Autoregulatory system of soybean controls both rhizobial modulation and arbuscular mycorrhizal colonization

摘要

Roots of soybean establish symbioses with nodule-inducing rhizobia and arbuscular mycorrhizal (AM) fungi. Rhizobia secrete a signal molecule, Nod factors and induce nodulation. The existing nodules systemically suppress subsequent nodulation in other parts of the root, a phenomenon termed autoregulation. We examined AM colonization in the roots of non-nodulating (Nod-) and hyper-nodulating (Nod++) mutants of soybean to clarify the common pathway involving both nodulation and AM colonization. In Expt.l, seven Nod- and five Nod++ mutants were screened for AM colonization. The two Nod++ mutants En6500 and Nod 1-3 had higher degree of colonization with 2.5-4.5 times higher arbuscular abundance than the respective wild types. The Nod- mutants showed the same or a decrease in mycorrhizal parameters compared with the wildtype. However, none of these had the non-mycorrhizal phenotype (Myc-). In Expt.2, soybean cvs. Enrei, En1282 (Nod-) and En6500 (Nod++) were cultivated in a field soil to form nodulation and AM colonization by indigenous rhizobia and AM fungi. En1282 (Nod-) formed no nodules, but its level of AM colonization was similar to that of the wild type. En6500 (Nod++) showed a 3.3-fold higher nodule number and higher degree of AM colonization with 1.6-fold higher arbuscular abundance than the wild type. In this study, we found that arbuscule formation of soybean by AM fungi was high in hyper-nodulating mutant compared with the wild type, suggesting that autoregulation system of soybean controls both rhizobial nodulation and AM colonization.