Does dormancy protect seeds against attack by the pathogenic fungus <Emphasis Type="Italic">Fusarium tricinctum</Emphasis> in a semiarid grassland of Northwest China?

Aims

Soil fungal pathogens can result in the failure of seedling establishment, but the effects of fungicide applications on seed/seedling survival have differed among studies. We assumed that the variation may relate to seed dormancy/germination characteristics and hypothesized that nondormant germinating seeds are more likely to be killed by fungal pathogens than dormant seeds.

Methods

Dormant and nondormant seeds of Stipa bungeana and Lespedeza davurica were inoculated with a pathogenic fungus Fusarium tricinctum under laboratory and field conditions. The outcomes of seed/seedling fate and other parameters were evaluated.

Results

In the laboratory, nondormant seeds inoculated with F. tricinctum developed white tufts of mycelium on the radicles of germinating seeds causing them to quickly die, but dormant seeds remained intact. In contrast, in the field inoculation with F. tricinctum did not cause higher mortality of nondormant than dormant seeds but resulted in higher percentages of seedling death before they emerged from soil than the controls.

Conclusions

Our results suggest that dormancy protects seeds from being attacked by some pathogens by preventing germination, but the protection is lost once germination has commenced. Further study involving various plant species with more seeds is needed to assess the generality of this pathogen-seed interaction hypothesis.

     

Identification of an oleosin-like gene in seagrass seeds

Objective

To investigate the oil body protein and function in seeds of mature seagrass, Thalassia hemprichii.

Results

Seeds of mature seagrass T. hemprichii when stained with a fluorescent probe BODIPY showed the presence of oil bodies in intracellular cells. Triacylglycerol was the major lipid class in the seeds. Protein extracted from seagrass seeds was subjected to immunological cross-recognition with land plant seed oil body proteins, such as oleosin and caleosin, resulting in no cross-reactivity. An oleosin-like gene was found in seagrass seeds. Next generation sequencing and sequence alignment indicated that the deduced seagrass seed oleosin-like protein has a central hydrophobic domain responsible for their anchoring onto the surface of oil bodies. Phylogenetic analysis showed that the oleosin-like protein was evolutionarily closer to pollen oleosin than to seed oleosins.

Conclusion

Oil body protein found in seagrass seeds represent a distinct class of land seed oil body proteins.

     

Correction to: Neighbourhood stories: role of neighbour identity,spatial location and order of arrival in legume and non-legume initial interactions

Background and aims

We characterized fungal endophytes of seeds of invasive, non-native Phragmites from three sites in the Great Lakes region to determine if fungal symbiosis could contribute to invasiveness through their effects on seed germination and seedling growth.

Methods

Field-collected seeds were surface sterilized and plated on agar to culture endophytes for ITS sequencing. Prevalence of specific endophytes from germinated and non-germinated seeds, and from seedlings, was compared.

Results

One-third of 740 seeds yielded endophyte isolates. Fifteen taxa were identified with Alternaria sp. representing 54% of all isolates followed by Phoma sp. (21%) and Penicillium corylophilum (12%). Overall germination of seeds producing an isolate (36%) was significantly higher than seeds not producing an isolate (20%). Penicillium in particular was strongly associated with increased germination of seeds from one site. Sixty-three isolates and 11 taxa were also obtained from 30 seedlings where Phoma, Penicillium and Alternaria respectively were most prevalent. There was a significant effect of isolating an endophyte from the seed on seedling growth.

Conclusions

These results suggest that many endophyte taxa are transmitted in seeds and can increase seed germination and seedling growth of invasive Phragmites. The role of fungal endophytes in host establishment, growth and invasiveness in nature requires further research.

     

A seed-recruited microbiome protects developing seedlings from disease by altering homing responses of <Emphasis Type="Italic">Pythium aphanidermatum</Emphasis> zoospores

Aims

We investigated potential mechanisms by which a seed microbiome recruited from vermicomposted dairy manure alters Pythium aphanidermatum zoospore mediated pathogenesis in cucumber.

Methods

Bioassays were conducted to measure arrival of zoospores at the seed surface via qPCR and subsequent seedling disease incidence. Seed exudates were collected at relevant time points for use in zoospore microscopy assays. Metabolomic analysis was used to characterize seed exudates.

Results

Microbes recruited by the germinating seed from a disease suppressive substrate within 8 hours of sowing prevented zoospore arrival at the seed surface, modified seed exudates and reduced disease incidence. In vitro exposure to microbially modified seed exudates altered zoospore homing responses and reduced both encystment and germination compared to control exudates. Combining modified and control exudates failed to restore zoospore attraction to levels observed with control exudates. Observed zoosporolytic activity of the modified exudates was unique to the ethyl acetate fraction and metabolomic analysis revealed several putative zoosporolytic compounds present at higher relative abundance when compared to control exudates.

Conclusions

The observed disease suppression was likely due to the production of a specific zoosporolytic compound or set of compounds in the spermosphere by one or more members of the seed-recruited vermicompost microbiome.

     

Niches and routes of transmission of <Emphasis Type="Italic">Xanthomonas citri</Emphasis> pv. <Emphasis Type="Italic">fuscans</Emphasis> to bean seeds

Aims

Seeds are vectors of a diversified microbiota including plant pathogens. To better understand transmission of common bacterial blight (CBB) agents to bean seeds, we analyzed the role of non-pathogenic xanthomonads on seed transmission efficiency and investigated the location of Xanthomonas citri pv. fuscans (Xcf) into seeds and plantlets.

Methods

Competition between CBB and NP strains was initially assessed in vitro and then extended in planta to monitor the impact of co-inoculation on Xcf seed transmission. Moreover, location of Xcf strains in seeds and seedlings was visualized using a combination of gfp-tagged strain and DOPE-FISH/CSLM.

Results

Whereas CBB agent growth was inhibited in vitro by some seed-borne non-pathogenic xanthomonads strains, these strains did not transmit efficiently to seed through floral pathway and did not affect Xcf seed transmission. Xcf cells were observed entering seed through vascular elements and parenchyma of funiculus, but also micropyle and testa. Xcf cells were observed, moreover, among other bacteria on radicle surfaces, especially tip, in cotyledons, and plumules.

Conclusions

CBB agents are more efficient than non-pathogenic xanthomonads in using the floral route to colonize seeds. CBB agents are located within different niches in the seed tissues up to the embryonic axis.

     

Molecular dynamics in germinating,endophyte-colonized quinoa seeds

Aims

The pseudo-cereal quinoa has an outstanding nutritional value. Seed germination is unusually fast, and plant tolerance to salt stress exceptionally high. Seemingly all seeds harbor bacterial endophytes. This work examines mitogen-activated protein kinase (MAPK) activities during early development. It evaluates possible contribution of endophytes to rapid germination and plant robustness.

Methods

MAPK activities were monitored in water- and NaCl-imbibed seeds over a 4-h-period using an immunoblot-based approach. Cellulolytic and pectinolytic abilities of bacteria were assessed biochemically, and cellular movement, biofilm, elicitor and antimicrobial compound synthesis genes sequenced. GyrA-based, cultivation-independent studies provided first insight into endophyte diversity.

Results

Quinoa seeds and seedlings exhibit remarkably complex and dynamic MAPK activity profiles. Depending on seed origin, variances exist in MAPK patterns and probably also in endophyte assemblages. Mucilage-degrading activities enable endophytes to colonize seed surfaces of a non-host species, chia, without apparent adverse effects.

Conclusions

Owing to their motility, cell wall-loosening and elicitor-generating abilities, quinoa endophytes have the potential to drive cell expansion, move across cell walls, generate damage-associated molecular patterns and activate MAPKs in their host. Bacteria may thus facilitate rapid germination and confer a primed state directly upon seed rehydration. Transfer into non-native crops appears both desirable and feasible.

     

Community structure and diversity of endophytic bacteria in seeds of three consecutive generations of <Emphasis Type="Italic">Crotalaria pumila</Emphasis> growing on metal mine residues

Aims

We investigated the possible transgenerational transfer of bacterial seed endophytes across three consecutive seed generations of Crotalaria pumila growing on a metal mining site in Mexico.

Methods

Seeds were collected during three successive years in the semi-arid region of Zimapan, Mexico. Total communities of seed endophytes were investigated using DNA extraction from surface sterilized seeds and 454 pyrosequencing of the V5-V7 hypervariable regions of the 16S rRNA gene.

Results

The communities consisted of an average of 75 operational taxonomic units (OTUs); richness and diversity did not change across years. Methylobacterium, Staphylococcus, Corynebacterium, Propionibacterium and eight other OTUs constituted >60% of the community in each generation. The microbiome was dominated by Methylobacterium (present in >80% of samples). Functions associated with the microbiome were C and N fixation, oxidative phosphorylation and photosynthesis activity.

Conclusions

The bacterial endophytic communities were similar across three consecutive seed generations. Among the core microbiome Methylobacterium strains were the most abundant and they can contribute to nutrient acquisition, plant growth promotion and stress resilience to their host in metal contaminated mine residues. Identification of the seed microbiome of C. pumila may lead to novel and more efficient inoculants for microbe-assisted phytoremediation.

     

A novel method for single-grain-based metabolic profiling of Arabidopsis seed

Introduction

In plant metabolomics, metabolite contents are often normalized by sample weight. However, accurate weighing of very small samples, such as individual Arabidopsis thaliana seeds (approximately 20 µg), is difficult, which may lead to irreproducible results.

Objectives

We aimed to establish alternative normalization methods for seed-grain-based comparative metabolomics of A. thaliana.

Methods

Arabidopsis thaliana seeds were assumed to have a prolate spheroid shape. Using a microscope image of each seed, the lengths of major and minor axes were measured by fitting a projected 2-dimensional shape of each seed as an ellipse. Metabolic profiles of individual diploid or tetraploid A. thaliana seeds were measured by our highly sensitive protocol (“widely targeted metabolomics”) that uses liquid chromatography coupled with tandem quadrupole mass spectrometry. Mass spectrometric analysis of 1 µL of solution extract identified more than 100 metabolites. The data were normalized by various seed-size measures, including seed volume (single-grain-based analysis). For comparison, metabolites were extracted from 4 mg of diploid and tetraploid A. thaliana seeds and their metabolic profiles were analyzed by normalization of weight (weight-based analysis).

Results

A small number of metabolites showed statistically significant differences in the single-grain-based analysis compared to weight-based analysis. A total of 17 metabolites showed statistically different accumulation between ploidy types with similar fold changes in both analyses.

Conclusion

Seed-size measures obtained by microscopic imaging were useful for data normalization. Single-grain-based analysis enables evaluation of metabolism of each seed and elucidates the metabolic profiles of precious bioresources by using small amounts of samples.

     

Disease protection and allelopathic interactions of seed-transmitted endophytic pseudomonads of invasive reed grass (<Emphasis Type="Italic">Phragmites australis</Emphasis>)

Background and aims

Non-native Phragmites australis (haplotype M) is an invasive grass that decreases biodiversity and produces dense stands. We hypothesized that seeds of Phragmites carry microbes that improve seedling growth, defend against pathogens and maximize capacity of seedlings to compete with other plants.

Methods

We isolated bacteria from seeds of Phragmites, then evaluated representatives for their capacities to become intracellular in root cells, and their effects on: 1.) germination rates and seedling growth, 2.) susceptibility to damping-off disease, and 3.) mortality and growth of competitor plant seedlings (dandelion (Taraxacum officionale F. H. Wigg) and curly dock (Rumex crispus L.)).

Results

Ten strains (of 23 total) were identified and characterized; seven were identified as Pseudomonas spp. Strains Sandy LB4 (Pseudomonas fluorescens) and West 9 (Pseudomonas sp.) entered root meristems and became intracellular. These bacteria improved seed germination in Phragmites and increased seedling root branching in Poa annua. They increased plant growth and protected plants from damping off disease. Sandy LB4 increased mortality and reduced growth rates in seedlings of dandelion and curly dock.

Conclusions

Phragmites plants associate with endophytes to increase growth and disease resistance, and release bacteria into the soil to create an environment that is favorable to their seedlings and less favorable to competitor plants.

     

Identity of plant,lichen and moss species connects with microbial abundance and soil functioning in maritime Antarctica

Background and aims

Plant breeding activities shape the rhizosphere microbiome but less is known about the relationship of both with the seed microbiome. We analyzed the composition of bacterial communities of seeds and rhizospheres of Styrian oil pumpkin genotypes in comparison to bulk soil to elucidate specific microbial signatures to support a concept involving plant-microbe interactions in breeding strategies.

Methods

The seed and rhizosphere microbiomes of 14 genotypes of oilseed pumpkin and relatives were analyzed using a 16S rRNA gene amplicon sequencing approach, which was assessed by bioinformatics and statistical methods.

Results

All analyzed microhabitats were characterized by diverse bacterial communities, but the relative proportions of phyla and the overall diversity was different. Seed microbiomes were characterized by the lowest diversity and dominant members of Enterobacteriaceae including potential pathogens (Erwinia, Pectobacterium). Potential plant-beneficial bacteria like Lysobacter, Paenibacillus and Lactococcus contributed to the microbial communities in significant abundances. Interestingly, strong genotype-specific microbiomes were detected for seeds but not for the rhizospheres.

Conclusions

Our study indicates a strong impact of the Cucurbita pepo genotype on the composition of the seed microbiome. This should be considered in breeding of new cultivars that are more capable of exploiting beneficial indigenous microbial communities.

     

A fungal endophyte defensive symbiosis affects plant-nematode interactions in cotton

Background and aims

Most investigations of fungi as nematode antagonists have focused on their interactions with nematodes in the soil. This study tested a foliar-isolated endophytic Phialemonium inflatum for its effects against the root-knot nematode as an endophyte in cotton using a seed treatment inoculation.

Methods

Cotton seeds were inoculated with P. inflatum spore suspensions prior to planting. Nematode infection and reproduction were quantified at Day 12 and 6 weeks after nematode egg inoculation, respectively. To establish whether the observed negative effects on nematodes were due to P. inflatum in the soil or as an endophyte in the plant, we also applied a soil fungicide treatment at the seedling stage to kill the fungi outside the plant.

Results

Persistent suppression of nematode penetration and galling, as well as subsequent reproduction, were observed in endophyte-treated plants independent of fungicide treatment, consistent with an endophytic mode of nematode suppression; and these negative effects did not depend on the concentration of fungal inoculum used to treat to the seed.

Conclusions

Our study highlights a novel role for P. inflatum as part of a plant-fungal defensive symbiosis in cotton, as well as the need for a broader understanding of endophyte-plant-nematode ecological interactions.

     

Bacterial endophytes from rice cut grass (<Emphasis Type="Italic">Leersia oryzoides</Emphasis> L.) increase growth,promote root gravitropic response,stimulate root hair formation,and protect rice seedlings from disease

Background and Aims

Leersia oryzoides, a wild relative of rice (Oryza sativa), may carry potential seed-borne bacterial endophytes which could be used to enhance growth of rice. We hypothesized that seed-associated bacteria from L. oryzoides would be compatible with rice and promote seedling growth, development, and survival.

Methods

We isolated bacteria from seed of L. oryzoides and checked compatibility with rice as well as Bermuda grass seeds for seedling growth promotion. Internal colonisation of bacteria into root cells was observed by ROS staining and microscopic observation. Growth promoting bacteria were evaluated for IAA production, phosphate solubilization and antifungal activities.

Results

Overall, ten bacteria were found to be growth promoting in rice seedlings with effects including restoration of root gravitropic response, increased root and shoot growth, and stimulation of root hair formation. All bacteria were identified by 16S rDNA sequencing. Six bacteria were found to become intracellular in root parenchyma and root hairs in rice and in Bermuda grass seedlings. Six bacteria were able to produce IAA in LB broth with highest (47.06 ± 1.99 μg ml^?1) by LTE3 (Pantoea hericii). Nine isolates solubilized phosphate and inhibited at least one soil borne fungal pathogen.

Conclusions

Seed bacteria of L. oryzoides are compatible with rice. Many of these bacteria become intracellular, induce root gravitropic response, increase root and shoot growth, and stimulate root hair formation in both rice and Bermuda grass seedlings. Presence of bacteria protects seedlings from soil pathogens during seedling establishment. This research suggests that bioprospecting microbes on near relatives of rice and other crop plants may be a viable strategy to obtain microbes to improve cultivation of crops.

     

Metabolomic analysis of tomato seed germination

Introduction

Seed germination is inherently related to seed metabolism, which changes throughout its maturation, desiccation and germination processes. The metabolite content of a seed and its ability to germinate are determined by underlying genetic architecture and environmental effects during development.

Objective

This study aimed to assess an integrative approach to explore genetics modulating seed metabolism in different developmental stages and the link between seed metabolic- and germination traits.

Methods

We have utilized gas chromatography-time-of-flight/mass spectrometry (GC-TOF/MS) metabolite profiling to characterize tomato seeds during dry and imbibed stages. We describe, for the first time in tomato, the use of a so-called generalized genetical genomics (GGG) model to study the interaction between genetics, environment and seed metabolism using 100 tomato recombinant inbred lines (RILs) derived from a cross between Solanum lycopersicum and Solanum pimpinellifolium.

Results

QTLs were found for over two-thirds of the metabolites within several QTL hotspots. The transition from dry to 6 h imbibed seeds was associated with programmed metabolic switches. Significant correlations varied among individual metabolites and the obtained clusters were significantly enriched for metabolites involved in specific biochemical pathways.

Conclusions

Extensive genetic variation in metabolite abundance was uncovered. Numerous identified genetic regions that coordinate groups of metabolites were detected and these will contain plausible candidate genes. The combined analysis of germination phenotypes and metabolite profiles provides a strong indication for the hypothesis that metabolic composition is related to germination phenotypes and thus to seed performance.

     

Improved campesterol production in engineered <Emphasis Type="Italic">Yarrowia lipolytica</Emphasis> strains

Objectives

To engineer Yarrowia lipolytica for improving the heterologous production of campesterol (a key precursor to manufacture pharmaceutical steroids).

Results

By screening 7-dehydrocholesterol reductase (DHCR7) from diverse species, DHCR7 from Danio rerio was the best candidate for campesterol synthesis. Overexpression of ACL (ATP: citrate lyase) or POX2 (peroxisome acyl-CoA oxidase 2) were key to improving campesterol production. The highest yield of campesterol was 942 mg/l was with the strain overexpressing POX2 in a 5 l bioreactor via high cell density fermentation process with a restricted supply of carbon sourc, sunflower seed oil.

Conclusions

A promising platform to synthesize downstream steroid drugs was established. Efficient approaches were provided to improve the production of desired molecules in Y. lipolytica with high oil utilization efficiency.

     

Extraction of natural products from bark of <Emphasis Type="Italic">Betula pendula</Emphasis> using ionic liquids

Introduction

Aqueous–methanol mixtures have successfully been applied to extract a broad range of metabolites from plant tissue. However, a certain amount of material remains insoluble.

Objectives

To enlarge the metabolic compendium, two ionic liquids were selected to extract the methanol insoluble part of trunk from Betula pendula.

Methods

The extracted compounds were analyzed by LC/MS and GC/MS.

Results

The results show that 1-butyl-3-methylimidazolium acetate (IL-Ac) predominantly resulted in fatty acids, whereas 1-ethyl-3-methylimidazolium tosylate (IL-Tos) mostly yielded phenolic structures. Interestingly, bark yielded more ionic liquid soluble metabolites compared to interior wood.

Conclusion

From this one can conclude that the application of ionic liquids may expand the metabolic snapshot.

     

Soil micro-food web interactions and rhizosphere priming effect

Background

Seeds host bacterial inhabitants but only a limited knowledge is available on which taxa inhabit seed, which niches could be colonized, and what the routes of colonization are.

Scope

Within this commentary, a discussion is provided on seed bacterial inhabitants, their taxa, and from where derive the seed colonizers.

Conclusions

Seeds/and grains host specific bacteria deriving from the anthosphere, carposphere, or from cones of gymnosperms and inner tissues of plants after a long colonization from the soil to reproductive organs.

     

Dynamic of reserve compounds of mesocarp and seeds of macaw palm (<Emphasis Type="Italic">Acrocomia aculeata)</Emphasis> submitted to different storage conditions

Key message

Storage changed carbohydrate and protein levels, which can be related to embryo viability. The fatty acid profile was constant, and the embryo composition was similar to the mesocarp, not the endosperm.

Abstract

Macaw palm fruits have a diverse biochemical constitution, and there is significant commercial interest in this species among food, pharmaceutical, cosmetics, and bioenergy industries. We evaluated changes in the reserve compounds of macaw palm mesocarp and seeds from fruits stored for 1 year under three different conditions. Protein and carbohydrate levels were highest in the embryo than in the endosperm. Fatty acid profiles were very similar over time under all storage conditions and in each structure evaluated, with the embryo composition being very similar to the mesocarp. Macaw palm oil remained well preserved under all storage conditions tested, but seed reserves and seed viability are best maintained at room temperatures. The endosperm contained higher levels of saturated fatty acids than either the embryo or mesocarp, making seeds more resistant to oxidative deterioration than the mesocarp. The results showed that the composition of the mesocarp oil promises the production of high-quality biodiesel from this structure, and changes in carbohydrate and protein levels show that laboratory conditions are the most efficient for maintaining seed quality during storage.