TRANSFER OF PROTEINS FROM THE CHLOROPLAST TO VACUOLES IN <i>CHLAMYDOMONAS REINHARDTII</i> (CHLOROPHYTA): A PATHWAY FOR DEGRADATION

Park, Hyoungshin; Eggink, Laura L.; Roberson, Robert W.; Hoober, J. Kenneth

doi:10.1046/j.1529-8817.1999.3530528.x

Cited by 45 publications

(32 citation statements)

References 44 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…These globules secreted from the chloroplast were suggested to carry the photosynthetic components to the cytoplasm or the vacuoles to be degraded. Park et al (1999) reported a similar phenomenon, namely transfer of proteins from chloroplasts to vacuoles for degradation in Chlamydomonas reinhardtii. Leaf senescence in atapg9-1 may depend on these other degradative processes.…”

Section: Discussionmentioning

confidence: 76%

Leaf Senescence and Starvation-Induced Chlorosis Are Accelerated by the Disruption of an Arabidopsis Autophagy Gene

et al. 2002

View full text Add to dashboard Cite

Autophagy is an intracellular process for vacuolar bulk degradation of cytoplasmic components. The molecular machinery responsible for yeast and mammalian autophagy has recently begun to be elucidated at the cellular level, but the role that autophagy plays at the organismal level has yet to be determined. In this study, a genome-wide search revealed significant conservation between yeast and plant autophagy genes. Twenty-five plant genes that are homologous to 12 yeast genes essential for autophagy were discovered. We identified an Arabidopsis mutant carrying a T-DNA insertion within AtAPG9, which is the only ortholog of yeast Apg9 in Arabidopsis (atapg9-1). AtAPG9 is transcribed in every wild-type organ tested but not in the atapg9-1 mutant. Under nitrogen or carbon-starvation conditions, chlorosis was observed earlier in atapg9-1 cotyledons and rosette leaves compared with wild-type plants. Furthermore, atapg9-1 exhibited a reduction in seed set when nitrogen starved. Even under nutrient growth conditions, bolting and natural leaf senescence were accelerated in atapg9-1 plants. Senescence-associated genes SEN1 and YSL4 were up-regulated in atapg9-1 before induction of senescence, unlike in wild type. All of these phenotypes were complemented by the expression of wild-type AtAPG9 in atapg9-1 plants. These results imply that autophagy is required for maintenance of the cellular viability under nutrient-limited conditions and for efficient nutrient use as a whole plant.Protein degradation is an important process in almost every facet of plant physiology and development. In plants, three major degradation pathways have been described: the ubiquitin-dependent pathway and the chloroplast and the vacuolar degradation pathways (for review, see Vierstra, 1996). Among these pathways, vacuolar degradation is assumed to be involved in bulk protein degradation by virtue of the resident proteases in the vacuole. Two types of vacuoles have been described in plants: the storage vacuole and the lytic central vacuole (for review, see Marty, 1999). However, there may be additional vacuole types that await discovery. Protein storage vacuoles are often found in seed tissues and accumulate proteins that are mobilized and used as the main nutrient resource for germination. Most cells in vegetative tissues have a large central vacuole, containing a wide range of proteases in an acidic environment. Substrate proteins must be transported and sequestered into this vacuole for degradation.Autophagy, a ubiquitous eukaryotic process, is responsible for this sequestration. Two types of autophagy have been described, namely macroautophagy and microautophagy (for review, see Klionsky and Ohsumi, 1999). In yeast macroautophagy, a portion of the cytoplasm is first enclosed by a doublemembrane structure, the autophagosome. The outer membrane of the autophagosome then fuses to the vacuolar membrane, so that its inner membrane structure, the autophagic body, is delivered into the vacuolar lumen. The contents of the autophagic body are then digest...

show abstract

Section: Discussionmentioning

confidence: 76%

Leaf Senescence and Starvation-Induced Chlorosis Are Accelerated by the Disruption of an Arabidopsis Autophagy Gene

et al. 2002

View full text Add to dashboard Cite

show abstract

“…from contractile vacuoles via protrusion of the outer membrane of the plastid envelope (Park et al, 1999). However, the participation of autophagy in this degradative process has not been demonstrated.…”

Section: Discussionmentioning

confidence: 99%

Inhibition of Target of Rapamycin Signaling and Stress Activate Autophagy in Chlamydomonas reinhardtii

2010

View full text Add to dashboard Cite

Autophagy is a catabolic membrane-trafficking process whereby cells recycle cytosolic proteins and organelles under stress conditions or during development. This degradative process is mediated by autophagy-related (ATG) proteins that have been described in yeast, animals, and more recently in plants. In this study, we report the molecular characterization of autophagy in the unicellular green alga Chlamydomonas reinhardtii. We demonstrate that the ATG8 protein from Chlamydomonas (CrATG8) is functionally conserved and may be used as a molecular autophagy marker. Like yeast ATG8, CrATG8 is cleaved at the carboxyl-terminal conserved glycine and is associated with membranes in Chlamydomonas. Cell aging or different stresses such as nutrient limitation, oxidative stress, or the accumulation of misfolded proteins in the endoplasmic reticulum caused an increase in CrATG8 abundance as well as the detection of modified forms of this protein, both landmarks of autophagy activation. Furthermore, rapamycin-mediated inhibition of the Target of Rapamycin signaling pathway, a major regulator of autophagy in eukaryotes, results in identical effects on CrATG8 and a relocalization of this protein in Chlamydomonas cells similar to the one observed upon nutrient limitation. Thus, our findings indicate that Chlamydomonas cells may respond to stress conditions by inducing autophagy via Target of Rapamycin signaling modulation.

show abstract

“…A pathway for protein degradation through the extrusion of chloroplast proteins to the vacuoles was proposed for C. reinhardtii (White et al, 1996;Park et al, 1999). Major pulse-labeled polypeptides synthesized on chloroplast ribosomes were recovered in small granules in cytoplasmic vacuoles.…”

Section: Genes Regulated By Clpp1 Depletion But Not By Rapamycin Treamentioning

confidence: 99%

Conditional Depletion of the Chlamydomonas Chloroplast ClpP Protease Activates Nuclear Genes Involved in Autophagy and Plastid Protein Quality Control

et al. 2014

View full text Add to dashboard Cite

Plastid protein homeostasis is critical during chloroplast biogenesis and responses to changes in environmental conditions. Proteases and molecular chaperones involved in plastid protein quality control are encoded by the nucleus except for the catalytic subunit of ClpP, an evolutionarily conserved serine protease. Unlike its Escherichia coli ortholog, this chloroplast protease is essential for cell viability. To study its function, we used a recently developed system of repressible chloroplast gene expression in the alga Chlamydomonas reinhardtii. Using this repressible system, we have shown that a selective gradual depletion of ClpP leads to alteration of chloroplast morphology, causes formation of vesicles, and induces extensive cytoplasmic vacuolization that is reminiscent of autophagy. Analysis of the transcriptome and proteome during ClpP depletion revealed a set of proteins that are more abundant at the protein level, but not at the RNA level. These proteins may comprise some of the ClpP substrates. Moreover, the specific increase in accumulation, both at the RNA and protein level, of small heat shock proteins, chaperones, proteases, and proteins involved in thylakoid maintenance upon perturbation of plastid protein homeostasis suggests the existence of a chloroplast-to-nucleus signaling pathway involved in organelle quality control. We suggest that this represents a chloroplast unfolded protein response that is conceptually similar to that observed in the endoplasmic reticulum and in mitochondria.

show abstract

TRANSFER OF PROTEINS FROM THE CHLOROPLAST TO VACUOLES IN CHLAMYDOMONAS REINHARDTII (CHLOROPHYTA): A PATHWAY FOR DEGRADATION

Cited by 45 publications

References 44 publications

Leaf Senescence and Starvation-Induced Chlorosis Are Accelerated by the Disruption of an Arabidopsis Autophagy Gene

Leaf Senescence and Starvation-Induced Chlorosis Are Accelerated by the Disruption of an Arabidopsis Autophagy Gene

Inhibition of Target of Rapamycin Signaling and Stress Activate Autophagy in Chlamydomonas reinhardtii

Conditional Depletion of the Chlamydomonas Chloroplast ClpP Protease Activates Nuclear Genes Involved in Autophagy and Plastid Protein Quality Control

Contact Info

Product

Resources

About