addition the presence/absence of introns in trnA and trnI (trnA.i and trnI.i) were determined in all five major lineages of charophytes. We found that the psbB gene cluster occurs in most surveyed charophytes and embryophytes except Spirogyra (Zygnematales) which lacks it due to intra-genomic rearrangement. All four introns are absent in Chlorokybus but present in some or all of the other four charophyte lineages (Klebsormidiales, Zygnematales, Coleochaetales, and Charales). In addition, Chlorokybus is distinguished from other charophytes and embryophytes by having an unusually long spacer (over 2 kb) between psbH-petB. The results indicate that Chlorokybus diverged before the intron gains but after psbB gene cluster formation, placing the other charophyte lineages closer to embryophytes.

• ALGAE
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• 제17권1호
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• pp.59-68
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• 2002

A phylogenetic affinity between charophytes and embryophytes (land plants) has been explained by a few chloroplast genomic characters including gene and intron (Manhart and Palmer 1990; Baldauf et al. 1990; Lew and Manhart 1993). Here we show that a charophyte, Spirogyra maxima, has the largest operon of angiosperm chloroplast genomes, rpl23 operon (trnⅠ-rpl23-rpl2-rps19-rpl22-rps3-rpl16-rpl14-rps8-infA-rpl36-rps11-rpoA) containing both embryophyte introns, rpl16.i and rpl2.i. The rpl23 gene cluster of Spirogyra contains a distinct eubacterial promoter sequence upstream of rpl23, which is the first gene of the green algal rpl23 gene cluster. This sequence is completely absent in angiosperms but is present in non-flowering plants. The results imply that, in the rpl23 gene cluster, early charophytes had at least two promoters, one upstream of trnⅠ and and another upstream of rpl23, which partially or completely lost its function in land plants. A comparison of gene clusters of prokaryotes, algal chloroplast DNAs and land plant cpDNAs indicated a loss of numerous genes in chlorophyll a+b eukaryotes. A phylogenetic analysis using presence/absence of genes and introns as characters produced trees with a strongly supported clade containing chlorophyll a+b eukaryotes. Spirogyra and embryophytes formed a clade characterized by the loss of rpl5 and rps9 and the gain of trnⅠ (CAU) and introns in rpl2 and rpl16. The analyses support the hypothesis that the rpl23 gene cluster and the rpl2 and rpl16 introns of land plants originated from a common ancestor of Spirogyra and land plants.