The mitochondrial genome of Ophiostoma himal-ulmi and comparison with other fungi causing Dutch elm disease

The mitogenomes of Leptographium aureum, Leptographium sp., and Grosmannia fruticeta: expansion by introns

Introduction

Many members of the Ophiostomatales are of economic importance as they are bark-beetle associates and causative agents for blue stain on timber and in some instances contribute towards tree mortality. The taxonomy of these fungi has been challenging due to the convergent evolution of many traits associated with insect dispersal and a limited number of morphological characters that happen to be highly pleomorphic. This study examines the mitochondrial genomes for three members of Leptographium sensu lato [Leptographium aureum (also known as Grosmannia aurea), Grosmannia fruticeta (also known as Leptographium fruticetum), and Leptographium sp. WIN(M)1376)].

Methods

Illumina sequencing combined with gene and intron annotations and phylogenetic analysis were performed.

Results

Sequence analysis showed that gene content and gene synteny are conserved but mitochondrial genome sizes were variable: G. fruticeta at 63,821 bp, Leptographium sp. WIN(M)1376 at 81,823 bp and L. aureum at 104,547 bp. The variation in size is due to the number of introns and intron-associated open reading frames. Phylogenetic analysis of currently available mitochondrial genomes for members of the Ophiostomatales supports currently accepted generic arrangements within this order and specifically supports the separation of members with Leptographium-like conidiophores into two genera, with L. aureum grouping with Leptographium and G. fruticeta aligning with Grosmannia.

Discussion

Mitochondrial genomes are promising sequences for resolving evolutionary relationships within the Ophiostomatales.

Mitochondrial characteristics of the powdery mildew genus Erysiphe revealed an extraordinary evolution in protein-coding genes

The genus Erysiphe was an obligate parasite causing powdery mildew disease on a wide range of higher plants. However, the knowledge of their mitogenome architecture for lifestyle adaptability was scarce. Here, we assembled the first complete mitogenome (190,559 bp in size) for rubber tree powdery mildew pathogen Erysiphe quercicola. Comparable analysis of the Erysiphe mitogenomes exhibited conserved gene content, genome organization and codon usage bias, but extensive dynamic intron gain/loss events were presented between Erysiphe species. The phylogeny of the Ascomycota species constructed in the phylogenetic analysis showed genetic divergences of the Erysiphe species. Compared with other distant saprophytic and plant pathogenic fungi, Erysiphe had a flat distribution of evolutionary pressures on fungal standard protein-coding genes (PCGs). The Erysiphe PCGs had the highest mean selection pressure. In particular, Erysiphe's cox1, nad1, cob and rps3 genes had the most elevated selection pressures among corresponding PCGs across fungal genera. Altogether, the investigations provided a novel insight into the potential evolutionary pattern of the genus Erysiphe to adapt obligate biotrophic lifestyle and promoted the understanding of the high plasticity and population evolution of fungal mitogenomes.

The compact mitogenome of Ceratocystiopsis pallidobrunnea

Ceratocystiopsis is a fungal genus that has been assigned to the Ophiostomatales, fungi known for their association with various bark beetles and other arthropods. The mitochondrial genome of Ceratocystiopsis pallidobrunnea has been characterized and compared with other members of the genus Ceratocystiopsis and Ophiostomatales. At 29 022 bp, the mitogenome of C. pallidobrunnea is the smallest reported so far for this genus. Gene arrangement was observed to be conserved for this group of fungi and mitogenome variation appears to be mostly due to the absence and presence of introns. The long-term goal is to apply mitogenomes to resolve taxonomic issues within the Ophiostomatales and within the various genera that comprise the Ophiostomataceae.

The mitogenome of Urnula craterium

Urnula craterium (Schwein.) Fr. (1851) has been reported from North America, Europe, and Asia, and can be a pathogen on various hardwood species. In this study we investigated the mitochondrial genome of U. craterium. The biology and taxonomy of this fungus is poorly studied and there are no mitogenomes currently available for any member of the Sarcosomataceae (Order Pezizales). The complete mitogenome of U. craterium comprises 43 967 bps and encodes 14 protein-coding genes, a complete set of tRNAs and rRNA genes. A novel feature of the mitogenome is the presence of a single subunit DNA polymerase coding region that is typically associated with linear invertron-type plasmids. The mitogenome may offer insights into the evolution of mitogenomes among members of the Pezizales with regards to gene content and order, mobile elements, and genome sizes.