Coleochaete, another of the more complex types among the Charophyceae, has been shown to contain lignin, a substance thought to be absent from green algae ( Delwiche et al., 1989). Based on cytological and chemical similarities, land plants (embryophytes) are considered to have evolved from a charophycean green alga. In its morphology, Chara is one of the most complex types of Charophyceae, which is a well-defined group with a very long geographical history ( Round, 1984). For these reasons it is most unlikely that CAV originated in a recent transfer of some rod-shaped virus from an angiosperm host to Chara. It appears to have strongest affinity with the Furovirus group and has no known angiosperm host. Thus, CAV appears to share features of genome organization and sequences found in several groups of rod-shaped viruses infecting angiosperms. Gibbs, quoted in Matthews, 1991): (1) the coat protein of CAV has a composition closer to BNYVV, and is closer to TRV than to TMV (2) the GDD-polymerase motif of CAV is closest to that of BNYVV and (3) the two GKT nucleotide-binding motifs found in CAV are arranged in a manner similar to that found in potexviruses. However, its genome is much larger (11 kb, rather than 6.4 kb for TMV), and about 7 kb of the genome has been sequenced, revealing other relationships (A.J. The rod-shaped virus from the eukaryotic alga Chara australis (CAV) has some properties like those of tobamoviruses. Basically, there are two types of viruses, isometric ones that have dsDNA genomes and most closely resemble phage, and a rod-shaped virus with an RNA genome. These are described in Chapter 2 (Section V.A). Virus-like particles (VLPs) have been observed in thin sections of many eukaryotic algal species belonging to the Chlorophyceae, Rhodophyceae and Phaeophyceae. Viruses infecting photosynthetic eukaryotes below the angiosperms Roger Hull, in Matthews' Plant Virology (Fourth Edition), 2002 2. 700–900 nm) virus particles have been found associated with dieback symptoms in the brown alga Eklonia radiata in New Zealand ( Easton et al., 1997). Thus, the virus described in Chara is probably the oldest recorded virus infecting a plant on or near the lineage that ultimately gave rise to the angiosperms. Tree construction suggests that the Charophyceae may have acquired the introns 400 to 500 million years ago. Manhart and Palmer (1990) have shown that introns are present in three members of the Charophyceae in the same arrangement as in Marchantia, giving strong support to the view that they are related to the lineage that gave rise to land plants. All the algae and eubacteria examined have uninterrupted genes. Group II introns have been found in the tRNA ala and tRNA ile genes of all land plant chloroplast DNAs examined. Molecular genetic evidence supports a charophycean origin for land plants.
It appears to have strongest affinity with the Furovirus genus and has no known angiosperm host. However, its genome is much larger (11 kb, rather than 6.4 kb for TMV), and about 7 kb of the genome has been sequenced, revealing other relationships ( Matthews, 1991): (1) the coat protein of CAV has a composition closer to BNYVV, and to TRV than to TMV (2) the GDD-polymerase motif of CAV is closest to that of BNYVV and (3) the two GKT nucleotide-binding motifs found in CAV are arranged in a manner similar to that found in potexviruses. The virus (CAV) has rod-shaped particles and some other properties like those of tobamoviruses. (1976) described a virus infecting the eukaryotic alga Chara australis.
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