The cyanobacterium, Nostoc punctiforme can protect against programmed cell death and induce defence genes in Arabidopsis thaliana.
Ontology highlight
ABSTRACT: Many cyanobacteria can form nitrogen-fixing symbioses with a broad range of plant species. Unlike other plant-bacteria symbioses, little is understood about the immunological responses induced by plant cyanobionts (symbiotic cyanobacteria). Here, we used Arabidopsis thaliana suspension cell cultures as a model system to demonstrate that the model plant-symbiotic cyanobacteria, Nostoc punctiforme is capable of protecting against plant programmed cell death (PCD). We also profiled the early transcriptomic changes that were induced in response to conditioned medium (CM) from N. punctiforme cell cultures. Interestingly, the PCD reduction was preceded by the induction of genes associated with defence and immunity, the most striking of which were a number of WRKY-family transcription factors. Down-regulated included genes involved in the regulation of cell growth and differentiation. This work is the first to show that a cyanobacteria can regulate plant PCD and provides a useful transcriptome resource for studying early plant cell responses to symbiotic cyanobacteria.
Project description:Plant-cyanobacteria symbiosis is considered one of the pivotal events in the history of life. In this symbiosis, the cyanobacterium provides to the plant fixed nitrogen compounds and plant hormones and, in return, the plant provides to the cyanobacterium fixed carbon. Despite the large knowledge in the physiology and ecology of plant-cyanobacteria symbioses, little is known about the molecular mechanisms involved in the crosstalk between partners. It has been shown recently that Nostoc punctiforme is able to stablish an endophytic symbiosis with Oryza sativa. This finding opens a door to explore this symbiotic interaction as a sustainable alternative to nitrogen fertilization of paddy fields. However, molecular mechanisms behind Oryza-Nostoc endosymbiosis are still not clarified. To gain further insights, an LC-MS/MS based label-free quantitative technique was used to evaluate the differential proteomics under N. punctiforme treatment vs. control plants at 1 day and 7 days. Differential expression profiling reveals a significant number of proteins to be down-regulated or missing in both partners, while others were more abundant or only expressed when both partners were in contact. In N. punctiforme, the differential protein expression was primarily connected to primary metabolism, signal transduction and perception, transport of substances and photosynthesis. In O. sativa, the differential protein expression was connected to a wide range of biological functions regulating carbon and nitrogen metabolism and response to biotic and abiotic stresses.
Project description:Change in gene expression for a wild-type (Nostoc punctiforme ATCC 29133) and hmpD-deletion strain (UCD 543) of Nostoc punctiforme ATCC 29133 over the time course of hormogonium development This study is further descirbed in Risser, D.D. and Meeks, J.C. 2013. Comparative transcriptomics with a motility deficient mutant leads to identification of a novel polysaccharide secretion system in Nostoc punctiforme. Molecular Microbiology
Project description:Change in gene expression for a wild-type (Nostoc punctiforme ATCC 29133) and hmpD-deletion strain (UCD 543) of Nostoc punctiforme ATCC 29133 over the time course of hormogonium development This study is further descirbed in Risser, D.D. and Meeks, J.C. 2013. Comparative transcriptomics with a motility deficient mutant leads to identification of a novel polysaccharide secretion system in Nostoc punctiforme. Molecular Microbiology Total RNA from 3 biological replicates at each time point from 0 to 24 hours after hormogonium induction was converted to cDNA, dye-labled and hybridized to nimblegen 12x135k array slides
Project description:Nostoc cyanobacteria are capable to form symbiotic relationships with plants, transitioning to a heterotrophic lifestyle in return for providing bioavailable nitrogen to the host. The diazotrophic photoautotrophs also serve as a hub for a specialized heterotrophic bacterial community whose physiological contributions are poorly understood. By comparing the axenic strain N. punctiforme PCC 73102 and the related strains Nostoc sp. KVJ2 and KVJ3, which still maintain their heterotrophic microbiome, we were able to demonstrate an almost obligate dependence of the cyanobacteria on the heterotrophic partners under carbon-limiting conditions. Detailed analysis of the intimate bilateral relationship between Nostoc punctiforme and the isolate Agrobacterium tumefaciens Het4 using multi-omics technologies and microscopy uncovered a complex partnership characterized, among other traits, by competition for iron and facilitation for carbon. Although competitive interactions with A. tumefaciens Het4 compromise nitrogen fixation and stimulate the degradation of cyanophycin, mutualistic dependency prevails under inorganic carbon limitation. Both the absence of the high affinity bicarbonate uptake transporter SbtA and the prevalent extracarboxysomal localization of the carbon-fixing enzyme RubisCO as detected by immunofluorescence microscopy suggest a weak carbon concentrating mechanism in N. punctiforme that enforces a dependence on heterotrophic bacteria. Further, immunofluorescence, electron microscopic and proteomic analyses reveal a pronounced extracellular recycling of proteins under N- and C-limiting conditions. The pivotal influence of heterotrophic bacteria on symbiotic Nostoc strains should be considered when analyzing these strains, especially in the free-living state, and also sheds new light on the benefit to Nostoc of the provision of organic carbon by plant hosts.
Project description:Heterocysts, cells specialized for nitrogen fixation in certain filamentous cyanobacteria, appear singly in a nonrandom spacing pattern along the chain of vegetative cells. A two-stage, biased initiation and competitive resolution model has been proposed to explain the establishment of this spacing pattern. There is substantial evidence that competitive resolution of a subset of cells initiating differentiation occurs by interactions between a self enhancing activator, HetR, and a diffusible inhibitor PatS-5 (RGSGR). Results presented here show that the absence of a unique membrane protein, PatN, in Nostoc punctiforme strain ATCC 29133 leads to a threefold increase in heterocyst frequency and a fourfold decrease in the vegetative cell interval between heterocysts. A PatN-GFP translational fusion shows a pattern of biased inheritance in daughter vegetative cells of ammonium-grown cultures. Inactivation of another heterocyst patterning gene, patA, is epistatic to inactivation of patN, and transcription of patA increases in a patN- deletion strain, implying that patN may function by modulating levels of patA. The presence of PatN is hypothesized to decrease the competency of a vegetative cell to initiate heterocyst differentiation, and the cellular concentration of PatN is dependent on cell division that results in cells transiently depleted of PatN. We suggest that biased inheritance of cell-fate determinants is a phylogenetic domain- spanning paradigm in the development of biological patterns. Change in gene expression for a wild-type (UCD 153) and patN-deletion strain, (UCD 524) of Nostoc punctiforme ATCC 29133 over the time course of heterocyst developments. Total RNA from 3 biological replicates at each time point from 0 to 120 hours after removal of combined nitrogen (Nitrogen step-down) was converted to cDNA, dye-labled and hybridized to nimblegen 12x135k array slides.