The PHO pathway regulates white-opaque switching and sexual mating in the human fungal pathogen Candida albicans

Farnesol and phosphorylation of the transcriptional regulator Efg1 affect Candida albicans white-opaque switching rates

Candida albicans is a normal member of the human microbiome and an opportunistic fungal pathogen. This species undergoes several morphological transitions, and here we consider white-opaque switching. In this switching program, C. albicans reversibly alternates between two cell types, named "white" and "opaque," each of which is normally stable across thousands of cell divisions. Although switching under most conditions is stochastic and rare, certain environmental signals or genetic manipulations can dramatically increase the rate of switching. Here, we report the identification of two new inputs which affect white-to-opaque switching rates. The first, exposure to sub-micromolar concentrations of (E,E)-farnesol, reduces white-to-opaque switching by ten-fold or more. The second input, an inferred PKA phosphorylation of residue T208 on the transcriptional regulator Efg1, increases white-to-opaque switching ten-fold. Combining these and other environmental inputs results in a variety of different switching rates, indicating that a given rate represents the integration of multiple inputs.

A transcriptional activator from Rhizophagus irregularis regulates phosphate uptake and homeostasis in AM symbiosis during phosphorous starvation

Introduction

Phosphorus (P) is one of the most important nutrient elements for plant growth and development. Under P starvation, arbuscular mycorrhizal (AM) fungi can promote phosphate (Pi) uptake and homeostasis within host plants. However, the underlying mechanisms by which AM fungal symbiont regulates the AM symbiotic Pi acquisition from soil under P starvation are largely unknown. Here, we identify a HLH domain containing transcription factor RiPho4 from Rhizophagus irregularis.

Methods

To investigate the biological functions of the RiPho4, we combined the subcellular localization and Yeast One-Hybrid (Y1H) experiments in yeasts with gene expression and virus-induced gene silencing approach during AM symbiosis.

Results

The approach during AM symbiosis. The results indicated that RiPho4 encodes a conserved transcription factor among different fungi and is induced during the in planta phase. The transcription of RiPho4 is significantly up-regulated by P starvation. The subcellular localization analysis revealed that RiPho4 is located in the nuclei of yeast cells during P starvation. Moreover, knock-down of RiPho4 inhibits the arbuscule development and mycorrhizal Pi uptake under low Pi conditions. Importantly, RiPho4 can positively regulate the downstream components of the phosphate (PHO) pathway in R. irregularis.

Discussion

In summary, these new findings reveal that RiPho4 acts as a transcriptional activator in AM fungus to maintain arbuscule development and regulate Pi uptake and homeostasis in the AM symbiosis during Pi starvation.

The Molecular Mechanism of Yellow Mushroom (Floccularia luteovirens) Response to Strong Ultraviolet Radiation on the Qinghai-Tibet Plateau

The Qinghai-Tibet Plateau (QTP) is the highest plateau in the world, and its ultraviolet (UV) radiation is much greater than that of other regions in the world. Yellow mushroom (Floccularia luteovirens) is a unique and widely distributed edible fungus on the QTP. However, the molecular mechanism of F. luteovirens’s response to strong UV radiation remains unclear. Herein, we reported the 205 environmental adaptation and information processing genes from genome of F. luteovirens. In addition, we assembled the RNA sequence of UV-affected F. luteovirens at different growth stages. The results showed that in response to strong UV radiation, a total of 11,871 significantly different genes were identified, of which 4,444 genes in the vegetative mycelium (VM) stage were significantly different from the young fruiting bodies (YFB) stage, and only 2,431 genes in the YFB stage were significantly different from fruiting bodies (FB) stage. A total of 225 differentially expressed genes (DEGs) were found to be involved in environmental signal transduction, biochemical reaction preparation and stress response pathway, pigment metabolism pathway, and growth cycle regulation, so as to sense UV radiation, promote repair damage, regulate intracellular homeostasis, and reduce oxidative damage of UV radiation. On the basis of these results, a molecular regulation model was proposed for the response of F. luteovirens to strong UV radiation. These results revealed the molecular mechanism of adaptation of F. luteovirens adapting to strong UV radiation, and provided novel insights into mechanisms of fungi adapting to extreme environmental conditions on the QTP; the production the riboflavin pigment of the endemic fungi (Yellow mushroom) in the QTP was one of the response to extreme environment of the strong UV radiation.

Parasexuality of Candida Species

While most fungi have the ability to reproduce sexually, multiple independent lineages have lost meiosis and developed parasexual cycles in its place. Emergence of parasexual cycles is particularly prominent in medically relevant fungi from the CUG paraphyletic group of Candida species. Since the discovery of parasex in C. albicans roughly two decades ago, it has served as the model for Candida species. Importantly, parasex in C. albicans retains hallmarks of meiosis including genetic recombination and chromosome segregation, making it a potential driver of genetic diversity. Furthermore, key meiotic genes play similar roles in C. albicans parasex and highlights parallels between these processes. Yet, the evolutionary role of parasex in Candida adaptation and the extent of resulting genotypic and phenotypic diversity remain as key knowledge gaps in this facultative reproductive program. Here, we present our current understanding of parasex, the mechanisms governing its regulation, and its relevance to Candida biology.