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Strain breeding is much less advanced in the edible and medicinal species Agaricus subrufescens than in Agaricus bisporus, the button mushroom. Both species have a unifactorial system of sexual incompatibility, a mating type locus tightly linked to a centromere, and basidia producing both homokaryotic (n) and heterokaryotic (n + n) spores. In A. bisporus, breeding is mainly based on direct selection among the heterokaryotic offspring and on hybridization between homokaryotic offspring. The parental heterozygosity is highly maintained in the heterokaryotic offspring due to suppression of recombination and preferential pairing in the spores of nuclei, each one per second meiotic divisions; such "non-sister nuclei" heterokaryons are fertile. In A. subrufescens, recent studies revealed that recombination is not suppressed and that nuclei from the same second meiotic division can also be paired in a spore that give rise to a "sister nuclei" heterokaryon in which the nuclei bear the same mating type allele. The objective of the present work was to investigate the potential function of the different categories of spores in A. subrufescens and their possible use in a genetic breeding program. Using eight co-dominant molecular markers, we found that half of the offspring of the A. subrufescens strain WC837 were heterokaryotic, one quarter of them being sister nuclei heterokaryons. These heterokaryons were infertile and behaved like homokaryons, being even able to cross between each other. In contrast, non-sister nuclei heterokaryons could fruit but inconsistently due to inbreeding depression. Potential roles of these two categories of heterokaryons in nature and consequences for strain breeding are discussed.

Intraspecific mitochondrial variability was studied in ten strains of A. bisporus var. bisporus, in a strain representative of A. bisporus var. eurotetrasporus and in a strain of the closely related species Agaricus devoniensis. In A. bisporus, the cox1 gene is the richest in group I introns harboring homing endonuclease genes (heg). This study led to identify group I introns as the main source of cox1 gene polymorphism. Among the studied introns, two groups were distinguished according to the heg they contained. One group harbored heg maintained putatively functional. The other group was composed of eroded heg sequences that appeared to evolve toward their elimination. Low nucleotide substitution rates were found in both types of intronic sequences. This feature was also shared by all types of studied mitochondrial sequences, not only intronic but also genic and intergenic ones, when compared with nuclear sequences. Hence, the intraspecific evolution of A. bisporus mitochondrial genome appears characterized by both an important mobility (presence/absence) of large group I introns and by low nt substitution rates. This stringent conservation of mitochondrial sequences, when compared with their nuclear counterparts, appears irrespective of their apparent functionality and contrasts to what is widely accepted in fungal sequence evolution. This strengthens the usefulness of mtDNA sequences to get clues on intraspecific evolution.

Agaricus subrufescens is one of the most important culinary-medicinal cultivable mushrooms with potentially high-added-value products and extended agronomical valorization. The development of A. subrufescens-related technologies is hampered by, among others, the lack of suitable molecular tools. Thus, this mushroom is considered as a genomic orphan species with a very limited number of available molecular markers or sequences. To fill this gap, this study reports the generation and analysis of the first set of expressed sequence tags (EST) for A. subrufescens. cDNA fragments obtained from young sporophores (SP) and vegetative mycelium in liquid culture (CL) were sequenced using 454 pyrosequencing technology. After assembly process, 4,989 and 5,125 sequences were obtained in SP and CL libraries, respectively. About 87% of the EST had significant similarity with Agaricus bisporus-predicted proteins, and 79% correspond to known proteins. Functional categorization according to Gene Ontology could be assigned to 49% of the sequences. Some gene families potentially involved in bioactive compound biosynthesis could be identified. A total of 232 simple sequence repeats (SSRs) were identified, and a set of 40 EST-SSR polymorphic markers were successfully developed. This EST dataset provides a new resource for gene discovery and molecular marker development. It constitutes a solid basis for further genetic and genomic studies in A. subrufescens.

Sun mushroom is a cultivated mushroom extensively studied for its medicinal properties for several years and literature abounds on the topic. Besides, agronomical aspects were investigated in Brazil, the country the mushroom comes from, and some studies focus on the biology of the fungus. This review aimed to present an overview of the non-medicinal knowledge on the mushroom. Areas of commercial production and marketing trends are presented. Its specific fragrance, taste, nutritional value and potential use of extracts as food additives are compared to those of the most cultivated fungi and laboratory models. The interest of the mushroom for lignocellulosic enzyme production and source of biomolecules for the control of plant pathogens are shown. Investigation of genetic variability among cultivars is reported. Growing and storage of mycelium, as well as cultivation conditions (substrate and casing generally based on local products; indoor and outdoor cultivation; diseases and disorders) are described and compared to knowledge on Agaricus bisporus.

Trichothecenes are toxic secondary metabolites produced by filamentous fungi mainly belonging to the Fusarium genus. Production of these mycotoxins occurs during infection of crops and is a threat to human and animal health. Although the pathway for biosynthesis of trichothecenes is well established, the regulation of the Tri genes implicated in the pathway remains poorly understood. Most of the Tri genes are gathered in a cluster which contains two transcriptional regulators controlling the expression of the other Tri genes. The regulation of secondary metabolites biosynthesis in most fungal genera has been recently shown to be controlled by various regulatory systems in response to external environment. The control of the "Tri cluster" by non-cluster regulators in Fusarium was not clearly demonstrated until recently. This review covers the recent advances concerning the regulation of trichothecene biosynthesis in Fusarium and highlights the potential implication of various general regulatory circuits. Further studies on the role of these regulatory systems in the control of trichothecene biosynthesis might be useful in designing new strategies to reduce mycotoxin accumulation.

Developing the production of ectomycorrhizal (ECM) mushrooms in forest has become a challenge. Only a few ECM species are currently cultivable. Controlled mycorrhization practices offer promising advance to produce currently uncultivable ECM mushrooms. The persistence of the production of edible species, either cultivated or wild, depends on both the tree and the ecological environment (fungal communities, climate, soil, tree development). Developing adapted forest management practices appears to be means to improve production of edible ECM mushrooms. This review summarises current knowledge on the development of a science-based mycosilviculture for the production of edible ECM mushrooms.