Covering the bases: Population genomic structure of Lemna minor and the cryptic species L. japonica in Switzerland.

Duckweeds, including the common duckweed Lemna minor, are increasingly used to test eco-evolutionary theories. Yet, despite its popularity and near-global distribution, the understanding of its population structure (and genetic variation therein) is still limited. It is essential that this is resolved, because of the impact genetic diversity has on experimental responses and scientific understanding. Through whole-genome sequencing, we assessed the genetic diversity and population genomic structure of 23 natural Lemna spp. populations from their natural range in Switzerland. We used two distinct analytical approaches, a reference-free kmer approach and the classical reference-based one. Two genetic clusters were identified across the described species distribution of L. minor, surprisingly corresponding to species-level divisions. The first cluster contained the targeted L. minor individuals and the second contained individuals from a cryptic species: Lemna japonica. Within the L. minor cluster, we identified a well-defined population structure with little intra-population genetic diversity (i.e., within ponds) but high inter-population diversity (i.e., between ponds). In L. japonica, the population structure was significantly weaker and genetic variation between a subset of populations was as low as within populations. This study revealed that L. japonica is more widespread than previously thought. Our findings signify that thorough genotype-to-phenotype analyses are needed in duckweed experimental ecology and evolution.

Marasmius oreades agglutinin enhances resistance of Arabidopsis against plant-parasitic nematodes and a herbivorous insect.

BACKGROUND: Plant-parasitic nematodes and herbivorous insects have a significant negative impact on global crop production. A successful approach to protect crops from these pests is the in planta expression of nematotoxic or entomotoxic proteins such as crystal proteins from Bacillus thuringiensis (Bt) or plant lectins. However, the efficacy of this approach is threatened by emergence of resistance in nematode and insect populations to these proteins. To solve this problem, novel nematotoxic and entomotoxic proteins are needed. During the last two decades, several cytoplasmic lectins from mushrooms with nematicidal and insecticidal activity have been characterized. In this study, we tested the potential of Marasmius oreades agglutinin (MOA) to furnish Arabidopsis plants with resistance towards three economically important crop pests: the two plant-parasitic nematodes Heterodera schachtii and Meloidogyne incognita and the herbivorous diamondback moth Plutella xylostella. RESULTS: The expression of MOA does not affect plant growth under axenic conditions which is an essential parameter in the engineering of genetically modified crops. The transgenic Arabidopsis lines showed nearly complete resistance to H. schachtii, in that the number of female and male nematodes per cm root was reduced by 86-91 % and 43-93 % compared to WT, respectively. M. incognita proved to be less susceptible to the MOA protein in that 18-25 % and 26-35 % less galls and nematode egg masses, respectively, were observed in the transgenic lines. Larvae of the herbivorous P. xylostella foraging on MOA-expression lines showed a lower relative mass gain (22-38 %) and survival rate (15-24 %) than those feeding on WT plants. CONCLUSIONS: The results of our in planta experiments reveal a robust nematicidal and insecticidal activity of the fungal lectin MOA against important agricultural pests which may be exploited for crop protection.

Expression of a Fungal Lectin in Arabidopsis Enhances Plant Growth and Resistance Toward Microbial Pathogens and a Plant-Parasitic Nematode.

Coprinopsis cinerea lectin 2 (CCL2) is a fucoside-binding lectin from the basidiomycete C. cinerea that is toxic to the bacterivorous nematode Caenorhabditis elegans as well as animal-parasitic and fungivorous nematodes. We expressed CCL2 in Arabidopsis to assess its protective potential toward plant-parasitic nematodes. Our results demonstrate that expression of CCL2 enhances host resistance against the cyst nematode Heterodera schachtii. Surprisingly, CCL2-expressing plants were also more resistant to fungal pathogens including Botrytis cinerea, and the phytopathogenic bacterium Pseudomonas syringae. In addition, CCL2 expression positively affected plant growth indicating that CCL2 has the potential to improve two important agricultural parameters namely biomass production and general disease resistance. The mechanism of the CCL2-mediated enhancement of plant disease resistance depended on fucoside-binding by CCL2 as transgenic plants expressing a mutant version of CCL2 (Y92A), compromised in fucoside-binding, exhibited wild type (WT) disease susceptibility. The protective effect of CCL2 did not seem to be direct as the lectin showed no growth-inhibition toward B. cinerea in in vitro assays. We detected, however, a significantly enhanced transcriptional induction of plant defense genes in CCL2- but not CCL2-Y92A-expressing lines in response to infection with B. cinerea compared to WT plants. This study demonstrates a potential of fungal defense lectins in plant protection beyond their use as toxins.

Silica nanoparticles enhance disease resistance in Arabidopsis plants.

In plants, pathogen attack can induce an immune response known as systemic acquired resistance that protects against a broad spectrum of pathogens. In the search for safer agrochemicals, silica nanoparticles (SiO2 NPs; food additive E551) have recently been proposed as a new tool. However, initial results are controversial, and the molecular mechanisms of SiO2 NP-induced disease resistance are unknown. Here we show that SiO2 NPs, as well as soluble Si(OH)4, can induce systemic acquired resistance in a dose-dependent manner, which involves the defence hormone salicylic acid. Nanoparticle uptake and action occurred exclusively through the stomata (leaf pores facilitating gas exchange) and involved extracellular adsorption in the air spaces in the spongy mesophyll of the leaf. In contrast to the treatment with SiO2 NPs, the induction of systemic acquired resistance by Si(OH)4 was problematic since high Si(OH)4 concentrations caused stress. We conclude that SiO2 NPs have the potential to serve as an inexpensive, highly efficient, safe and sustainable alternative for plant disease protection.

S-methyl Methanethiosulfonate: Promising Late Blight Inhibitor or Broad Range Toxin?

(1) Background: S-methyl methanethiosulfonate (MMTS), a sulfur containing volatile organic compound produced by plants and bacterial species, has recently been described to be an efficient anti-oomycete agent with promising perspectives for the control of the devastating potato late blight disease caused by Phytophthora infestans. However, earlier work raised questions regarding the putative toxicity of this compound. To assess the suitability of MMTS for late blight control in the field, the present study thus aimed at evaluating the effect of MMTS on a wide range of non-target organisms in comparison to P. infestans. (2) Methods: To this end, we exposed P. infestans, as well as different pathogenic and non-pathogenic fungi, bacteria, the nematode Caenorhabditis elegans as well as the plant Arabidopsis thaliana to MMTS treatment and evaluated their response by means of in vitro assays. (3) Results: Our results showed that fungi (both mycelium and spores) tolerated MMTS better than the oomycete P. infestans, but that the compound nevertheless exhibited non-negligible toxic effects on bacteria, nematodes and plants. (4) Conclusions: We discuss the mode of action of MMTS and conclude that even though this compound might be too toxic for chemical application in the field, its strong anti-oomycete activity could still be exploited when naturally released at the site of infection by plant-associated microbes inoculated as biocontrol agents.

Assessment of performance ability of three diagnostic methods for detection of Potato Leafroll virus (PLRV) using different visualizing systems.

To diminish the time required for some diagnostic assays including reverse transcription PCR (RT-PCR), reverse transcription loop-mediated isothermal amplification (RT-LAMP; due to mainly RNA extraction step) and also DAS-ELISA into a minimum level, an innovative immunocapture RT-LAMP (IC-RT-LAMP) and immunocapture reverse transcription (IC/RT-PCR) protocol on the basis of Potato Leafroll virus (PLRV) genome were used and optimized. In this regard, all six IC-RT-LAMP primers (i.e. F3, B3, FIP, BIP, LF and LB) together with IC/RT-PCR primers were designed on the basis of the highly conserved sequence (ORF3) of coat protein gene (GenBank accession number: U73777) of PLRV genome. Even though DAS-ELISA, IC/RT-PCR and IC-RT-LAMP assays could successfully detect positive infected plant samples, considering the time, safety, sensitivity, cost and simplicity, the last one was overall superior. Meanwhile, among five different visual dyes to accurately detect IC-RT-LAMP products, both hydroxynaphthol blue and GeneFinder™ could produce long stable colour change and brightness in a close tube-based approach to prevent cross-contamination risk, concluded eventually as the best ones. Altogether, as IC-RT-LAMP is sensitive, cost-effective, fairly user friendly and also can generate more accurate results than previous diagnostic procedures, we accordingly propose this colorimetric assay as a highly reliable alternative viral recognition system regarding PLRV recognition and probably other viral-based diseases.