Mutants defective in the peroxisome-tethered ATPase complex implicated peroxins in oil body utilization during Arabidopsis seedling development
Gonzalez, Kim Lani
Doctor of Philosophy
Catabolism of fatty acids stored in oil bodies is essential for Arabidopsis seed germination and seedling development. In plants, this β-oxidation occurs exclusively in peroxisomes, conserved organelles that are delimited by a single lipid bilayer. Enzyme import into peroxisomes is facilitated by peroxin proteins including PEX5, a receptor that delivers peroxisomal matrix proteins to the organelle. After cargo delivery, PEX5 is removed from the peroxisomal membrane by the interacting PEX1 and PEX6 ATPases, which are tethered to the peroxisome by the tail-anchored membrane protein PEX26. Arabidopsis pex6 and pex26 mutants were recovered from a screen for seedlings with inefficient β-oxidation. These mutants displayed reduced PEX5 levels and disparate defects in growth, metabolism, and protein import into peroxisomes. Peroxisomes were clustered around persisting oil bodies in pex6 and pex26 seedlings. Moreover, pex6, pex26, and a subset of other peroxin mutant seedlings retained oleosin, a membrane protein embedded in oil bodies that is degraded shortly after germination in wild-type seedlings. Screening for second-site mutations that suppressed pex6-1 growth defects revealed a pex1 missense allele (pex1-1). This genetic suppressor restored growth and oil body consumption in pex6 mutants while worsening the defects of a pex26 mutant. pex1-1 also slightly improved the rate of oleosin degradation in pex6-1. The disparate phenotypes of these mutants suggest novel functions of the peroxisome-tethered ATPase complex beyond PEX5 recycling, including a possible role in oil body utilization.