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The integral peroxisomal membrane proteins PEX1O, PEX2, and PEX12 contain a zinc RING finger close to the C terminus. Loss of function of these peroxins causes embry lethality at the heart stage in Arabidopsis. Preventing the coordination of Zn2 ions by amino acid substitutions in PEX1O, PEX2, and PEX12 and over- expressing the resulting conditional sublethal mutations in WT uncovered additional functions of PEX1O. Plants overexpressing Zn-mutant PEX1O display deformed peroxisomal shapes causing diminished contact with chloroplasts and possibly with mitochon- dna. These changes correlated with impaired metabolite transfer and, at high CO2. recoverable defective photorespiration plus dwarf- ish phenotype. The N-terminal PEX1O domain is critical for peroxi- some biogenesis and plant development. A point mutation in the highly conserved TLGEEY motif results in vermiform peroxisome shape without impairing organelle contact. Addition of an N-termi- nal T7 tag to WI PEXO resulted in partially recoverable reduced growth and defective inflorescences persisting under high CO2. In contrast, plants overexpressing PEX2-Zn-T7 grow like WI in normal atmosphere, contain normal-shaped peroxisomes, but display im- paired peroxisomal matrix protein import. PEX12-Zn-T7 mutants exhibit unimpaired import of matrix protein and normal- shaped peroxisomes when grown in normal atmosphere. During seed germination, glyoxysomes form a reticulum around the lipid bodies for mobilization of storage oil. The formation of this glyoxy somal reticulum seemed to be impaired in PEX1O-tZn but not in PEX2-Zn-T7 or PEX12-Zn-fl plants. Both cytosolic PEX1O domains seem essential for peroxisome structure but differ in metabolic function, suggesting a role for this plant peroxin in addition to the import of matrix protein via ubiquitination of PEX5. [ABSTRACT FROM AUTHOR]

Plant peroxisomes perform multiple vital metabolic processes including lipid mobilization in oil-storing seeds, photorespiration, and hormone biosynthesis. Peroxisome biogenesis requires the function of peroxin (PEX) proteins, including PEX10, a C3HC4 Zn RING finger peroxisomal membrane protein. Loss of function of PEX10 causes embryo lethality at the heart stage. We investigated the function of PEX10 with conditional sublethal mutants. Four T-DNA insertion lines expressing pex10 with a dysfunctional RING finger were created in an Arabidopsis WI background (ΔZn plants). They could be normalized by growth in an atmosphere of high CO2 partial pressure, indicating a defect in photorespiration. β-Oxidation in mutant glyoxysomes was not affected. However, an abnormal accumulation of the photorespiratory metabolite glyoxylate. a lowered content of carotenoids and chlorophyll a and b, and a decreased quantum yield of photosystem II were detected under normal atmosphere, suggesting impaired leaf peroxisomes. Light and transmission electron microscopy demonstrated leaf peroxisomes of the ΔZn plants to be more numerous, multilobed, clustered, and not appressed to the chloroplast envelope as in WT. We suggest that inactivation of the RING finger domain in PEX10 has eliminated protein interaction required for attachment of peroxisomes to chloroplasts and movement of metabolites between peroxisomes and chloroplasts. [ABSTRACT FROM AUTHOR]