1. ENDOPLASMIC RETICULUM

2. INTRODUCTION ER is found in Eukaryotes.
In plant cells, ER occurs as - system of membrane tubules and sheets (cisternae) -distributed throughout the cytoplasm
Two different types, ER
Smooth ER Rough ER
Mostly tubules Cisternae, sheets
Seen as a continuous network with nuclear envelope.
Connected with the Golgi bodies.

5. ROLES cytoplasm RER RER SER Metabolic processes Protein synthesis
. Lipids
- Steroids
- Phospholipids
Metabolizes the carbohydrate
Detoxifying the drugs
Protein synthesis
Post transitional modification of proteins
PROTEINS
cytoplasm RER
both has ribosomes
end up in nucleus secreted into CM,
mitochondria, integrated in peroxisomes, cytoplasm, ER,
Stay back golgi bodies,
lysosomes.

7. ER Dynamics and Mobility
ER tubular extension
Sliding dynamics(SD)
Tip Attachment Complex(TAC)
SD : By sliding of ER tubules along the microtubule (MT) cytoskeleton
More predominant and faster.
TAC : Physical interaction b/w ER Resident protein (STI M1)
And
MT plus end binding protein (EB1)
STI M1 has the MT binding domain ( STI M ER tubule movement)
ER-MT connections for ER remodeling.
Rab 10- ER specific Rab GTPase – ER tubule extension along MT.
used as a marker to find the new ER tubule growth.

9. Shaping ER tubules Reticulon (RTN) and DP1/Yop1p family members (RHD3)
closely spaced TMD’s (Trans-membrane Domains)
RTN and DP1/Yop1p are required for
Shaping of tubules (network formation)
Tubule formation in cos-7 cells
Responsible for curved edges of ER sheets and nuclear pores
Overexpressed
Induces constrictions results so from cisternae to tubules
highly curvature membrane

10. Three way junctions
The ER network of COS-7 cells is labeled with mCherry-KDEL (red) and the junctions are labeled with Lnp1-GFP (green).

11. GTPase is the mediator for the formation of the network junctions.
Three way junction:
GTPase is the mediator for the formation of the network junctions.
Sey 1p (yeast) and RHD 3 (Arabidopsis)
plant homologue of atlastin
Lnp1p (protein of lunapark family) – localises the ER network in yeast and mammalian cells.
binds to
Reticulon / Yop1p ER tubule junctions (stabilizes)
ER movement in plants  Actin – Myosin dependent
XI-K
XI-1, XI-2

12. a) b) ER PM
APC
actin ER
myosin
Tubule c) d)
Fusion complex
Cisternae
a) Tubule growth or retraction
b) Anchor points
c) Tubule fusion and three way junction formation
d) Tabulation versus cisternalisation (due to displacement of RTN’s)
APC- Anchor Point Complex
Fusion/tethering complex – RHD3

13. Vesicle formation COP I and COP II – Vesicle coat protein occurs @ TER
ER proteins –(COP II) Golgi Apparatus
*TER– Transitional ER
ERGIC- ER Golgi Intermediate complex
TGN- Trans Golgi Network

14. Cortical MT associated ER sites
Cortical ER network and its nearby MT’s intersect with each other.
signal transduction , movement of molecules
* ER membranes -- supported by Actin network – Myosin motors
This interaction is CMER’S (anchoring points)
pausing them
organelles meet, exchange of components CM PM a) ER MT MT
Cortical ER networks are continuous between adjacent cells and through plasmodesmata and are alligned with actin filaments.
(a) Proximity of cortical endoplasmic reticulum (ER), microtubules (MT) and plasma membrane (PM) beneath the cell wall
(CW). (b) Surface view of the cortical ER and adjacent MTs. C-MERs are highlighted in red. b)

15. Many plant viruses exploit C-MER’S for replication and PD targeting
Myosin
Actin
Golgi C ER MT
Kinesin
The ER membranes are associated with actin filaments that drive organelle movements along the membrane (e.g. Golgi; or other compartment carrying cargo (C)) with support of myosin motor proteins. Organelles may carry MT-associated proteins (e.g. kinesin) that cause pausing at C-MERs through binding to the MTs.
Many plant viruses exploit C-MER’S for replication and PD targeting

16. Summary Network of membranes Smooth and Rough ER
Roles – metabolizes , protein synthesis, post transitional modification
Tubule extension by sliding dynamics or TAC
Reticulons and Dp1/YOP 1p involved for shaping of ER
Three was junctions or network formations
COP II protein involved for vesicle formation
Cortical MT associated ER sites

17. References
Pen E J , Heinlein M: Cortical microtubule-associated ER sites: organization centers of cell polarity and communication. Curr Opin Cell Biol 2013, 16:1–10.
Sparkes I, Hawes C, Frigerio L: FrontiERs: Movers and shapers of the higher plant cortical endoplasmic reticulum. Curr Opin Cell Biol 2011, 14:658–665.
Chen S, Novick P, Novick S F: ER structure and function. Curr Opin Cell Biol 2013, 25:1–6.
Thank you