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Disparate peroxisome‐related defects in Arabidopsis pex6 and pex26 mutants link peroxisomal retrotranslocation and oil body utilization
Author(s) -
Gonzalez Kim L.,
Fleming Wendell A.,
Kao YunTing,
Wright Zachary J.,
Venkova Savina V.,
Ventura Meredith J.,
Bartel Bonnie
Publication year - 2017
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1111/tpj.13641
Subject(s) - peroxisome , biology , arabidopsis , microbiology and biotechnology , peroxisomal targeting signal , mutant , proteasome , biochemistry , organelle , gene
Summary Catabolism of fatty acids stored in oil bodies is essential for seed germination and seedling development in Arabidopsis. This fatty acid breakdown occurs in peroxisomes, organelles that sequester oxidative reactions. Import of peroxisomal enzymes is facilitated by peroxins including PEX 5, a receptor that delivers cargo proteins from the cytosol to the peroxisomal matrix. After cargo delivery, a complex of the PEX 1 and PEX 6 ATP ases and the PEX 26 tail‐anchored membrane protein removes ubiquitinated PEX 5 from the peroxisomal membrane. We identified Arabidopsis pex6 and pex26 mutants by screening for inefficient seedling β‐oxidation phenotypes. The mutants displayed distinct defects in growth, response to a peroxisomally metabolized auxin precursor, and peroxisomal protein import. The low PEX 5 levels in these mutants were increased by treatment with a proteasome inhibitor or by combining pex26 with peroxisome‐associated ubiquitination machinery mutants, suggesting that ubiquitinated PEX 5 is degraded by the proteasome when the function of PEX 6 or PEX 26 is reduced. Combining pex26 with mutations that increase PEX 5 levels either worsened or improved pex26 physiological and molecular defects, depending on the introduced lesion. Moreover, elevating PEX 5 levels via a 35S: PEX 5 transgene exacerbated pex26 defects and ameliorated the defects of only a subset of pex6 alleles, implying that decreased PEX 5 is not the sole molecular deficiency in these mutants. We found peroxisomes clustered around persisting oil bodies in pex6 and pex26 seedlings, suggesting a role for peroxisomal retrotranslocation machinery in oil body utilization. The disparate phenotypes of these pex alleles may reflect unanticipated functions of the peroxisomal ATP ase complex.