RT Journal Article SR Electronic T1 The transcriptome of Paraphelidium tribonemae illuminates the ancestry of Fungi and Opisthosporidia JF bioRxiv FD Cold Spring Harbor Laboratory SP 233882 DO 10.1101/233882 A1 Guifré Torruella A1 Xavier Grau-Bové A1 David Moreira A1 Sergey A. Karpov A1 John A. Burns A1 Arnau Sebé-Pedrós A1 Eckhard Völcker A1 Purificación López-García YR 2017 UL http://biorxiv.org/content/early/2017/12/13/233882.abstract AB Aphelids constitute a group of diverse, yet poorly known, parasites of algae [1, 2]. Their life cycle and morphology resemble those of zoosporic fungi (chytrids) and rozellids (Cryptomycota/Rozellosporidia), another specious group of parasites of fungi and oomycetes [3, 4]. Unlike fungi, which are osmotrophs, aphelids and rozellids are phagotrophs, feeding on the host’s cytoplasm. Combined RNA polymerase and rRNA gene trees [5] suggested that aphelids and rozellids relate to Microsporidia, extremely reduced parasites with remnant mitochondria [6]. Accordingly, aphelids, rozellids and Microsporidia were proposed to form a monophyletic clade sister to Fungi, called Opisthosporidia [1]. Microsporidia would have subsequently lost the ancestral opisthosporidian phagotrophy. However, the limited phylogenetic signal of those genes combined with microsporidian fast-evolving sequences have resulted in incongruent tree topologies, showing either rozellids [5, 7] or aphelids [8] as the earliest-branching lineages of Opisthosporidia, and challenging their monophyly. We have generated the first transcriptome data for one aphelid species, Paraphelidium tribonemae [2]. Multi-gene phylogenomic analyses clearly confirm the monophyly of Opisthosporidia, placing aphelids as the earliest-branching opisthosporidian lineage. This is consistent with the rich proteome inferred for P. tribonemae, which includes cellulases likely involved in algal cell-wall penetration, enzymes involved in chitin biosynthesis and several metabolic pathways that were lost in the comparatively reduced Rozella allomycis genome [9]. Contrary to recent claims suggesting a parasitic root for Fungi, our results suggest that Fungi and Opisthosporidia evolved from a free-living phagotrophic ancestor that became osmotrophic at the fungal root and evolved towards phagotrophic parasitism in the opisthosporidian line.