A transcription factor, MrMsn2, in the dimorphic fungus Metarhizium rileyi is essential for dimorphism transition, aggravated pigmentation, conidiation and microsclerotia formation

Abstract

SummaryMicrosclerotia (MS) are pseudoparenchymatous aggregations of hyphae of fungi that can be induced in liquid culture for biocontrol applications. Previously, we determined that the high‐osmolarity glycerol (HOG) signalling pathway was involved in regulating MS development in the dimorphic insect pathogen Metarhizium rileyi. To further investigate the mechanisms by which the signalling pathway is regulated, we characterized the transcriptional factor MrMsn2, a homologue of the yeast C2H2 transcriptional factor Msn2, which is predicted to function downstream of the HOG pathway in M. rileyi. Compared with wild‐type and complemented strains, disruption of MrMsn2 increased the yeast‐to‐hypha transition rate, enhanced conidiation capacity and aggravated pigmentation in M. rileyi. The ▵MrMsn2 mutants were sensitive to stress, produced morphologically abnormal clones and had significantly reduced MS formation and decreased virulence levels. Digital expression profiling revealed that genes involved in antioxidation, pigment biosynthesis and ion transport and storage were regulated by MrMsn2 during conidia and MS development. Taken together, our findings confirm that MrMsn2 controlled the yeast‐to‐hypha transition, conidia and MS formation, and virulence.

GATA‐type transcription factor MrNsdD regulates dimorphic transition, conidiation, virulence and microsclerotium formation in the entomopathogenic fungus Metarhizium rileyi

“…However, the mechanisms by which the dimorphic transition occurs are not well defined. Previous investigations had confirmed that the dimorphic transition process was associated with increased reactive oxygen species (ROS) levels (Song et al , 2018b). Further transcriptomics investigations of the mutant found that the expression of many genes annotated as being related to ROS detoxification was up‐ or down‐regulated during the dimorphic transition in the Δ MrNsdD mutant (Figs S6 and S10).…”

“…Interestingly, the identification of DEGs from the carbon metabolism pathway led to the discovery that MrNsdD was involved in the metabolism of different carbon sources. Previous investigations had proposed that ROS were associated with both dimorphic transition and microsclerotium development (Song, 2018; Song et al , 2018a, 2018b). Peroxisomes are among the main organelles for ROS production in fungi.…”

“…Unlike the above‐mentioned filamentous fungi, M. rileyi has a special dimorphic lifestyle with yeast cells forming on SMAY medium for 2–4 days, before transformation into the filamentous form and conidium production after 6 days (Pendland and Boucias, 1997). Previous investigations had shown that the delay in making the dimorphic transition in regulatory gene mutants in M. rileyi resulted in decreased conidiation (Wang et al , 2018, 2019; Song et al , 2018a), whereas advancing the time of dimorphic transition in gene mutants increased conidial production (Song et al , 2018b). The delay in the dimorphic transition in the Δ MrNsdD mutant (Fig.…”

“…Aliquots (2.5 μl) of conidial suspensions (10 6 , 10 7 , or 10 8 conidia ml −1 ) of tested strains were pipetted centrally onto SMAY plates (9‐cm diameter) and incubated at 25 °C under continuous light for 12 d. From 6 d onwards, three culture plugs were taken each day at 3‐days intervals using a borer. The aerial conidiation capacity of each strain was quantified according to previously described methods (Song et al , 2018b). Colony morphology was examined, and images were collected using a digital camera (60‐mm Macro lens, Canon Inc., Tokyo, Japan) and a light microscope.…”

Advances in >i<Metarhizium>/i< blastospores production and formulation and transcriptome studies of the yeast and filamentous growth

“…The fungus requires a more complex medium such as SMAY (Sabouraud maltose agar with yeast) in order to germinate and sporulate when compared with other Metarhizium species (Alves et al, 1998, Edelstein et al, 2004) that can easily grow in simple PDA (potato dextrose agar) medium. When grown in SMAY medium, M. rileyi conidial germ tubes switch to a yeast-like (blastospores) phase after 2-4 days of inoculation and grow in mucoid colonies for 1-7 days (depending on strain) (Song et al, 2018;Boucias and Pandland, 1984). After this period blastospores switch to mycelial growth followed by the formation of conidia.…”