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Entamoeba histolytica is believed to be devoid of peroxisomes, like most anaerobic protists. In this work, we provided the first evidence that peroxisomes are present in E . histolytica , although only seven proteins responsible for peroxisome biogenesis (peroxins) were identified (Pex1, Pex6, Pex5, Pex11, Pex14, Pex16, and Pex19). Targeting matrix proteins to peroxisomes is reduced to the PTS1-dependent pathway mediated via the soluble Pex5 receptor, while the PTS2 receptor Pex7 is absent. Immunofluorescence microscopy showed that peroxisomal markers (Pex5, Pex14, Pex16, Pex19) are present in vesicles distinct from mitosomes, the endoplasmic reticulum, and the endosome/phagosome system, except Pex11, which has dual localization in peroxisomes and mitosomes. Immunoelectron microscopy revealed that Pex14 localized to vesicles of approximately 90–100 nm in diameter. Proteomic analyses of affinity-purified peroxisomes and in silico PTS1 predictions provided datasets of 655 and 56 peroxisomal candidates, respectively; however, only six proteins were shared by both datasets, including myo -inositol dehydrogenase ( myo -IDH). Peroxisomal NAD-dependent myo -IDH appeared to be a dimeric enzyme with high affinity to myo -inositol (Km 0.044 mM) and can utilize also scyllo -inositol, D-glucose and D-xylose as substrates. Phylogenetic analyses revealed that orthologs of myo -IDH with PTS1 are present in E . dispar , E . nutalli and E . moshkovskii but not in E . invadens , and form a monophyletic clade of mostly peroxisomal orthologs with free-living Mastigamoeba balamuthi and Pelomyxa schiedti . The presence of peroxisomes in E . histolytica and other archamoebae breaks the paradigm of peroxisome absence in anaerobes and provides a new potential target for the development of antiparasitic drugs.

Benthic diatoms are the main primary producers in shallow freshwater and coastal environments, fulfilling important ecological functions such as nutrient cycling and sediment stabilization. However, little is known about their evolutionary adaptations to these highly structured but heterogeneous environments. Here, we report a reference genome for the marine biofilm-forming diatom Seminavis robusta , showing that gene family expansions are responsible for a quarter of all 36,254 protein-coding genes. Tandem duplications play a key role in extending the repertoire of specific gene functions, including light and oxygen sensing, which are probably central for its adaptation to benthic habitats. Genes differentially expressed during interactions with bacteria are strongly conserved in other benthic diatoms while many species-specific genes are strongly upregulated during sexual reproduction. Combined with re-sequencing data from 48 strains, our results offer insights into the genetic diversity and gene functions in benthic diatoms. Available genomics studies have mostly focused on planktonic centric diatom. Here, the authors report the genome assembly of the marine biofilm-forming diatom Seminavis robusta and the resequencing data of a panel of accessions to reveal their evolutionary adaptations.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.An amendment to this paper has been published and can be accessed via a link at the top of the paper.

A unique cell size sensing mechanism is at the heart of the life cycle of diatoms. During population growth, cell size decreases until a Sexual Size Threshold (SST) is reached, below which cells become sexually competent. In most pennate diatoms, the two mating types undergo biochemical and behavioral differentiation below the SST, although the molecular pathways underlying their size-dependent maturation remain unknown. Here, we developed a method to shorten the generation time of Cylindrotheca closterium through single-cell microsurgery, enabling the transcriptomic comparison of genetically identical large and undifferentiated cells with small, sexually competent cells for six different genotypes. We identified 21 genes upregulated in small cells regardless of their mating type, revealing how cells undergo specific transcriptional reprogramming when passing the SST. Furthermore, we revealed a size-regulated gene cluster with three mating type-specific genes susceptible to sex-inducing pheromones. In addition, comparative transcriptomics confirmed the shared mating type specificity of Mating-type Related Minus 2 homologs in three pennate diatoms, suggesting them to be part of a conserved partner-recognition mechanism. This study sheds light on how diatoms acquire sexual competence in a strictly size-dependent manner, revealing a complex machinery underlying size-dependent maturation, mating behavior, and heterothally in pennate diatoms.