Spore Germination of the Obligate Biotroph Spongospora subterranea: Transcriptome Analysis Reveals Germination Associated Genes

For soilborne pathogens, germination of the resting or dormant propagule that enables persistence within the soil environment is a key point in pathogenesis. Spongospora subterranea is an obligate soilborne protozoan that infects the roots and tubers of potato causing root and powdery scab disease for which there are currently no effective controls. A better understanding of the molecular basis of resting spore germination of S. subterranea could be important for development of novel disease interventions. However, as an obligate biotroph and soil dwelling organism, the application of new omics techniques for the study of the pre-infection process in S. subterranea has been problematic. Here, RNA sequencing was used to analyse the reprogramming of S. subterranea resting spores during the transition to zoospores in an in-vitro model. More than 63 million mean high-quality reads per sample were generated from the resting and germinating spores. By using a combination of reference-based and de novo transcriptome assembly, 6,664 unigenes were identified. The identified unigenes were subsequently annotated based on known proteins using BLAST search. Of 5,448 annotated genes, 570 genes were identified to be differentially expressed during the germination of S. subterranea resting spores, with most of the significant genes belonging to transcription and translation, amino acids biosynthesis, transport, energy metabolic processes, fatty acid metabolism, stress response and DNA repair. The datasets generated in this study provide a basic knowledge of the physiological processes associated with spore germination and will facilitate functional predictions of novel genes in S. subterranea and other plasmodiophorids. We introduce several candidate genes related to the germination of an obligate biotrophic soilborne pathogen which could be applied to the development of antimicrobial agents for soil inoculum management.

Draft Genome Sequence of the Globally Distributed Cockroach-Infecting Fungus Herpomyces periplanetae Strain D. Haelew. 1187d

Herpomyces periplanetae is an obligate biotroph of Periplaneta americana, the American cockroach. Its nearly cosmopolitan distribution is shaped by its globally invasive host and the international pet trade. Here, we report the draft genome sequence of H. periplanetae, based on a thallus from P. americana collected in Cambridge, Massachusetts.

A Diagnostic Guide for Basil Downy Mildew

Downy mildew, caused by the oomycete pathogen Peronospora belbahrii, is one of the most important diseases affecting sweet basil worldwide. Field- and greenhouse-grown basil may be affected, and crop losses are observed as the reduction of marketable leaves during both the production and postharvest handling stages. As an obligate biotroph, P. belbahrii cannot be cultured and maintained without live plant tissue, which may complicate efforts to diagnose and identify the causal agent. Thus, the goal of this diagnostic guide is to outline the appropriate methods required to identify basil downy mildew based on the symptoms of the disease and signs of the pathogen. Additionally, methods for pathogen identification, pathogen isolation, storage of single-sporangium cultures on live plants, and pathogenicity testing are described in detail.

An oomycete effector impairs autophagy in evolutionary distant organisms and favors host infection

An arsenal of effector proteins from plant pathogenic Phytophthora species manipulates their host from inside the cells. Phytophthora parasitica produces the effector AVH195 during an initial, biotrophic phase of infection. The protein transiently impairs plant immune-associated hypersensitive cell death in Nicotiana. ATG8 Interaction Motifs in the protein indicate that the effector targets the autophagic core machinery. We selected a photosynthetic microalga with a single copy ATG8 gene as an alternative model to dissect AVH195-induced autophagic perturbation. AVH195 slows down autophagic flux in Chlamydomonas reinhardtii thus promoting the accumulation of cargo-rich vesicles. In yeast, membrane-associated AVH195 interacts with ATG8 from Chlamydomonas and with different ATG8 isoforms from Arabidopsis thaliana. The overexpression of Avh195 in Arabidopsis promotes growth of both infecting P. parasitica and Hyaloperonospora arabidopsidis, an obligate biotroph. To our knowledge, this report provides first evidence that an oomycete effector non-selectively targets ATG8 in different organisms from the green lineage to slow down autophagic flux for infection.

Melampsoridium hiratsukanum – invasive rust species in Lithuania, and its co-occurrence with eriophylid mite

An invasive East Asian rust fungus <em>Melampsoridium hiratsukanum, </em>obligate biotroph belonging to <em>Pucciniastraceae</em>, Pucciniales (Basidiomycota) is found widely spread on leaves of <em>Alnus incana </em>in eastern, central and southern parts of Lithuania. On <em>Alnus glutinosa </em>this fungus is rare, sometimes occurring with an alder leaf pest, a microscopic eriophyid gall mite <em>Acalitus brevitarsus. </em>Information on the distribution patterns, ecological and morphological characters of this neomycete is given.