Obligately phagotrophic aphelids turned out to branch with the earliest-diverging fungi

摘要

Reconstructing the early evolution of fungi and metazoans, two of the kingdoms of multicellular eukaryotes thriving on earth, is a challenging task for biologists. Among extant organisms having characters intermediate between fungi and hypothetical protistan ancestors, from which both fungi and metazoans are believed to have evolved, aphelids are unfairly neglected. The phylogenetic position of these microalgal endoparasites remained uncertain, since no nucleotide sequence data have been reported to date. Aphelids resemble some primitive zoosporic fungi in life cycle, but, unlike fungi, they live by phagotrophy. Here we present a phylogeny, in which a cultured aphelid species, Amoeboaphelidium protococcarum, forms a monophyletic group with Rozella and microsporidia as a sister group to Fungi. We also report a non-canonical nuclear genetic code in A. protococcarum.