The Ma gene for complete-spectrum resistance to Meloidogyne species in Prunus is a TNL with a huge repeated C-terminal post-LRR region

Root-knot nematode (RKN) Meloidogyne species are major polyphagous pests of most crops worldwide, and cultivars with durable resistance are urgently needed because of nematicide bans. The Ma gene from the Myrobalan plum (Prunus cerasifera) confers complete-spectrum, heat-stable, and high-level resistance to RKN, which is remarkable in comparison with the Mi-1 gene from tomato (Solanum lycopersicum), the sole RKN resistance gene cloned. We report here the positional cloning and the functional validation of the Ma locus present at the heterozygous state in the P.2175 accession. High-resolution mapping totaling over 3,000 segregants reduced the Ma locus interval to a 32-kb cluster of three Toll/Interleukin1 Receptor-Nucleotide Binding Site-Leucine-Rich Repeat (LRR) genes (TNL1-TNL3), including a pseudogene (TNL2) and a truncated gene (TNL3). The sole complete gene in this interval (TNL1) was validated as Ma, as it conferred the same complete-spectrum and high-level resistance (as in P.2175) using its genomic sequence and native promoter region in Agrobacterium rhizogenes-transformed hairy roots and composite plants. The full-length cDNA (2,048 amino acids) of Ma is the longest of all Resistance genes cloned to date. Its TNL structure is completed by a huge post-LRR (PL) sequence (1,088 amino acids) comprising five repeated carboxyl-terminal PL exons with two conserved motifs. The amino-terminal region (213 amino acids) of the LRR exon is conserved between alleles and contrasts with the high interallelic polymorphisms of its distal region (111 amino acids) and of PL domains. The Ma gene highlights the importance of these uncharacterized PL domains, which may be involved in pathogen recognition through the decoy hypothesis or in nuclear signaling.     

Predation, individual variability and vertebrate population dynamics

Both predation and individual variation in life history traits influence population dynamics. Recent results from laboratory predator–prey systems suggest that differences between individuals can also influence predator–prey dynamics when different genotypes experience different predation-associated mortalities. Despite the growing number of studies in this field, there is no synthesis identifying the overall importance of the interactions between predation and individual heterogeneity and their role in shaping the dynamics of free-ranging populations of vertebrates. We aim to fill this gap with a review that examines how individual variability in prey susceptibility, in predation costs, in predator selectivity, and in predatory performance, might influence prey population dynamics. Based on this review, it is clear that (1) predation risk and costs experienced by free-ranging prey are associated with their phenotypic attributes, (2) many generalist predator populations consist of individual specialists with part of the specialization associated with their phenotypes, and (3) a complete understanding of the population dynamic consequences of predation may require information on individual variability in prey selection and prey vulnerability. Altogether, this work (1) highlights the importance of maintaining long-term, detailed studies of individuals of both predators and prey in contrasting ecological conditions, and (2) advocates for a better use of available information to account for interactive effects between predators and their prey when modelling prey population dynamics.     

Dispensing synthetic green leaf volatiles in maize fields increases the release of sesquiterpenes by the plants, but has little effect on the attraction of pest and beneficial insects

Maize plants respond to feeding by arthropod herbivores by producing a number of secondary plant compounds, including volatile organic compounds (VOCs). These herbivore-induced VOCs are not only known to attract natural enemies of the herbivores, but they may also prime inducible defences in neighbouring plants, resulting in stronger and faster defence responses in these VOC-exposed plants. Among the compounds that cause this priming effect, green leaf volatiles (GLVs) have received particular attention, as they are ubiquitous and rapidly emitted upon damage. In this study, we investigated their effects under realistic conditions by applying specially devised dispensers to release four synthetic GLVs at physiologically relevant concentrations in a series of experiments in maize fields. We compared the VOC emission of GLV-exposed maize plants to non-exposed plants and monitored the attraction of herbivores and predators, as well as parasitism of the caterpillar Spodoptera frugiperda, the most common herbivore in the experimental maize fields. We found that maize plants that were exposed to GLVs emitted increased quantities of sesquiterpenes compared to non-exposed plants. In several replicates, herbivorous insects, such as adult Diabrotica beetles and S. frugiperda larvae, were observed more frequently in GLV-treated plots and caused more damage to GLV-exposed plants than to non-exposed plants. Parasitism of S. frugiperda was only weakly affected by GLVs and overall parasitism rates of S. frugiperda were similar in GLV-exposed and non-exposed plots. The effects on insect presence depended on the distance from the GLV-dispensers at which the plants were located. The results are discussed in the context of strategies to improve biological control by enhancing plant-mediated attraction of natural enemies.     

Peroxisomal localisation of the final steps of the mevalonic acid pathway in<Emphasis Type="Italic"> planta</Emphasis>

In plants, the mevalonic acid (MVA) pathway provides precursors for the formation of triterpenes, sesquiterpenes, phytosterols and primary metabolites important for cell integrity. Here, we have cloned the cDNA encoding enzymes catalysing the final three steps of the MVA pathway from Madagascar periwinkle (Catharanthus roseus), mevalonate kinase (MVK), 5-phosphomevalonate kinase (PMK) and mevalonate 5-diphosphate decarboxylase (MVD). These cDNA were shown to functionally complement MVA pathway deletion mutants in the yeast Saccharomyces cerevisiae. Transient transformations of C. roseus cells with yellow fluorescent protein (YFP)-fused constructs reveal that PMK and MVD are localised to the peroxisomes, while MVK was cytosolic. These compartmentalisation results were confirmed using the Arabidopsis thaliana MVK, PMK and MVD sequences fused to YFP. Based on these observations and the arguments raised here we conclude that the final steps of the plant MVA pathway are localised to the peroxisome.     

Antifungal activity displayed by cereulide, the emetic toxin produced by Bacillus cereus

In this study, the fungistatic activity of Bacillus cereus cereulide-producing strains was demonstrated against nine fungal species. The role of cereulide was confirmed using plasmid-cured derivatives and ces knockout mutants. The fungistatic spectra of cereulide and valinomycin, a chemically related cyclododecadepsipeptide, were also compared and found to be similar but distinct.     

Ligands of Thermophilic ABC Transporters Encoded in a Newly Sequenced Genomic Region of Thermotoga maritima MSB8 Screened by Differential Scanning Fluorimetry

The chromosome of Thermotoga maritima strain MSB8 was found to have an 8,870-bp region that is not present in its published sequence. The isolate that was sequenced by The Institute for Genomic Research (TIGR) in 1999 is apparently a laboratory variant of the isolate deposited at the Deutsche Sammlung von Mikroorganismen und Zellkulturen (DSM 3109) in 1986. This newly sequenced region from the DSMZ culture was located between TM1848 (cbp, cellobiose phosphorylase) and TM1847 (the 3′ end of a truncated ROK regulator). The new region contained seven genes: a beta glucosidase gene (bglA), three trehalose ABC transporter genes (treEFG), three xylose ABC transporter genes (xylE2F2K2), and the 5′ end of a gene encoding the ROK regulator TM1847. We present a new differential scanning fluorimetry method using a low pH that was necessary to screen potential ligands of these exceptionally thermostable periplasmic substrate-binding proteins. This method showed that trehalose, sucrose, and glucose stabilized TreE, and their binding was confirmed by measuring changes in intrinsic fluorescence upon ligand binding. Binding constants of 0.024 μM, 0.300 μM, and 56.78 μM at 60°C, respectively, were measured. XylE2 ligands were similarly determined and xylose, glucose, and fucose bound with K_d (dissociation constant) values of 0.042 μM, 0.059 μM, and 1.436 μM, respectively. Since there is no discernible phenotypic difference between the TIGR isolate and the DSMZ isolate despite the variance in their genomes, we propose that they be called genomovars: T. maritima MSB8 genomovar TIGR and T. maritima MSB8 genomovar DSM 3109, respectively.     

The swarming motility of Pseudomonas aeruginosa is blocked by cranberry proanthocyanidins and other tannin-containing materials

Bacterial motility plays a key role in the colonization of surfaces by bacteria and the subsequent formation of resistant communities of bacteria called biofilms. Derivatives of cranberry fruit, predominantly condensed tannins called proanthocyanidins (PACs) have been reported to interfere with bacterial adhesion, but the effects of PACs and other tannins on bacterial motilities remain largely unknown. In this study, we investigated whether cranberry PAC (CPAC) and the hydrolyzable tannin in pomegranate (PG; punicalagin) affected the levels of motilities exhibited by the bacterium Pseudomonas aeruginosa. This bacterium utilizes flagellum-mediated swimming motility to approach a surface, attaches, and then further spreads via the surface-associated motilities designated swarming and twitching, mediated by multiple flagella and type IV pili, respectively. Under the conditions tested, both CPAC and PG completely blocked swarming motility but did not block swimming or twitching motilities. Other cranberry-containing materials and extracts of green tea (also rich in tannins) were also able to block or impair swarming motility. Moreover, swarming bacteria were repelled by filter paper discs impregnated with many tannin-containing materials. Growth experiments demonstrated that the majority of these compounds did not impair bacterial growth. When CPAC- or PG-containing medium was supplemented with surfactant (rhamnolipid), swarming motility was partially restored, suggesting that the effective tannins are in part acting by a rhamnolipid-related mechanism. Further support for this theory was provided by demonstrating that the agar surrounding tannin-induced nonswarming bacteria was considerably less hydrophilic than the agar area surrounding swarming bacteria. This is the first study to show that natural compounds containing tannins are able to block P. aeruginosa swarming motility and that swarming bacteria are repelled by such compounds.     

A long peptide from MELOE-1 contains multiple HLA class II T cell epitopes in addition to the HLA-A*0201 epitope: an attractive candidate for melanoma vaccination

CD4⁺ T cells contribute importantly to the antitumor T cell response, and thus, long peptides comprising CD4 and CD8 epitopes may be efficient cancer vaccines. We have previously identified an overexpressed antigen in melanoma, MELOE-1, presenting a CD8⁺ T cell epitope, MELOE-1_36–44, in the HLA-A*0201 context. A T cell repertoire against this epitope is present in HLA-A*0201+ healthy subjects and melanoma patients and the adjuvant injection of TIL containing MELOE-1 specific CD8⁺ T cells to melanoma patients was shown to be beneficial. In this study, we looked for CD4⁺ T cell epitopes in the vicinity of the HLA-A*0201 epitope. Stimulation of PBMC from healthy subjects with MELOE-1_26–46 revealed CD4 responses in multiple HLA contexts and by cloning responsive CD4⁺ T cells, we identified one HLA-DRβ1*1101-restricted and one HLA-DQβ1*0603-restricted epitope. We showed that the two epitopes could be efficiently presented to CD4⁺ T cells by MELOE-1-loaded dendritic cells but not by MELOE-1+ melanoma cell-lines. Finally, we showed that the long peptide MELOE-1_22–46, containing the two optimal class II epitopes and the HLA-A*0201 epitope, was efficiently processed by DC to stimulate CD4⁺ and CD8⁺ T cell responses in vitro, making it a potential candidate for melanoma vaccination.