Figure 6.

Model relating pea sym loci to steps in nodulation. Mutations in sym8 and sym19 block both Nod-factor-induced calcium spiking and mycorrhizal infection. Because mutation of sym10 blocks calcium spiking but not mycorrhizal infection, we postulate that sym10 acts upstream of the common steps to nodulation and mycorrhizal infection. Mutation of sym9 and sym30 blocks root-hair deformation and mycorrhizal infections but not calcium spiking. Mutation of sym7 blocks infection thread formation induced by Rhizobium but not root-hair deformation or calcium spiking The sym2^A locus inhibits nodulation by the strain of R. leguminosarum bv. viciae used herein, but some infections are found. The data on mycorrhizal infection were as described (37, 38).