Arabidopsis of legumes

[Julia Frugoli]

OK, I admit I have a bias here (I work in this 
system), but in the discussion on symbiosis, no one 
has mentioned Medicago truncatula, the diploid 
alfalfa that's revolutionizing nitrogen fixation 
genetics (see "Model legumes get the Nod" Plant Cell 
9:275-281). After scarification (we treat for 12 
minutes with straight H2SO4, followed by 2 hours in 
sterile H2O) truncatula seeds germinate in 3 days (2 
days in the cold, followed by one day at RT).  We 
grow them in hydroponic conditions, because we are 
looking at nodulation genes, so I'm not sure how the 
following would translate to soil, but the symbiont 
is Rhizobium meliloti, the same bacterium that forms 
a symbiosis with Medicago sativa (commercial 
tetraploid alfalfa).  5 days after placing the 
germinated seedlings in the tank, we inoculate them 
with a log phase culture of Rhizobia, and 10 days 
later nodules are fully formed.  This is the kind of 
time scale that might be adaptable to lab.  The 
plants take 3 months seed to seed, so it might even 
be possible over the course of a term to see a 
difference in nodulated vs non-nodulated plants.