Plant-Rhizobial Symbiosis

Question 1

Describe how plant-rhizobial symbiosis takes place

Answer 1

1. NOD factors (lipochito-oligosaccharides) bind LysMRLK
2. The root folds over its rhizobial partner (LysM-RLK), forming an infection pocket which enters the nodule.
3. The nodule provides a low oxygen environment for N fixation to take place, Ca2+ flux oscillates.

Question 2

What controls Ca2+ flux in nodules?

Answer 2

SYMRK
CASTOR
POLLUX

Question 3

What controls nuclear pore flux in nodules?

Answer 3

NUP133

Question 4

What controls Ca2+ oscillations in nodules?

Answer 4

CCaMK. This is a kinase which activates the transcription factor NIN

Question 5

How is nitrogen fixation rate maximised?

Answer 5

Rhizobia nodules have a low oxygen environment. Rhizobia combines with plant holoprotein to forms leghaemaglobin which binds oxygen
Maximise respiration rate

Question 6

Why are there 2 copies of NFR5/NFP genes?

Answer 6

They perceive NOD and Myc factors

Question 7

Describe how plant-mycorrhizal symbiosis takes place

Answer 7

1. Spore detects binding partner on plant cell wall
2. Hyphae infiltrate into the cortical layer of the root
3. Arbiscules receives carbon from the plant to exchange with fungi phosphates.

Question 8

How does G.diazotrophicus prevent oxygen inactivating nitrogenase

Answer 8

FeSII binds to nitrogenase, inactivating it, but also protecting it from oxygen

Question 9

Describe G. diazotrophicus

Answer 9

Non-nodulating bacteria that fixes nitrogen
Provides 60% of a plant’s N needs
No evidence it intracellularly colonises plants
Makes mucoid bacteria to limit oxygen diffusion
High acid tolerance around pH3
Spreads intracellularly via an unknown mechanism