On the role of the global regulator RlcA in red-light sensing in Aspergillus nidulans

Isolation of endophytic fungi from Cotoneaster multiflorus and screening of drought-tolerant fungi and evaluation of their growth-promoting effects

In the context of climate change and human factors, the drought problem is a particularly serious one, and environmental pollution caused by the abuse of chemical fertilizers and pesticides is increasingly serious. Endophytic fungi can be used as a protection option, which is ecologically friendly, to alleviate abiotic stresses on plants, promote plant growth, and promote the sustainable development of agriculture and forestry. Therefore, it is of great significance to screen and isolate endophytic fungi that are beneficial to crops from plants in special habitats. In this study, endophytic fungi were isolated from Cotoneaster multiflorus, and drought-tolerant endophytic fungi were screened by simulating drought stress with different concentrations of PEG-6000, and the growth-promoting effects of these drought-tolerant strains were evaluated. A total of 113 strains of endophytic fungi were isolated and purified from different tissues of C. multiflorus. After simulated drought stress, 25 endophytic fungi showed strong drought tolerance. After ITS sequence identification, they belonged to 7 genera and 12 species, including Aspergillus, Fusarium, Colletotrichum, Penicillium, Diaporthe, Geotrichum, and Metarhizium. According to the identification and drought stress results, 12 strains of endophytic fungi with better drought tolerance were selected to study their abilities of dissolving inorganic phosphorus and potassium feldspar powder and producing indole-3-acetic acid (IAA). It was found that the amount of dissolved phosphorus in 7 strains of endophytic fungi was significantly higher than that of CK, and the content of soluble phosphorus was 101.98-414.51 μg. ml-1; 6 endophytic fungi had significantly higher potassium solubilization than CK, and the content of water-soluble potassium ranged from 19.17 to 30.94 mg·l-1; 6 strains have the ability to produce IAA, and the yield of IAA ranged between 0.04 and 0.42 mg. ml-1. This study for the first time identified the existence of endophytic fungi with drought tolerance and growth-promoting function in C. multiflorus, which could provide new direction for plant drought tolerance and growth promotion fungi strain resources. It also provides a theoretical basis for the subsequent application of endophytic fungi of C. multiflorus in agricultural and forestry production to improve plant tolerance.

Light regulation of secondary metabolism in fungi

Fungi have evolved unique metabolic regulation mechanisms for adapting to the changing environments. One of the key features of fungal adaptation is the production of secondary metabolites (SMs), which are essential for survival and beneficial to the organism. Many of these SMs are produced in response to the environmental cues, such as light. In all fungal species studied, the Velvet complex transcription factor VeA is a central player of the light regulatory network. In addition to growth and development, the intensity and wavelength of light affects the formation of a broad range of secondary metabolites. Recent studies, mainly on species of the genus Aspergillus, revealed that the dimer of VeA-VelB and LaeA does not only regulate gene expression in response to light, but can also be involved in regulating production of SMs. Furthermore, the complexes have a wide regulatory effect on different types of secondary metabolites. In this review, we discussed the role of light in the regulation of fungal secondary metabolism. In addition, we reviewed the photoreceptors, transcription factors, and signaling pathways that are involved in light-dependent regulation of secondary metabolism. The effects of transcription factors on the production of secondary metabolites, as well as the potential applications of light regulation for the production of pharmaceuticals and other products were discussed. Finally, we provided an overview of the current research in this field and suggested potential areas for future research.

Use of red, far-red, and near-infrared light in imaging of yeasts and filamentous fungi

Abstract

While phototoxicity can be a useful therapeutic modality not only for eliminating malignant cells but also in treating fungal infections, mycologists aiming to observe morphological changes or molecular events in fungi, especially when long observation periods or high light fluxes are warranted, encounter problems owed to altered regulatory pathways or even cell death caused by various photosensing mechanisms. Consequently, the ever expanding repertoire of visible fluorescent protein toolboxes and high-resolution microscopy methods designed to investigate fungi in vitro and in vivo need to comply with an additional requirement: to decrease the unwanted side effects of illumination. In addition to optimizing exposure, an obvious solution is red-shifted illumination, which, however, does not come without compromises. This review summarizes the interactions of fungi with light and the various molecular biology and technology approaches developed for exploring their functions on the molecular, cellular, and in vivo microscopic levels, and outlines the progress towards reducing phototoxicity through applying far-red and near-infrared light.

Key points

• Fungal biological processes alter upon illumination, also under the microscope

• Red shifted fluorescent protein toolboxes decrease interference by illumination

• Innovations like two-photon, lightsheet, and near IR microscopy reduce phototoxicity

The sulfur metabolism regulator MetR is a global regulator controlling phytochrome-dependent light responses in Aspergillus nidulans

Phytochrome-dependent light signaling has been studied in several fungi. In Aspergillus nidulans light-stimulated phytochrome activates the high-osmolarity glycerol (HOG) signaling pathway and thereby controls the expression of a large number of genes, many of which are related to stress responses. In a genome-wide expression analysis in A. nidulans we found that phytochrome, fphA, is under strict expression control of the central regulator of the sulfur-starvation response, MetR. This transcriptional regulator is required for the expression of genes involved in inorganic sulfur assimilation. In the presence of organic sulfur, MetR is probably ubiquitinated and possibly degraded and the transcription of sulfur-assimilation genes, e.g., sulfate permease, is turned off. The expression analysis described here revealed, however, that MetR additionally controls the expression of hundreds of genes, many of which are required for secondary metabolite production. We also show that metR mutation phenocopies fphA deletion, and five other histidine-hybrid kinases are down-regulated in the metR1 mutant. Furthermore, we found that light and phytochrome regulate the expression of at least three carbon-sulfur hydrolases. This work is a further step towards understanding the interplay between light sensing and metabolic pathways.

A light life together: photosensing in the plant microbiota

Bacteria and fungi of the plant microbiota can be phytopathogens, parasites or symbionts that establish mutually advantageous relationships with plants. They are often rich in photoreceptors for UVA-Visible light, and in many cases, they exhibit light regulation of growth patterns, infectivity or virulence, reproductive traits, and production of pigments and of metabolites. In addition to the light-driven effects, often demonstrated via the generation of photoreceptor gene knock-outs, microbial photoreceptors can exert effects also in the dark. Interestingly, some fungi switch their attitude towards plants in dependence of illumination or dark conditions in as much as they may be symbiotic or pathogenic. This review summarizes the current knowledge about the roles of light and photoreceptors in plant-associated bacteria and fungi aiming at the identification of common traits and general working ideas. Still, reports on light-driven infection of plants are often restricted to the description of macroscopically observable phenomena, whereas detailed information on the molecular level, e.g., protein-protein interaction during signal transduction or induction mechanisms of infectivity/virulence initiation remains sparse. As it becomes apparent from still only few molecular studies, photoreceptors, often from the red- and the blue light sensitive groups interact and mutually modulate their individual effects. The topic is of great relevance, even in economic terms, referring to plant-pathogen or plant-symbionts interactions, considering the increasing usage of artificial illumination in greenhouses, the possible light-regulation of the synthesis of plant-growth stimulating substances or herbicides by certain symbionts, and the biocontrol of pests by selected fungi and bacteria in a sustainable agriculture.

The Third International Symposium on Fungal Stress - ISFUS

Stress is a normal part of life for fungi, which can survive in environments considered inhospitable or hostile for other organisms. Due to the ability of fungi to respond to, survive in, and transform the environment, even under severe stresses, many researchers are exploring the mechanisms that enable fungi to adapt to stress. The International Symposium on Fungal Stress (ISFUS) brings together leading scientists from around the world who research fungal stress. This article discusses presentations given at the third ISFUS, held in São José dos Campos, São Paulo, Brazil in 2019, thereby summarizing the state-of-the-art knowledge on fungal stress, a field that includes microbiology, agriculture, ecology, biotechnology, medicine, and astrobiology.