AUTOPHAGY

Parvinderdeep Singh Kahlon

PCDU Seminar

WS 2015/2016

https://goo.gl/gz5oJA 1

CONTENT

Introduction

Role of Autophagy

Types of Autophagic Processes

Summary

http://www.contentfirst.com/images/information_Istock.jpg

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INTRODUCTION

Autophagy, the process of cellular self-eating, is

an important protein degradation pathway,

particularly during starvation or stress.

It is as a bulk process which degrade long-lived

proteins and organelles such as the endoplasmic

reticulum, mitochondria, peroxisomes, the

nucleus and ribosomes [2,3]

In contrast to the ubiquitin–proteasome system (UPS),

which targets individual short-lived proteins

[1] http://pilotfire.com/wp-content/uploads/autophagy.png

[2] Mizushima, N. & Klionsky, D. J. 2007. Protein turnover via autophagy: implications for metabolism. Annu. Rev. Nutr. 27, 19–40.

[3] Stolz, A., Ernst, A. & Dikic, I. 2014. Cargo recognition and trafficking in selective autophagy. Nat. Cell Biol. 16, 495–501 .

[1]

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ROLE OF AUTOPHAGY

Autophagic degradation promotes the recycling

and salvage of cellular nutrients, thereby

enabling cell survival during starvation.

Along with the UPS, helps in protein homeostasis

and quality control.

It also plays a key part in mobilizing diverse

cellular energy and nutrient stores, including

carbohydrates, lipids and minerals.

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Kaur J and Debnath J. 2015. Autophagy at the crossroads of catabolism and anabolism. Nature Reviews : 16;461 472

TYPES

Autophagy refers to a collection of tightly

regulated catabolic processes, all of which deliver

cytoplasmic components to the lysosome for

degradation

In animals and yeasts, autophagy is often divided

into three main types:

Chaperone-mediated autophagy,

Microautophagy,

Macroautophagy.

5 http://www.nature.com/nrgastro/journal/v11/n3/images/nrgastro

.2013.211-f1.jpg

DETAILED PROCESS

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Kaur J and Debnath J. 2015. Autophagy at the crossroads of catabolism and anabolism. Nature Reviews : 16;461 472

CHAPERONE-MEDIATED

AUTOPHAGY

Target protein binds to a chaperone

protein.

The target protein then is transported

to a lysosome, becomes unfolded and is

taken up by direct translocation

across the lysosomal membrane.

It occurs only in mammalian cells but it cannot

be excluded that a similar mechanism occurs in

plants.

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Doorn WG and Papini A. 2013. Ultrastructure of autophagy in plant cells .Autophagy 9:12, 1–15

MICROAUTOPHAGY

It is the process of uptake of cellular constituents

by the lysosomal/vacuolar membrane.

The membrane surrounds a portion of the

cytoplasm, merges with itself, and then

undergoes scission.

This results in a portion of the cytoplasm,

surrounded by a piece of lysosomal/vacuolar

membrane, inside the lysosome/ vacuole.

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May AI, Devenish RJ, Prescott M. 2012 The many faces of mitochondrial autophagy: Making sense of contrasting observations

in recent research. Int J Cell Biol,1-18.

DIAGRAMMATIC OVERVIEW

9 Doorn WG and Papini A. 2013. Ultrastructure of autophagy in plant cells .Autophagy 9:12, 1–15

(A) Invagination (A1) or

protrusion (A2) of

the vacuolar membrane,

resulting in the uptake

of a portion of the

cytoplasm.

(B) Invagination

membrane-bound

vesicle in the cytoplasm

is taken up by the

vacuole

EXAMPLE OF MICROAUTOPHAGY

(A and B) Invaginations into the vacuole. (C)

Rubber particles in cytoplasm and vacuole

D) Senescing petals of carnation flowers

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Doorn WG and Papini A. 2013. Ultrastructure of autophagy in plant cells .Autophagy 9:12, 1–15

MACROAUTOPHAGY

Macroautophagy is performed in the cytoplasm,

whereby a portion of the cytoplasm is

sequestered inside a doublemembrane-bound

organelle.

Hydrolases take place, away from the vacuole.

The cytoplasmic material is broken down inside

this structure by small tubules formation or

membranes formation at the ER

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Bassham DC, Laporte M, Marty F, Moriyasu Y, Ohsumi Y, Olsen LJ, Yoshimoto K. 2006. Autophagy in development and

stress responses of plants. Autophagy 2:2-11.

DIAGRAMMATIC OVERVIEW

(A) small tubules are formed in

the cytoplasm (B) membranes

with an ER-like structure are

formed at theER

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Doorn WG and Papini A. 2013. Ultrastructure of autophagy in plant cells .Autophagy 9:12, 1–15

(A) Formation of a cage-

like structure (B–D)

Various stages of

autophagosome/

autolysosome formation

13 Doorn WG and Papini A. 2013. Ultrastructure of autophagy in plant cells .Autophagy 9:12, 1–15

EXAMPLE OF MACROAUTOPHAGY

PROGRAMMED CELL DEATH (PCD)

1. during normal development and after abiotic

stress (developmental PCD)

2. after invasion by a pathogen (pathogen-related

PCD).

Massive autophagy (called mega-autophagy) is

typical for the final phase of developmental PCD.

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• rupture of the vacuolar membrane

• release of large amounts of hydrolases into the cytoplasm.

• degrade the cytoplasm

• This results in cell death

Doorn WG and Papini A. 2013. Ultrastructure of autophagy in plant cells .Autophagy 9:12, 1–15

PCD AT TIME OF BACTERIAL INFECTION

In plants, (AtMC1) positively regulates HR cell death mediated by NB-LRR recognition of the invading pathogen at the site of infection.

LSD1 negatively regulates cell death propagation in cells surrounding the infection site presumably by binding to AtMC1 and holding it inactive in the cytoplasm..

Coll NS et al., 2011. Programmed cell death in

the plant immune system. Cell Death and

Differentiation18, 1247–1256.

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INTERNAL DEGENERATION OF

CHLOROPLASTS

Membrane bound vesicles with

degradation products are formed inside

the organelle.

These vesicles move into the cytoplasm

and are subsequently taken up by the

vacuole where they become degraded.

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Doorn WG and Papini A. 2013. Ultrastructure of autophagy in plant cells .Autophagy 9:12, 1–15

SCHEMATIC OVERVIEW

Proposed model of

the degradation

of Rubisco and

possibly other

stromal proteins

by ATG-

dependent

autophagy via

RCBs

Ishida H et al., 2008. Mobilization of Rubisco and Stroma-Localized Fluorescent Proteins

of Chloroplasts to the Vacuole by an ATG Gene-Dependent Autophagic Process.. Plant

Physiology, 148: 142-155

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SUMMARY

Autophagy, the process of cellular self-

eating

In yeast and mammals majorly divided

into three main types, plants have

addition types

recycling and salvage of cellular nutrients,

protein homeostasis, mobilizing diverse

cellular energy and nutrient stores

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Thank You 19

•Presently little is known

about the ultrastructure

of autophagy in plants

•Extensive research is yet

needed to know the

unknown