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

Abstract

Plant peroxisomes play a pivotal role during postgerminative growth by breaking down fatty acids to provide fixed carbons for seedlings before the onset of photosynthesis. The enzyme composition of peroxisomes changes during the transition of the seedling from a heterotrophic to an autotrophic state; however, the mechanisms for the degradation of obsolete peroxisomal proteins remain elusive. One candidate mechanism is autophagy, a bulk degradation pathway targeting cytoplasmic constituents to the lytic vacuole. We present evidence supporting the autophagy of peroxisomes in Arabidopsis thaliana hypocotyls during seedling growth. Mutants defective in autophagy appeared to accumulate excess peroxisomes in hypocotyl cells. When degradation in the vacuole was pharmacologically compromised, both autophagic bodies and peroxisomal markers were detected in the wild-type vacuole but not in that of the autophagy-incompetent mutants. On the basis of the genetic and cell biological data we obtained, we propose that autophagy is important for the maintenance of peroxisome number and cell remodeling in Arabidopsis hypocotyls.

The Endosomal Protein CHARGED MULTIVESICULAR BODY PROTEIN1 Regulates the Autophagic Turnover of Plastids in Arabidopsis

“…The following lines were used in this study: chmp1a/CHMP1A chmp1b/ chmp1b (Spitzer et al, 2009), ProUBQ10:GFP-ATG8a (Kim et al, 2013), CaMV35S:RecA-GFP (Köhler et al, 1997), ProPVD1:PDV1-GFP (Miyagishima et al, 2006); CaMV35S:MEX1-YFP (Niittylä et al, 2004), CaMV35S:CHUP1-GFP (Oikawa et al, 2008); atg5-1 and atg7-2 (Thompson et al, 2005;Chung et al, 2010), ProUBQ10:mCherry-ATG8a, and CaMV35S:YFP-ATG1a (Suttangkakul et al, 2011). Fluorescent protein expression cassettes were introgressed into CHMP1A/chmp1a chmp1b/chmp1b, atg5-1, and atg7-2 plants by crossing.…”

The life of the peroxisome: from birth to death

“…These results suggest that PexAD, mediated by LON2, and autophagy can function together to remove obsolete proteins. ICL and MLS stabilisation and increased peroxisome number was also seen in hypocotyls of atg7-2 and atg5-1 mutants [48]. Light-triggered ATG7-dependent pexophagy, and the blocking of vacuolar degradation allowed visualisation of bodies labelled with peroxisomal-targeted CFP within the vacuole in wild-type but not in the atg7-2 mutant [48].…”

“…ICL and MLS stabilisation and increased peroxisome number was also seen in hypocotyls of atg7-2 and atg5-1 mutants [48]. Light-triggered ATG7-dependent pexophagy, and the blocking of vacuolar degradation allowed visualisation of bodies labelled with peroxisomal-targeted CFP within the vacuole in wild-type but not in the atg7-2 mutant [48]. ATG8a which marks the pre-autophagosomal structure, partially overlapped with a peroxisomal marker.…”

“…This process has been shown to occur in plants (Figure 2) [45,46]. Very recently four studies [47][48][49][50] have shown selective autophagy of peroxisomes also occurs in plants and intriguingly LON2, a peroxisomal protease, plays a role in both pexophagy and PexAD [47,51].…”

Peroxisome Function, Biogenesis, and Dynamics in Plants

“…Arabidopsis pexophagy was recently demonstrated (Farmer et al, 2013;Kim et al, 2013;Shibata et al, 2013). During seedling development, peroxisome functions shift from fatty acid utilization to photorespiration (Titus and Becker, 1985;Nishimura et al, 1986;Sautter, 1986;.…”