Transcriptional responses to arbuscular mycorrhizal symbiosis development are conserved in the liverwort Marchantia paleacea
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ABSTRACT: The mutualistic arbuscular mycorrhizal (AM) symbiosis arose in land plants more than 450 million years ago. This symbiosis is still widely found across major land plant lineages, including bryophytes. Despite its broad taxonomic distribution, little is known about the molecular components underpinning symbiosis outside of flowering plants. Here, we demonstrate that a broad AM genetic programme is conserved amongst land plants. In this study, we characterised the dynamic response of the liverwort Marchantia paleacea to Rhizophagus irregularis colonization by time-resolved transcriptomics across three stages of symbiosis. Comparative analysis of transcriptional responses to symbiosis in the liverwort M. paleacea and the legume Medicago truncatula further revealed evolutionarily conserved expression patterns for genes underpinning pre-symbiotic signalling, intracellular colonization and nutrient exchange. This study demonstrates that the genetic machinery regulating key aspects of symbiosis in plant hosts is largely conserved and coregulated across land plants.
Project description:Pathways underlying miRNA biogenesis, degradation, and activity were established early in land plant evolution, but the 24-nt siRNA pathway that guides DNA methylation was incomplete in early land plants, especially lycophytes. We show that the functional diversification of key gene families such as DICER-LIKE and ARGONAUTE (AGO) as observed in angiosperms occurred early in land plants followed by parallel expansion of the AGO family in ferns and angiosperms. We uncovered an unexpected AGO family specific to lycophytes and ferns. Our phylogenetic analyses of miRNAs in lycophytes, bryophytes, ferns, and angiosperms refined the temporal origination of conserved miRNA families in land plants.
Project description:Land plants evolved from an ancestral alga around 470 million years ago, evolving complex multicellularity in both haploid gametophyte and diploid sporophyte generations. The evolution of water conducting tissues in the sporophyte generation was crucial for the success of land plants, paving the way for the colonization of a variety of terrestrial habitats. Class II KNOX (KNOX2) genes are major regulators of secondary cell wall formation and seed mucilage (pectin) deposition in flowering plants. Here we show that in the liverwort Marchantia polymorpha loss-of-function alleles of the KNOX2 ortholog, MpKNOX2, or its dimerization partner MpBELL1, have defects in capsule wall secondary cell wall and spore pectin biosynthesis. Both genes are expressed in the gametophytic calyptra surrounding the sporophyte and exhibits maternal effects, suggesting an intergenerational regulation from the maternal gametophyte to the sporophyte generation. These findings also suggest the presence of a “vascular-like” program in the non-vascular liverwort capsule wall.
Project description:The lipid-derived phytohormone jasmonoyl-isoleucine (JA-Ile) regulates plant immunity, growth and development in vascular plants by activating genome-wide transcriptional reprogramming. In Arabidopsis, this is largely orchestrated by the master regulator MYC2 and related transcription factors (TFs). However, the TFs activating this pathway in basal plant lineages are currently unknown. We report the functional conservation of MYC-related TFs between the eudicot Arabidopsis thaliana and the liverwort Marchantia polymorpha, a plant belonging to one of the most basal land-plants lineages. Phylogenetic analysis suggests that MYC function first appeared in charophycean algae, and therefore predates the evolutionary appearance of any other jasmonate pathway component. Marchantia possesses two functionally interchangeable MYC genes, one in females and one in males. Similar to AtMYC2, MpMYCs showed nuclear localization, interaction with JAZ-repressors, and regulation by light. Phenotypic and molecular characterization of loss- or gain-of-function mutants demonstrated that MpMYCs are necessary and sufficient for the activation of the pathway in Marchantia, but unlike their Arabidopsis orthologs, do not regulate fertility. Our results show that despite 450 million years of independent evolution, MYCs are functionally conserved between bryophytes and eudicots. Genetic conservation in one of the most basal lineages suggests that MYC function existed in the common ancestor of land plants and evolved from a pre-existing MYC function in charophycean algae.
Project description:JAZ genes are negative regulators of jasmonate responses with a dual function as repressors of transcription factors and co-receptors, together with COI1, of the hormone jasmonoyl-isoleucine (JA-Ile). This family has been mainly studied in angiosperms, where high gene redundancy hinders the characterization of a complete depletion of JAZ function. Moreover, the recent discovery that JA-Ile is not the sole COI1/JAZ ligand in land plants, as dn-OPDA is the bioactive ligand in Marchantia polymorpha, underscores the importance of studying JAZ co-receptors in bryophytes. Here we exploited the low gene redundancy of the liverwort Marchantia polymorpha to characterize the function of the single MpJAZ in this early-divergent plant lineage. We demonstrate that MpJAZ is the ortholog of AtJAZ and acts as a repressor of dinor-OPDA responses in Marchantia. Mpjaz mutants show a dwarf phenotype and severe developmental defects related to growth inhibition, consistent with a constitutive activation of the dinor-OPDA pathway and the overaccumulation of both dinor-OPDA and its precursor OPDA. The expression of AtJAZ3 in Mpjaz complements MpJAZ repressor function, indicating that JAZ function is conserved across land plants. However, AtJAZ3 is unable to form co-receptor complexes with MpCOI1 and dn-OPDA, which evidences that the Jas domain, and not only COI1, determines ligand specificity.
Project description:Broad-host root endophytes establish long-term interactions with a large variety of plants, thereby playing a significant role in natural and managed ecosystems and in evolution of land plants. To exploit plants as living substrates and to establish a compatible interaction with morphologically and biochemically extremely different hosts, endophytes must respond and adapt to different plant signals and host metabolic states. Here we identified host-adapted colonization strategies and host-specific effector candidates of the mutualistic root endophyte Piriformospora indica by a global investigation of fungal transcriptional responses to barley and Arabidopsis at different symbiotic stages. Additionally we examined the role played by nitrogen in these two diverse associations. Cytological studies and colonization analyses of a barley mutant and fungal RNAi strains show that distinct physiological and metabolic signals regulate host-specific lifestyle in P. indica. This is the foundation for exploring how distinct fungal and host symbiosis determinants modulate biotrophy in one host and saprotrophy in another host and, ultimately, gives hints into the mechanisms underlying host adaptation in root symbioses.
Project description:affy_med_2011_09: In natural ecosystems most vascular plants develop symbiosis with arbuscular mycorrhizal (AM) fungi which help them acquire nutrients such as phosphorus (P) and nitrogen (N). P has long been known to control AM symbiosis which takes place only when P is limiting. For N, however, its role in controlling mycorrhization is less clear. We have chosen the model plant Medicago truncatula to analyze the impact of P limitation and both P and N limitation on Medicago root transcriptome in response to the AM fungus Rhizophagus irregularis (formerly Glomus intraradices (BEG141)). These analyses may help us uncover signaling events involved in the interaction between these symbionts as well as genes encoding transporters potentially important for nutrient exchanges in these conditions. --We will compare the root transcriptome of Medicago truncatula plants inoculated with Rhizophagus irregularis to that of non-inoculated plants grown under P limitation (or both P and N limitation) after 4 weeks of culture 12 arrays - Medicago; wt vs mutant comparison
Project description:Broad-host root endophytes establish long-term interactions with a large variety of plants, thereby playing a significant role in natural and managed ecosystems and in evolution of land plants. To exploit plants as living substrates and to establish a compatible interaction with morphologically and biochemically extremely different hosts, endophytes must respond and adapt to different plant signals and host metabolic states. Here we identified host-adapted colonization strategies and host-specific effector candidates of the mutualistic root endophyte Piriformospora indica by a global investigation of fungal transcriptional responses to barley and Arabidopsis at different symbiotic stages. Additionally we examined the role played by nitrogen in these two diverse associations. Cytological studies and colonization analyses of a barley mutant and fungal RNAi strains show that distinct physiological and metabolic signals regulate host-specific lifestyle in P. indica. This is the foundation for exploring how distinct fungal and host symbiosis determinants modulate biotrophy in one host and saprotrophy in another host and, ultimately, gives hints into the mechanisms underlying host adaptation in root symbioses. Arabidopsis and barley roots were inoculated with Piriformospora indica and grown for 14 days. Additionally P. indica was grown on 1/10 PNM medium alone. Samples were taken 3 and 14 dpi (Arabidopsis), 14 dpi (barley) and 3dpi (1/10 PNM). Each experiment was performed in three independent biological repetitions. Piriformospora indica gene expression examined only.
Project description:affy_med_2011_09: In natural ecosystems most vascular plants develop symbiosis with arbuscular mycorrhizal (AM) fungi which help them acquire nutrients such as phosphorus (P) and nitrogen (N). P has long been known to control AM symbiosis which takes place only when P is limiting. For N, however, its role in controlling mycorrhization is less clear. We have chosen the model plant Medicago truncatula to analyze the impact of P limitation and both P and N limitation on Medicago root transcriptome in response to the AM fungus Rhizophagus irregularis (formerly Glomus intraradices (BEG141)). These analyses may help us uncover signaling events involved in the interaction between these symbionts as well as genes encoding transporters potentially important for nutrient exchanges in these conditions. --We will compare the root transcriptome of Medicago truncatula plants inoculated with Rhizophagus irregularis to that of non-inoculated plants grown under P limitation (or both P and N limitation) after 4 weeks of culture
Project description:Arbuscular mycorrhizal (AM) associations enhance the phosphorous and nitrogen nutrition of host plants, but little is known about their role in potassium (K+) nutrition. Medicago truncatula plants were co-cultured with the AM fungus Rhizophagus irregularis under high and low K+ regimes for six weeks. We determined how K+ deprivation affects plant development, mineral acquisition, and how these negative effects are tempered by the AM colonization. The transcriptional response of AM roots under K+ deficiency was analyzed by whole genome RNA-seq. K+ deprivation decreased root biomass, external K+ uptake, and modulated oxidative stress gene expression in M. truncatula roots. AM colonization induced specific transcriptional responses to K+ deprivation that seem to temper these negative effects. A gene network analysis revealed putative key regulators of these responses. This study confirmed that AM associations provide some tolerance to K+ deprivation to host plants, revealed that AM symbiosis modulates the expression of specific root genes to cope with this nutrient stress, and identified putative regulators participating in these tolerance mechanisms.
Project description:In plants, miR390 directs the production of tasiRNAs from TRANS-ACTING SIRNA 3 (TAS3) transcripts to regulate AUXIN RESPONSIVE FACTOR (ARF) genes, transcription factors critical for auxin signaling; these tasiRNAs are known as tasiARFs. This pathway is highly conserved, with the TAS3 as the only one noncoding gene present almost ubiquitously in land plants. To understand the evolution of this miR390-TAS3-ARF pathway, we characterized homologs of these three genes from thousands of plant species, from bryophytes to angiosperms. Both miR390 and TAS3 are present and functional in liverworts, confirming their ancestral role to regulate ARFs in land plants. We found the lower-stem region of MIR390 genes, critical for accurate DCL1 (DICER-LIKE 1) processing, is conserved in sequence in seed plants. We propose a model for the transition of functional tasiRNA sequences in TAS3 genes occurred at the emergence of vascular plants, in which the two miR390 target sites of TAS3 genes showed distinct pairing patterns in different plant lineages. Based on the cleavability of miR390 target sites and the distance between target site and tasiARF we inferred a potential bidirectional processing mechanism exists for some TAS3 genes. We also demonstrated a tight mutual selection between tasiARF and its target genes, and characterized unusual aspects and diversity of regulatory components of this pathway. Taken together, these data illuminate the evolutionary path of the miR390-TAS3-ARF pathway in land plants, and demonstrate the significant variation that occurs in the production of phasiRNAs in plants, even in the functionally important and archetypal miR390-TAS3-ARF regulatory circuit.