Natural variation of GmRj2/Rfg1 determines symbiont differentiation in soybean.

Symbiotic nitrogen fixation (SNF) provides much of the N utilized by leguminous plants throughout growth and development. Legumes may simultaneously establish symbiosis with different taxa of microbial symbionts. Yet, the mechanisms used to steer associations toward symbionts that are most propitious across variations in soil types remain mysterious. Here, we demonstrate that GmRj2/Rfg1 is responsible for regulating symbiosis with multiple taxa of soybean symbionts. In our experiments, the GmRj2/Rfg1SC haplotype favored association with Bradyrhizobia, which is mostly distributed in acid soils, whereas the GmRj2/Rfg1HH haplotype and knockout mutants of GmRj2/Rfg1SC associated equally with Bradyrhizobia and Sinorhizobium. Association between GmRj2/Rfg1 and NopP, furthermore, appeared to be involved in symbiont selection. Furthermore, geographic distribution analysis of 1,821 soybean accessions showed that GmRj2/Rfg1SC haplotypes were enriched in acidic soils where Bradyrhizobia were the dominant symbionts, whereas GmRj2/Rfg1HH haplotypes were most prevalent in alkaline soils dominated by Sinorhizobium, and neutral soils harbored no apparent predilections toward either haplotype. Taken together, our results suggest that GmRj2/Rfg1 regulates symbiosis with different symbionts and is a strong determinant of soybean adaptability across soil regions. As a consequence, the manipulation of the GmRj2/Rfg1 genotype or application of suitable symbionts according to the haplotype at the GmRj2/Rfg1 locus might be suitable strategies to explore for increasing soybean yield through the management of SNF.

Environmental and genetic regulation of plant height in soybean.

BACKGROUND: Shoot architecture is fundamentally crucial to crop growth and productivity. As a key component of shoot architecture, plant height is known to be controlled by both genetic and environmental factors, though specific details remain scarce. RESULTS: In this study, 308 representative soybean lines from a core collection and 168 F9 soybean progeny were planted at distinct field sites. The results demonstrated the presence of significant genotype × environment interaction (G × E) effects on traits associated with plant height in a natural soybean population. In total, 19 loci containing 51 QTLs (quantitative trait locus) for plant height were identified across four environments, with 23, 13 and 15 being QTLs for SH (shoot height), SNN (stem node number) and AIL (average internode length), respectively. Significant LOD ranging from 2.50 to 16.46 explained 2.80-26.10% of phenotypic variation. Intriguingly, only two loci, Loc11 and Loc19-1, containing 20 QTLs, were simultaneously detected across all environments. Results from Pearson correlation analysis and PCA (principal component analysis) revealed that each of the five agro-meteorological factors and four soil properties significantly affected soybean plant height traits, and that the corresponding QTLs had additive effects. Among significant environmental factors, AD (average day-length), AMaT (average maximum temperature), pH, and AN (available nitrogen) had the largest impacts on soybean plant height. Therefore, in spite of uncontrollable agro-meteorological factors, soybean shoot architecture might be remolded through combined efforts to produce superior soybean genetic materials while also optimizing soil properties. CONCLUSIONS: Overall, the comprehensive set of relationships outlined herein among environment factors, soybean genotypes and QTLs in effects on plant height opens new avenues to explore in work aiming to increase soybean yield through improvements in shoot architecture.

Functional assembly of root-associated microbial consortia improves nutrient efficiency and yield in soybean.

Root-associated microbes are critical for plant growth and nutrient acquisition. However, scant information exists on optimizing communities of beneficial root-associated microbes or the mechanisms underlying their interactions with host plants. In this report, we demonstrate that root-associated microbes are critical influencers of host plant growth and nutrient acquisition. Three synthetic communities (SynComs) were constructed based on functional screening of 1,893 microbial strains isolated from root-associated compartments of soybean plants. Functional assemblage of SynComs promoted significant plant growth and nutrient acquisition under both N/P nutrient deficiency and sufficiency conditions. Field trials further revealed that application of SynComs stably and significantly promoted plant growth, facilitated N and P acquisition, and subsequently increased soybean yield. Among the tested communities, SynCom1 exhibited the greatest promotion effect, with yield increases of up to 36.1% observed in two field sites. Further RNA-seq implied that SynCom application systemically regulates N and P signaling networks at the transcriptional level, which leads to increased representation of important growth pathways, especially those related to auxin responses. Overall, this study details a promising strategy for constructing SynComs based on functional screening, which are capable of enhancing nutrient acquisition and crop yield through the activities of beneficial root-associated microbes.

Functional Investigation of Plant Growth Promoting Rhizobacterial Communities in Sugarcane.

Plant microbiota are of great importance for host nutrition and health. As a C4 plant species with a high carbon fixation capacity, sugarcane also associates with beneficial microbes, though mechanisms underlying sugarcane root-associated community development remain unclear. Here, we identify microbes that are specifically enriched around sugarcane roots and report results of functional testing of potentially beneficial microbes propagating with sugarcane plants. First, we analyzed recruitment of microbes through analysis of 16S rDNA enrichment in greenhouse cultured sugarcane seedlings growing in field soil. Then, plant-associated microbes were isolated and assayed for beneficial activity, first in greenhouse experiments, followed by field trials for selected microbial strains. The promising beneficial microbe SRB-109, which quickly colonized both roots and shoots of sugarcane plants, significantly promoted sugarcane growth in field trials, nitrogen and potassium acquisition increasing by 35.68 and 28.35%, respectively. Taken together, this report demonstrates successful identification and utilization of beneficial plant-associated microbes in sugarcane production. Further development might facilitate incorporation of such growth-promoting microbial applications in large-scale sugarcane production, which may not only increase yields but also reduce fertilizer costs and runoff.