The Sym31 gene responsible for bacteroid differentiation is involved in nitrate-dependent nodule formation in pea plants

The effects of exogenous nitrate on the number of developing nodules and th eir leghemoglobin content in the original pea (Pisum sativum L.) line and i ts symbiotic mutants were studied. Mutation in the Swn31 gene conferred the tolerance to nitrate in the corresponding pea line and manifested itself a s the number of nodules independent of the nitrate concentration. Thus, the Sym31 gene was identified as the only known symbiotic gene involved in bot h the differentiation of symbiotic compartments and the nitrate-dependent p rocess of nodule formation. The presence of leghemoglobin in double mutants (sym13, sym31) indicates the possibility of the complementary contribution of these genes in the control of leghemoglobin synthesis.