Kraege, A. | bioRxiv Science

bioRxiv2023

High quality genome assembly and annotation (v1) of the eukaryotic terrestrial microalga Coccomyxa viridis SAG 216-4

Unicellular green algae of the genus Coccomyxa are recognized for their worldwide distribution and ecological versatility. Most species described to date live in close association with various host species, such as in lichen associations. However, little is known about the molecular mechanisms that drive such symbiotic lifestyles. We generated a high-quality genome assembly for the lichen photobiont Coccomyxa viridis SAG 216-4 (formerly C. mucigena). Using long-read PacBio HiFi and Oxford Nanopore Technologies in combination with chromatin conformation capture (Hi-C) sequencing, we assembled the genome into 21 scaffolds with a total length of 50.9 Mb, an N50 of 2.7 Mb and a BUSCO score of 98.6%. While 19 scaffolds represent full-length nuclear chromosomes, two additional scaffolds represent the mitochondrial and plastid genomes. Transcriptome-guided gene annotation resulted in the identification of 13,557 protein-coding genes, of which 68% have annotated PFAM domains and 962 are predicted to be secreted.

genomics↗

bioRxiv2023

The soil-borne white root rot pathogen Rosellinia necatrix expresses antimicrobial proteins during host colonization

Rosellinia necatrix is a prevalent soil-borne plant-pathogenic fungus that is the causal agent of white root rot disease in a broad range of host plants. The limited availability of genomic resources for R. necatrix has complicated a thorough understanding of its infection biology. Here, we sequenced nine R. necatrix strains with Oxford Nanopore sequencing technology, and with DNA proximity ligation we generated a gapless assembly of one of the genomes into ten chromosomes. Whereas many filamentous pathogens display a so-called two-speed genome with more dynamic and more conserved compartments, the R. necatrix genome does not display such genome compartmentalization. It has recently been proposed that fungal plant pathogens may employ effectors with antimicrobial activity to manipulate the host microbiota to promote infection. In the predicted secretome of R. necatrix, 26 putative antimicrobial effector proteins were identified, nine of which are expressed during plant colonization. Two of the candidates were tested, both of which were found to possess selective antimicrobial activity. Intriguingly, some of the inhibited bacteria are antagonists of R. necatrix growth in vitro and can alleviate R. necatrix infection on cotton plants. Collectively, our data show that R. necatrix encodes antimicrobials that are expressed during host colonization and that may contribute to modulation of host-associated microbiota to stimulate disease development.

plant biology↗