A viable Arabidopsis pex13 missense allele confers severe peroxisomal defects and decreases PEX5 association with peroxisomes

Abstract

Peroxisomes are organelles that catabolize fatty acids and compartmentalize other oxidative metabolic processes in eukaryotes. Using a forward-genetic screen designed to recover severe peroxisome-defective mutants, we isolated a viable allele of the peroxisome biogenesis gene PEX13 with striking peroxisomal defects. The pex13-4 mutant requires an exogenous source of fixed carbon for pre-photosynthetic development and is resistant to the protoauxin indole-3-butyric acid. Delivery of peroxisome-targeted matrix proteins depends on the PEX5 receptor docking with PEX13 at the peroxisomal membrane, and we found severely reduced import of matrix proteins and less organelle-associated PEX5 in pex13-4 seedlings. Moreover, pex13-4 physiological and molecular defects were partially ameliorated when PEX5 was overexpressed, suggesting that PEX5 docking is partially compromised in this mutant and can be improved by increasing PEX5 levels. Because previously described Arabidopsis pex13 alleles either are lethal or confer only subtle defects, the pex13-4 mutant provides valuable insight into plant peroxisome receptor docking and matrix protein import.

E3 ubiquitin ligase SP1 regulates peroxisome biogenesis in Arabidopsis

“…Moreover, maintaining the balance between cargo translocation into the peroxisome/receptor docking and receptor recycling back to the cytosol appears to be important for the functional integrity of peroxisomes in plants. For example, as is consistent with both PEX13 and PEX14 being involved in receptor docking at the peroxisome membrane, the peroxisomal defects of pex14-2 are enhanced by pex13-1, a weak allele with mildly reduced PEX13 mRNA levels (17,18,34). However, the same pex13-1 allele partially suppressed the peroxisomal phenotypes of the late-acting peroxin mutant pex4-1, which is deficient in the translocation of PEX5 out of the peroxisome.…”

“…PEX13 and PEX14 mediate receptor docking and cargo translocation, which are early steps of peroxisome protein import (3,17,18,34). To determine whether SP1 also impacts peroxins that act in other steps of matrix protein import, we generated additional double mutants, namely sp1 pex5-10 and sp1 lon2-2.…”

“…In Arabidopsis, PEX5 is also required for PTS2 protein import (16). Two membrane proteins, PEX13 and PEX14, form the docking site for PEX5 and PEX7 (17,18). After receptor docking, cargo proteins translocate into the matrix before receptors are recycled to the cytosol (19)(20)(21).…”

Defects in Peroxisomal 6-Phosphogluconate Dehydrogenase Isoform PGD2 Prevent Gametophytic Interaction in Arabidopsis thaliana

“…S10) plus lack pollen tube arrest/discharge. AMC/Pex13p is a membrane protein that forms part of the docking complex linked to transient peroxisome import pores in yeast and Arabidopsis (Meinecke et al, 2010;Woodward et al, 2014) and interacts with PTS1 receptor Pex5p in the cytosol. Pex5p was shown to be needed mainly for the import of soluble proteins with C-terminal PTS1 signal but in Arabidopsis also for those with N-terminal PTS2 signal due to interaction with the PTS2 receptor Pex7p (for review, see LanyonHogg et al, 2010).…”

Peroxisome Function, Biogenesis, and Dynamics in Plants

“…However, Arabidopsis pex14 null alleles are viable (Monroe-Augustus et al, 2011), whereas pex13 null alleles confer lethality (Boisson-Dernier et al, 2008), hinting that some yeast PEX14 roles might be provided by PEX13 in plants. PEX13 dysfunction results in expected physiological defects; a pex13 RNAi line and two missense pex13 mutants, aberrant peroxisome morphology 2 (apm2) and pex13-4, display b-oxidation and matrix protein import defects (Mano et al, 2006;Nito et al, 2007;Woodward et al, 2014). Moreover, the pex13-4 mutation lowers PEX5 membrane association, and PEX5 overexpression ameliorates a subset of pex13-4 defects (Woodward et al, 2014), implying that the pex13-4 matrix protein import defects are due to impaired PEX5 docking.…”