Meiotic development initiation in the fungus Podospora anserina requires the peroxisome receptor export machinery.

Peroxisomes are versatile organelles essential for diverse developmental processes. One such process is the meiotic development of Podospora anserina. In this fungus, absence of the docking peroxin PEX13, the RING-finger complex peroxins, or the PTS2 co-receptor PEX20 blocks sexual development before meiocyte formation. However, this defect is not seen in the absence of the receptors PEX5 and PEX7, or of the docking peroxins PEX14 and PEX14/17. Here we describe the function of the remaining uncharacterized P. anserina peroxins predictably involved in peroxisome matrix protein import. We show that PEX8, as well as the peroxins potentially mediating receptor monoubiquitination (PEX4 and PEX22) and membrane dislocation (PEX1, PEX6 and PEX26) are indeed implicated in peroxisome matrix protein import in this fungus. However, we observed that elimination of PEX4 and PEX22 affects to different extent the import of distinct PEX5 cargoes, suggesting differential ubiquitination-complex requirements for the import of distinct proteins. In addition, we found that elimination of PEX1, PEX6 or PEX26 results in loss of peroxisomes, suggesting that these peroxins restrain peroxisome removal in specific physiological conditions. Finally, we demonstrate that all analyzed peroxins are required for meiocyte formation, and that PEX20 function in this process depends on its potential monoubiquitination target cysteine. Our results suggest that meiotic induction relies on a peroxisome import pathway, which is not dependent on PEX5 or PEX7 but that is driven by an additional cycling receptor. These findings uncover a collection of peroxins implicated in modulating peroxisome activity to facilitate a critical developmental cell fate decision.

Peroxisome dynamics during development of the fungus Podospora anserina.

Peroxisomes are versatile and dynamic organelles that are required for the development of diverse eukaryotic organisms. We demonstrated previously that in the fungus Podospora anserina different peroxisomal functions are required at distinct stages of sexual development, including the initiation and progression of meiocyte (ascus) development and the differentiation and germination of sexual spores (ascospores). Peroxisome assembly during these processes relies on the differential activity of the protein machinery that drives the import of proteins into the organelle, indicating a complex developmental regulation of peroxisome formation and activity. Here we demonstrate that peroxisome dynamics is also highly regulated during development. We show that peroxisomes in P. anserina are highly dynamic and respond to metabolic and environmental cues by undergoing changes in size, morphology and number. In addition, peroxisomes of vegetative and sexual cell types are structurally different. During sexual development peroxisome number increases at two stages: at early ascus differentiation and during ascospore formation. These processes are accompanied by changes in peroxisome structure and distribution, which include a cell-polarized concentration of peroxisomes at the beginning of ascus development, as well as a morphological transition from predominantly spherical to elongated shapes at the end of the first meiotic division. Further, the mostly tubular peroxisomes present from second meiotic division to early ascospore formation again become rounded during ascospore differentiation. Ultimately the number of peroxisomes dramatically decreases upon ascospore maturation. Our results reveal a precise regulation of peroxisome dynamics during sexual development and suggest that peroxisome constitution and function during development is defined by the coordinated regulation of the proteins that control peroxisome assembly and dynamics.

Distinct Contributions of the Peroxisome-Mitochondria Fission Machinery During Sexual Development of the Fungus Podospora anserina.

Mitochondria and peroxisomes are organelles whose activity is intimately associated and that play fundamental roles in development. In the model fungus Podospora anserina, peroxisomes and mitochondria are required for different stages of sexual development, and evidence indicates that their activity in this process is interrelated. Additionally, sexual development involves precise regulation of peroxisome assembly and dynamics. Peroxisomes and mitochondria share the proteins mediating their division. The dynamin-related protein Dnm1 (Drp1) along with its membrane receptors, like Fis1, drives this process. Here we demonstrate that peroxisome and mitochondrial fission in P. anserina depends on FIS1 and DNM1. We show that FIS1 and DNM1 elimination affects the dynamics of both organelles throughout sexual development in a developmental stage-dependent manner. Moreover, we discovered that the segregation of peroxisomes, but not mitochondria, is affected upon elimination of FIS1 or DNM1 during the division of somatic hyphae and at two central stages of sexual development-the differentiation of meiocytes (asci) and of meiotic-derived spores (ascospores). Furthermore, we found that FIS1 and DNM1 elimination results in delayed karyogamy and defective ascospore differentiation. Our findings reveal that sexual development relies on complex remodeling of peroxisomes and mitochondria, which is driven by their common fission machinery.