Paiano M.O., Del Cortona A., Costa J.F., Liu S.L., Verbruggen H., De Clerck O. & Necchi Jr O.
Organization of plastid genomes in the freshwater red algal order Batrachospermales (Rhodophyta)
Journal of Phycology: in press


Little is known about genome organization in members of the freshwater red algal order Batrachospermales and the infra-ordinal relationship remains unresolved. Plastid (cp) genomes of seven members of the freshwater red algal order Batrachospermales were sequenced aiming to: 1) describe the characteristics of cp genomes and compare with other red algal groups; 2) infer the phylogenetic relationships among these members trying to have a better understanding of the infra-ordinal classification. The cp genomes of the Batrachospermales are large, with several cases of gene loss, gene-dense and have highly conserved gene order. The phylogeny based on concatenated nucleotide genome data roughly supports the current taxonomic system for the order. Comparative analyses confirm previous studies of members of the Florideophyceae that the cp genome in the Batrachospermales is highly conserved, with little variation in gene composition. However, some relevant new features were revealed in our study: genome sizes in members of the Batrachospermales are near the lowest values reported for the Florideophyceae; the differences in cp genome size within the order are high in comparison to other orders where more than one member was sequenced (Ceramiales, Gelidiales, Gracilariales, Hildenbrandiales and Nemaliales); members of the Batrachospermales have the lowest number of protein coding genes among the Florideophyceae. In terms of gene loss, it is noteworthy the lack of apcF in all sequenced taxa of Batrachospermales, which encodes the allophycocyanin beta subunit. We reinforce that the interordinal relationships between the freshwater orders Batrachospermales and Thoreales within the Nemaliophycidae is not well resolved due to limited taxon sampling.

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