Dynamic evolution of inverted repeats in Euglenophyta plastid genomes

Photosynthetic euglenids (Euglenophyta) are a monophyletic group of unicellular eukaryotes characterized by the presence of plastids, which arose as the result of the secondary endosymbiosis. Many Euglenophyta plastid (pt) genomes have been characterized recently, but they represented mainly one family – Euglenaceae. Here, we report a comparative analysis of plastid genomes from eight representatives of the family Phacaceae. Newly sequenced plastid genomes share a number of features including synteny and gene content, except for genes mat2 and mat5 encoding maturases. The observed diversity of intron number and presence/absence of maturases corroborated previously suggested correlation between the number of maturases in the pt genome and intron proliferation. Surprisingly, pt genomes of taxa belonging to Discoplastis and Lepocinclis encode two inverted repeat (IR) regions containing the rDNA operon, which are absent from the Euglenaceae. By mapping the presence/absence of IR region on the obtained phylogenomic tree, we reconstructed the most probable events in the evolution of IRs in the Euglenophyta. Our study highlights the dynamic nature of the Euglenophyta plastid genome, in particular with regards to the IR regions that underwent losses repeatedly.