The peroxisome protein translocation machinery is developmentally regulated in the fungus Podospora anserina

Abstract

ABSTRACT Peroxisomes are versatile organelles that are essential for diverse developmental processes. Peroxisome function critically depends on its matrix proteins, which are imported from the cytosol by the receptors Pex5 and Pex7. These receptors cycle into and out of peroxisomes through two membrane protein channels. Cargo-loaded Pex5 is imported into peroxisomes through the docking/translocation machinery, which is composed of Pex13 and Pex14. After cargo delivery, Pex5 is exported through the peroxisome ubiquitin ligase complex. This complex also ubiquitinates the receptors dictating their membrane extraction by the peroxisome AAA ATPase complex. In the fungus Podospora anserina, peroxisomes are required for meiotic induction. This process relies on PEX13 but not on PEX14. In addition, PEX14 is partially dispensable for peroxisome protein import during meiotic development, suggesting a developmental regulation of the translocation machinery. Here we show that PEX13 abundance in hyphae is maintained at low levels by the activity of the peroxisome ubiquitin ligase complex and the ubiquitin-conjugating enzyme PEX4, in conjunction with PEX14, PEX5, and with the peroxin that bridges the ubiquitination and the docking/translocation machineries, PEX8. Moreover, we found that the AAA ATPase complex and the peroxins that drive peroxisome membrane formation—PEX3 and PEX19—are also required to restrain PEX13 levels and that in their absence PEX13 associates with mitochondria. Furthermore, we found that PEX13 levels are higher throughout sexual development, where they are further increased during meiocyte and meiotic-spore differentiation. Our findings show that the peroxisome protein translocation machinery is subject to complex developmental regulation, which finely modulates PEX13 along sexual development. IMPORTANCE Sexual reproduction allows eukaryotic organisms to produce genetically diverse progeny. This process relies on meiosis, a reductional division that enables ploidy maintenance and genetic recombination. Meiotic differentiation also involves the renewal of cell functioning to promote offspring rejuvenation. Research in the model fungus Podospora anserina has shown that this process involves a complex regulation of the function and dynamics of different organelles, including peroxisomes. These organelles are critical for meiosis induction and play further significant roles in meiotic development. Here we show that PEX13—a key constituent of the protein conduit through which the proteins defining peroxisome function reach into the organelle—is subject to a developmental regulation that almost certainly involves its selective ubiquitination-dependent removal and that modulates its abundance throughout meiotic development and at different sexual differentiation processes. Our results show that meiotic development involves a complex developmental regulation of the peroxisome protein translocation system.

Keywords

• peroxisomes
• meiosis
• sexual development
• organelle protein import
• filamentous fungi
• Podospora