Improving Photosynthesis

Question 1

What are the three main grand challenges in plant biology regarding crop growth?

Answer 1

• Fertiliser limitations (N,P,K) and their environmental / energy
• Drought stress increasingly limiting crop growth
• Changing face of disease due to climate change and new variants

Question 2

What are the three main approaches to improving crop yield?

Answer 2

• Improving photosynthesis
• Improving WUE
• Improving nitrogen uptake

Question 3

What is CRISPR used for in plant genetics?

Answer 3

CRISPR allows for precise and novel modification of genomes, enabling highly specific modifications in plant genetic engineering

Question 4

What are two main applications of GM crops?

Answer 4

• Pest resistance (using Bt toxin from B. thuringiensis)
• Herbicide tolerance (glyphosate resistance through modified EPSP synthase)

Question 5

What are the three main targets for improving light-independent photosynthesis?

Answer 5

• RuBisCO
• Photorespiration
• Regeneration of RuBP

Question 6

What is the competition problem with RuBisCO?

Answer 6

CO2 and oxygen compete for RuBisCO
High CO2 levels favour photosynthesis, while high O2 levels favour photorespiration

Question 7

What are Carbon Concentrating Mechanisms (CCMs)?

Answer 7

Structures like pyrenoids and carboxysomes that increase CO2 concentration around RuBisCO to improve photosynthetic efficiency
Also CAM and C4 photosynthesis

Question 8

Why is C4 rice engineering significant?

Answer 8

Could lead to:
- Increases in yield (up to 50%)
- Potential to grow in more conditions
- Potential to grow over larger areas

Question 9

When did C4 photosynthesis evolve?

Answer 9

Monocots: 21-35 mya
Dicots: 15-21 mya
Has about 62 independent origins
Evolved in low CO2 levels, in hot, dry areas

Question 10

What is photoinhibition?

Answer 10

When excess light energy is absorbed by light harvesting complexes with nowhere to go, it can damage photosynthesis machinery (especially PISII), leading to photoinhibition where photosynthesis eventually stops

Question 11

How can photosynthesis be protected from light damage?

Answer 11

• Overexpression of D1 enzymes to protect from thermal damage
• Manipulation of zeaxanthin / violaxanthin cycle to safely dissipate excess light

Question 12

How can photorespiration be reduced?

Answer 12

• Rescue glycolate and return it to the Calvin cycle
• Stimulating RuBP regeneration, increasing productivity and water-sue efficiency
• ? Can leaf structure be manipulated to improve flux of CO2 inside the leaf to chloroplast?