Peanut (Arachis hypogaea) is a widely cultivated legume crop that can fix nitrogen by forming root nodules with compatible rhizobia. The initiation and formation of these nodules require complex molecular communication between legumes and rhizobia, involving the precise regulation of multiple legume genes. However, the mechanism underlying nodulation in peanuts remains poorly understood. In this study, we identified a gene associated with nodulation in peanuts, named Peanut unique gene for nodulation 1.1 (AhPUGN1.1). Multiple lines of evidence indicate that AhPUGN1.1 is primarily expressed in peanut nodules. Silencing or knocking out AhPUGN1.1 in peanut resulted in fewer nodules, as well as lower fresh weight and nitrogenase activity, while overexpressing AhPUGN1.1 significantly enhanced nodulation ability and nitrogenase activity. Modulating the expression of AhPUGN1.1 also influenced the expression levels of genes associated with the Nod factor signaling pathway and infection via crack entry. Comparative transcriptome analysis revealed that AhPUGN1.1 likely regulates peanut nodulation by affecting the expression of genes involved in the cytokinin and calcium signaling pathways. Our data thus show that AhPUGN1.1 acts as a crucial regulator promoting symbiotic nodulation in peanuts.

In plant-bacteria symbiosis, frontiers between mutualism and parasitism are often crossed. Here, the authors identify a bacterial clade that includes rhizobial strains displaying both pathogenic and n...

C-terminally encoded peptides (CEPs) are small secreted signalling peptides that promote in legumes

Soybean is an important legume crop and understanding how soil nitrogen affects nodulation can promote sustainable agriculture. The study summarizes nitrate-regulated nodulation while drawing paralle...

Non-symbiotic Bradyrhizobium are among the most abundant and ubiquitous microbes in bulk soils globally. Despite this, most available genomic resources for Bradyrhizobium are derived from plant-associ...

Rhizobia are soil-dwelling proteobacteria that can enter into symbiotic nitrogen-fixing relationships with compatible leguminous plants. Taxonomically, rhizobia are divided into alpha-rhizobia, which belong to the class Alpharoteobacteria, and beta-rhizobia, which belong to the class Betaproteobacteria. To date, all bona fide alpha-rhizobia belong to the order Hyphomicrobiales. However, a recent study suggested that Sphingomonas sediminicola DSM 18106T is also a rhizobium and is capable of nodulating pea plants (Pisum sativum), which would expand the known taxonomic distribution of alpha-rhizobia to include the order Sphingomonadales. Here, we attempted to replicate the results of that previous study. Resequencing and computational analysis of the genome of S. sediminicola DSM 18106T failed to identify genes encoding proteins involved in legume nodulation or nitrogen fixation. In addition, experimental plant assays indicated that S. sediminicola DSM 18106T is unable to nodulate the two cultivars of pea tested in our study, unlike the rhizobium Rhizobium johnstonii 3841T. Taken together, and in contrast to the previous study, these results suggest that S. sediminicola DSM 18106T is not capable of inducing root nodule formation on pea, meaning that the taxonomic distribution of all known alpha-rhizobia remains limited to the class Hyphomicrobiales.

Growth of the common bean plant Phaseolus vulgaris is tightly linked to its symbiotic relationship w

Maximizing the nitrogen fixation occurring in rhizobia-legume associations represents an opportunity to sustainably reduce nitrogen fertilizer inputs in agriculture. High-throughput measurement of symbiotic traits has the potential to accelerate the identification of elite rhizobium/legume associations and enable novel research approaches. Plasmid-ID technology, recently deployed in Rhizobium leguminosarum, facilitates the concurrent assessment of rhizobium nitrogen-fixing effectiveness and competitiveness for root nodulation. This study adapts Plasmid-ID technology to function in Sinorhizobium species that are central models for studying rhizobium-legume associations and form economically important symbioses with alfalfa. New Sino-Plasmid-IDs were developed and tested for stability and their ability to measure competitiveness for root nodulation and nitrogen-fixing effectiveness. Rhizobial competitiveness is measured by identifying strain-specific nucleotide barcodes using Next-Generation Sequencing while effectiveness is measured by GFP fluorescence driven by the synthetic nifH promoter. Sino-Plasmid-IDs allow researchers to efficiently study competitiveness and effectiveness in a multitude of Sinorhizobium strains simultaneously.

In plant-bacteria symbiosis, frontiers between mutualism and parasitism are often crossed. Here, the authors identify a bacterial clade that includes rhizobial strains displaying both pathogenic and n...

The CPSMV-based VIGS protocol enables rapid functional analysis of nodulation in soybean. VIGS effectively downregulates target genes in below- and aboveground tissues overcoming limitations of curre...