Leucomyxa plasmidifera Raw sequence reads. Leucomyxa plasmidifera

Complete plastid loss seems to be very rare among secondarily non-photosynthetic eukaryotes. Based on a previous investigation by transmission electron microscopy (TEM), Leukarachnion sp. PRA-24, an amoeboid colourless protist related to the photosynthetic algal class Synchromophyceae (Ochrophyta), is a candidate for such a case. Here we provide a detailed characterisation of this organism and describe it as Leucomyxa plasmidifera, gen. et sp. nov. While we could not unambiguously recognize a plastid by TEM, we recovered a complete plastid genome with a reduced gene set similar to plastomes of other non-photosynthetic ochrophytes yet even more extreme in sequence divergence. Identification of components of the plastid protein import machinery in the L. plasmidifera transcriptome assembly corroborated the organism possesses a cryptic plastid organelle. According to our bioinformatic reconstruction the plastid contains a unique combination of biosynthetic pathways producing haem, a folate precursor, and tocotrienols. As another twist to its organellar biology, L. plasmidifera turned out to contain an unusual long insertion in its mitogenome related to a newly discovered mitochondrial plasmid exhibiting unprecedented features in terms of its size and coding capacity. Combined, our work uncovered further striking outcomes of the evolutionary course of semiautonomous organelles in protists.