Natural GmACO1 allelic variations confer drought tolerance and influence nodule formation in soybean

Soybean[Glycine max(L.)Merr.]is one of the most important,but a drought-sensitive,crops.Identifying the genes controlling drought tolerance is important in soybean breeding.Here,through a genome-wide association study,we identified one significant association locus,located on chromosome 8,which conferred drought tolerance variations in a natural soybean population.Allelic analysis and genetic validation demonstrated that GmACO1,encoding for a 1-aminocyclopropane-1-carboxylate oxidase,was the causal gene in this association locus,and positively regulated drought tolerance in soybean.Meanwhile,we determined that GmACO1 expression was reduced after rhizobial infection,and that GmACO1 negatively regulated soybean nodule formation.Overall,our findings provide insights into soybean cultivars for future breeding.

Functional relationships of nodulation response and biomass production at nursery stages of two fast-growing, leguminous-multipurpose tree species in Bangladesh: Albizia saman and Leucaena leucocephala

This study was carried out to assess the relationship of the status of nodulation(i.e., the number of nodules, their shape and size) in root and biomass production of plant growth parameters(i.e., number of leaves, root and shoot lengths, root biomass and shoot biomass) in Albizia saman and Leucaena leucocephala. The assessment started 60 days after seeding. The study revealed that nodulation response and biomass production in both species showed significant differences over time(p < 0.05) in all variables except in the root-shoot ratio(oven-dry) of L. leucocephala. The study also showed significant differences(p < 0.05) in nodule formation and biomass production at the end of the study period between the two species except in the number of nodules and leaves and the green root-shoot ratio. There were strong positive correlations between nodule formation and biomass production, i.e., the number of nodules and the age of plants, the number of nodules and leaves, as well as the number of nodules and biomass(root biomass and shoot biomass) in both species. The results obtained using principal component analysis(PCA) and correlation coefficients of the different characteristics of nodulation and biomass production were similar in both species. The PCA showed that shoot biomass(shoot green weight and shoot oven-dry weight) is positively correlated with PC1(with an eigenvalue of 7.50) and root length is positively correlated with PC2(with an eigenvalue of 0.19) in the case of A. saman. In the case of L. leucocephala, the PCA revealed that root biomass(root green weight and root oven-dry weight), shoot biomass and shoot length are also positively correlated with PC1, while nodule formation and the number of leaves are positively correlated with PC2(with an eigenvalue PC1 of 6.92 and PC2 of 0.49).

SEPARATION AND ACCUMULATION OF Mn, Fe AND THE FORMATION OF Mn NODULES

The sediment samples (including various layers) obtained from 12 stations, 35 Mn nodule samples from 16 stations and water body samples were collected during Mn nodule investigation made in the Pacific Ocean in summer, 1983. The coexisting, separating and accumulating regularities and their relation concerning the formation of Mn nodules are approached through the distribution and partition characteristics of Mn and Fe combined with the data from nearshore area in the East China Sea continental shelf.

GSK3-mediated stress signaling inhibits legume-rhizobium symbiosis by phosphorylating GmNSP1 in soybean

Legumes establish symbiotic associations with rhizobia for biological nitrogen fixation.This process is highly regulated by various abiotic stresses,but the underlying genetic and molecular mechanisms remain largely unknown.In this study,we discovered that the glycogen synthase kinase 3(GSK3)-like kinase,GmSK2-8,plays an important role in inhibiting symbiotic signaling and nodule formation in soybean(Glycine max)under salt stress.We found that GmSK2-8 is strongly induced in soybean under high-salt conditions,while GmSK2-8 could interact with two G.max Nodulation Signaling Pathway 1(GmNSP1)proteins,GmNSP1a and GmNSP1b;these key transcription factors are essential for rhizobial infection,nodule initiation,and symbiotic gene expression in soybean.Furthermore,we demonstrated that GmSK2-8 phosphorylates the LHRI domain of GmNSP1a,inhibits its binding to the promoters of symbiotic genes,and thus suppresses nodule formation under salt stress.Knockdown of GmSK2-8 and its close homologs also resulted in reduced plant sensitivity to salt stress during nodule formation.Taken together,our findings indicate that GSK3-like kinases directly regulate the activities of GmNSP1s to mediate salt-inhibited legume–rhizobium symbiosis,providing novel targets for improving symbiotic nitrogen fixation under environmental stress conditions in soybean and possibly other legumes.