Rubisco genes indicate a close phylogenetic relation between the plastids of Chromophyta and Rhodophyta

Abstract

The genes for both subunits of Rubisco (rbcL, rbcS) are located on the plastome of the brown alga Ectocarpus siliculosus (Chromophyta, Phaeophyceae). The organization of these genes in the form of an operon was similar to that found in rhodoplasts, cyanobacteria and the plastids of Cryptomonas phi. Sequence analysis of the complete operon revealed a high degree of homology and great structural similarities to corresponding genes from two red algae. In contrast, sequence homology to Rubisco genes from chloroplasts and cyanobacteria was much lower. This clearly indicated a close phylogenetic relationship between the plastids of Rhodophyta and Chromophyta which seem to have evolved independently from the chloroplasts (polyphyletic origin). Our data suggest that the plastids of Chromophyta and Cryptophyta have originated from endosymbiotic unicellular red algae. Surprisingly, red and brown algal Rubiscos show a significantly higher degree of homology to that from a hydrogen bacterium than to those from cyanobacteria.

Structural features of the plastid ribosomal RNA operons of two red algae: Antithamnion sp. and Cyanidium caldarium

“…5A and B based on the 16S rDNA similarity scores also display a large difference between red algal plastids and those of green algae and higher plants. These findings confirm previously reported results of cotranscribed red algal and chromophytic rbcS and rbcL genes in contrast to the situation in green algae and higher plants [9,20,21,22] and were also supported by 5S rRNA analyses which see rhodoplasts closer related to cyanobacteria than are chloroplasts [ 23 ]. As was found by Kostrzewa et al [ 9] for the rbcL genes there also is a large evolutionary distance between Cyanidium and Antithamnion on the 16S rDNA and the rDNA spacer level.…”

“…For this reason more data on red algal plastoms from different genera are needed to get an idea of evolutionary tendencies within this group. More data could prove theories explaining the origin of chromophytic algae by the endosymbiosis between an eucaryotic host cell and an unicellular red alga [5,22]. …”

Glutamate synthase is plastid-encoded in a red alga: implications for the evolution of glutamate synthases

“…Evidence is accumulating that chromophytic plastids may have originated from secondary endosymbioses of red algae in colourless eucaryotic host cells [ 11,50,51]. This hypothesis implies similarities in plastid genome organization when rhodophytic and chromophytic plastids are compared.…”

“…It has been postulated that chromophytic plastids descend from red algal plastids [ 11,50,51 ]. If this hypothesis were true, gene content of these plastids should be very similar.…”

The single, ancient origin of chromist plastids

“…Because the rbcL gene of the green and glaucophyte algae are of a cyanobacterial origin, whereas those in the red algae and red algal-derived plastids are of proteobacterial origin (e.g., ref. 22), the evolutionarily distantly related green and glaucophyte rbcL sequences were coded as missing data in the phylogenetic analyses.…”