Dipeptidase PEPDA is required for the conidiation pattern shift in Metarhizium acridum

Filamentous fungi conduct two types of conidiation, typical conidiation from mycelia and microcycle conidiation (MC). Fungal conidiation can shift between the two patterns, which involved a large number of genes in the regulation of this process. In this study, we investigated the role of a dipeptidase gene pepdA in conidiation pattern shift in Metarhizium acridum , which is upregulated in MC pattern compared to typical conidiation. Results showed that disruption of the pepdA resulted in a shift of conidiation pattern from MC to typical conidiation. Metabolomic analyses of amino acids showed that the levels of 19 amino acids significantly changed in Δ pepdA mutant. The defect of MC in Δ pepdA can be rescued when nonpolar amino acids, α-alanine, β-alanine or proline, were added into s ucrose y east extract a gar (SYA) medium. Digital gene expression profiling analysis revealed that PEPDA mediated transcription of sets of genes which were involved in hyphal growth and development, sporulation, cell division, and amino acid metabolism. Our results demonstrated that PEPDA played important roles in the regulation of MC by manipulating the levels of amino acids in M. acridum . IMPORTANCE Conidia, as the asexual propagules in many fungi, are start and end of fungal lifecycle. In entomopathogenic fungi, conidia are the infective form essential for their pathogenicity. Filamentous fungi conduct two types of conidiation, typical conidiation from mycelia and microcycle conidiation. The mechanisms of the shift between the two conidiation patterns remain to be elucidated. In this study, we demonstrated that the dipeptidase PEPDA, a key enzyme from the insect-pathogenic fungus Metarhizium acridum for the hydrolysis of dipeptides, is associated with a shift of conidiation pattern. The conidiation pattern of the Δ pepdA mutant was restored when supplemented with the nonpolar amino acids rather than polar amino acids. Therefore, this report highlights that the dipeptidase PEPDA regulates MC by manipulating the levels of amino acids in M. acridum.

Micafungin-Induced Cell Wall Damage Stimulates Morphological Changes Consistent with Microcycle Conidiation in Aspergillus nidulans

Fungal cell wall receptors relay messages about the state of the cell wall to the nucleus through the Cell Wall Integrity Signaling (CWIS) pathway. The ultimate role of the CWIS pathway is to coordinate repair of cell wall damage and to restore normal hyphal growth. Echinocandins such as micafungin represent a class of antifungals that trigger cell wall damage by affecting synthesis of β-glucans. To obtain a better understanding of the dynamics of the CWIS response and its multiple effects, we have coupled dynamic transcriptome analysis with morphological studies of Aspergillus nidulans hyphae in responds to micafungin. Our results reveal that expression of the master regulator of asexual development, BrlA, is induced by micafungin exposure. Further study showed that micafungin elicits morphological changes consistent with microcycle conidiation and that this effect is abolished in the absence of MpkA. Our results suggest that microcycle conidiation may be a general response to cell wall perturbation which in some cases would enable fungi to tolerate or survive otherwise lethal damage.

Micafungin-induced Cell Wall Damage Stimulates Microcycle Conidiation in Aspergillus nidulans

Fungal cell wall receptors relay messages about the state of the cell wall to the nucleus through the Cell Wall Integrity Signaling (CWIS) pathway. The ultimate role of the CWIS pathway is to coordinate repair of cell wall damage and to restore normal hyphal growth. Echinocandins such as micafungin represent a class of antifungals that trigger cell wall damage by affecting synthesis of beta-glucans, filamentous fungal response to these antifungals are fundamentally unknown. To obtain a better understanding of the dynamics of the CWIS response and its multiple effects, we have coupled dynamic transcriptome analysis with morphological studies of Aspergillus nidulans hyphae responding to micafungin. Our results reveal that expression of the master regulator of asexual development, BrlA, is induced by micafungin exposure. Further study showed that micafungin elicits microcycle conidiation in a BrlA-dependent manner, and that this response is abolished in the absence of MpkA. Our results suggest that microcycle conidiation may be a general response to cell wall perturbation which in some cases would enable fungi to tolerate or survive otherwise lethal damage.

Fungal senescence induced by the Neurospora sen mutation and mitochondrial plasmids - the contributions of Ramesh Maheshwari

This article describes some of the research contributions made by Prof. Ramesh Maheshwari and his colleagues at the Indian Institute of Science, Bangalore. These include (1) the understanding of the Neurospora life cycle in agricultural (sugarcane) fields, (2) identification of Neurospora mutants that trigger vegetative spore development via microcycle conidiation, and (3) isolation of wild Neurospora strains in which the essential immortality of the fungal mycelia is subverted.

WetA Is Required for Conidiogenesis and Conidium Maturation in the Ascomycete Fungus Fusarium graminearum

ABSTRACTFusarium graminearum, a prominent fungal pathogen that infects major cereal crops, primarily utilizes asexual spores to spread disease. To understand the molecular mechanisms underlying conidiogenesis inF. graminearum, we functionally characterized theF. graminearumortholog ofAspergillus nidulanswetA, which has been shown to be involved in conidiogenesis and conidium maturation. Deletion ofF. graminearumwetAdid not alter mycelial growth, sexual development, or virulence, but thewetAdeletion mutants produced longer conidia with fewer septa, and the conidia were sensitive to acute stresses, such as oxidative stress and heat stress. Furthermore, the survival rate of aged conidia from theF. graminearumwetAdeletion mutants was reduced. ThewetAdeletion resulted in vigorous generation of single-celled conidia through autophagy-dependent microcycle conidiation, indicating that WetA functions to maintain conidial dormancy by suppressing microcycle conidiation inF. graminearum. Transcriptome analyses demonstrated that most of the putative conidiation-related genes are expressed constitutively and that only a few genes are specifically involved inF. graminearumconidiogenesis. The conserved and distinct roles identified for WetA inF. graminearumprovide new insights into the genetics of conidiation in filamentous fungi.