Actinorhizal symbiosis

Question 1

What genus of bacteria do actinorhizal plants interact with

Answer 1

Frankia genus

Question 2

Tell me some background about Frankia and its hosts

Answer 2

Frankia is a filamentous actinobacteria that can produce spores.
hosts are trees/shrubs belonging to Fagales, Cucurbitales and Rosales orders.
The symbiosis is specific!

Question 3

What are the conditions required and what’s the process of Frankia formation

Answer 3

under NH3- depleted aerobic conditions, Frankia develop spherical multicellular structures called vesicles (Nitrogenase expressed inside)

Question 4

What’s rare about vesicles?

Answer 4

other than vesicles and heterocyst’s, N2 fixing cellular structures are rare in nature

Question 5

what other soil interactions are there?

Answer 5

helper bacteria (with cellulase activity) may be involved in early interactions, enhancing infection
Frankia has also been found to fixate N2 in a free living state

Question 6

to fix or not to fix

Answer 6

Actinorhizal nodules can effectively fixate N2 but only if Frankia differentiate into vesicles and produce nitrogenase, otherwise you can get non-fixing nodules

Question 7

what is the plants side of signalling?

Answer 7

Chemoattraction and proliferation of bacteria in the Rhizosphere. The presence of exudates especially favours infection and nodulation process

Question 8

what is the bacterial side of signalling?

Answer 8

only some Frankia contain Nod-ABC genes
There are two mechanisms of nodulation:
- LCO dependent
- LCO independent

Question 9

What is involved in decoding the Ca2+ spike?

Answer 9

subset of genes required to decode in cytoplasm and induce in nucleus. i.e. Symbiosis like receptor kinase, two ion channels and nucleoporin proteins