Free proline content and sensitivity to desiccation and heat during yeast sporulation and spore germination

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 ΔpepdA mutant. The defect of MC in ΔpepdA can be rescued when nonpolar amino acids, α-alanine, β-alanine or proline, were added into sucrose yeast extract agar (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 ΔpepdA 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.

A method for the selection of deletion mutations in the L-proline catabolism gene cluster of Aspergillus nidulans

Interest in the selection of mutations affecting L-proline catabolism inAspergillus nidulansis heightened by the involvement of one of the very few examples of a cluster of functionally related genes in an eukaryote and by an increasing awareness of the biological phenomena in which proline and proline catabolism participate. ThesasA-60 (semialdehyde sensitive) mutation inA. nidulansresults in toxicity of catabolic precursors of L-glutamic γ-semialdehyde (or its internal Schiff base L-Δ1-pyrroline-5-carboxylate) and succinic semialdehyde, apparently without affecting the catabolic pathways concerned. AssasA-60 is unlinked to theprngene cluster, specifying the gene products necessary for L-proline catabolism and as L-proline, a precursor of L-glutamic γ-semialdehyde, is highly toxic tosasA-60 strains, this forms the basis of a powerful positive selection technique for obtaining a number of types ofprnmutations. Many of theseprnmutations can be directly classified according to the gene product(s) affected on the basis of growth phenotype with respect to L-arginine and L-ornithine utilization, proline-dependent resistance to certain toxic amino acid analogues and effect on supplementation of proline auxotrophies. The availability of both a positive selection technique and an extensive nutritional screening system has enabled the identification of fourteen spontaneous deletion mutations, recognized as extending into theprnB gene, specifying the principal L-proline permease, and into at least one otherprngene. These deletion mutations have been partially characterized both genetically and biochemically. In particular their use has greatly facilitated fine-structure mapping of theprncluster and aided studies of the regulation ofprngene expression.