Symbiosis

Evidence against mutualism in an aeolid nudibranch associated with Symbiodiniaceae dinoflagellates Abstract The symbiotic association with Symbiodiniaceae dinoflagellates has been more investigated for reef-building corals than for other metazoan taxa. Nudibranchs are relevant hosts as they present a wide variety of relationships with Symbiodiniaceae that range from predation to mutualistic association. The aeolid Berghia stephanieae is perhaps the best model for ecological studies in the mollusk-dinoflagellate association due to its hardiness, short life cycle and simple aquaculture protocols. However, it remains untested if B. stephanieae and Symbiodiniaceae actually engage in mutualism. Therefore, this study experimentally investigated the following aspects pertaining to the relationship between the two organisms: (i) Symbiodiniaceae retention time in the host tissue, (ii) effect of Symbodiniaceae presence in the prey item on host growth, and (iii) host capability to obtain free-living Symbiodiniaceae. Three experiments were performed: (i) monitoring of Symbiodiniaceae concentration in the cerata of starved B. stephanieae, (ii) offer of different-sized prey with and without symbionts and measuring B. stephanieae growth, and (iii) offer of free-living Symbiodiniaceae to B. stephanieae. Results show that the retention time (3–5 days) is much shorter than for many symbiont-associated nudibranchs. Berghia stephanieae growth is influenced by prey size, and apparently not affected by symbiont presence. Finally, this species is unable to obtain free-living Symbiodiniaceae. These results indicate that B. stephanieae does not meet criteria for a mutualistic relationship with Symbiodiniaceae, such as long-term retention and metabolite or favor exchange. This relationship may be in an evolutionary transitional stage, unlike the fully functional mutualism found in other organisms such as reef-building corals.

Comparative study of secondary metabolites and bioactive properties of the lichen Cladonia foliacea with and without the lichenicolous fungus Heterocephalacria bachmannii Abstract The phenolic, flavonoid, tannin and proanthocyanidin content of the lichen Cladonia foliacea with and without its lichenicolous fungus Heterocephalacria (Syzygospora) bachmannii was investigated. The phenolic compounds were quantified in organic extracts using ultrasonic extraction (acetone and methanol) and in milled material (the ground material diluted with microcrystalline cellulose). The total phenolic content depended on the solvent polarity, the extraction technique and the species. The results demonstrated that the highest total phenolic content was recorded in untreated milled material (935.75 μg GAE/g DW) of H. bachmannii plus C. foliacea, followed by C. foliacea (668.29 μg GAE/g DW). The antioxidant activities were evaluated by the in vitro scavenging capacity, iron reducing power, and iron chelating power. The results showed that the highest scavenging capacity were obtained in methanol extracts of C. foliacea with IC50 = 0.015 mg/mL, followed by methanolic extract of H. bachmannii plus C. foliacea that had a scavenging capacity and iron reducing power of (IC50 = 0.030 mg/mL and IC50 = 0.054 mg/mL, respectively). The milled material showed the highest iron chelating power (IC50 = 0.279 mg/mL). We conclude that Cladonia foliacea when parasitized by H. bachmanniipossesses a high antioxidant potential in the methanolic extract. Acetone and methanol extracts, showed that extracts from lichen plus lichenicolous fungus contained different and possibly more effective bioactive molecules than the lichen alone. These included phenolic acids, alkanes and aromatic compounds. This is the first study to investigate the phenolic content and antioxidant capacity of a lichenicolous fungus, albeit based on differences between the lichen with and without the mycoparasite H. bachmannii .

Obliteration of phosphorus deficiency in plants by microbial interceded approach Abstract Phosphorus plays an indispensable part in keeping up soil richness and securing global sustenance production, however, its chief proportions remain interlocked in various insoluble forms of Ca, Fe and Al ion precipitates that cannot be taken by the plants proficiently. This prompts to an indiscriminate application of phosphatic chemical fertilizers to the crop field which has led to substantial pollution of soil, air, water and deleterious effects on soil health due to leaching and run-off of phosphorus into soil and water table. Microorganisms such as bacteria, fungi, actinobacteria, and cyanobacteria play a crucial role in mobilizing inorganic and organic P in the soil and simultaneously increases P uptake by the plant. In the present review, endeavors have been made to emphasize on the occurrence, mechanism, the role of phosphate solubilizing bacteria in solubilization of fixed phosphorus and genetics of phosphate solubilizing microorganisms.

A first glimpse at genes important to the Azolla–Nostoc symbiosis Abstract Azolla is a small genus of diminutive aquatic ferns with a surprisingly vast potential to benefit the environment and agriculture, as well as to provide insight into the evolution of plant-cyanobacterial symbioses. This capability is derived from the unique relationship Azolla spp. have with their obligate, nitrogen-fixing cyanobacterial symbiont, Nostoc azollae, that resides in their leaves. Although previous work has specified the importance of the exchange of ammonium and sucrose metabolites between these two partners, we have yet to determine the underlying molecular mechanisms that make this symbiosis so successful. The newly sequenced and annotated reference genome of Azolla filiculoides has allowed us to investigate gene expression profiles of A. filiculoides—both with and without its obligate cyanobiont, N. azollae—revealing genes potentially essential to the Azolla-Nostoc symbiosis. We observed the absence of differentially expressed glutamine synthetase (GS) and glutamate synthase (GOGAT) genes, leading to questions about how A. filiculoides regulates the machinery it uses for nitrogen assimilation. Ushering A. filiculoides into the era of transcriptomics sets the stage to truly begin to understand the uniqueness of the Azolla-Nostoc symbiosis.

Response of dry bean ( Phaseolus vulgaris L.) to inoculation with indigenous and commercial Rhizobium strains under organic farming systems in Minnesota Abstract Organic farmers recognize the importance of using Rhizobium to meet crop N fertility needs and to reduce use of chemical fertilizers. Field experiments were conducted during the 2015 and 2016 seasons at different organic fields to assess the effect of indigenous Rhizobium leguminosarum bv. phaseoli (OrgK9) and commercial R. tropici (CIAT899) strains on symbiotic performance and grain yield of bean varieties, Eclipse and Redhawk. Averaged for both varieties, nodule numbers on plants inoculated with CIAT899 (35.2 ± 3.7 and 26.3 ± 2.6 /plant) and OrgK9 (29.6 ± 2.5 and 26.8 ± 2.1 /plant) were significantly greater (P < 0.0001) than the control (18.9 ± 2.2 and 10.5 ± 3.1) in 2015 and 2016, respectively. Bean genotype Eclipse cultivated at Lamberton and inoculated with OrgK9 had (P < 0.0001) greater number of nodules compared with CIAT899-inoculated or non-inoculated plants. The N-content (3.3 ± 0.04%) of plants inoculated with CIAT899 was greater (P < 0.0001) compared with plants inoculated with OrgK9. Strain CIAT899 increased nodule occupancy by 29 and 62% and 4 and 26% on Red Hawk cultivated in the Lamberton and Farmington fields compared with the control in season 2015 and 2016, respectively. The majority of nodules formed on Red Hawk (76%) and Eclipse (64%) at Farmington were occupied by CIAT899 and OrgK9 in 2015 and 2016, respectively. Eclipse inoculated with OrgK9 had a significantly greater seed yields (2683 ± 402 and 2546 ± 247 kg/ha) compared with control (2265 ± 996 and 2058 ± 51 kg/ha) in both years, respectively. These results clearly indicate that symbiotic performance and grain yield of dry bean can be significantly increased by using Rhizobium inoculation under organic farming systems.

Do silver nanoparticles stimulate the formation of ectomycorrhizae in seedlings of pedunculate oak ( Quercus robur L.)? Abstract Metal nanoparticles are gaining ever-wider application in agriculture and forestry, as alternatives to chemical agents used as fertilisers, growth stimulators and pesticides, establishing a need for eco-toxicological risk assessment of these agents. We tested the effects of foliar-applied silver nanoparticles (AgNPs) on chlorophyll a fluorescence and on abundance and species composition of ectomycorrhizal (ECM) colonisation. The application of AgNPs at concentrations of 5, 25 and 50 ppm was found to stimulate the formation of mycorrhizae in seedlings of pedunculate oak, with the highest effect at intermediate concentrations (25 ppm). There were non-linear effects on the relative abundance of ECM fungal species. The proportion of dominant T. terrestris was highest in the control group, whereas the shares of ECM formed by the two other species, S. brunnea and P. involutus, were higher in the treatments with intermediate and maximal concentrations of AgNPs, respectively. Maximum quantum yield of photosystem II (Fv/fm) assessed by chlorophyll a fluorescence measurements revealed slight debilitation of oak seedlings irrespective of the application of AgNPs and their concentrations. This result offered an indirect indication that photosynthesis capacity had no influence on the level of mycorrhization. We hypothesise that foliar AgNPs treatments at concentrations below thresholds of acute toxicity and in the absence of significant effects on chlorophyll a fluorescence may still exert significant influence on biotic interactions including mycorrhizal symbioses by impacting plant hormonal balance, particularly ethylene, and regulatory pathways involved in host control of ECM colonisation.

Evolution of substrate specificity and fungal symbiosis in filmy ferns (Hymenophyllaceae): a Bayesian approach for ambiguous character state reconstruction Abstract Ferns, as landplants in general, originally form a symbiosis involving Arbuscular Mycorrhizal Fungi (AMF), which are prevalent in habitats directly connected to the soil, including low epiphytic sites, but are largely absent in the high epiphytic habitat. High probabilities of AMF should be expected in chiefly terrestrial lineages whereas truly, fully adapted epiphytic lineages should be lacking fungal endophytes or may have switched to other types of fungi; e.g. Dark Septate Endophytes (DSE), a morphological class of mostly unspecified fungi that is often found in epiphytic ferns and may include potentially symbiotic ascomycetes. We used a Bayesian approach for a comparison of the ambiguous character of preferred substrate with the incompletely known mycorrhization status for an ancient lineage of ferns, the Hymenophyllaceae or filmy ferns. The majority of the analysed 167 species prefers either the saxicolous, terrestrial or epiphytic habitat (differentiated into low and high epiphytic), but there are also many generalists without clear preference. For the whole family Hymenophyllaceae and one of the two main clades of the subfamily Trichomanoidae, the terrestrial habitat and AMF received the highest probability for representing the ancestral state. For the subfamily Hymenophylloidae, the low epiphytic habitat and DSE received the highest probability as ancestral state, whereas that for AMF was very low. The other main clade of the subfamily Trichomanoidae as well as the whole subfamily was found most likely to be originally terrestrial; but in both cases the probability values did not differ much from the values for low epiphytism, with all values around 50 ± 5%. The high epiphytic habitat, which in its present condition is thought to be possible only in angiosperm-dominated vegetation, did not receive high probability to be the ancestral state in any clade. This decouples the evolution of epiphytism in filmy ferns in time from the advent of the angiosperms, which is hypothesized to have triggered the radiation of all other major epiphytic fern lineages.

Gene expression profiling of tomato roots interacting with Pseudomonas fluorescens unravels the molecular reprogramming that occurs during the early phases of colonization Abstract The concerns of people over the wide use of chemicals are determining an increasing attention to more eco-friendly management practices in agriculture. Plant growth promoting rhizobacteria (PGPR) are emerging as important beneficial microbial inoculants because of their capability to promote plant growth and improve plant protection. We performed RNASeq to analyze gene expression profiling at 24, 48 and 72 h post inoculation (hpi) by Pseudomonas fluorescens strain CREA 16 (Pf-16), a PGPR previously isolated from Pisum sativum rhizosphere and with proven growth promotion activity on tomato plants, to unravel the extent of transcriptome reprogramming of tomato roots during the colonization. Pf-16 induces transcriptional reprogramming mainly at 24 and 72 hpi particularly affecting the down-regulation of genes. During the investigated time span, two phases can be clearly distinguished. In the first phase, within the first 48 h, Pf-16 strongly represses R-genes, calcium/calmodulin-mediated signaling and various transcription factors involved in the salicylic and jasmonic acid metabolism. Even more, Pf-16 blocks ethylene biosynthesis/signaling and protease-dependent mechanisms. At a later stage, from 48/72 h onwards, an intimate relationship between tomato roots and Pf-16 is established as a result of cell wall modifications. Finally, Pf-16 triggers the up-regulation of genes associated with plant growth promotion. Based on the main findings derived from this research, a model that gathers and describes the molecular events of outmost importance during tomato roots-Pf-16 interaction is proposed.

The role of seed-vectored endophytes in seedling development and establishment Abstract Seed-vectored endophytes internally colonize plant seeds and remain without eliciting disease symptoms. Microbes are carried by seeds generation after generation to benefit the host during and following seed germination. Seed-vectored endophytes have been poorly investigated and research targeted at understanding their biology will have immense applications in agriculture and horticulture. Some reports are available on the roles of seed endophytes in plant growth promotion via nutrient acquisition and biocontrol of soil borne diseases, but mechanisms of interaction at the endophyte-host interface, especially during seed germination and seedling establishment, have not been explored adequately. The present paper is intended to review the role of seed vectored endophytes in seed germination, seedlings development and in developing the rhizosphere community. The mechanisms of interaction and movement of seed inhabiting endophytic bacteria are explained with the help of pictorial models.

Plant growth promoting rhizobacteria in sustainable agriculture: from theoretical to pragmatic approach Abstract Plant growth promoting rhizobacteria (PGPR) are the residents of rhizosphere that are known to influence plant growth and survival through the production of various regulatory chemicals under a variety of circumstances. This growth promotion is accomplished by both direct and indirect means. Direct effects of PGPR encompass two major activities, that is, Bio-fertilization (Enhancement of nutrient uptake including nitrogen and phosphorous primarily) and phytostimulation (Production of plant growth promoting hormones). Indirect effects of PGPR are majorly contained within their ability as biocontrol agents that antagonize the growth and survival of phytopathogens either by the production of antagonizing chemicals (Local antagonism) or by the induction of systemic resistance throughout the plant against pathogens. The understanding of such diverse growth promoting abilities of PGPR has led to their application as potent biofertilizers for sustainable agriculture. However, further analyses of the agro-ecosystem with complex biotic and abiotic mechanisms should not be overlooked for their extensive commercial applications and future prospects.