Adding a missing piece to the puzzle of oomycete phylogeny: the placement of Rhipidium interruptum (Rhipidiaceae)

Oomycetes are a group of fungus-like organisms, which phylogenetically comprise early diverging lineages that are mostly holocarpic, and two crown classes, the Peronosporomycetes and Saprolegniomycetes, including many well-investigated pathogens of plants and animals. However, there is a poorly studied group, the Rhipidiales, which placement amongst the crown oomycetes is ambiguous. It accommodates several taxa with a sophisticated vegetative and reproductive cycle, as well as structural organisation, that is arguably the most complex in the oomycete lineage. Despite the remarkable morphological complexity and their notable perseverance in the face of faster-growing saprotrophic oomycetes and fungi, the knowledge on Rhipidiales is limited to date, as the most complex members are not easily cultured, even by targeted approaches. This also leads to inadequate sequence data for the order, which was sourced from only the two least complex out of seven introduced genera, i.e. Sapromyces and Salispina. In the present study, ex-situ baiting was done using various fruit substrates, and naturally-shed twigs or fruits acquired from water bodies were examined. As a result of these efforts, the species Rhipidium interruptum was obtained and gross cultivation was accomplished using poplar (Populus nigra) twigs as substrate, which allowed further documentation of both asexual and sexual reproduction. This enabled phylogenetic and detailed morphological study, as well as an epitypification of the species. Phylogenetic analyses based on cox2 and nrLSU sequences revealed Rhipidium as the sister genus of Sapromyces. The morphological studies done support a conspecificity of R. interruptum and R. continuum, which might in turn be conspecific with R. americanum. Though several further studies will be required to fit the scattered missing pieces of knowledge on Rhipidiales together revealing a more complete picture of oomycete evolution, we hope that the current study can serve as a cornerstone for future investigations in the group. Citation: Tsai I, Thines M (2023). Adding a missing piece to the puzzle of oomycete phylogeny: the placement of Rhipidium interruptum (Rhipidiaceae). Fungal Systematics and Evolution 11: 95-108. doi: 10.3114/fuse.2023.11.08.

Linear ubiquitination by LUBEL has a role in Drosophila heat stress response

The HOIP ubiquitin E3 ligase generates linear ubiquitin chains by forming a complex with HOIL‐1L and SHARPIN in mammals. Here, we provide the first evidence of linear ubiquitination induced by a HOIP orthologue in Drosophila. We identify Drosophila CG11321, which we named Linear Ubiquitin E3 ligase (LUBEL), and find that it catalyzes linear ubiquitination in vitro. We detect endogenous linear ubiquitin chain‐derived peptides by mass spectrometry in Drosophila Schneider 2 cells and adult flies. Furthermore, using CRISPR/Cas9 technology, we establish linear ubiquitination‐defective flies by mutating residues essential for the catalytic activity of LUBEL. Linear ubiquitination signals accumulate upon heat shock in flies. Interestingly, flies with LUBEL mutations display reduced survival and climbing defects upon heat shock, which is also observed upon specific LUBEL depletion in muscle. Thus, LUBEL is involved in the heat response by controlling linear ubiquitination in flies.

Cigarette smoke inhalation affects the reproductive system of female hamsters

The purpose of this study was to determine if inhalation of mainstream (MS) or sidestream (SS) smoke affects the reproductive organs of female hamsters. Females inhaled smoke from one or two cigarettes twice per day for 30 d prior to mating using a smoking machine equipped for nose breathing. Serum cotinine levels were within the ranges found in active and passive humans smokers. On day 7 of pregnancy, the reproductive organs of controls and smokers were evaluated for the total number of corpora lutea (CL), the percentage of normal, pink, and small CL, the vascular area in the CL, the ultrastructure of the oviductal epithelium, the ratio of ciliated to secretory cells in the ampulla of the oviduct, the stretchability of the uterine horns, the percentage of implantation sites, and the percentage of touching implantation sites. All parameters, except the percentages of implantation sites and of small CL, were affected by exposure to smoke. To determine if the effects of smoking on the ovary and uterus could be reversed, females smoked for 30 d, remained in their cages without smoking for 30 d, and then were mated and evaluated on day 7 of pregnancy. In this reversal experiment, all ovarian and uterine parameters (except total CL) previously affected by smoking were normal in MS and SS females. These experimental observations show that components in both MS and SS smoke, when delivered at levels comparable to those human smokers receive, can affect the ovary, oviduct, and uterus.