Arabidopsis LON2 Is Necessary for Peroxisomal Function and Sustained Matrix Protein Import

Publication Type:Journal Article
Year of Publication:2009
Authors:Lingard, MJ, Bartel, B
Journal:Plant Physiology
Date Published:2009
ISBN Number:00320889

Relatively little is known about the small subset of peroxisomal proteins with predicted protease activity. Here, we report that the peroxisomal LON2 (At5g47040) protease facilitates matrix protein import into Arabidopsis (Arabidopsis thaliana) peroxisomes. We identified T-DNA insertion alíeles disrupted in five of the nine confirmed or predicted peroxisomal proteases and found only two—Ion2 and deg15, a mutant defective in the previously described PTS2-processing protease(DEG15/At1g28320)—with phenotypes suggestive of peroxisome metabolism defects. Both Ioni and degl5 mutants were mildly resistant to the inhibitory effects of indole-3-butyric acid (IBA) on root elongation, but only lon2 mutants were resistant to the stimulatory effects of IBA on lateral root production or displayed Sue dependence during seedling growth. lon2 mutants displayed defects in removing the type 2 peroxisome targeting signal (PTS2) from peroxisomal malate dehydrogenase and reduced accumulation of 3-ketoacyl-CoA thiolase, another PTS2-containing protein; both defects were not apparent upon germination but appeared in 5- to 8-d-old seedlings. In lon2 cotyledon cells, matrix proteins were localized to peroxisomes in 4-d-old seedlings but mislocalized to the cytosol in 8-d-old seedlings. Moreover, a PTS2-GFP reporter sorted to peroxisomes in lon2 root tip cells but was largely cytosolic in more mature root cells. Our results indicate that LON2 is needed for sustained matrix protein import into peroxisomes. The delayed onset of matrix protein sorting defects may account for the relatively weak Sue dependence following germination, moderate IBA-resistant primary root elongation, and severe defects in IBAinduced lateral root formation observed in lon2 mutants.

Short Title:Plant Physiology
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Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith