A Non-Mendelian MAPK-Generated Hereditary Unit Controlled by a Second MAPK Pathway inPodospora anserina

Abstract

The Podospora anserina PaMpk1 MAP kinase (MAPK) signaling pathway can generate a cytoplasmic and infectious element resembling prions. When present in the cells, this C element causes the crippled growth (CG) cell degeneration. CG results from the inappropriate autocatalytic activation of the PaMpk1 MAPK pathway during growth, whereas this cascade normally signals stationary phase. Little is known about the control of such prion-like hereditary units involved in regulatory inheritance. Here, we show that another MAPK pathway, PaMpk2, is crucial at every stage of the fungus life cycle, in particular those controlled by PaMpk1 during stationary phase, which includes the generation of C. Inactivation of the third P. anserina MAPK pathway, PaMpk3, has no effect on the development of the fungus. Mutants of MAPK, MAPK kinase, and MAPK kinase kinase of the PaMpk2 pathway are unable to present CG. This inability likely relies upon an incorrect activation of PaMpk1, although this MAPK is normally phosphorylated in the mutants. In PaMpk2 null mutants, hyphae are abnormal and PaMpk1 is mislocalized. Correspondingly, stationary phase differentiations controlled by PaMpk1 are defective in the mutants of the PaMpk2 cascade. Constitutive activation of the PaMpk2 pathway mimics in many ways its inactivation, including an effect on PaMpk1 localization. Analysis of double and triple mutants inactivated for two or all three MAPK genes undercover new growth and differentiation phenotypes, suggesting overlapping roles. Our data underscore the complex regulation of a prion-like element in a model organism.

Simple Genetic Tools to Study Fruiting Body Development in Fungi

“…Conversely, perithecia will arrest at a precise stage if the gene is required at this stage in the zygotic tissues. We have used this method to analyze the PaMpk1, PaMpk2, PaNox1, PaNoxR, IDC1 mutants [14,18,19] confirming and completing previous data: PaMpk1, PaMpk2 are required only in the mycelium, PaNox1 and PaNoxR only in the maternal tissues of the fruiting bodies and IDC1 both in the mycelium and in the maternal tissues. We have also analyzed the pah5 beak defect [8] and showed that it was indeed due to a problem in the maternal tissues, as expected since the beak is made from maternal cells and not zygotic ones.…”

“…Note that recovery of high numbers of mosaic perithecia would indicate a non-autonomous action of the mutated gene, i.e., only a fraction of the cells from the fruiting bodies being wild-type would be sufficient to promote normal development, possibly because the product of the wild-type gene would diffuse in the whole fruiting body. We have used this method to analyze mutants of the PaNox1, PaNoxR, PaMpk1, PaMpk2 and IDC1 genes [14,16,18,19]. The results confirmed and completed those of the grafting analysis: PaMpk1 and PaMpk2 are not required in the perithecium, but only in the mycelium; PaNox1 and PaNoxR are required only in the fruiting body and IDC1 is required in both the mycelium and the fruiting body.…”

“…In this way, we have studied the role of the genes IDC1 (coding a large protein of unknown function), PaMpk1 and PaMpk2 (both coding for MAP kinases), as well as PaNox1 (coding a catalytic subunit of a NADPH oxidase) and PaNoxR (coding a cytosolic regulator of PaNox1). All these mutants do not form any fruiting body, although they differentiate male and female gametes [11,14]. We also studied a mutant of PaAlr1, which codes for a magnesium transporter.…”

Plant biomass degrading ability of the coprophilic ascomycete fungus Podospora anserina

“…Genetic analysis has shown that the production of the P. anserina appressorium-like structures is under the control of signalling pathways, which include the PaMpk2/PaMKK2/PaTLK2 MAP kinase module, as well as the PaNox1 and PaNox2 NADPH oxidase enzymes and their regulatory subunits, PaNoxD/PaNoxR and PaPls1/PaNoxR, respectively (Brun et al, 2009;Lalucque et al, 2012;Lacaze et al, 2015). However, it does not depend on the PaMpk1 or PaMpk3 pathways or the PaNox3 NADPH oxidase (Brun et al, 2009;Lalucque et al, 2012).…”

“…However, it does not depend on the PaMpk1 or PaMpk3 pathways or the PaNox3 NADPH oxidase (Brun et al, 2009;Lalucque et al, 2012). The PaNox2 complex and the PaMpk2 MAP kinase are important for the initial reorientation phase, while the PaNox1 complex is involved in the generation of the needle-like hyphae.…”