Project description:Legume GRAS-type transcription factors NSP1 and NSP2 are essential for Rhizobium Nod factor-induced nodulation. Both proteins are considered to be Nod factor response factors regulating gene expression upon symbiotic signalling. However, legume NSP1 and NSP2 can be functionally replaced by non-legume orthologs; including rice (Oryza sativa) OsNSP1 and OsNSP2. This shows that both proteins are functionally conserved in higher plants, suggesting an ancient function that was conserved during evolution. Here we show that NSP1 and NSP2 are indispensable for strigolactone biosynthesis in the legume Medicago truncatula as well as rice. Mutant nsp1-nsp2 plants hardly produce strigolactones. The lack of strigolactone biosynthesis coincides with strongly reduced DWARF27 expression in both species. Rice and Medicago represent distinct phylogenetic lineages that split ~150 million years ago. Therefore we conclude that regulation of strigolactone biosynthesis by NSP1 and NSP2 is an ancestral function conserved in higher plants. Since strigolactone biosynthesis is highly regulated by environmental conditions like phosphate starvation, NSP1 and NSP2 will be important tools in future studies on the molecular mechanisms by which environmental sensing is translated into regulation of strigolactone biosynthesis. As NSP1 and NSP2 are single copy genes in legumes, it implies that a single protein complex fulfills a dual regulatory function of different downstream targets; symbiotic and non-symbiotic, respectively. Three biological replications are used for roots of wild type A17, nsp1 and nsp2 mutant plants
Project description:Legume GRAS-type transcription factors NSP1 and NSP2 are essential for Rhizobium Nod factor-induced nodulation. Both proteins are considered to be Nod factor response factors regulating gene expression upon symbiotic signalling. However, legume NSP1 and NSP2 can be functionally replaced by non-legume orthologs; including rice (Oryza sativa) OsNSP1 and OsNSP2. This shows that both proteins are functionally conserved in higher plants, suggesting an ancient function that was conserved during evolution. Here we show that NSP1 and NSP2 are indispensable for strigolactone biosynthesis in the legume Medicago truncatula as well as rice. Mutant nsp1-nsp2 plants hardly produce strigolactones. The lack of strigolactone biosynthesis coincides with strongly reduced DWARF27 expression in both species. Rice and Medicago represent distinct phylogenetic lineages that split ~150 million years ago. Therefore we conclude that regulation of strigolactone biosynthesis by NSP1 and NSP2 is an ancestral function conserved in higher plants. Since strigolactone biosynthesis is highly regulated by environmental conditions like phosphate starvation, NSP1 and NSP2 will be important tools in future studies on the molecular mechanisms by which environmental sensing is translated into regulation of strigolactone biosynthesis. As NSP1 and NSP2 are single copy genes in legumes, it implies that a single protein complex fulfills a dual regulatory function of different downstream targets; symbiotic and non-symbiotic, respectively.
Project description:Salt stress is a major agricultural concern inhibiting not only plant growth but also the symbiotic association between legume roots and the soil bacteria rhizobia. This symbiotic association is initiated by a molecular dialogue between the two partners, leading to the activation of a signaling cascade in the legume host and ultimately the formation of nitrogen-fixing root nodules. Here we show that a moderate salt stress increases the responsiveness of early symbiotic genes in Medicago truncatula to its symbiotic partner, Sinorhizobium meliloti, while conversely, inoculation with S. meliloti counteracts salt-regulated gene expression, restoring one-third to control levels. Our analysis of Early Nodulin 11 shows that salt-induced expression is dynamic, Nod-factor dependent, and requires the ionic, but not the osmotic, component of salt. We demonstrate that salt stimulation of rhizobium-induced gene expression requires NSP2, which functions as a node to integrate the abiotic and biotic signals. In addition, our work reveals that inoculation with Sinorhizobium meliloti succinoglycan mutants also hyperinduces ENOD11 expression in the presence or absence of salt, suggesting a possible link between rhizobial exopolysaccharide and the plant response to salt stress. Finally, we identify an accessory set of genes that are induced by rhizobium only under conditions of salt stress and have not been previously identified as being nodulation-related genes. Our data suggests that interplay of core nodulation genes with different accessory sets, specific for different abiotic conditions, function to establish the symbiosis. Together, our findings reveal a complex and dynamic interaction between plant, microbe, and environment.
Project description:Our global transcriptomic approach to study Myc-LCO signalling in M. truncatula used an experimental design of three genotypes â A17 (WT), dmi3 and nsp1 â and three treatments â sulphated Myc-LCOs (S Myc-LCOs), nonsulphated Myc-LCOs (NS Myc-LCOs), and solvent controls (acetonitrile, ACN). We pooled two early treatment time points (2 + 4 h) based on preliminary data and reports of transcriptional changes occurring within hours of Myc-LCO treatment. Three biological replicates were sequenced per condition. We used M. truncatula dmi3 and nsp1 mutants, described originally as NodâMycâ and NodâMyc+, respectively, and the two major types of Myc-LCOs (sulphated and nonsulphated) to determine overlaps and specificities of Myc-LCO responses. Myc-LCOs were used at 10â6 M because they are biologically active at about a 100-fold higher concentration than Nod factors, which have been used at 10â7, 10â8 M in transcriptomic studies.
Project description:Arbuscular mycorrhiza (AM) interactions between plants and Glomeromycota fungi primarily support phosphate aquisition by the host. To unravel the role of the AM-specific GRAS transcription factors MtGras1 and MtRam1, we performed genome-wide transcriptome profiling in RNAi-mediated MtGras1 knockdown and MtRam1 (ram1-1) mutant roots. Specifically, we used GeneChip Medicago Transcriptome Assays to identify genes differentially regulated in mycorrhizal MtGras1 knockdown or MtRam1 (ram1-1) mutant roots in comparison to control roots.
Project description:Legumes interact with soil microbes, leading to the development of nitrogen-fixing root nodules and arbuscular mycorrhizal (AM) roots. While nodule initiation by diffusible lipochitooligosaccharide (LCO) Nod-factors of bacterial origin (Nod-LCOs) is well characterized, diffusible AM fungal signals were only recently identified as sulphated and non-sulphated LCOs (sMyc-LCOs and nsMyc-LCOs). Applying Myc-LCOs in parallel to Nod-LCOs, we used GeneChips to detail the global programme of gene expression in response to the external application of symbiotic LCOs.