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

Abstract

Endosomal Sorting Complex Required for Transport (ESCRT)-III proteins mediate membrane remodeling and the release of endosomal intraluminal vesicles into multivesicular bodies. Here, we show that the ESCRT-III subunit paralogs CHARGED MULTIVESICULAR BODY PROTEIN1 (CHMP1A) and CHMP1B are required for autophagic degradation of plastid proteins in Arabidopsis thaliana. Similar to autophagy mutants, chmp1a chmp1b (chmp1) plants hyperaccumulated plastid components, including proteins involved in plastid division. The autophagy machinery directed the release of bodies containing plastid material into the cytoplasm, whereas CHMP1A and B were required for delivery of these bodies to the vacuole. Autophagy was upregulated in chmp1 as indicated by an increase in vacuolar green fluorescent protein (GFP) cleavage from the autophagic reporter GFP-ATG8. However, autophagic degradation of the stromal cargo RECA-GFP was drastically reduced in the chmp1 plants upon starvation, suggesting that CHMP1 mediates the efficient delivery of autophagic plastid cargo to the vacuole. Consistent with the compromised degradation of plastid proteins, chmp1 plastids show severe morphological defects and aberrant division. We propose that CHMP1 plays a direct role in the autophagic turnover of plastid constituents.

ESCRT-III-Associated Protein ALIX Mediates High-Affinity Phosphate Transporter Trafficking to Maintain Phosphate Homeostasis in Arabidopsis

“…In most cases, complete loss of function of ESCRT components has deleterious effects in plants, leading to lethality at early developmental stages. In accord with their indispensability, plant ESCRT components have been shown to mediate essential processes, including cytokinesis and autophagy, besides their implication in MVB-mediated trafficking of protein cargoes (Spitzer et al, 2006(Spitzer et al, , 2015Gao et al, 2015). Known targets of the MVB route in plants include, among others, transmembrane auxin carriers PIN1, PIN2, and AUX1, iron transporter IRT1, boron transporter BOR1, flagellin receptor FLS2, brassinosteroid receptor BRI1, and members of the PHT1 family of high-affinity Pi transporters (Geldner et al, 2001(Geldner et al, , 2007Kleine-Vehn et al, 2006Spitzer et al, 2009;Barberon et al, 2011;Bayle et al, 2011;Kasai et al, 2011;Spallek et al, 2013).…”

TRAF Family Proteins Regulate Autophagy Dynamics by Modulating AUTOPHAGY PROTEIN6 Stability in Arabidopsis

“…To determine the effect of TRAF1a and TRAF1b deletion on autophagosome formation, plants from the stable eGFP-ATG8e line (Xiao et al, 2010) were crossed with the traf1a/1b-1 mutant to generate the eGFP-ATG8e/traf1a/1b-1 double combination. Seven-day-old eGFP-ATG8e/Col-0 and eGFP-ATG8e/ traf1a/1b-1 seedlings grown on MS medium were transferred to MS medium with or without sucrose and nitrogen containing 1 mM CA (Sigma-Aldrich) as described by Spitzer et al (2015). Primary root cells were observed under an LSM 780 NLO laser scanning confocal microscope (Carl Zeiss).…”

Autophagic Recycling Plays a Central Role in Maize Nitrogen Remobilization

“…In addition, direct connections between autophagy and the turnover of chloroplast and mitochondrial constituents was provided by the study of autophagy mutants during leaf senescence (Ishida et al, 2008;Wada et al, 2009;Izumi et al, 2010;Li et al, 2014). For chloroplast turnover in particular, a special type of autophagy has been proposed whereby Rubisco-containing bodies bud from stromule projections and are then delivered to vacuoles for breakdown (Ishida et al, 2008;Spitzer et al, 2015). Autophagic recycling is accomplished by the sequestration of cytoplasmic material into a double membrane-bound compartment called the autophagosome.…”