Complete mitochondrial genome of plant pathogen Monilinia fructicola (Sclerotiniaceae, Helotiales)

Stone fruit phenolic and triterpenoid compounds modulate gene expression of Monilinia spp. in culture media

Phenolic and triterpenoid compounds are essential components in stone fruit skin and flesh tissues. They are thought to possess general antimicrobial activity. However, regarding brown rot disease, investigations were only confined to a limited number of phenolics, especially chlorogenic acid. The activity of triterpenoids against Monilinia spp., as an essential part of the peach cuticular wax, has not been studied before. In this work, the anti-fungal effect of some phenolics, triterpenoids, and fruit surface compound (FSC) extracts of peach fruit at two developmental stages were investigated on Monilinia fructicola and Monilinia laxa characteristics during in vitro growth. A new procedure for assaying anti-fungal activity of triterpenoids, which are notoriously difficult to assess in vitro because of their hydrophobicity, has been developed. Measurements of colony diameter, sporulation, and germination of second-generation conidia were recorded. Furthermore, the expression of twelve genes of M. fructicola associated with germination and/or appressorium formation and virulence-related genes was studied relative to the presence of the compounds. The study revealed that certain phenolics and triterpenoids showed modest anti-fungal activity while dramatically modulating gene expression in mycelium of M. fructicola on culture medium. MfRGAE1 gene was overexpressed by chlorogenic and ferulic acids and MfCUT1 by betulinic acid, at 4- and 7- days of mycelium incubation. The stage II FSC extract, corresponding to the period when the fruit is resistant to Monilinia spp., considerably up-regulated the MfLAE1 gene. These findings effectively contribute to the knowledge of biochemical compounds effects on fungi on in vitro conditions.

The First Mitochondrial Genome of Ciborinia camelliae and Its Position in the Sclerotiniaceae Family

Ciborinia camelliae is the causal agent of camellia flower blight (CFB). It is a hemibiotrophic pathogen, inoperculate Discomycete of the family Sclerotiniaceae. It shows host and organ specificity infecting only flowers of species belonging to the genus Camellia, causing serious damage to the ornamental component of the plant. In this work, the first mitochondrial genome of Ciborinia camellia is reported. The mitogenome was obtained by combining Illumina short read and Nanopore long read technology. To resolve repetitive elements, specific primers were designed and used for Sanger sequencing. The manually curated mitochondrial DNA (mtDNA) of the Italian strain DSM 112729 is a circular sequence of 114,660 bp, with 29.6% of GC content. It contains two ribosomal RNA genes, 33 transfer RNAs, one RNase P gene, and 62 protein-coding genes. The latter include one gene coding for a ribosomal protein (rps3) and the 14 typical proteins involved in the oxidative metabolism. Moreover, a partial mtDNA assembled from a contig list was obtained from the deposited genome assembly of a New Zealand strain of C. camelliae. The present study contributes to understanding the mitogenome arrangement and the evolution of this phytopathogenic fungus in comparison to other Sclerotiniaceae species and confirms the usefulness of mitochondrial analysis to define phylogenetic positioning of this newly sequenced species.

Deciphering the Monilinia fructicola Genome to Discover Effector Genes Possibly Involved in Virulence

Brown rot is the most economically important fungal disease of stone fruits and is primarily caused by Monilinia laxa and Monlinia fructicola. Both species co-occur in European orchards although M. fructicola is considered to cause the most severe yield losses in stone fruit. This study aimed to generate a high-quality genome of M. fructicola and to exploit it to identify genes that may contribute to pathogen virulence. PacBio sequencing technology was used to assemble the genome of M. fructicola. Manual structural curation of gene models, supported by RNA-Seq, and functional annotation of the proteome yielded 10,086 trustworthy gene models. The genome was examined for the presence of genes that encode secreted proteins and more specifically effector proteins. A set of 134 putative effectors was defined. Several effector genes were cloned into Agrobacterium tumefaciens for transient expression in Nicotiana benthamiana plants, and some of them triggered necrotic lesions. Studying effectors and their biological properties will help to better understand the interaction between M. fructicola and its stone fruit host plants.

First characterization of the complete mitochondrial genome of fungal plant-pathogen Monilinia laxa which represents the mobile intron rich structure

Monilinia laxa is an important fungal plant pathogen causing brown rot on many stone and pome fruits worldwide. Mitochondrial genome (mitogenome) plays a critical role in evolutionary biology of the organisms. This study aimed to characterize the complete mitogenome of M. laxa by using next-generation sequencing and approaches of de novo assembly and annotation. The total length of the mitogenome of M. laxa was 178,357 bp, and its structure was circular. GC content of the mitogenome was 30.1%. Annotation of the mitogenome presented 2 ribosomal RNA (rRNA) genes, 32 transfer RNA genes (tRNA), 1 gene encoding mitochondrial ribosomal protein S3, 14 protein-coding genes and 15 open reading frame encoding hypothetical proteins. Moreover, the group I mobile introns encoding homing endonucleases including LAGLIDADG and GIY-YIG families were found both within coding regions (genic) and intergenic regions of the mitogenome, indicating an enlarged size and a dynamic structure of the mitogenome. Furthermore, a comparative mitogenomic analysis was performed between M. laxa and the three closely related fungal phytopathogen species (Botryotinia fuckeliana, Sclerotinia sclerotiorum and, S. borealis). Due to the number and distribution of introns, the large extent of structural rearrangements and diverse mitogenome sizes were detected among the species investigated. Monilinia laxa presented the highest number of homing endonucleases among the fungal species considered in the analyses. This study is the first to report a detailed annotation of the mitogenome of an isolate of M. laxa, providing a solid basis for further investigations of mitogenome variations for the other Monilinia pathogens causing brown rot disease.