Abstract

Abstract

Light conditions during fungal growth are well known to cause several physiological adaptations in the produced conidia; thus, conidia of the insect-pathogenic fungi Metarhizium robertsii were produced on: 1) potato dextrose agar (PDA) medium in the dark; 2) PDA medium under white light; 3) PDA medium under blue light; and 4) PDA medium under red light. The conidial production, the speed of conidial germination, the virulence to the insect Tenebrio molitor, as well as gene expression, and tolerances to osmotic stress and to UV radiation were evaluated. Conidia produced under white light or blue light germinated faster and were the most tolerant to UV radiation and osmotic stress. White light improved conidial virulence as compared with conidia produced in the dark. Growth under blue light produced more conidia than the fungus grown in the dark. The small (Mrhsp30) and large (Mrhsp101) heat shock protein genes were highly up-regulated under white light condition, suggesting an active role of heat shock proteins in fungal exposition to the different visible spectrum components. The cytosolic catalase Mrcatc gene was not induced under all light conditions assayed. Conidia produced under red light germinated slower than conidia produced in the dark and were the least tolerant to osmotic stress and UV radiation. The virulence of conidia produced under red light was similar to conidia produced in the dark. In conclusion, white light produced conidia that germinated faster and killed the insects faster; in addition, blue light afforded the highest conidial production. Both white light and blue light afforded the highest tolerance to both stress conditions.

Abstract

Abstract

Adaptive manipulation of host behavior is an effective way for parasites to increase transmission rates. Manipulations resulting in summiting of insect hosts can be observed in Zygomycetes and Ascomycetes of the genera Entomophthora and Ophiocordyceps. Climbing, biting to fix the host at elevated positions, following death, and spore release all appear to display time-of-day synchronization. Biological clocks of the insect host and the fungal parasite, as well as environmental factors such as light and temperature, likely play an important role in these parasite-host interactions. To begin to test these hypotheses we use an integrative approach, combining ecology with behavioral analyses and next-generation sequencing, on a variety of Ophiocordyceps unilateralis sensu lato - carpenter ant interactions. Field data indicates that light influences the manipulated behavior of Ophiocordyceps-infected carpenter ants. This suggests that the fungal parasite, which is fully pulling the strings at this point, can sense light, and has a light entrainable biological clock. To demonstrate this, as well as identify candidate molecular clock components of Ophiocordyceps, we made use of bioinformatics and transcriptional profiling. We did this for the recently sequenced behavior-manipulating parasite Ophiocordyceps kimflemingiae (a named species of the O. unilateralis complex). Through a bioinformatics approach, we identified putative homologs of known clock genes. RNA-Seq was performed on 48 h time courses of O. kimflemingiae to determine daily rhythms and enrichment patterns in the transcriptome. Liquid media cultures were entrained under 24 h light-dark (LD) cycles and harvested at 4 h intervals under LD or continuous darkness. We identified a significant number of fungal transcription factors with peaked activity during the light phase (day time). In contrast, a significant number of secreted enzymes and small bioactive compounds, proteases, and toxins peaked during the dark phase or subjective night. These findings support a model whereby Ophiocordyceps species use their biological clock for phase-specific activity and light-dependent manipulation. This may be a general mechanism involved in parasite-host interactions across taxa.

Abstract

Abstract

Light and nutrient are crucial environmental factors influencing fungal sexual reproduction. Gene expressions influenced by such environmental factors in Coprinopsis cinerea were investigated. Blue light induces simultaneous hyphal knot formation in mycelia grown on low glucose (0.2%) media, but not in mycelia grown on high glucose (1%) media in C. cinerea. Many hyphal knots are visible in arc near the edge of the colony one day after a 15min of blue light stimulation. These suggest that blue light accelerates hyphal knot induction in nutrient limiting condition. Trascriptome (Super-SAGE) analysis revealed that gene expression after light exposure divided into at least two major stages. In the first stage, genes coding for fasciclin (fas1), cyclopropane-fatty-acyl-phospholipid synthases (cfs1 and cfs2), and putative lipid exporter (nod1) are highly expressed at 1h after light exposure in the mycelial region where the hyphal knot will be developed. It is reported that the cfs1 mutated strain was defected in fruiting body development. These genes were up-regulated by blue light, and not influenced by glucose condition and mating. These results suggest that although some of the genes are critical for induction of the hyphal knots, they are not sufficient for hyphal knot development. In the second gene expression stage, genes encoding galectins (cgl1-3), farnesyl cysteine-carboxyl methyltransferases, mating pheromone containing protein, nucleus protein (ich1) and laccase (lcc1) are specifically upregulated at 10-16 h after blue light exposure when the mycelia are cultivated on low glucose media. These might be involved in building architecture of hyphal knot or signal transduction for further fruiting body development. These results contribute to the understanding of the effect of environmental factors on sexual reproduction in basidiomycetous fungi.