Development Of Disease Symptoms Research Articles

Salicylic Acid-Induced syntaxin Gene Expression Coexists with Enhanced Resistance against Colletotrichum gloeosporioides Infection in Cassava

The major challenge of cassava cultivation is phytopathogen damage and lack of resistant cultivars. Investigating the defense mechanism in cassava should provide insights into the development of new disease control strategies. Colletotrichum gloeosporioides f. sp. manihotis (CAD) is a fungal pathogen that causes cassava anthracnose disease, which is a serious disease worldwide, affecting cassava production and yield loss. Syntaxins contribute to mediate vesicles fusion in trafficking pathway by specifically forming as ternary SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptors) complex to transport defense components to site of microbe infection between the plasma membrane and plant cell wall. The function of syntaxins is largely unknown in resistance to Colletotrichum spp. in cassava. To manipulate resistance against Colletotrichum spp., the role of syntaxin genes and plant hormones; salicylic acid (SA) and jasmonic acid (JA) in triggering various responses to biotic stress was studied. All syntaxin genes in cassava genome were identified, and gene expression was investigated in CAD-resistant (HB60) and -susceptible (HN) cultivars of cassava. MePR1 was highly up-regulated in HB60 upon CAD infection. SA-pretreatment induced MeSYP121 expression and coexisted with delayed development of disease symptoms in HB60. In contrast, the different expression patterns of both genes were demonstrated in HN, and JA-pretreatment could not induce CAD-resistance. Altogether, the results suggest the role of SA-induced syntaxin gene expression to mediate vesicle trafficking and trigger defense-associated factors for more disease resistance in cassava. This investigation could be useful for the development of effective crop protection strategies and plant disease management in modern agriculture.

Acibenzolar-S-Methyl Activates Stomatal-Based Defense Systemically in Japanese Radish.

Acibenzolar-S-methyl (ASM) is a well-known plant activator, which is a synthetic analog of salicylic acid (SA). Recently, copper fungicides and antibiotics are major strategies for controlling bacterial diseases. However, resistant strains have already been found. Therefore, there is an increasing demand for sustainable new disease control strategies. We investigated the ASM disease control effect against Pseudomonas cannabina pv. alisalensis (Pcal), which causes bacterial blight on Japanese radish. In this study, we demonstrated that ASM effectively suppressed Pcal disease symptom development associated with reduced bacterial populations on Japanese radish leaves. Interestingly, we also demonstrated that ASM activated systemic acquired resistance (SAR), including stomatal-based defense on ASM-untreated upper and lower leaves. Reactive oxygen species (ROS) are essential second messengers in stomatal-based defense. We found that ASM induced stomatal closure by inducing ROS production through peroxidase. These results indicate that stomatal closure induced by ASM treatment is effective for preventing Pcal pathogen invasion into plants, and in turn reduction of disease development.

Air pollution and airport apron workers: A neglected occupational setting in epidemiological research.

Airport apron workers are occupationally exposed to jet exhaust and major concern is related to the exposure to ultrafine particles (UFP) from aircrafts. To date, little attention has been given to occupational exposures to aircraft-related UFP, although aircraft engines have high emissions of ultrafine particles, which are orders of magnitude higher than residential exposure. UFP could possibly contribute to the development of cancer, heart disease, mental illness, and respiratory symptoms. In addition to particulate matter, apron workers are exposed to other polluting substances associated with vehicles, aircraft exhaust or direct fuel emissions. We performed a scoping review on occupational health hazards due to air pollution among apron workers. Only three epidemiological studies were identified: two cross-sectional studies are of limited relevance due to a small sample size and a lack of quantitative exposure data. One sizeable cohort study performed an individual exposure measurement for UFP and considered relevant confounders. However, current studies are not numerous enough to evaluate an association of occupational air pollution with potential health effects among airport workers. The results suggest that current scientific evidence on this topic is sparse. Further observational studies in this occupational work force is highly recommended. For a better understanding of adverse health effects due to air pollution and especially UFP, studies in different countries are essential, since working environments, medical monitoring of workers or safety standards might differ internationally.

Pathophysiology of Fusarium oxysporum f. Sp. Dianthi in carnation (Dianthus caryophyllus L.)

The bio-chemical changes occurred in the carnation after inoculation with F. oxysporum f.sp. dianthi was studied under in vitro. Carnation plants inoculated with fourteen isolates of F.oxysporum f.sp.dianthi and monitored for their ability to production of fungal pectin-degrading enzymes viz., Pectin Methyl Esterase (PME), Polygalacturonase (PG) and Pectin Trans Eliminase (PTE) involved in development of disease symptoms. Production of pectinolytic enzymes in carnation plants were assessed from 2 days up to 8 days after inoculation at 48h intervals. The accumulation of these enzymes increased in two days after inoculation and attained a peak at six days after inoculation and slowly declined thereafter in all the inoculated plants. Among the fourteen isolates, YRPFOD2 had maximum ability to increase the activity of pectinolytic enzymes viz., Pectin Methyl Esterase (0.49 μ mole hydrogen ion / min / ml), Polygalacturonase (16.11% reduction in viscosity) and Pectin Trans Eliminase (57.59 % reduction in viscosity) after six days of inoculation in infected plants.

Local and Systemic Changes in Photosynthetic Parameters and Antioxidant Activity in Cucumber Challenged with Pseudomonas syringae pv lachrymans.

We studied changes in gas exchange, photochemical activity and the antioxidant system in cucumber leaves locally infected with Pseudomonas syringae pv lachrymans and in uninfected systemic ones. Infection-induced declined net photosynthesis rate and the related changes in transpiration rate, the intracellular CO2 concentration, and prolonged reduction in maximal PSII quantum yield (Fv/Fm), accompanied by an increase in non-photochemical quenching (NPQ), were observed only in the infected leaves, along with full disease symptom development. Infection severely affected the ROS/redox homeostasis at the cellular level and in chloroplasts. Superoxide dismutase, ascorbate, and tocopherol were preferentially induced at the early stage of pathogenesis, whereas catalase, glutathione, and the ascorbate–glutathione cycle enzymes were activated later. Systemic leaves retained their net photosynthesis rate and the changes in the antioxidant system were partly like those in the infected leaves, although they occurred later and were less intense. Re-balancing of ascorbate and glutathione in systemic leaves generated a specific redox signature in chloroplasts. We suggest that it could be a regulatory element playing a role in integrating photosynthesis and redox regulation of stress, aimed at increasing the defense capacity and maintaining the growth of the infected plant.

Epidemiological Factors Influencing the Development of Pigeonpea Sterility Mosaic Virus Disease in Pigeonpea

Background: In a region of Karnataka, India with a varied type climate PPSMV infection on pigeonpea occurs in a severe form and considered as green plague and one of the most devastating diseases as it appear in severe form resulting in reduction of 100% yield loss transmitted by vector eriophyid mite Aceriacajani Channabasavanna. However, not much systematic and strategic research work being carried out on epidemiology. In spite of various control measures, Sterility Mosaic Disease has continued to be major constraint in pigeonpea production. A lot of variation exists among the genetic background of different varieties in different regions. These variations render it difficult to evolve a common management strategy to control SMD epidemics. Therefore, it is necessary to know the severity of disease and factors associated with disease development which helps in devising suitable management practices. Methods: To study the influence of sowing dates on SMD and vector population under field conditions. A total of twelve sets of sowings were made at different time interval starting from first week of January 2012 to December, 2012. The SMD disease incidence and mite population were recorded in each treatment at fifteen days interval. Under artificial environment, pigeonpea seedlings of variety ICP8863 were raised. Inoculation of virus was done at different stage of plant growth viz., 15, 30, 45, 60, 75, 90 days after sowing. The observation on terminal disease incidence was recorded at 90 DAS to study the impact of host age on SMD. The eight pigeonpea varieties were sown near the SMD infected plot so as to facilitate the movement of vector population under natural conditions to study the reaction of pigeonpea varieties to SMD. Naturally grown weeds present in and around the sterility mosaic screening nursery were collected at weekly interval to see the presence of mites. In a glass house experiment, twenty-three cultivated species of economic importance and three Nicotiana species were sown three replications to see the alternate host for the virus. Results: The fluctuation in disease incidence and mite population was recorded throughout the year and early stage of crop growth recorded less disease incidence with lower mite population and gradual increase was recorded at later stage of crop growth period. The maximum disease incidence and mite population was recorded in crop sown during month of June and July where mean temperature was 24 to 26oC, RH 67 to 71% and rainfall of 2.13mm. The disease incidence recorded at different months of sowing had a significant positive correlation with mite population. Pigeonpea plants inoculated up to age of 30 days showed complete sterility with 100% disease incidence. The Resistant genotypes recorded less per cent disease incidence and symptom development at 60DAS. Whereas susceptible variety recorded maximum diseases incidence at early stage of crop growth and showed complete sterility. PPSMV and its vector survived on the ratooned pigeonpea plants and its wild relatives Atylosiascaraboeides during off season.

Sweet Immunity: The Effect of Exogenous Fructans on the Susceptibility of Apple (Malus × domestica Borkh.) to Venturia inaequalis.

There is an urgent need for novel, efficient and environmentally friendly strategies to control apple scab (Venturia inaequalis), for the purpose of reducing overall pesticide use. Fructans are recently emerging as promising “priming” compounds, standing out for their safety and low production costs. The objective of this work was to test a fructan-triggered defense in the leaves of apple seedlings. It was demonstrated that exogenous leaf spraying can reduce the development of apple scab disease symptoms. When evaluated macroscopically and by V. inaequalis-specific qPCR, levan-treated leaves showed a significant reduction of sporulation and V. inaequalis DNA in comparison to mock- and inulin-treated leaves, comparable to the levels in fosetyl-aluminum-treated leaves. Furthermore, we observed a significant reduction of in vitro mycelial growth of V. inaequalis on plates supplemented with levans when compared to controls, indicating a direct inhibition of fungal growth. Variations in endogenous sugar contents in the leaves were followed during priming and subsequent infection, revealing complex dynamics as a function of time and leaf ontogeny. Our data are discussed in view of the present theories on sugar signaling and fructan-based immunity, identifying areas for future research and highlighting the potential use of fructans in apple scab management in orchards.

Mycorrhizal autochthonous consortium induced defense-related mechanisms of olive trees against Verticillium dahliae

The present work aimed to investigate the effect of an autochthonous mycorrhizal consortium in enhancing olive tree tolerance against Verticillium dahliae. The bio-protective effect of this consortium “Rhizolive” on olive “Picholine Marocaine cultivar” infected with V. dahliae was assessed through monitoring disease symptoms development and through measuring the activities of enzymes involved in basal defense and secondary metabolism. The results revealed that “Rhizolive consortium” significantly (p < 0.05) reduced disease severity and incidence by 31% and 29%, respectively. The defoliation rate was also reduced by 35% in mycorrhizal-infected olive plants. “Rhizolive consortium” increased the lignin deposition and stimulated the phenylpropanoid pathway by increasing the phenylalanine ammonia-lyase (PAL) activity and accumulation of phenolic compounds in both roots and stems of plants infected with V. dahliae. The reduction in disease severity was accompanied by increased levels of lignin concentration, PAL activity and polyphenol content, particularly in the stems of olive plants. Our results clearly show that “Rhizolive consortium” inoculum protects olive tree from V. dahliae attacks and could thus constitute a biological approach contributing to the suppression of this telluric vascular pathogen.

Impact of phenolic compounds on progression of Xylella fastidiosa infections in susceptible and PdR1-locus containing resistant grapevines

Pierce’s disease is of major concern for grapevine (Vitis vinifera) production wherever the bacterial pathogen Xylella fastidiosa and its vectors are present. Long-term management includes the deployment of resistant grapevines such as those containing the PdR1 locus from the wild grapevine species Vitis arizonica, which do not develop Pierce’s disease symptoms upon infection. However, little is understood about how the PdR1 locus functions to prevent disease symptom development. Therefore, we assessed the concentrations of plant defense-associated compounds called phenolics in healthy and X. fastidiosa-infected PdR1-resistant and susceptible grapevine siblings over time. Soluble foliar phenolic levels, especially flavonoids, in X. fastidiosa-infected PdR1-resistant grapevines were discovered to be significantly lower than those in infected susceptible grapevines. Therefore, it was hypothesized that PdR1-resistant grapevines, by possessing lowered flavonoid levels, affects biofilm formation and causes reduced X. fastidiosa intra-plant colonization, thus limiting the ability to increase pathogen populations and cause Pierce’s disease. These results therefore reveal that differences in plant metabolite levels might be a component of the mechanisms that PdR1 utilizes to prevent Pierce’s disease.

Massarilactones D and H, phytotoxins produced by Kalmusia variispora, associated with grapevine trunk diseases (GTDs) in Iran

A strain of Kalmusia variispora associated with grapevine trunk diseases (GTDs) was identified in Iran and induced disease symptoms on the host in greenhouse conditions. The grapevine pathogens are able to produce a plethora of toxic metabolites belonging to different classes of naturally occurring compounds. Two homogeneous compounds were isolated from the organic extract of K. variispora culture filtrates. They were identified by physic (specific optical rotation), and spectroscopic (essentially 1D 1H and 13C NMR and HR ESIMS) methods as the fungal polyketides massarilactones D and H (1 and 2). The unassigned absolute configuration of massarilactone D was unambiguously determined by X-ray diffractometric analysis. Massarilactones D and H showed phytotoxic activity on Vitis vinifera L. at two concentrations used and depending from the days of inoculation. Phytotoxicity is also increased when the 3,4,7-O,O',O"-triacetyl derivative of massarilactone D (3) was assayed on the host plant. This is the first report on the investigation of phytotoxic metabolites produced by K. variispora isolated from infected grapevine in Iran and they seem to be involved in the development of disease symptoms.

A LysM Domain-Containing Protein LtLysM1 Is Important for Vegetative Growth and Pathogenesis in Woody Plant Pathogen Lasiodiplodia theobromae.

Lysin motif (LysM) proteins are reported to be necessary for the virulence and immune response suppression in many herbaceous plant pathogens, while far less is documented in woody plant pathogens. In this study, we preliminarily characterized the molecular function of a LysM protein LtLysM1 in woody plant pathogen Lasiodiplodia theobromae. Transcriptional profiles revealed that LtLysM1 is highly expressed at infectious stages, especially at 36 and 48 hours post inoculation. Amino acid sequence analyses revealed that LtLysM1 was a putative glycoprotein with 10 predicted N-glycosylation sites and one LysM domain. Pathogenicity tests showed that overexpressed transformants of LtLysM1 displayed increased virulence on grapevine shoots in comparison with that of wild type CSS-01s, and RNAi transformants of LtLysM1 exhibited significantly decreased lesion length when compared with that of wild type CSS-01s. Moreover, LtLysM1 was confirmed to be a secreted protein by a yeast signal peptide trap assay. Transient expression in Nicotiana benthamiana together with protein immunoblotting confirmed that LtLysM1 was an N-glycosylated protein. In contrast to previously reported LysM protein Slp1 and OsCEBiP, LtLysM1 molecule did not interact with itself based on yeast two hybrid and co-immunoprecipitation assays. These results indicate that LtLysM1 is a secreted protein and functions as a critical virulence factor during the disease symptom development in woody plants.

An Optimized in situ Quantification Method of Leaf H2O2 Unveils Interaction Dynamics of Pathogenic and Beneficial Bacteria in Wheat.

Hydrogen peroxide (H2O2) functions as an important signaling molecule in plants during biotic interactions. However, the extent to which H2O2 accumulates during these interactions and its implications in the development of disease symptoms is unclear. In this work, we provide a step-by-step optimized protocol for in situ quantification of relative H2O2 concentrations in wheat leaves infected with the pathogenic bacterium Pseudomonas syringae pv. atrofaciens (Psa), either alone or in the presence of the beneficial bacterium Herbaspirillum seropedicae (RAM10). This protocol involved the use of 3-3′diaminobenzidine (DAB) staining method combined with image processing to conduct deconvolution and downstream analysis of the digitalized leaf image. The application of a linear regression model allowed to relate the intensity of the pixels resulting from DAB staining with a given concentration of H2O2. Decreasing H2O2 accumulation patterns were detected at increasing distances from the site of pathogen infection, and H2O2 concentrations were different depending on the bacterial combinations tested. Notably, Psa-challenged plants in presence of RAM10 accumulated less H2O2 in the leaf and showed reduced necrotic symptoms, pointing to a potential role of RAM10 in reducing pathogen-triggered H2O2 levels in young wheat plants.

Integrated control of potato late blight with a combination of the photosynthetic bacterium Rhodopseudomonas palustris strain GJ-22 and fungicides

Late blight caused by the oomycete Phytophthora infestans is the major yield-threatening disease in potato production. An isolate of the photosynthetic bacterium Rhodopseudomonas palustris, GJ-22, was previously evaluated for its ability to promote the growth and enhance the immune response of solanaceous plants. In the present study, GJ-22 was shown to significantly repress disease symptom development caused by P. infestans in potato tubers. Curzate (cymoxanil plus mancozeb), a widely used fungicide with high activity against P. infestans, was selected for use in combination with GJ-22. The sensitivity of GJ-22 to the fungicides cymoxanil and mancozeb was tested. The growth of GJ-22 was unaffected by up to 100 mg l−1 cymoxanil or 50 mg l−1 mancozeb in photosynthetic medium. In greenhouse and field experiments, the combined application of GJ-22 and curzate resulted in better disease control than the use of either agent alone. In addition, treatment with 1 × 107 CFU ml−1 GJ-22 plus 700 mg l−1 curzate showed synergistic effects in the field trial. Our results highlight the potential to control potato late blight with the combination of R. palustris strain GJ-22 and curzate, providing environmentally friendly protection with a reduced level of fungicide application.

Biochemical and electrophoretic study for diagnosis of the disease stage in patients with asthmatic bronchitis

BackgroundAsthmatic bronchitis is a chronic allergic airway disease diagnosed after development of chronic obstructive pulmonary disease symptoms. This study was designed to reveal relation of the different electrophoretic patterns to impairment of the lung functions in patients with asthmatic bronchitis.Materials and methodsPatients were categorized into patients at mild stage (n = 10) and those at severe stage (n = 12) in comparison to healthy group (n = 21). The major blood components, arterial blood gases and electrolytes were immediately assayed in addition to assessment of liver enzymes and kidney functions. The pulmonary indices including forced expiratory volume in one second (FEV1), forced vital capacity (FVC), ratio of FEV1 to FVC and maximal expiratory pressure (MEP) were assayed. Furthermore, protein, lipid and calcium moieties of native protein patterns in addition to isoenzemes were electrophoretically detected.ResultsIt was found that liver and kidney functions were significantly (P < 0.05) elevated in asthmatic bronchitis patients. Ca2+ is the only electrolyte that decreased significantly (P < 0.05) at the severe stage. Electrophoretic patterns showed that asthmatic bronchitis disease at mild and severe stages were physiologically similar to control by 54.5 and 75.6% (protein), 73.1 and 41.6% (lipid moiety), 66.4 and 30.6% (calcium moiety), respectively. As regards to electrophoretic isoenzymes, the disease at mild and severe stages were similar to control by 95.2 and 35.4% (catalase (CAT)), 40.1 and 50.5% (peroxidase (POX)), 67.9 and 69.6% (α-esterase (α-EST)), 83.1 and 73.1% (β-esterase (β-EST)), respectively.ConclusionThe native electrophoretic patterns used as diagnostic tool for determining the stage at which the patients with asthmatic bronchitis exist.

The Potential Risk of Plant-Virus Disease Initiation by Infected Tomatoes.

During 2019, tomato fruits showing viral-like symptoms of marbled yellow spots were abundant in Israel. The new symptoms were distinctive from those typical of tomato brown rugose fruit virus (ToBRFV) infection but resembled symptoms of pepino mosaic virus (PepMV) infection. RT-PCR analysis and the serological tests (enzyme linked immunosorbent assay, western blot and in situ immunofluorescence) revealed and confirmed the presence of both the tobamovirus ToBRFV and the potexvirus PepMV in the symptomatic fruits. A mixture of rod-like and filamentous particles, characteristic of viruses belonging to tobamovirus and potexvirus genera, was visualized by transmission electron microscopy of the tomato fruit viral extract. Sanger sequencing of amplified PepMV-coat protein gene segments showed ~98% sequence identity to the Chilean (CH2)-strain. In a biological assay testing the contribution of traded infected tomatoes to the establishment of tomato plant disease, we applied direct and indirect inoculation modes using Tm-22-resistant tomato plants. The results, assessed by disease symptom development along with serological and molecular analyses, showed that the ToBRFV and PepMV co-infected fruits were an effective inoculum source for disease spread only when fruits were damaged. Importantly, intact fruits did not spread the viral disease. These results added a new factor to disease epidemiology of these viruses.

Tomato T2 ribonuclease LE is involved in the response to pathogens

T2 ribonucleases (RNases) are RNA‐degrading enzymes that function in various cellular processes, mostly via RNA metabolism. T2 RNase‐encoding genes have been identified in various organisms, from bacteria to mammals, and are most diverse in plants. The existence of T2 RNase genes in almost every organism suggests an important biological function that has been conserved through evolution. In plants, T2 RNases are suggested to be involved in phosphate scavenging and recycling, and are implicated in defence responses to pathogens. We investigated the function of the tomato T2 RNase LE, known to be induced by phosphate deficiency and wounding. The possible involvement of LE in pathogen responses was examined. Expression analysis showed LE induction during fungal infection and by stimuli known to be associated with pathogen inoculation, including oxalic acid and hydrogen peroxide. Analysis of LE‐suppressed transgenic tomato lines revealed higher susceptibility to oxalic acid, a cell death‐inducing factor, compared to the wild type. This elevated sensitivity of LE‐suppressed lines was evidenced by visual signs of necrosis, and increased ion leakage and reactive oxygen species levels, indicating acceleration of cell death. Challenge of the LE‐suppressed lines with the necrotrophic pathogen Botrytis cinerea resulted in accelerated development of disease symptoms compared to the wild type, associated with suppressed expression of pathogenesis‐related marker genes. The results suggest a role for plant endogenous T2 RNases in antifungal activity.

Plant microbiome analysis after Metarhiziumamendment reveals increases in abundance of plant growth-promoting organismsand maintenance of disease-suppressive soil.

The microbial community in the plant rhizosphere is vital to plant productivity and disease resistance. Alterations in the composition and diversity of species within this community could be detrimental if microbes suppressing the activity of pathogens are removed. Species of the insect-pathogenic fungus, Metarhizium, commonly employed as biological control agents against crop pests, have recently been identified as plant root colonizers and provide a variety of benefits (e.g. growth promotion, drought resistance, nitrogen acquisition). However, the impact of Metarhizium amendment on the rhizosphere microbiome has yet to be elucidated. Using Illumina sequencing, we examined the community profiles (bacteria and fungi) of common bean (Phaseolus vulgaris) rhizosphere (loose soil and plant root) after amendment with M. robertsii conidia, in the presence and absence of an insect host. Although alpha diversity was not significantly affected overall, there were numerous examples of plant growth-promoting organisms that significantly increased with Metarhizium amendment (Bradyrhizobium, Flavobacterium, Chaetomium, Trichoderma). Specifically, the abundance of Bradyrhizobium, a group of nitrogen-fixing bacteria, was confirmed to be increased using a qPCR assay with genus-specific primers. In addition, the ability of the microbiome to suppress the activity of a known bean root pathogen was assessed. The development of disease symptoms after application with Fusarium solani f. sp. phaseoli was visible in the hypocotyl and upper root of plants grown in sterilized soil but was suppressed during growth in microbiome soil and soil treated with M. robertsii. Successful amendment of agricultural soils with biocontrol agents such as Metarhizium necessitates a comprehensive understanding of the effects on the diversity of the rhizosphere microbiome. Such research is fundamentally important towards sustainable agricultural practices to improve overall plant health and productivity.

Rice Stripe Mosaic Virus–Encoded P4 Is a Weak Suppressor of Viral RNA Silencing and Is Required for Disease Symptom Development

Viral suppressors of RNA silencing (VSRs) are a cluster of viral proteins that have evolved to counteract eukaryotic antiviral RNA silencing pathways, thereby contributing to viral pathogenicity. In this study, we revealed that the matrix protein P4 encoded by rice stripe mosaic virus (RSMV), which is an emerging cytoplasmic rhabdovirus, is a weak RNA silencing suppressor. By conducting yeast two-hybrid, bimolecular fluorescence complementation, and subcellular colocalization assays, we proved that P4 interacts with the rice endogenous suppressor of gene silencing 3 (OsSGS3). We also determined that P4 overexpression has no effect on OsSGS3 transcription. However, P4 can promote the degradation of OsSGS3 via ubiquitination and autophagy. Additionally, a potato virus X-based expression system was used to confirm that P4 enhances the development of mosaic symptoms on Nicotiana benthamiana leaves by promoting hydrogen peroxide accumulation but not cell death. To verify whether P4 is a pathogenicity factor in host plants, we generated transgenic P4-overexpressing rice plants that exhibited disease-related developmental defects including decreased plant height and excessive tillering. Our data suggest that RSMV-encoded P4 serves as a weak VSR that inhibits antiviral RNA silencing by targeting OsSGS3.

Bacteriophytochromes from Pseudomonas syringae pv. tomato DC3000 modulate the early stages of plant colonization during bacterial speck disease

Living organisms have evolved the ability to perceive and respond to light of different wavelengths within the visible spectrum by the generation of photoreceptor proteins. Recent studies revealed the participation of these proteins in the virulence of plant pathogenic bacteria. Pseudomonas syringae pv. tomato DC3000 (Pto) is responsible for the bacterial speck, which affects tomato crops. Pto genome contains two genes encoding red/far-red light photoreceptors (BphP1: PSPTO_1902 and BphP2: PSPTO_2652). This work demonstrates the participation of Pto phytochromes and light in the bacterial physiology and during the interaction with tomato plants. We found that Pto phytochromes are implicated in the control of some features related with the bacteria capability to enter into the plant apoplast and cause bacterial speck disease, such as motility, biofilm formation, adhesion and emulsification capability. Red light and bacteriophytochromes are important during the early colonization stage of tomato phyllosphere, affecting Pto virulence. In addition, the development of disease symptoms in infiltrated leaflets is affected by light, which may be the consequence of type-two secretion system regulation.

Silencing of transcription factor encoding gene StTCP23 by small RNAs derived from the virulence modulating region of potato spindle tuber viroid is associated with symptom development in potato.

Viroids are small, non-protein-coding RNAs which can induce disease symptoms in a variety of plant species. Potato (Solanum tuberosum L.) is the natural host of Potato spindle tuber viroid (PSTVd) where infection results in stunting, distortion of leaves and tubers and yield loss. Replication of PSTVd is accompanied by the accumulation of viroid-derived small RNAs (sRNAs) proposed to play a central role in disease symptom development. Here we report that PSTVd sRNAs direct RNA silencing in potato against StTCP23, a member of the TCP (teosinte branched1/Cycloidea/Proliferating cell factor) transcription factor family genes that play an important role in plant growth and development as well as hormonal regulation, especially in responses to gibberellic acid (GA). The StTCP23 transcript has 21-nucleotide sequence complementarity in its 3ʹ untranslated region with the virulence-modulating region (VMR) of PSTVd strain RG1, and was downregulated in PSTVd-infected potato plants. Analysis using 3ʹ RNA ligase-mediated rapid amplification of cDNA ends (3ʹ RLM RACE) confirmed cleavage of StTCP23 transcript at the expected sites within the complementarity with VMR-derived sRNAs. Expression of these VMR sRNA sequences as artificial miRNAs (amiRNAs) in transgenic potato plants resulted in phenotypes reminiscent of PSTVd-RG1-infected plants. Furthermore, the severity of the phenotypes displayed was correlated with the level of amiRNA accumulation and the degree of amiRNA-directed down-regulation of StTCP23. In addition, virus-induced gene silencing (VIGS) of StTCP23 in potato also resulted in PSTVd-like phenotypes. Consistent with the function of TCP family genes, amiRNA lines in which StTCP23 expression was silenced showed a decrease in GA levels as well as alterations to the expression of GA biosynthesis and signaling genes previously implicated in tuber development. Application of GA to the amiRNA plants minimized the PSTVd-like phenotypes. Taken together, our results indicate that sRNAs derived from the VMR of PSTVd-RG1 direct silencing of StTCP23 expression, thereby disrupting the signaling pathways regulating GA metabolism and leading to plant stunting and formation of small and spindle-shaped tubers.