Peroxisomes are small yet critical organelles that are present in nearly all eukaryotes. Peroxisomes house a broad range of metabolic and biochemical pathways that are vital for organismal development and metabolism. Unlike mitochondria and chloroplasts, which possess DNA transcription and protein translation machineries, almost all peroxisome matrix proteins are post–translationally targeted to peroxisomes after they are translated on free polyribosomes in the cytosol. Therefore, it is important to understand peroxisome protein import as well as degradation mechanisms. A number of proteins involved in peroxisome matrix protein import have been identified. However, our knowledge towards matrix protein degradation is still scarce. In this research, I explored the function of a newly identified component of the peroxisomal localized ubiquitin–proteasome system, i.e. ubiquitin–conjugating enzyme 22 (UBC22) in Arabidopsis. I provide evidence that AtUBC22 targets to peroxisomes through its C–terminal tri–peptide KRL>. Mutant analysis shows that UBC22 might act as a negative regulator of peroxisome IBA metabolism. UBC22 also has an effect on seed formation and seedling development. Homologous sequences of AtUBC22 that contain peroxisomal targeting signal type 1 are present in other plant species, indicating a plant–specific role of UBC22 in the peroxisome.
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