Organelle Ecology - The Chloroplasts

Question 1

Structure

Answer 1

1. Intro to chloroplasts
2. Chloroplast size
3. Chloroplast division
4. Stromules

Question 2

algal chloroplasts

Answer 2

1. cup-shaped
2. spiral
3. discoidal

Question 3

What is the implication of differently shaped algal chloroplasts?

Answer 3

CCMs: HCO3- pyrenoids

Question 4

higher plant chloroplasts

Answer 4

ovoid

Question 5

Leaf architectural trade-off

Answer 5

• air spaces: diffusion
• photosynthesising tissue: fixation

Question 6

Chloroplast localisation is important for

Answer 6

light and CO2 stimuli

Question 7

accumulation and replication of chloroplasts (arc) mutants

Answer 7

• different no, size
• lower SA-air space interaction
• less mesophyll conductance
• less assimilation

Question 8

What happens if chloroplasts are too large?

Answer 8

• limits mesophyll conductance

Question 9

Midpoint selection

Answer 9

1. MinD binds MinC; inhibits FtsZ
2. MinE forms ring; attacks MinD
3. MinD-ADP phosphorylation; reassociation at remote membrane; oscillation
4. ARC6 connects FtsZ contractile ring to IEM
5. PARC6, PDV1/2 link DRP ring to OEM + IEM
6. ARC5/DRP5B drive FtsZ constriction

Question 10

FtsZ

Answer 10

• filamentous temperature sensitive Z
• homologous to microtubules
• analogous to microfilaments

Question 11

ARC5/DRP5B

Answer 11

• dynamin-like GTPases
• allow self-assembly

Question 12

red algae

Answer 12

• MinD homolog not found

Question 13

stromules

Answer 13

• narrow, tubular
• stroma and envelope membrane
• can facilitate small molecules
• no DNA or ribosomes
• ensure plastid connectivity; network (WBE model)
• microtubules: necessary (nocadazole)

Question 14

AtLACS9oe

Answer 14

enhanced stromule formation

Question 15

LACS9

Answer 15

• long chain fatty acid CoA synthetase
• OEM

Question 16

ER

Answer 16

• surrounds chloroplasts as mesh
• stromules move along channels
• remodelling-competent
• ^SA
• bidirectional exchange of ions, lipids and metabolites at specific MCSs

Question 17

MCS

Answer 17

membrane contact site

Question 18

Describe lipid synthesis

Answer 18

1. fatty acid synthesis starts in stroma
2. lipid export -> ER
3. retrotranslocation

Question 19

Photorespiration

Answer 19

• stromules are closely associated with the peroxisomes

Question 20

Chloroplastic immunity

Answer 20

• nuclear connections via stromules
• ROS signalling

Question 21

SA

Answer 21

• pro-defence signal
• stromule induction

Question 22

ex1

Answer 22

• EXECUTER 1 mutant
• susceptible to PstDC3000

Question 23

EXECUTER 1

Answer 23

a chloroplastic, ROS sensing protein; initiates nuclear signalling cascade

Question 24

inter-organellar communication (Park et al., 2018)

Answer 24

“a general strategy for translating various stimuli into cellular acclimation responses by adjusting metabolism, to ensure optimal growth under specific conditions”

Question 25

Chloroplastic phototaxis

Answer 25

- strong (blue) light: move to anticlinal walls to reduce risk of photo damage - weak (blue) light: move to periclinal walls to increase light harvest - darkness: random!

Question 26

actin

Answer 26

- localised polymerisation may drive movement - foci @ leading edge of moving chloroplasts

Question 27

photoreceptors

Answer 27

- phototropin 1 and 2

Question 28

CHUP1

Answer 28

- Chloroplast Unusual Positioning 1 - required for movement

Question 29

Polymerisation model for chloroplast movement

Answer 29

1) Phot1/2 accumulate @ PM 2) CHUP1 initiates actin polymerisation 3) Thrumini1 anchors actin bundle to PM 4) chloroplast moves forward by continued actin polymerisation