The importomer peroxins are differentially required for peroxisome assembly and meiotic development in Podospora anserina: insights into a new peroxisome import pathway

Peroxisome biogenesis relies on two known peroxisome matrix protein import pathways that are mediated by the receptors PEX5 and PEX7. These pathways converge at the importomer, a peroxisome-membrane complex that is required for protein translocation into peroxisomes and consists of docking and RING-finger subcomplexes. In the fungus Podospora anserina, the RING-finger peroxins are crucial for meiocyte formation, while PEX5, PEX7 or the docking peroxin PEX14 are not. Here we show that PEX14 and the PEX14-related protein PEX14/17 are differentially involved in peroxisome import during development. PEX14/17 activity does not compensate for loss of PEX14 function, and elimination of both proteins has no effect on meiocyte differentiation. In contrast, the docking peroxin PEX13, and the peroxins implicated in peroxisome membrane biogenesis PEX3 and PEX19, are required for meiocyte formation. Remarkably, the PTS2 coreceptor PEX20 is also essential for meiocyte differentiation and this function does not require PEX5 or PEX7. This finding suggests that PEX20 can mediate the import receptor activity of specific peroxisome matrix proteins. Our results suggest a new pathway for peroxisome import, which relies on PEX20 as import receptor and which seems critically required for specific developmental processes, like meiocyte differentiation in P. anserina.