Increased Disease Resistance Research Articles

Comparison of disease resistance between diploid, induced-triploid, and intercross-triploid rainbow trout including trout selected for resistance to Flavobacterium psychrophilum

All-female triploid fish are advantageous in rainbow trout (Oncorhynchus mykiss) aquaculture due to sterility and the consequent superior filet quality, growth, and feed conversion achieved at reproductive size. Triploid fish are commonly produced by pressure or temperature shock of the zygote (induced-triploids, 3NP), but can also be produced by mating a tetraploid parent with a diploid (2N) parent (intercross-triploids, 3NC). Little is known about the disease resistance of 3NC fish. In this study, we measured post-challenge survival of genetically-related 2N, 3NP and 3NC families after exposure to Flavobacterium psychrophilum the etiological agent of bacterial cold water disease (BCWD). The families used in this study originated from either an unselected commercial stock or BCWD resistant or susceptible line of rainbow trout. The overall survival of 2N fish was slightly higher than the respective 3NP and 3NC fish. Although 3NC fish tended to show higher survival than 3NP fish, this response was not sufficiently consistent to promote intercross production of triploids for increasing disease resistance. The survival of ten sets of 3NP, 3NC and 2N families, created from BCWD resistant and susceptible line parents, demonstrated overall similar inherent relative survival differences among the ploidy types both among families and between lines, although family differences in response to triploidization and triploidization strategy were observed. In summary, minimal survival difference between 3NP and 3NC families following experimental challenge suggests that innate resistance to F. psychrophilum is not substantially altered by the triploidization strategy and progress in family-based selective breeding of diploid fish for BCWD resistance will substantially translate into improved survival when triploids are derived either by shock treatment or intercross breeding.

β-Aminobutyric acid induces resistance of mango fruit to postharvest anthracnose caused by Colletotrichum gloeosporioides and enhances activity of fruit defense mechanisms

The effect of β-aminobutyric acid (BABA) on control of anthracnose caused by Colletotrichum gloeosporioides in mango fruit and its possible mechanisms were investigated. The results show that BABA treatments effectively suppressed the expansion of lesion in mango fruit inoculated with C. gloeosporioides during storage at 25°C, with the greatest efficacy being obtained using 100mM BABA. However, BABA at 25–400mM did not exhibit direct antifungal activity against C. gloeosporioides in vitro. Furthermore, BABA treatment at 100mM enhanced the activities of β-1,3-glucanase (GLU), chitinase (CHT) and phenylalanine ammonia lyase (PAL). BABA treatment also contributed to the accumulation of hydrogen peroxide (H2O2), while decreasing the rate of superoxide radical (O2−) production. Concurrently, BABA increased the activity of superoxide dismutase (SOD), while inhibiting catalase (CAT) and ascorbate peroxidase (APX) activities. These results indicate that increased disease resistance of mango fruit after BABA treatment during storage might be attributed to an elicitation of defense response involving in the enhancement of defense-related enzyme activities and modulation of antioxidant system activities.

Genetic Requirements for Signaling from an Autoactive Plant NB-LRR Intracellular Innate Immune Receptor

Plants react to pathogen attack via recognition of, and response to, pathogen-specific molecules at the cell surface and inside the cell. Pathogen effectors (virulence factors) are monitored by intracellular nucleotide-binding leucine-rich repeat (NB-LRR) sensor proteins in plants and mammals. Here, we study the genetic requirements for defense responses of an autoactive mutant of ADR1-L2, an Arabidopsis coiled-coil (CC)-NB-LRR protein. ADR1-L2 functions upstream of salicylic acid (SA) accumulation in several defense contexts, and it can act in this context as a “helper” to transduce specific microbial activation signals from “sensor” NB-LRRs. This helper activity does not require an intact P-loop. ADR1-L2 and another of two closely related members of this small NB-LRR family are also required for propagation of unregulated runaway cell death (rcd) in an lsd1 mutant. We demonstrate here that, in this particular context, ADR1-L2 function is P-loop dependent. We generated an autoactive missense mutation, ADR1-L2D484V, in a small homology motif termed MHD. Expression of ADR1-L2D848V leads to dwarfed plants that exhibit increased disease resistance and constitutively high SA levels. The morphological phenotype also requires an intact P-loop, suggesting that these ADR1-L2D484V phenotypes reflect canonical activation of this NB-LRR protein. We used ADR1-L2D484V to define genetic requirements for signaling. Signaling from ADR1-L2D484V does not require NADPH oxidase and is negatively regulated by EDS1 and AtMC1. Transcriptional regulation of ADR1-L2D484V is correlated with its phenotypic outputs; these outputs are both SA–dependent and –independent. The genetic requirements for ADR1-L2D484V activity resemble those that regulate an SA–gradient-dependent signal amplification of defense and cell death signaling initially observed in the absence of LSD1. Importantly, ADR1-L2D484V autoactivation signaling is controlled by both EDS1 and SA in separable, but linked pathways. These data allows us to propose a genetic model that provides insight into an SA–dependent feedback regulation loop, which, surprisingly, includes ADR1-L2.

Sex-Specific Effect of Juvenile Diet on Adult Disease Resistance in a Field Cricket

Food limitation is expected to reduce an individual’s body condition (body mass scaled to body size) and cause a trade-off between growth and other fitness-related traits, such as immunity. We tested the condition-dependence of growth and disease resistance in male and female Gryllus texensis field crickets by manipulating diet quality via nutrient content for their entire life and then subjecting individuals to a host resistance test using the live bacterium Serratia marcescens. As predicted, crickets on a high-quality diet eclosed more quickly, and at a larger body size and mass. Crickets on a high-quality diet were not in better condition at the time of eclosion, but they were in better condition 7–11 days after eclosion, with females also being in better condition than males. Despite being in better condition, however, females provided with a high-quality diet had significantly poorer disease resistance than females on a low-quality diet and in poor condition. Similarly, males on low- and high-quality diets did not differ in their disease resistance, despite differing in their body condition. A sex difference in disease resistance under diet-restriction suggests that females might allocate resources toward immunity during development if they expect harsh environmental conditions as an adult or it might suggest that females allocate resources toward other life history activities (i.e. reproduction) when food availability increases. We do not know what immune effectors were altered under diet-restriction to increase disease resistance, but our findings suggest that increased immune function might provide an explanation for the sexually-dimorphic increase in longevity generally observed in diet-restricted animals.

Microbial growth in fresh-cut lettuce increases when wound-induced phenolic accumulation is suppressed

Wounding lettuce (Lactuca sativa L. Longifolia) leaf mid-rib tissue initiates physiological responses that include increased synthesis and accumulation of phenolic compounds. Chlorogenic acid is the predominant wound-induced phenolic compound that accumulates in excised lettuce leaf tissue held at 10°C for 2 days. The growth of five bacterial isolates associated with lettuce decay (Erwinia carotovora, Erwinia chrisanthemi, Pseudomonas putida, Pseudomonas fluorescens, or Pseudomonas syringae) on TSA (tryptic soy agar) media was not markedly reduced by concentrations of chlorogenic acid identical to those found in wounded lettuce. Growth of E. carotovora and P. fluorescens was stimulated when prepared with TSA media containing homogenized non-wounded lettuce mid-rib tissue, while the increase was much less when the media was prepared with 5mm thick mid-rib tissue segments that were held for 2 days at 10°C after excision. Inhibiting the wound-induced increase in phenolic content with a 1-hexanol or heat-shock treatment allowed E. carotovora to grow on media prepared with excised tissue that had been held at 10°C for 2 days at significantly higher rates than on media prepared with non-treated excised tissue. Hexanol is thought to interfere with the synthesis and/or propagation of the wound signal, so delaying its application to excised mid-rib tissue reduces its effectiveness. Delaying application of the inhibitor for 4h, allowed increased accumulation of wound-induced phenolic compounds in 2 day old lettuce tissue that resulted in a concomitant reduction in the growth of E. carotovora on media prepared with this tissue. Neither the hexanol nor the heat-shock treatment themselves made the excised lettuce tissue a better substrate for microbial growth. It appears that treatments that suppress wound-induced increases in antimicrobial phenolic compounds reduce the ability of excised lettuce tissue to suppress the growth of bacteria associated with lettuce decay by limiting the production and accumulation of these antimicrobial compounds. A critical distinction is made between whether a treatment renders the tissue more susceptible to microbial growth, or whether a treatment prevents the wound-induced increase in disease resistance that limits microbial growth. If all treatments that reduce tissue browning by interfering with the wound-induced accumulation of phenolic compounds also inadvertently make the tissue more susceptible to microbial growth, then research should be directed to prevent the production of brown pigments from the wound-induced accumulated phenolic compounds, rather than devising treatments that reduce their accumulation.

Effects of dietary supplementation of citrus by‐products fermented with a probiotic microbe on growth performance, innate immunity and disease resistance against Edwardsiella tarda in juvenile olive flounder, Paralichthys olivaceus (Temminck & Schlegel)

Two consecutive studies were conducted to evaluate the dietary supplementation of citrus by-products (CB) fermented with probiotic bacteria on growth performance, feed utilization, innate immune responses and disease resistance of juvenile olive flounder. In Experiment I, five diets were formulated to contain 0% (control) or 3% four different CB fermented with Bacillus subtilis (BS), Enterococcus faecium (EF), Lactobacillus rhamnosus (LR) and L. plantarum (LP) (designated as CON, CBF-BS, CBF-EF, CBF-LR and CBF-LP, respectively). During 10 weeks of a feeding trial, growth performance and feed efficiency were not significantly different among all the fish groups. However, fish fed CBF containing diets had significantly higher survivals than the CON group. Disease resistance of fish against Edwardsiella tarda was increased by the fermentation of CB. In Experiment II, we chose the BS as a promising probiotic and formulated five diets to contain 0%, 2%, 4%, 6% and 8% CBF-BS. Growth performance was not significantly affected by the CBF-BS supplementation during 6 weeks of a feeding trial. Innate immunity of fish was significantly enhanced by CBF-BS supplementation. Myeloperoxidase and lysozyme activities were increased in a dose-dependent manner by dietary CBF-BS inclusions. In a consecutive challenge test against E. tarda, an increased disease resistance was found by CBF-BS supplementation. These studies indicate that the fermentation process of CB with probiotic has beneficial effects on innate immunity and thereby increases disease resistance of olive flounder against E. tarda. Bacillus subtilis can be used as a promising probiotic microbe for by-product fermentation in fish feeds.

Effect of mixed use of thyme and fennel oils on biochemical properties and electrolytes in rainbow trout as a response to Yersinia ruckeri infection

The aim of study was to compare the effects of supplementation of food with herbal oils (Thymus vulgaris and Foeniculum vulgare) on biochemical properties and electrolytes of rainbow trout infected with Yersinia ruckeri. In total, 120 healthy fish (mean weight 84 ± 1.02 g) were equally divided into four experimental groups. The experimental study was carried out for one week. The first group was control without supplementation and infection, the second group was infected and without oil supplementation, the third group was supplemented with oils (10 ml·100 g-1 rates) for one week and infected with Y. ruckeri and the last group was oil supplemented without infection. Results indicated that fish fed with dietary supplements showed enhanced bactericidal activity, total protein, albumin, cholesterol, triglyceride and bilirubin compared to the control (P < 0.05). As the value of herbal oils was increased in diets, the plasma glucose level decreased. The levels of K, Na, Ca, and Mg increased whereas Cl values decreased, compared to the control. It can be concluded that diet supplementation with herb oils used in this study can increase disease resistance by increasing levels of some biochemical parameters and electrolytes in rainbow trout to Y. ruckeri infection.

A Strong Immune Response in Young Adult Honeybees Masks Their Increased Susceptibility to Infection Compared to Older Bees

Honeybees, Apis mellifera, show age-related division of labor in which young adults perform maintenance (“housekeeping”) tasks inside the colony before switching to outside foraging at approximately 23 days old. Disease resistance is an important feature of honeybee biology, but little is known about the interaction of pathogens and age-related division of labor. We tested a hypothesis that older forager bees and younger “house” bees differ in susceptibility to infection. We coupled an infection bioassay with a functional analysis of gene expression in individual bees using a whole genome microarray. Forager bees treated with the entomopathogenic fungus Metarhizium anisopliae s.l. survived for significantly longer than house bees. This was concomitant with substantial differences in gene expression including genes associated with immune function. In house bees, infection was associated with differential expression of 35 candidate immune genes contrasted with differential expression of only two candidate immune genes in forager bees. For control bees (i.e. not treated with M. anisopliae) the development from the house to the forager stage was associated with differential expression of 49 candidate immune genes, including up-regulation of the antimicrobial peptide gene abaecin, plus major components of the Toll pathway, serine proteases, and serpins. We infer that reduced pathogen susceptibility in forager bees was associated with age-related activation of specific immune system pathways. Our findings contrast with the view that the immunocompetence in social insects declines with the onset of foraging as a result of a trade-off in the allocation of resources for foraging. The up-regulation of immune-related genes in young adult bees in response to M. anisopliae infection was an indicator of disease susceptibility; this also challenges previous research in social insects, in which an elevated immune status has been used as a marker of increased disease resistance and fitness without considering the effects of age-related development.

Imprimatins A and B

Plant activators are agrochemicals that protect plants from a broad range of pathogens by activating the plant immune system. Unlike pesticides, they do not target pathogens; therefore, plant activators provide durable effects that are not overcome by pathogenic microbes. Although certain plant activators have been applied to paddy fields for more than 30 years, the molecular basis of the underlying immune induction are unclear. From the screening of 10,000 diverse chemicals by a high-throughput screening procedure to identify compounds that specifically enhance pathogen-induced cell death in Arabidopsis cultured cells, we identified 7 compounds, which we designated as immune priming chemicals (Imprimatins). These compounds increased disease resistance against pathogenic Pseudomonas bacteria in Arabidopsis plants. Pretreatments increased the accumulation of endogenous salicylic acid (SA) but reduced its metabolite, SA-O-β-D-glucoside (SAG). Imprimatins inhibited the enzymatic activities of 2 SA glucosyltransferases (SAGTs) in vitro at concentrations effective for immune priming. Single and double knockout Arabidopsis plants for both SAGTs consistently exhibited enhanced disease resistance and SA accumulation. Our results demonstrate that the control of the free SA pool through SA-inactivating enzymes can be a useful methodology to confer disease resistance in plants. SAGTs can pave the way for target-based discovery of novel crop protectants.

Trichoderma Secondary Metabolites that Affect Plant Metabolism

Recently, there have been many exciting new developments relating to the use of Trichoderma spp. as agents for biocontrol of pathogens and as plant growth promoters. Several mechanisms have been proposed to explain the positive effects of these microorganisms on the plant host. One factor that contributes to their beneficial biological activities is related to the wide variety of metabolites that they produce. These metabolites have been found not only to directly inhibit the growth and pathogenic activities of the parasites, but also to increase disease resistance by triggering the system of defence in the plant host. In addition, these metabolites are also capable of enhancing plant growth, which enables the plant to counteract the disease with compensatory vegetative growth by the augmented production of root and shoot systems. This review takes into account the Trichoderma secondary metabolites that affect plant metabolism and that may play an important role in the complex interactions of this biocontrol agent with the plant and pathogens.

Use of Probiotics in Aquaculture

The growth of aquaculture as an industry has accelerated over the past decades; this has resulted in environmental damages and low productivity of various crops. The need for increased disease resistance, growth of aquatic organisms, and feed efficiency has brought about the use of probiotics in aquaculture practices. The first application of probiotics occurred in 1986, to test their ability to increase growth of hydrobionts (organisms that live in water). Later, probiotics were used to improve water quality and control of bacterial infections. Nowadays, there is documented evidence that probiotics can improve the digestibility of nutrients, increase tolerance to stress, and encourage reproduction. Currently, there are commercial probiotic products prepared from various bacterial species such as Bacillus sp., Lactobacillus sp., Enterococcus sp., Carnobacterium sp., and the yeast Saccharomyces cerevisiae among others, and their use is regulated by careful management recommendations. The present paper shows the current knowledge of the use of probiotics in aquaculture, its antecedents, and safety measures to be carried out and discusses the prospects for study in this field.

From the Editors—Animal selection: The genomics revolution

The rapid improvements in high-throughput single nucleotide polymorphism (SNP) genotyping technologies, ever-denser SNP arrays accompanied by reduced costs for genotyping and for sequencing, open the possibility of using genomic information in livestock selection. The industry is thus facing the new paradigm of “genomic selection,” in which genomic information may reduce costs and accelerate genetic gain by reducing generation intervals. Genetic markers, or SNP, are highly abundant in the genome, and highthroughput molecular technologies allow the inheritance of hundreds of thousands of such markers to be traced through generations for currently less than US $200 per animal. Even if the mutations themselves do not directly affect the phenotype, they can track for the variability of causal mutations in their vicinity. By summing the effects assigned to each SNP, we can create a numeric value (genomic breeding value) that allows the genetic potential of a breeding animal to be assessed. This is an enormously valuable tool for choosing breeding animals as parents of the next generation. In addition, genomic selection may allow the identifi cation of superior individuals for traits not currently considered in animal breeding plans because of technical diffi culties. For example, the fatty acid composition of dairy and beef food products, increased disease resistance (and thus increased animal welfare), and decreased methane emissions in cattle help to address the needs of consumers and society for sustainable and cost-effective food production. The animal breeding industry is currently adapting selection procedures in each species to include this innovative tool. This is causing a worldwide restructuring of the animal breeding industry. As an example in dairy cattle, large international consortia are being formed to develop joint precompetitive research and tools. For similar reasons, in the future, genomic selection might help close the gap between countries with greater and lesser production. The scope of this issue of Animal Frontiers is to provide a worldwide overview and various perspectives on intermediate-term scenarios resulting from the application of genomic tools in different livestock species. Genomic selection has already had a huge impact in genetic selectionrelated industries. Such industries have had the same structure for at least 3 decades. Subsequent to the research conducted by animal geneticists in the 1960s and 1970s, mainly by Charles Henderson and his group, animal selection remained the same for many years. Of course, new traits were included and new species were selected in addition to dairy cattle, but the industry structure generally remained the same. During these years, genetic selection also incorporated new computer technologies and animal reproduction discoveries to improve the identifi cation of superior animals. The genomic revolution created large changes in this structure. New actors appeared on the scene. In this issue of Animal Frontiers, relevant technicians and scientists were invited to focus on the impact of the genomic revolution on the genetics industry and to forecast future developments.

Uses and implications of field disease data for livestock genomic and genetics studies.

This paper identifies issues associated with field disease data and their implications on the interpretation of estimated genetic parameters and experimental designs. The main focus is on concepts relating to the impacts of diagnostic test properties and exposure to infection, and how exposure to infection is intricately related to within-herd epidemic dynamics. The following are raised challenges: (i) to more fully understand and describe the dynamic impacts of disease epidemics on genetic interpretations; (ii) to develop statistical methods to jointly estimate epidemiological and genetic parameters from complex epidemiological data; (iii) to develop and explore optimal experimental designs for case-control studies, exploiting field disease data. Solving these problems would add insight to both disease genetic and epidemiological studies, as well as enabling us to better select animals for increased disease resistance.

Sulfonamides identified as plant immune-priming compounds in high-throughput chemical screening increase disease resistance in Arabidopsis thaliana

Plant activators are agrochemicals that protect crops from diseases by activating the plant immune system. To isolate lead compounds for use as practical plant activators, we screened two different chemical libraries composed of various bioactive substances by using an established screening procedure that can selectively identify immune-priming compounds. We identified and characterized a group of sulfonamide compounds – sulfameter, sulfamethoxypyridazine, sulfabenzamide, and sulfachloropyridazine – among the various isolated candidate molecules. These sulfonamide compounds enhanced the avirulent Pseudomonas-induced cell death of Arabidopsis suspension cell cultures and increased disease resistance in Arabidopsis plants against both avirulent and virulent strains of the bacterium. These compounds did not prevent the growth of pathogenic bacteria in minimal liquid media at 200 μM. They also did not induce the expression of defense-related genes in Arabidopsis seedlings, at least not at 24 and 48 h after treatment, suggesting that they do not act as salicylic acid analogs. In addition, although sulfonamides are known to be folate biosynthesis inhibitors, the application of folate did not restore the potentiation effects of the sulfonamides on pathogen-induced cell death. Our data suggest that sulfonamides potentiate Arabidopsis disease resistance by their novel chemical properties.

Infection before pregnancy affects immunity and response to social challenge in the next generation

Natural selection should favour parents that are able to adjust their offspring's life-history strategy and resource allocation in response to changing environmental and social conditions. Pathogens impose particularly strong and variable selective pressure on host life histories, and parental genes will benefit if offspring are appropriately primed to meet the immunological challenges ahead. Here, we investigated transgenerational immune priming by examining reproductive resource allocation by female mice in response to direct infection with Babesia microti prior to pregnancy. Female mice previously infected with B. microti gained more weight over pregnancy, and spent more time nursing their offspring. These offspring generated an accelerated response to B. microti as adults, clearing the infection sooner and losing less weight as a result of infection. They also showed an altered hormonal response to novel social environments, decreasing instead of increasing testosterone production upon social housing. These results suggest that a dominance-resistance trade-off can be mediated by cues from the previous generation. We suggest that strategic maternal investment in response to an infection leads to increased disease resistance in the following generation. Offspring from previously infected mothers downregulate investment in acquisition of social dominance, which in natural systems would reduce access to mating opportunities. In doing so, however, they avoid the reduced disease resistance associated with increased testosterone and dominance. The benefits of accelerated clearance of infection and reduced weight loss during infection may outweigh costs associated with reduced social dominance in an environment where the risk of disease is high.

The Potential for Oysters,Crassostrea virginica, to Develop Resistance to Dermo Disease in the Field: Evaluation using a Gene-Based Population Dynamics Model

Today, populations of eastern oysters, Crassostrea virginica, are commonly limited by disease mortality. Resistance to MSX disease has developed in a number of cases, but the development of resistance to Dermo disease would appear to be limited, despite the high mortality rates and frequency of epizootics. Can aspects of the host's genetics or population dynamics limit the response to the disease despite the apparent opportunity afforded by alleles conferring disease resistance or tolerance? To answer this question, we use a gene-based population dynamics model, configured for C. virginica, to simulate the development of disease resistance using mortality as the agent of selection. Simulated populations were exposed to 4 levels of mortality covering the range in mortality observed in Delaware Bay in the 1990s. In each case, disease resistance increased in the simulated population over time, normally proportional to the increase in mortality rate imposed by the disease. However, simulations show that the population responds even at its most rapid rate on multidecadal to half-century timescales. As the mortality rate declines with increasing disease resistance, the rate of further improvement in disease resistance likewise declines. Thus, disease resistance develops over decadal timescales at a 40%-per-year mortality rate, but, as mortality rate falls to 25% per year, the rate of further development of disease resistance extends to half-century timescales. The discouraging profundity is that a mortality rate of 25% per year, yielding a rate of selection profoundly slow, is still very high. In northern climes, significant decrements in oyster abundance will occur. Evidence from fisheries retrospectives suggests that oysters cannot withstand a constant removal at this scale without compromising population integrity noticeably. So, a mortality rate that grievously limits the development of disease resistance still sorely strains the species' ability to maintain a vibrant population necessary to its long-term survival.

No benefit in diversity? The effect of genetic variation on survival and disease resistance in a polygynous social insect

1. Multiple mating by queens has been shown to enhance disease resistance in insect societies, because higher genetic diversity among nestmates improves collective immune defences or offers a certain level of herd immunity. However, it has remained ambiguous whether polygynous societies with large numbers of queens also benefit from increased genetic diversity. 2. We used one of the very few ant species that can be reared across generations, the pharaoh ant, Monomorium pharaonis Linnaeus, to create experimental colonies with two types of enhanced genetic diversity: (i) mixed workers from three divergent inbred lineages representing the ‘polygyny-equivalent' of multiple mating by queens (i.e. increased between-worker variation); and (ii) uniform workers whose overall heterozygosity was increased by two subsequent generations of crossing between the same divergent inbred lineages (i.e. increased within-worker variation). 3. We found significant differences in worker survival among the three inbred lineages, with exposure to conidiospores of the fungal pathogen Beauveria bassiana causing significant mortality to the workers independently of their diversity type. Increased diversity did not improve the resistance to Beauveria. 4. Enhanced heterozygosity colonies had worker survival rates similar to the most resistant inbred lineage, whereas colonies with mixed workers from the three inbred lineages had lower worker and larval survival. Workers did not show any infection-avoidance behaviour. 5. Average larval survival appeared unaffected by the presence of conidiospores. It benefitted from increased heterozygosity but was reduced in mixed colonies independent of infection. This suggests that negative, but cryptic social interactions in mixed colonies may affect overall survival. 6. The present results do not provide evidence for or against a link between increased genetic variation and increased disease resistance in pharaoh ants, but show that colonies differ considerably in general survival. Thus, increasing the genetic diversity of pharaoh ant colonies may not provide survival advantages in the face of pathogen exposure, and polygyny and polyandry may not be directly comparable mechanisms for creating adaptive resistance towards pathogens.

Perturbation of spermine synthase gene expression and transcript profiling provide new insights on the role of the tetraamine spermine in Arabidopsis defense against Pseudomonas viridiflava.

The role of the tetraamine spermine in plant defense against pathogens was investigated by using the Arabidopsis (Arabidopsis thaliana)-Pseudomonas viridiflava pathosystem. The effects of perturbations of plant spermine levels on susceptibility to bacterial infection were evaluated in transgenic plants (35S::spermine synthase [SPMS]) that overexpressed the SPMS gene and accumulated spermine, as well as in spms mutants with low spermine levels. The former exhibited higher resistance to P. viridiflava than wild-type plants, while the latter were more susceptible. Exogenous supply of spermine to wild-type plants also increased disease resistance. Increased resistance provided by spermine was partly counteracted by the polyamine oxidase inhibitor SL-11061, demonstrating that the protective effect of spermine partly depends on its oxidation. In addition, global changes in gene expression resulting from perturbations of spermine levels were analyzed by transcript profiling 35S::SPMS-9 and spms-2 plants. Overexpression of 602 genes was detected in 35S::SPMS-9 plants, while 312 genes were down-regulated, as compared to the wild type. In the spms-2 line, 211 and 158 genes were up- and down-regulated, respectively. Analysis of gene ontology term enrichment demonstrated that many genes overexpressed only in 35S::SPMS-9 participate in pathogen perception and defense responses. Notably, several families of disease resistance genes, transcription factors, kinases, and nucleotide- and DNA/RNA-binding proteins were overexpressed in this line. Thus, a number of spermine-responsive genes potentially involved in resistance to P. viridiflava were identified. The obtained results support the idea that spermine contributes to plant resistance to P. viridiflava.

Dietary arginine and repeated handling increase disease resistance and modulate innate immune mechanisms of Senegalese sole ( Solea senegalensis Kaup, 1858)

Stress is known to impair immune function and disease resistance in fish. In the present study, repeated handling was employed as a chronic stressor in order to verify whether its attributed immunosuppressive effects could be minimized by dietary arginine supplementation. Therefore, Senegalese sole ( Solea senegalensis) were air exposed daily for 3 min during 14 days (handling) or left undisturbed (control). In addition, both control and handled specimens were fed 3 diets with graded levels of arginine (Arg 4.4, Arg 5.7 and Arg 6.9 g 16 g −1 N). Following the 14 days stress challenge and feeding on those diets, fish were infected with Photobacterium damselae subsp. piscicida (strain PC566.1; LD 50 5 × 10 3 cfu mL −1) and fed the same experimental diets. Respiratory burst activity and nitric oxide production of head–kidney leucocytes increased parallel to dietary arginine supplementation. HIF-1, HAMP-1, MIP1-alpha and gLYS expression values and some humoral parameters augmented in control specimens fed the Arg 5.7 and Arg 6.9 diets. Interestingly, repeated acute stress increased both disease resistance and some innate immune mechanisms in handled fish. The role of dietary arginine and repeated handling on Senegalese sole innate immunity and disease resistance are discussed.

Temporary effect of postharvest UV-C irradiation on gene expression profile in tomato fruit

To obtain an overall view on gene expression during the early stage (24 h) of tomato fruit in response to postharvest UV-C irradiation (4 kJ/m 2), we performed a microarray analysis by using Affymetrix Tomato Genechip. The results showed that 274 and 403 genes were up- or down-regulated, respectively, more than two folds in postharvest tomato fruit irradiated with UV-C as compared with that in control fruit. The up-regulated genes mainly involve in signal transduction, defense response and metabolism. Conversely, genes related to cell wall disassembly, photosynthesis and lipid metabolism were generally down-regulated. These results opened ways to probe into the molecular mechanisms of the effects of postharvest UV-C irradiation on increased disease resistance, delayed softening, better quality maintenance and prolonged postharvest life in tomato fruit.