Highly conserved organellar genomes in the Gracilariales as inferred using new data from the Hawaiian invasive alga Gracilaria salicornia (Rhodophyta)

The phylum Rhodophyta contains of a wide range of ecologically and economically important species distributed worldwide. One taxon, Gracilaria salicornia, was an introduced and invasive species in the Hawaiian Islands that had displaced native flora and fauna, and caused widespread ecological damage. We presented the chloroplast and mitochondrial genomic sequences of G. salicornia from Hawaiian material and compared them to sequences of closely related species. We found that the gene content and synteny of both organellar genomes were very similar to the sequences of other closely related Gracilariales (Gracilaria tenuistipitata var. liui for the chloroplast and Gracilariopsis andersonii and Gracilariophila oryzoides for the mitochondrion). Minor changes included the absence of the horizontally transferred leuC/D operon in the G. salicornia chloroplast genome and the absence in the G. salicornia mitochondrial genome of an approximately 2Kb region found in Gp. andersonii. Overall, this study indicated that organellar genome structures in the order Gracilariales were remarkably well maintained.