Improving Photosynthesis II

Question 1

What is a photorespiratory bypass?

Answer 1

Installing non-native genes into plants to avoid the export of glycolate from the chloroplast, avoiding carbon loss

Question 2

What is an example of a successful photorespiratory bypass?

Answer 2

2018
Transgenic tobacco
40% increase in yield

Question 3

What were the 3 constructs tobacco was transformed with while researching photorespiratory bypasses?

Answer 3

AP1:
- Targetted the E.coli glycolate oxidation pathway in chloroplasts
- Converted glycolate to CO2 and glyoxylate in the chloroplast
- But produced H2O2
AP2:
- Plant based and E.coli based catalase
- Glycolate oxidase (from Arabidopsis)
- Malate synthase (from pumpkin)
- Catalase (from E.coli
- But produced H2O2
AP3:
- Glycolate dehydrogenase from green algae
- Converts glycolate without producing H2O2
- Malate synthase from pumpkin processes glyoxylate
- No need for catalase, no H2O2 produced

Addition
- RNAi knockdown if PLGG1 keeps glycolate in the chloroplast, not into the photorespiratory pathway

Question 4

What were the results of the photorespiratory bypasses transgenic tobacco?

Answer 4

• AP3 > AP2 > AP1 > EV control
• AP3 + PLGG1 RNAi had highest yield (40% increase)
• Western blot of AP3 confirmed foreign protein expression in the chloroplast
• Improved tolerance to respiration shown by less photodamage in chlorophyll fluorescent imaging
• AP3 plants had higher CO2 assimilation rates and RuBisco efficiency with no increase in RuBisco levels, showing more CO2 was retained in the chloroplast due to less waste from photorespiration
• Similar results from potatoes

Question 5

What are the benefits and negatives of AP3 expression?

Answer 5

BENEFITS:
- No / less H2O2 produced
- Concentrates CO2 in the chloroplast, reducing carbon loss
- Less energy cost

NEGATIVES:
- More reducing power in the chloroplast
- Might need optimising to work in other crops