Plant Peroxisomes: Biogenesis and Function

Abstract

Peroxisomes are eukaryotic organelles that are highly dynamic both in morphology and metabolism. Plant peroxisomes are involved in numerous processes, including primary and secondary metabolism, development, and responses to abiotic and biotic stresses. Considerable progress has been made in the identification of factors involved in peroxisomal biogenesis, revealing mechanisms that are both shared with and diverged from non-plant systems. Furthermore, recent advances have begun to reveal an unexpectedly large plant peroxisomal proteome and have increased our understanding of metabolic pathways in peroxisomes. Coordination of the biosynthesis, import, biochemical activity, and degradation of peroxisomal proteins allows for highly dynamic responses of peroxisomal metabolism to meet the needs of a plant. Knowledge gained from plant peroxisomal research will be instrumental to fully understanding the organelle's dynamic behavior and defining peroxisomal metabolic networks, thus allowing the development of molecular strategies for rational engineering of plant metabolism, biomass production, stress tolerance, and pathogen defense.

Autophagy-Related Proteins Are Required for Degradation of Peroxisomes inArabidopsisHypocotyls during Seedling Growth

“…PEX4 is a ubiquitin-conjugating enzyme and PEX22 is a peroxisomal membrane protein that interacts with PEX4. Although the ubiquitylation targets of PEX4 have yet to be identified in Arabidopsis, PEX4 was proposed to be involved in PEX5 recycling and/or PexAD (Hu et al, 2012;). PEX14, presumed to form a docking point for PEX5, is another peroxisomal membrane protein that is important for the import of proteins containing a peroxisomal targeting signal Three possible mechanisms of peroxisomal degradation are shown in the model: degradation by resident proteases, PexAD, and autophagy.…”

“…The mechanism of degradation of obsolete peroxisomal proteins is not well understood in plant cells (reviewed by Hu et al, 2012). Matrix proteins like ICL and MLS may be degraded within peroxisomes, but the peroxisomal proteases responsible for their degradation are yet to be identified.…”

“…For example,~70 to 80% of peroxisomes in mouse liver appear to be degraded by autophagy, which was estimated from an analysis of Atg7 conditional knockout mice (Iwata et al, 2006). Whether pexophagy occurs in plant cells is not clear (Hu et al, 2012), despite evidence supporting it. First, electron microscopic observation suggested pexophagy in castor bean (Ricinus communis) endosperm (Vigil, 1970), although similar observations have not been reported.…”

Peroxisome Function, Biogenesis, and Dynamics in Plants

“…2). The Arabidopsis paralogs of yeast FISSION1 (Kemper et al, 2008), FIS1A and FIS1B, are tail-anchored membrane proteins acting in both mitochondrial and peroxisomal fission (for review, see Hu et al, 2012). Knocking down FIS1A and FIS1B decreases peroxisome numbers in protoplasts (Lingard et al, 2008), and insertional fis1a alleles display larger and fewer peroxisomes (Zhang and Hu, 2009) and mitochondria (Scott et al, 2006) than wild type.…”

“…The early acting peroxins PEX3, PEX16, and PEX19 ( Fig. 2) help insert peroxisomal membrane proteins (PMPs) directly into the peroxisomal membrane (group II PMPs) or into a peroxisomedestined region of the ER membrane (group I PMPs; for review, see Hu et al, 2012). PEX16 recruits the PEX3 membrane protein to the ER in mammals .…”