A convenient, soil-free method for the production of root nodules in soybean to study the effects of exogenous additives

A spatially resolved multiomic single-cell atlas of soybean development

Cis-regulatory elements (CREs) precisely control spatiotemporal gene expression in cells. Using a spatially resolved single-cell atlas of gene expression with chromatin accessibility across ten soybean tissues, we identified 103 distinct cell types and 303,199 accessible chromatin regions (ACRs). Nearly 40% of the ACRs showed cell-type-specific patterns and were enriched for transcription factor (TF) motifs defining diverse cell identities. We identified de novo enriched TF motifs and explored conservation of gene regulatory networks underpinning legume symbiotic nitrogen fixation. With comprehensive developmental trajectories for endosperm and embryo, we uncovered the functional transition of the three sub-cell types of endosperm, identified 13 sucrose transporters sharing the DOF11 motif that were co-up-regulated in late peripheral endosperm and identified key embryo cell-type specification regulators during embryogenesis, including a homeobox TF that promotes cotyledon parenchyma identity. This resource provides a valuable foundation for analyzing gene regulatory programs in soybean cell types across tissues and life stages.

GmBES1-1 dampens the activity of GmNSP1/2 to mediate brassinosteroid inhibition of nodulation in soybean

Soybean (Glycine max) forms root nodules to house rhizobial bacteria for biological nitrogen fixation. The development of root nodules is intricately regulated by endogenous and exogenous cues. The phytohormones brassinosteroids (BRs) have been shown to negatively regulate nodulation in soybean, but the underlying genetic and molecular mechanisms remain largely unknown. Here, we performed transcriptomic analyses and revealed that BR signaling negatively regulates nodulation factor (NF) signaling. We found that BR signaling inhibits nodulation through its signaling component GmBES1-1 by dampening NF signaling and nodule formation. In addition, GmBES1-1 can directly interact with both GmNSP1 and GmNSP2 to inhibit their interaction and the DNA-binding activity of GmNSP1. Furthermore, BR-induced nuclear accumulation of GmBES1-1 is essential for inhibiting nodulation. Taken together, our results demonstrate that regulation of GmBES1-1 subcellular localization by BRs plays a key role in the legume-rhizobium symbiosis and plant development, indicating a crosstalk mechanism between phytohormone and symbiosis signaling pathways.

SymRK-dependent phosphorylation of Gα protein and its role in signaling during soybean (Glycine max) nodulation

Heterotrimeric G proteins, comprised of Gα, Gβ and Gγ subunits, influence signaling in most eukaryotes. In metazoans, G proteins are activated by G protein-coupled receptor (GPCR)-mediated GDP to GTP exchange on Gα; however, the role(s) of GPCRs in regulating plant G-protein signaling remains equivocal. Mounting evidence suggests the involvement of receptor-like kinases (RLKs) in regulating plant G-protein signaling, but their mechanistic details remain scarce. We have previously shown that during Glycine max (soybean) nodulation, the nod factor receptor 1 (NFR1) interacts with G-protein components and indirectly affects signaling. We explored the direct regulation of G-protein signaling by RLKs using protein-protein interactions, receptor-mediated in vitro phosphorylations and the effects of such phosphorylations on soybean nodule formation. Results presented in this study demonstrate a direct, phosphorylation-based regulation of Gα by symbiosis receptor kinase (SymRK). SymRKs interact with and phosphorylate Gα at multiple residues in vitro, including two in its active site, which abolishes GTP binding. Additionally, phospho-mimetic Gα fails to interact with Gβγ, potentially allowing for constitutive signaling by the freed Gβγ. These results uncover an unusual mechanism of G-protein cycle regulation in plants where the receptor-mediated phosphorylation of Gα not only affects its activity but also influences the availability of its signaling partners, thereby exerting a two-pronged check on signaling.

Growth regulators promote soybean productivity: a review

Soybean [Glycine max (L.) Merrill] is a predominant edible plant and a major supply of plant protein worldwide. Global demand for soybean keeps increasing as its seeds provide essential proteins, oil, and nutraceuticals. In a quest to meet heightened demands for soybean, it has become essential to introduce agro-technical methods that promote adaptability to complex environments, improve soybean resistance to abiotic stress , and increase productivity. Plant growth regulators are mainly exploited to achieve this due to their crucial roles in plant growth and development. Increasing research suggests the influence of plant growth regulators on soybean growth and development, yield, quality, and abiotic stress responses. In an attempt to expatiate on the topic, current knowledge, and possible applications of plant growth regulators that improve growth and yield have been reviewed and discussed. Notably, the application of plant growth regulators in their appropriate concentrations at suitable growth periods relieves abiotic stress thereby increasing the yield and yield components of soybean. Moreover, the regulation effects of different growth regulators on the morphology, physiology, and yield quality of soybean are discoursed in detail.

Improvement of Medicago sativa Crops Productivity by the Co-inoculation of Sinorhizobium meliloti-Actinobacteria Under Salt Stress

Biotic and abiotic stresses are severely limiting plant production and productivity. Of notable importance is salt stress that not only limits plant growth and survival, but affects the soil fertility and threatens agricultural ecosystems sustainability. The problem is exacerbated in fragile arid and semi-arid areas where high evaporation, low precipitation and the use of salty water for irrigation is accelerating soil salinization. Legumes, considered very nutritious foods for people and providing essential nutrients for ecosystems are a fundamental element of sustainable agriculture. They can restore soil health by their ability to fix nitrogen in a symbiotic interaction with the rhizobia of the soil. However, salt stress is severely limiting productivity and nitrogen fixation ability in legumes. Plant growth-promoting rhizobacteria (PGPR) and mainly actinobacteria promote plant growth by producing phytohormones, siderophores, antibiotics and antifungal compounds, solubilizing phosphate and providing antagonism to phytopathogenic microorganisms. In addition, actinobacteria have beneficial effects on nodulation and growth of legumes. In this study, actinobacteria isolated from different niches and having PGP activities were used in co-inoculation experiments with rhizobia in Medicago sativa plants rhizosphere submitted to salt stress. The results indicate that drought- and salinity-tolerant Actinobacteria with multiple PGP traits can potentially increase alfalfa growth under saline conditions, in the presence or absence of symbiotic rhizobial bacteria. Actinobacteria discovered in this study can, therefore, be suitable biofertilizers in the formulation of agricultural products improving plant development, health and productivity in saline soils, a necessary alternative for modern agriculture and sustainable development.

GmbZIP1 negatively regulates ABA-induced inhibition of nodulation by targeting GmENOD40-1 in soybean

BACKGROUND

Abscisic acid (ABA) plays an important role in plant growth and adaptation through the ABA signaling pathway. The ABA-responsive element binding (AREB/ABF) family transcriptional factors are central regulators that integrate ABA signaling with various signaling pathways. It has long been known that ABA inhibits rhizobial infection and nodule formation in legumes, but the underlying molecular mechanisms remain elusive.

RESULTS

Here, we show that nodulation is very sensitive to ABA and exogenous ABA dramatically inhibits rhizobial infection and nodule formation in soybean. In addition, we proved that GmbZIP1, an AREB/ABF transcription factor, is a major regulator in both nodulation and plant response to ABA in soybean. GmbZIP1 was specifically expressed during nodule formation and development. Overexpression of GmbZIP1 resulted in reduced rhizobial infection and decreased nodule number. Furthermore, GmbZIP1 is responsive to ABA, and ectopic overexpression of GmbZIP1 increased sensitivity of Arabidopsis plants to ABA during seed germination and postgerminative growth, and conferred enhanced drought tolerance of plants. Remarkably, we found that GmbZIP1 directly binds to the promoter of GmENOD40-1, a marker gene for nodule formation, to repress its expression.

CONCLUSION

Our results identified GmbZIP1 as a node regulator that integrates ABA signaling with nodulation signaling to negatively regulate nodule formation.