Abstract
Filamentous fungi frequently undergo bistable phenotypic switches. Crippled Growth of Podospora anserina is one such bistable switch, which seems to rely upon the mis-activation of a self-regulated PaMpk1 MAP kinase regulatory pathway. Here, we identify two new partners of this pathway: PaPro1, a transcription factor orthologous to Sordaria macrospora pro1 and Neurospora crassa ADV-1, and IDC4, a protein with an AIM24 domain. Both PaPro1 and IDC4 regulate stationary phase features, as described for the other actors of the PaMpk1 signaling pathway. However, PaPro1 is also involved in the control of fertilization by activating the transcription of the HMG8 and the mating type transcription factors, as well as the sexual pheromones and receptor genes. The roles of two components of the STRIPAK complex were also investigated by inactivating their encoding genes: PaPro22 and PaPro45. The mutants of these genes were found to have the same phenotypes as PaPro1 and IDC4 mutants as well as additional phenotypes including slow growth, abnormally shaped hyphae, pigment accumulation and blockage of the zygotic tissue development, indicating that the STRIPAK complex regulates, in addition to the PaMpk1 one, other pathways in P. anserina. Overall, the mutants of these four genes confirm the model by which Crippled Growth is due to the abnormal activation of the PaMpk1 MAP kinase cascade.
Highlights
Phenotypic switches visible as “sectors” in the thallus are of frequent occurrence in filamentous fungi [1]
To identify the genes affected in the three remaining IDC mutants, for whom no molecular data are yet available, we completely sequenced their genomes as described in the Materials and methods section
Through complete genome sequencing and targeted gene inactivation, we have identified two genes, PaPro1 and IDC4, involved in the development of crippled growth” (CG) and other important features of P. anserina life including differentiation of structures typical of stationary phase and sexual reproduction
Summary
Phenotypic switches visible as “sectors” in the thallus are of frequent occurrence in filamentous fungi [1]. Their etiology is often unknown, and sectors may originate from genetic or epigenetic modifications. When cultivated on minimal medium lacking YE (M2 medium), it grows profusely until it dies from senescence. On the contrary, when cultivated on M2 medium with YE (M2 + YE), it frequently presents sectors of the so called “crippled growth” (CG), characterized by slower growth rate, accumulation of pigment, lack of aerial hyphae and fruiting bodies. The reverse switch from CG to a normal growth (NG) can be obtained by stressing the cultures or by growing
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