Multiple pathways to homothallism in closely related yeast lineages in the Basidiomycota

Sexual reproduction in fungi relies on proteins with well-known functions encoded at the mating type (MAT) loci. In the Basidiomycota, MAT loci are often bipartite, the P/R locus encoding pheromone precursors and pheromone receptors and the HD locus encoding heterodimerizing homeodomain transcription factors (Hd1 and Hd2). The interplay between different alleles of these genes within a single species determines a variety of sexual systems and patterns, which may result in the emergence of hundreds of compatible mating types. However, a minority of species are homothallic, reproducing sexually without the need for a compatible partner. Here we examine the organization and function of the MAT loci of Cystofilobasidium capitatum, a species in the order Cystofilobasidiales, which is unusually rich in homothallic species. For this, we determined MAT gene content and organization in C. capitatum and found that it resembled a mating type of the closely related heterothallic species Cystofilobasidium ferigula. To explain the homothallic sexual reproduction observed in C. capitatum we examined HD -protein interactions in the two individual Cystofilobasidium species and determined C. capitatum MAT gene expression both in the natural setting and upon heterologous expression in Phaffia rhodozyma, a homothallic species belonging to a clade sister to the Cystofilobasidium. We conclude that the molecular basis for homothallism in C. capitatum appears to be distinct from that previously established for P. rhodozyma. Unlike the latter species, homothallism in C. capitatum may involve constitutive activation or dispensability of the pheromone receptor and the functional replacement of the usual Hd1/Hd2 heterodimer by an Hd2 homodimer. Overall, our results suggest that homothallism evolved multiple times in the Cystofilobasidiales, underpinned by diverse molecular mechanisms.

Characterization of mating type genes in heterothallic Neonectria species with emphasis on N. coccinea, N. ditissima, and N. faginata

Neonectria ditissima and N. faginata are canker pathogens involved in an insect-fungus disease complex of American beech (Fagus grandifolia) commonly known as beech bark disease (BBD). In Europe, both N. ditissima and N. coccinea are involved in BBD on European beech (Fagus sylvatica). Field observations across the range of BBD indicate that new infections occur primarily via ascospores. Both heterothallic (self-sterile) and homothallic (self-fertile) mating strategies have been reported for Neonectria fungi. As such, investigations into mating strategy are important for understanding both the disease cycle and population genetics of Neonectria. This is particularly important in the U.S. given that over time N. faginata dominates the BBD pathosystem despite high densities of non-beech hosts for N. ditissima. This study utilized whole-genome sequences of BBD-associated Neonectria spp. along with other publicly available Neonectria and Corinectria genomes and in vitro mating assays to characterize mating type (MAT) loci and confirm thallism for select members of Neonectria and Corinectria. MAT gene-specific primer pairs were developed to efficiently characterize the mating types of additional single ascospore strains of N. ditissima, N. faginata, and N. coccinea and several other related species lacking genomic data. In vitro mating assays were used in combination with molecular results to confirm thallism. These assays also comfirmed the sexual compatibility among N. ditissima strains from different plant hosts. Maximum likelihood phylogenetic analysis of both MAT1-1-1 and MAT1-2-1 sequences recovered trees with similar topology to previously published phylogenies of Neonectria and Corinectria. The results of this study indicate that all Neonectria and Corinectria tested are heterothallic based on our limited sampling and, as such, thallism cannot help explain the inevitable dominance of N. faginata in the BBD pathosystem.

Treatment of Chronic Liver Injuries in Mice by Oral Administration of Ethanolic Extract of the Fruit ofHovenia dulcis

The present study examined the effects of an ethanolic extract of the fruit of Hovenia dulcis (EHD) on chronic hepatitis induced by carbon tetrachloride ( CCl4) in mice. CCl4(5%; 0.1 ml/10 g body weight) was given twice a week for 9 weeks, and mice received EHD throughout the entire experimental period. Plasma activities of GPT and GOT, and hepatic levels of malondialdehyde were significantly lowered in mice treated with EHD as compared to mice treated with CCl4only. Histological evaluation showed that EHD could attenuate the liver fibrosis and necrosis caused by CCl4. RT-qPCR analysis also showed that EHD treatment decreased hepatic collagen (α1)(I) and collagen (α1)(III) mRNA expressions. Chronic CCl4treatment caused liver injuries in mice, characterized by an increase in hepatic methionine adenosyltransferase (MAT) 2A gene expression, and decreased MAT1A gene expression. EHD significantly reduced the changes in MAT gene expression due to the chronic CCl4treatment. These results clearly demonstrate that the EHD can reduce hepatic injuries in mice induced by CCl4.

Changes in methionine adenosyltransferase during liver regeneration in the rat

Liver-specific and non-liver-specific methionine adenosyltransferase (MAT) are products of two genes (MAT1A and MAT2A, respectively) that catalyze the formation of S-adenosylmethionine (SAM), the principal methyl donor. We previously showed that MAT2A expression was associated with more rapid cell growth. Here we examined changes in hepatic MAT gene expression and related consequences after two-thirds partial hepatectomy (PH) in rats. The mRNA levels of both MAT forms increased from 3 to 6 h, but the MAT1A level then fell below baseline from 12 to 24 h, whereas the MAT2A level remained elevated up to 4 days after PH. The increase in the MAT2A mRNA level was due to increased gene transcription and mRNA stabilization. The change in the MAT1A mRNA level was posttranscriptional and did not require de novo protein synthesis. Changes in MAT activity were consistent with an increased amount of MAT isozymes. SAM levels, the ratio of SAM to S-adenosylhomocysteine (SAH), and DNA methylation fell from 6 to 24 h, whereas SAH levels increased slightly at 12 and 24 h after PH. Both increased SAM utilization and MAT2A gene expression likely contributed to the fall in SAM.