Siderophore Biosynthesis but Not Reductive Iron Assimilation Is Essential for the Dimorphic Fungus Nomuraea rileyi Conidiation, Dimorphism Transition, Resistance to Oxidative Stress, Pigmented Microsclerotium Formation, and Virulence

Abstract

Iron is an indispensable factor for the dimorphic insect pathogenic Nomuraea rileyi to form persistent microsclerotia which can replace conidia or blastospores for commercial mass production. There are two high affinity iron acquisition pathways in N. rileyi, siderophore-assisted iron mobilization and reductive iron assimilation systems. Transcription of the two iron uptake pathways related genes is induced under iron-limiting conditions. Stage-specific iron uptake-related genes expression during microsclerotia development shows siderophore-mediated iron acquisition genes are rigorously upregulated specifically during the formation and mature period while reductive iron assimilation related genes just display a higher expression at the late maturation period. Abrogation of reductive iron assimilation, by the deletion of the high affinity iron permease (NrFtrA), has no visible effect on microsclerotia biogenesis in N. rileyi. In sharp contrast, N. rileyi L-ornithine-N5-monooxygenase (NrSidA), required for synthesis of all siderophores, is absolutely necessary for the development of pigmented microsclerotia. In agreement with the lower intracellular iron contents of microsclerotia in ΔNrSidA strains, not only the pigments, but both the number and the biomass are also noticeably reduced. Certain concentration of ROS is required for promoting microsclerotia biogenesis. Combined with expression pattern analysis of related genes and quantitative of intracellular iron or extracellular siderophore in WT and mutants, these data demonstrate the lack of adequate intracellular iron caused by the loss of the siderophore results in the deficiency of ROS detoxication. Furthermore, ΔNrSidA strains show significantly increased sensitivity to hydrogen peroxide. Besides, NrSidA, but not NrFtrA, play a crucial role in vegetative growth under iron-limiting conditions, conidiation, and dimorphic switching. Remarkably, the slower growth of the ΔNrSidA strains in vivo due to a reduced capacity for iron acquisition leads to the loss of virulence in Spodoptera litura while the ΔNrFtrA mutants behaved as WT during infection. Together, these results prove siderophore-assisted iron mobilization is the major pathway of cellular iron uptake and essential for conidiation, dimorphism transition, oxidative stress resistance, pigmented microsclerotium formation and full virulence.

Multi-Trait Biochemical Features of Metarhizium Species and Their Activities That Stimulate the Growth of Tomato Plants

“…Indirectly, siderophore production by plant growth promoting microorganisms can avoid the proliferation of plant pathogens through the sequestration of Fe 3+ around the rhizosphere (Gupta et al, 2015;Jha and Saraf, 2015). Some studies indicated that the siderophore production by M. robertsii can play an important role during insect infection and fungal virulence, as well as alleviate the sensitivity of conidia and microsclerotium to oxidative stress and sustain their development under ironlimited conditions (Krasnoff et al, 2014;Donzelli et al, 2015;Li et al, 2016;Sbaraini et al, 2016;Raya-Díaz et al, 2017). Our study was the first to report siderophore synthesis by M. anisopliae (ESALQ 1669) and M. humberi (ESALQ 1638), and our results indicate that siderophore production by some Metarhizium species could be involved in plant growth promotion.…”

Genome Sequencing and Comparative Genomics Analysis Revealed Pathogenic Potential in Penicillium capsulatum as a Novel Fungal Pathogen Belonging to Eurotiales

“…Fifth, the uptake of nutrients in the human internal environment is an essential for the success of a fungal pathogen ( Abad et al, 2010 ). Currently, no fewer than 37 genes have been associated with the uptake of nutrients in the human internal environment, including through normal nutrient uptake systems and other activated systems ( D’Enfert et al, 1996 ; Brown et al, 2000 ; Hissen et al, 2005 ; Moreno et al, 2007 ; Schrettl et al, 2007 ; Al-Bader et al, 2010 ; Amich et al, 2010 ; Li et al, 2016 ). Thirty-six of these 37 homologous genes have been found in P. capsulatum .…”

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

“…As mentioned, the signalling network that regulates the chitin synthesis‐ and pigment synthesis‐associated genes in solid SMAY and liquid AM culture is highly complicated. Major basal salts such as iron and calcium cations are necessary for MS formation (Song et al ., 2014) and SidA is the major pathway of cellular iron uptake for MS formation (Li et al ., 2016). We demonstrated that the iron importer and calcium transports, Ct‐1 and Ct‐2, were important in MS formation (Wang and Yin, unpublished data).…”

“…The switching rates of the tested strains were counted as previously described (Li et al ., 2016). Approximately 100 simple yeast cells were pipetted onto SMAY medium and grown at 25°C.…”

“…Clone pigments of tested strains were counted as described previously (Li et al ., 2016). Clones from 6‐day‐old, 9‐day‐old or 12‐day‐old SMAY cultures were isolated with 2% NaOH.…”