Abstract
Summary Peroxisomal biogenesis factor 11 (PEX11) proteins are found in yeasts, mammals and plants, and play a role in peroxisome morphology and regulation of peroxisome division. The moss Physcomitrella patens has six PEX11 isoforms which fall into two subfamilies, similar to those found in monocots and dicots.We carried out targeted gene disruption of the Phypa_PEX11‐1 gene and compared the morphological and cellular phenotypes of the wild‐type and mutant strains.The mutant grew more slowly and the development of gametophores was retarded. Mutant chloronemal filaments contained large cellular structures which excluded all other cellular organelles. Expression of fluorescent reporter proteins revealed that the mutant strain had greatly enlarged peroxisomes up to 10 μm in diameter. Expression of a vacuolar membrane marker confirmed that the enlarged structures were not vacuoles, or peroxisomes sequestered within vacuoles as a result of pexophagy. Phypa_PEX11 targeted to peroxisome membranes could rescue the knock out phenotype and interacted with Fission1 on the peroxisome membrane.Moss PEX11 functions in peroxisome division similar to PEX11 in other organisms but the mutant phenotype is more extreme and environmentally determined, making P. patens a powerful system in which to address mechanisms of peroxisome proliferation and division.
Highlights
Peroxisomes are organelles found in all eukaryotic cells from unicellular eukaryotes such as algae and baker’s yeast to complex multicellular organisms such as humans and flowering plants
A summary of gene identifiers in successive genome annotations is provided in Table S1, while Table 1 includes the gene and protein IDs according to the current V1.6 annotation
Mutation of the AtPEX11 genes results in aberrant peroxisome division, and the formation of larger peroxisomes (Lingard & Trelease, 2006; Orth et al, 2007), but these do not approach the size of those we observed in P. patens. To determine whether these unusual structures in the moss mutants might correspond to massively enlarged peroxisomes or were vacuolar compartments, we investigated the localization of vacuolar and peroxisomal reporters
Summary
Peroxisomes are organelles found in all eukaryotic cells from unicellular eukaryotes such as algae and baker’s yeast to complex multicellular organisms such as humans and flowering plants. Peroxisomes can be derived from the endoplasmic reticulum (ER) but can grow by post-translational import of membrane and matrix proteins, divide and segregate into daughter cells (Fagarasanu et al, 2007) the relative importance of de novo biogenesis versus organelle division remains hotly debated (Hettema et al, 2014) and it should be noted that in plants no direct evidence for ER luminal connections has been found (Barton et al, 2013). Peroxisomes are capable of proliferation under appropriate environmental conditions. Peroxisomes first tubulate or elongate, followed by constriction, often giving a ‘beads-on-a string’ appearance, and divide (Thoms & Erdmann, 2005; Kaur & Hu, 2009)
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