AthPEX10, a nuclear gene essential for peroxisome and storage organelle formation during Arabidopsis embryogenesis

Abstract

In yeasts and mammals, PEX10 encodes an integral membrane protein with a C3HC4 RING finger motif in its C-terminal domain and is required for peroxisome biogenesis and matrix protein import. In humans, its dysfunction in peroxisome biogenesis leads to severe Zellweger Syndrome and infantile Refsum disease. Here we show that dysfunction of a homologous gene in Arabidopsis leads to lethality at the heart stage of embryogenesis, impairing the biogenesis of peroxisomes, lipid bodies, and protein bodies. In a T-DNA insertion mutant disrupting the fourth exon of the Ath-PEX10 gene, ultrastructural analyses fail to detect peroxisomes characteristic for wild-type embryogenesis. Storage triacyl glycerides are not assembled into lipid bodies (oil bodies; oleosomes) surrounded by the phospholipid-protein monolayer membrane. Instead, the dysfunctional monolayer membranes, which derive from the bilayer membrane of the endoplasmic reticulum, accumulate in the cytosol. Concomitantly the transfer of the storage proteins from their site of synthesis at the endoplasmic reticulum to the vacuoles is disturbed. The mutant can be rescued by transformation with wild-type AthPEX10 cDNA. Transformants of wild-type Hansenula polymorpha cells with the AthPEX10 cDNA did produce the encoded protein without targeting it to peroxisomes. Additionally, the cDNA could not complement a Hansenula pex10 mutant unable to form peroxisomes. The ultrastructural knockout phenotype of AthPEX10p suggests that this protein in Arabidopsis is essential for peroxisome, oleosome, and protein transport vesicle formation.

Different functions of the C 3 HC 4 zinc RING finger peroxins PEX10, PEX2, and PEX12 in peroxisome formation and matrix protein import

“…S2A). Overexpression of the PEX10-WT-T7 cDNA in the pex10-KO mutant rescued the embryo-lethal phenotype, as did PEX10-WT cDNA (10). Rescued plants at flowering stage had a dwarfish phenotype in normal air that was rescued only slightly at high CO 2 ; they had shorter internodes, a nodding inflorescence, and smaller siliques than WT (Fig.…”

“…PEX10 and PEX12 can interact with PEX5 in mammals (14,15). Impairment of PEX5 ubiquitination and thus of receptor recycling should lead to impaired peroxisomal matrix protein import.In Arabidopsis, the lack of any of the RING finger peroxins results in embryo lethality (10,(16)(17)(18). We started to elucidate the function of these peroxins using conditional sublethal mutants of PEX10.…”

“…PEX12 binds only one Zn 2+ ion through its incomplete C5 RING that lacks three of the eight metal ligands (8). The TLGEEY motif (amino acids 91-96) and a highly conserved P motif (amino acid 126) in the N-terminal part of PEX10 are typical of the PEX10 subfamily of zinc-binding proteins (9,10).…”

“…In Arabidopsis, the lack of any of the RING finger peroxins results in embryo lethality (10,(16)(17)(18). We started to elucidate the function of these peroxins using conditional sublethal mutants of PEX10.…”

Peroxisome Function, Biogenesis, and Dynamics in Plants

“…The Arabidopsis PEX2, PEX10, and PEX12 RING peroxins all display in vitro ubiquitin-protein ligase activity and are essential for embryogenesis (Hu et al, 2002;Schumann et al, 2003;Sparkes et al, 2003;Fan et al, 2005;Prestele et al, 2010). Expressing truncated RING peroxins without the C-terminal catalytic zincbinding RING domains (DZn) in wild type confers dominant-negative matrix protein import defects for PEX2-DZn and photorespiration defects attributed to decreased peroxisome-chloroplast interactions for PEX10-DZn (Prestele et al, 2010).…”