TheArabidopsisPeroxisomal Targeting Signal Type 2 Receptor PEX7 Is Necessary for Peroxisome Function and Dependent on PEX5

Abstract

Plant peroxisomal proteins catalyze key metabolic reactions. Several peroxisome biogenesis PEROXIN (PEX) genes encode proteins acting in the import of targeted proteins necessary for these processes into the peroxisomal matrix. Most peroxisomal matrix proteins bear characterized Peroxisomal Targeting Signals (PTS1 or PTS2), which are bound by the receptors PEX5 or PEX7, respectively, for import into peroxisomes. Here we describe the isolation and characterization of an Arabidopsis peroxin mutant, pex7-1, which displays peroxisome-defective phenotypes including reduced PTS2 protein import. We also demonstrate that the pex5-1 PTS1 receptor mutant, which contains a lesion in a domain conserved among PEX7-binding proteins from various organisms, is defective not in PTS1 protein import, but rather in PTS2 protein import. Combining these mutations in a pex7-1 pex5-1 double mutant abolishes detectable PTS2 protein import and yields seedlings that are entirely sucrose-dependent for establishment, suggesting a severe block in peroxisomal fatty acid beta-oxidation. Adult pex7-1 pex5-1 plants have reduced stature and bear abnormally shaped seeds, few of which are viable. The pex7-1 pex5-1 seedlings that germinate have dramatically fewer lateral roots and often display fused cotyledons, phenotypes associated with reduced auxin response. Thus PTS2-directed peroxisomal import is necessary for normal embryonic development, seedling establishment, and vegetative growth.

Getting a camel through the eye of a needle: the import of folded proteins by peroxisomes

“…Mis-sense mutation of a universally conserved serine residue in the centre of the common sequence was shown to disrupt Pex7p binding in all species (Matsumura et al, 2000;Einwachter et al, 2001). In A. thaliana, the pex5-1 mis-sense mutant of this same serine residue is competent for PTS1 import, but deficient in PTS2 import (Woodward and Bartel, 2005). This suggests the conserved sequence forms a binding site for cargo-loaded Pex7p.…”

“…The auxiliary protein(s) for Pex7p-mediated import varies depending on the species (Figure 3): Pex18p and Pex21p in S. cerevisiae (Purdue et al, 1998); Pex20p in Hansenula polymorpha (Otzen et al, 2005), Neurospora crassa (Sichting et al, 2003), Pichia pastoris (Leon et al, 2006b) and Yarrowia lipolytica (Einwachter et al, 2001); and PEX5 in plants (Hayashi et al, 2005;Woodward and Bartel, 2005) and mammals. In mammals, only the PEX5L isoform can interact with PEX7 , and it is essential for PTS2 import (Matsumura et al, 2000).…”

Peroxisome Function, Biogenesis, and Dynamics in Plants

“…PTS1 proteins are recognized by PEX5 (van der Leij et al, 1993;Zolman et al, 2000), and PTS2 proteins are recognized by PEX7 ( Fig. 3; Marzioch et al, 1994;Braverman et al, 1997;Woodward and Bartel, 2005). Yeast PEX7 contains six WD40 domains forming a seven-bladed propeller that binds the PTS2 peptide on one face of PEX7 (Pan et al, 2013).…”

“…As in mammals (Braverman et al, 1998;Otera et al, 1998), PEX7-PEX5 interactions allow PTS2 protein delivery in plants (Hayashi et al, 2005;Woodward and Bartel, 2005). In humans, alternative splicing produces two PEX5 forms: a short form competent for PTS1 import and a long form facilitating both PTS1 and PTS2 import (Dodt et al, 1995;Braverman et al, 1998).…”

“…Expressing an N-terminal PEX5 domain in pex5-10 restores PTS2 processing, showing that the PEX5 N-terminal domain promotes PEX7 function in vivo (Khan and Zolman, 2010). Moreover, a special Arabidopsis pex5-1 (S318L) missense mutation confers inefficient b-oxidation and PTS2 import but normal PTS1 import (Zolman et al, 2000;Woodward and Bartel, 2005).…”