Complete sequence ofEuglena gracilischloroplast DNA

Abstract

We report the complete DNA sequence of the Euglena gracilis, Pringsheim strain Z chloroplast genome. This circular DNA is 143,170 bp, counting only one copy of a 54 bp tandem repeat sequence that is present in variable copy number within a single culture. The overall organization of the genome involves a tandem array of three complete and one partial ribosomal RNA operons, and a large single copy region. There are genes for the 16S, 5S, and 23S rRNAs of the 70S chloroplast ribosomes, 27 different tRNA species, 21 ribosomal proteins plus the gene for elongation factor EF-Tu, three RNA polymerase subunits, and 27 known photosynthesis-related polypeptides. Several putative genes of unknown function have also been identified, including five within large introns, and five with amino acid sequence similarity to genes in other organisms. This genome contains at least 149 introns. There are 72 individual group II introns, 46 individual group III introns, 10 group II introns and 18 group III introns that are components of twintrons (introns-within-introns), and three additional introns suspected to be twintrons composed of multiple group II and/or group III introns, but not yet characterized. At least 54,804 bp, or 38.3% of the total DNA content is represented by introns.

Rates and patterns of chloroplast DNA evolution.

“…Moreover, present evidence suggests that the association that led to land plants occurred only once in evolution (1). The (4); a bryophyte, Marchantia (5); a conifer, black pinet; a dicot, tobacco (6); a monocot, rice (7); and a parasitic dicot, Epifagus (8)]. With the possible exception of Euglena and Epifagus, the picture that has emerged is one of a relatively stable genome with marked conservation of gene content and a substantial conservation of structural organization.…”

“…Group III introns have thus far only been identified in the euglenophytes Euglena gracilis and Astasia longa (46,47) and appear to be truncated (or streamlined) group II introns. It is noteworthy that group I introns are absent from the newly sequenced plastid genomes of Euglena graciis (4) Comparative molecular sequence analyses also reveal aspects of the evolutionary process that would otherwise be opaque. For example, the recombinational processes that acted to convert 4irpl23 to the functional gene are only resolvable at the sequence level.…”

Complete nucleotide sequence of the chloroplast genome from the green algaChlorella vulgaris: The existence of genes possibly involved in chloroplast division

“…The Chlorella genome has 10 genes not found in land plant chloroplasts, whereas it lacks all 11 ndh genes found in photosynthetic land plants except black pine (19). Therefore, the number of known genes is similar to that of land plants (14-16, 19, 20) and also of Euglena (21). Many new genes not found in land plant chloroplasts have been reported in red and brown algal chloroplasts and cyanelles (4)(5)(6).…”

“…Lack of the C-terminal domain-like region in the putative ␣ subunit suggests the absence of class I-like transcription factors in Chlorella chloroplasts. rpoA is absent from the Euglena and Epifagus genomes (21,36), and the Chlamydomonas rpoA homologue consists of only 131 codons (37). Therefore, the possibility that rpoA in Chlorella does not produce a functional subunit of RNA polymerase cannot be ruled out.…”

The Structure and Gene Repertoire of an Ancient Red Algal Plastid Genome

“…Even Nephroselmis olivacea, a green alga, shows the quatripartite structure characteristic for higher green plants (Turmel et al 1999). Interestingly, a unicellular member of the green lineage, Chlorella vulgaris, contains no larger repeat regions (Wakasugi et al 1997), whereas Euglena gracilis strain Z, which most likely evolved from a secondary endosymbiosis, has three tandemly arranged direct repeat units containing the rRNA genes (Hallik et al 1993). C. caldarium and P. purpurea, the two known red algae, contain direct repeats.…”