Photosynthetic alterations of pea leaves infected systemically by pea enation mosaic virus: A coordinated decrease in efficiencies of CO(2) assimilation and photosystem II photochemistry

Formulations of synergistic microbial consortia for enhanced systemic resistance against Fusarium wilt in cumin

The study aimed to understand the dynamic interplay between plants and their associated microbes to develop an efficient microbial consortium for managing Fusarium wilt of cumin. A total of 601 rhizospheric and endophytic bacteria and fungi were screened for antagonistic activity against Fusarium oxysporum f.sp. cumini (Foc). Subsequently, ten bacteria and ten fungi were selected for characterizing their growth promotion traits and ability to withstand abiotic stress. Furthermore, a pot experiment was conducted to evaluate the bioefficacy of promising biocontrol isolates-1F, 16B, 31B, and 223B in mono and consortium mode, focusing on disease severity, plant growth, and defense responses in cumin challenged with Foc. Promising isolates were identified as Trichoderma atrobruneum 15F, Pseudomonas sp. 2B, Bacillus amyloliquefaciens 9B, and Bacillus velezensis 32B. In planta, results revealed that cumin plants treated with consortia of 15F, 2B, 9B, and 32B showed highest percent disease control (76.35%) in pot experiment. Consortia of biocontrol agents significantly enhanced production of secondary metabolites and activation of antioxidant-defense enzymes compared to individual strain. Moreover, consortium treatments effectively reduced electrolyte leakage over the individual strain and positive control. The four-microbe consortium significantly enhanced chlorophyll (~ 2.74-fold), carotenoid content (~ 2.14-fold), plant height (~ 1.8-fold), dry weight (~ 1.96-fold), and seed yield (~ 19-fold) compared to positive control in pot experiment. Similarly, four microbe consortia showed highest percent disease control (72.2%) over the positive control in field trial. Moreover, plant growth, biomass, yield, and yield attributes of cumin were also significantly increased in field trial over the positive control as well as negative control.

Comparison of the Efficiency of Hyperspectral and Pulse Amplitude Modulation Imaging Methods in Pre-Symptomatic Virus Detection in Tobacco Plants

Early detection of pathogens can significantly reduce yield losses and improve the quality of agricultural products. This study compares the efficiency of hyperspectral (HS) imaging and pulse amplitude modulation (PAM) fluorometry to detect pathogens in plants. Reflectance spectra, normalized indices, and fluorescence parameters were studied in healthy and infected areas of leaves. Potato virus X with GFP fluorescent protein was used to assess the spread of infection throughout the plant. The study found that infection increased the reflectance of leaves in certain wavelength ranges. Analysis of the normalized reflectance indices (NRIs) revealed indices that were sensitive and insensitive to infection. NRI700/850 was optimal for virus detection; significant differences were detected on the 4th day after the virus arrived in the leaf. Maximum (Fv/Fm) and effective quantum yields of photosystem II (ΦPSII) and non-photochemical fluorescence quenching (NPQ) were almost unchanged at the early stage of infection. ΦPSII and NPQ in the transition state (a short time after actinic light was switched on) showed high sensitivity to infection. The higher sensitivity of PAM compared to HS imaging may be due to the possibility of assessing the physiological changes earlier than changes in leaf structure.

Transcriptome analysis of Citrus limon infected with Citrus yellow vein clearing virus

BACKGROUND

Citrus yellow vein clearing virus (CYVCV) is the causative agent of citrus yellow vein clearing disease, and poses a serious threat to the lemon industry in Asia. The common symptoms of CYVCV-infected lemon plants are leaf crinkling, leaf chlorotic mottling, and yellow vein clearing. However, the molecular mechanisms underlying CYVCV-citrus interaction that responsible for symptom occurrence is still unclarified. In this study, RNA-seq was performed to analyze the gene expression patterns of 'Eureka' lemon (Citrus limon Burm. f.) plants in response to CYVCV infection.

RESULTS

There were 3691 differentially expressed genes (DEGs) identified by comparison between mock and CYVCV-infected lemon plants through RNA-seq. Bioinformatics analyses revealed that these DEGs were components of different pathways involved in phenylpropanoid biosynthesis, brassinosteroid biosynthesis, flavonoid biosynthesis and photosynthesis. Among these, the DEGs related to phytohormone metabolism and photosynthesis pathways were further enriched and analyzed. This study showed that different phytohormone-related genes had different responses toward CYVCV infection, however almost all of the photosynthesis-related DEGs were down-regulated in the CYVCV-infected lemon plants. The obtained RNA-seq data were validated by RT-qPCR using 12 randomly chosen genes, and the results of mRNA expression analysis were consistent with those of RNA-seq.

CONCLUSIONS

The phytohormone biosynthesis, signaling and photosynthesis-related genes of lemon plants were probably involved in systemic infection and symptom occurrence of CYVCV. Notably, CYVCV infection had regulatory effects on the biosynthesis and signaling of phytohormone, which likely improve systemic infection of CYVCV. Additionally, CYVCV infection could cause structural changes in chloroplast and inhibition of photosynthesis pathway, which probably contribute to the appearance of leaf chlorotic mottling and yellow vein clearing in CYVCV-infected lemon plants. This study illustrates the dynamic nature of the citrus-CYVCV interaction at the transcriptome level and provides new insights into the molecular mechanism underlying the pathogenesis of CYVCV in lemon plants.

Comparative Transcriptome Analysis of CMV or 2b-Deficient CMV-Infected dcl2dcl4 Reveals the Effects of Viral Infection on Symptom Induction in Arabidopsis thaliana

Due to the impaired antiviral RNAi, the dcl2dcl4 (dcl2/4) mutant is highly susceptible to viruses deficient of the viral suppressor of the RNA silencing (VSR) contrast to wild-type Arabidopsis. It was found that more severe disease symptoms were induced in dcl2/4 infected with VSR-deficient CMV (CMV-Δ2b or CMV-2aTΔ2b) compared to wild-type Arabidopsis infected with intact CMV. In order to investigate the underlying mechanism, comparative transcriptome analysis was performed with Col-0 and dcl2/4 that were infected by CMV, CMV-Δ2b and CMV-2aTΔ2b, respectively. Our analysis showed that the systematic infection of CMV, CMV-Δ2b and CMV-2aTΔ2b could cause hypoxia response and reduce photosynthesis. Asymptomatic infections of CMV-Δ2b or CMV-2aTΔ2b in Columbia (Col-0) promoted the expression of cell division-related genes and suppressed the transcription of metabolism and acquired resistance genes. On the other hand, immunity and resistance genes were highly induced, but photosynthesis and polysaccharide metabolism-related genes were suppressed in diseased plants. More interestingly, cell wall reorganization was specifically caused in modestly diseased Col-0 infected by CMV and a strong activation of SA signaling were correspondingly induced in severely diseased dcl2/4 by CMV or CMV mutants. Thus, our research revealed the nature of the Arabidopsis–CMV interaction at the transcriptome level and could provide new clues in symptom development and antiviral defense in plants.

Antagonistic Effect of Plant Growth-Promoting Fungi Against Fusarium Wilt Disease in Tomato: In vitro and In vivo Study

Fusarium wilt is considered one of the most destructive diseases for tomato plants. The novelty of this work was to investigate the antifungal and plant growth-promoting capabilities of some plant growth-promoting fungi (PGPF). Plant growth-promoting fungi (PGPF) improved the plant health and control plant infections. In this study, two fungal strains as PGPF were isolated and identified as Aspergillus fumigatus and Rhizopus oryzae using molecular method. The extracts of A. fumigatus and R. oryzae exhibited promising antifungal activity against F. oxysporum in vitro. Moreover, antagonistic effect of A. fumigatus and R. oryzae against F. oxysporum causing tomato wilt disease was evaluated in vivo. Disease severity and growth markers were recorded and in vitro antagonistic activity assay of the isolated A. fumigatus and R. oryzae against Fusarium oxysporum was measured. Physiological markers of defense in plant as response to stimulate systemic resistance (SR) were recorded. Our results indicated that A. fumigatus and R. oryzae decreased the percentage of disease severity by 12.5 and 37.5%, respectively. In addition, they exhibited relatively high protection percentage of 86.35 and 59.06% respectively. Fusarium wilt was declined the growth parameters, photosynthetic pigments, total soluble carbohydrate, and total soluble protein, whereas content of free proline, total phenols, and the activity of antioxidant enzymes activity increased under infection. Moreover, application of A. fumigatus and R. oryzae on infected plants successfully recovered the loss of morphological traits, photosynthetic pigment total carbohydrates, and total soluble proteins in comparison to infected control plants. PGPF strains in both non-infected and infected plants showed several responses in number and density of peroxidase (POD) and polyphenol oxidase (PPO) isozymes.

Development of a highly sensitive and rapid detection method for Pea enation mosaic virus using loop-mediated isothermal amplification assay

The Pea enation mosaic virus (PEMV) has infected plants in the family Leguminosae such as pea, chickpea, faba bean, and lentil plants worldwide that the virus can be transmitted by sap, aphids, and seeds. Among the damages that PEMV disease cause in plants are reduced crop productivity, severely misshapen pods, wart-like outgrowths or proliferation on the surface. Previously, enzyme-linked immunosorbent assay (ELISA), reverse transcription (RT)-nested polymerase chain reaction (PCR), and real-time PCR had been used to detect PEMV. However, these methods are time-consuming and require specific equipments. For this reason, the development of a highly specific and sensitive detection method has become necessary. In this study, a new method for PEMV-1 using the loop-mediated isothermal amplification (LAMP) assay has been developed with specific primer sets as inner- and outer primers. Results showed PEMV-1 has been successfully detected that LAMP could confirm a diluted PEMV-1 up to 10-6 cDNA. LAMP is about 10,000 times more sensitive than the RT-nested PCR and/or real-time PCR. Moreover, the processing time of the LAMP was decreased 3 h than RT-nested PCR. Although future validation will be required to confirm enablement in the field area, this study provides a valuable method to identify PEMV-1 that could offer some advantages including rapid detection, high specificity and high sensitivity than others.

Viruses Infecting Trees and Herbs That Produce Edible Fleshy Fruits with a Prominent Value in the Global Market: An Evolutionary Perspective

Trees and herbs that produce fruits represent the most valuable agricultural food commodities in the world. However, the yield of these crops is not fully achieved due to biotic factors such as bacteria, fungi, and viruses. Viruses are capable of causing alterations in plant growth and development, thereby impacting the yield of their hosts significantly. In this work, we first compiled the world's most comprehensive list of known edible fruits that fits our definition. Then, plant viruses infecting those trees and herbs that produce fruits with commercial importance in the global market were identified. The identified plant viruses belong to 30 families, most of them containing single-stranded RNA genomes. Importantly, we show the overall picture of the host range for some virus families following an evolutionary approach. Further, the current knowledge about plant-virus interactions, focusing on the main disorders they cause, as well as yield losses, is summarized. Additionally, since accurate diagnosis methods are of pivotal importance for viral diseases control, the current and emerging technologies for the detection of these plant pathogens are described. Finally, the most promising strategies employed to control viral diseases in the field are presented, focusing on solutions that are long-lasting.

Pre-Symptomatic Detection of Viral Infection in Tobacco Leaves Using PAM Fluorometry

Chlorophyll fluorescence imaging was used to study potato virus X (PVX) infection of Nicotiana benthamiana. Infection-induced changes in chlorophyll fluorescence parameters (quantum yield of photosystem II photochemistry (ΦPSII) and non-photochemical fluorescence quenching (NPQ)) in the non-inoculated leaf were recorded and compared with the spatial distribution of the virus detected by the fluorescence of GFP associated with the virus. We determined infection-related changes at different points of the light-induced chlorophyll fluorescence kinetics and at different days after inoculation. A slight change in the light-adapted steady-state values of ΦPSII and NPQ was observed in the infected area of the non-inoculated leaf. In contrast to the steady-state parameters, the dynamics of ΦPSII and NPQ caused by the dark-light transition in healthy and infected areas differed significantly starting from the second day after the detection of the virus in a non-inoculated leaf. The coefficients of correlation between chlorophyll fluorescence parameters and virus localization were 0.67 for ΦPSII and 0.76 for NPQ. In general, the results demonstrate the possibility of reliable pre-symptomatic detection of the spread of a viral infection using chlorophyll fluorescence imaging.

Photosynthetic characterization and expression profiles of sugarcane infected by Sugarcane mosaic virus (SCMV)

Sugarcane mosaic virus (SCMV), belonging to genus Potyvirus, family Potyviridae, is a severe pathogen of several agricultural important crops, mainly sugarcane. Due to complex nature of sugarcane, the effect of SCMV pathogenicity on sugarcane photosynthetic systems remains to be explored. In this study, we investigated the alterations occurring in the photosynthetic system in the sugarcane genotypes at the cytopathological, physiological and biological, transcriptome and proteome level. We generated the transcriptome assembly of two genotypes (susceptible Badila and resistant B-48) using Saccharum spontaneum L. as a reference genome. RNA-sequencing data revealed the significant upregulation of NAD(P)H, RubisCO, oxygen-evolving complex, chlorophyll a and b binding protein, Psb protein family, PSI reaction center subunit II, and IVgenes in B-48, as compared to its counterparts. Upregulated genes in B-48 are associated with various processes such as stability and assembly of photosystem, protection against photoinhibition and antiviral defense. The expression pattern of differentially abundant genes were further verified at the proteomics level. Overall, differentially expressed genes/proteins (DEGs/DEPs) showed the consistency of expression at both transcriptome and proteome level in B-48 genotype. Comprehensively, these data supported the efficiency of B-48 genotype under virus infection conditions and provided a better understanding of the expression pattern of photosynthesis-related genes in sugarcane.

TMT-based quantitative proteomic analysis of the effects of Pseudomonas syringae pv. tabaci (Pst) infection on photosynthetic function and the response of the MAPK signaling pathway in tobacco leaves

To reveal the mechanism of photosynthesis inhibition by infection and the response of the MAPK signaling pathway to pathogen infection, tobacco leaves were inoculated with Pseudomonas syringae pv. tabaci (Pst), and the effects of Pst infection on photosynthesis of tobacco leaves were studied by physiological and proteomic techniques, with a focus on MAPK signaling pathway related proteins. Pst infection was observed to lead to the degradation of chlorophyll (especially Chl b) in tobacco leaves and the down-regulation of light harvesting antenna proteins expression, thus limiting the light harvesting ability. The photosystem II and I (PSII and PSI) activities were also decreased, and Pst infection inhibited the utilization of light and CO2. Proteomic analyses showed that the number of differentially expressed proteins (DEPs) under Pst infection at 3 d were significantly higher than at 1 d, especially the number of down-regulated proteins. The KEGG enrichment of DEPs was mainly enriched in the energy metabolism processes such as photosynthesis antenna proteins and photosynthesis. The down-regulation of chlorophyll a-b binding protein, photosynthetic electron transport related proteins (e.g., PSII and PSI core proteins, the Cytb6/f complex, PC, Fd, FNR), ATP synthase subunits, and key enzymes in the Calvin cycle were the key changes associated with Pst infection that may inhibit tobacco photosynthesis. The effect of Pst infection on the PSII electron acceptor side was significantly greater than that on the PSII donor side. The main factor that decreased the photosynthetic ability of tobacco leaves with Pst infection at 1 d may be the inhibition of photochemical reactions leading to an insufficient supply of ATP, rather than decreased expression of enzymes involved in the Calvin cycle. At 1 d into Pst infection, the PSII regulated energy dissipation yield Y(NPQ) may play a role in preventing photosynthetic inhibition in tobacco leaves, but the long-term Pst infection significantly inhibited Y(NPQ) and the expression of PsbS proteins. Proteins involved in the MAPK signaling pathway were up-regulated, suggesting the MAPK signaling pathway was activated to respond to Pst infection. However, at the late stage of Pst infection (at 3 d), MAPK signaling pathway proteins were degraded, and the defense function of the MAPK signaling pathway in tobacco leaves was damaged.

NbTMP14 Is Involved in Tomato Spotted Wilt Virus Infection and Symptom Development by Interaction with the Viral NSm Protein

Tomato spotted wilt virus (TSWV) is one of the most destructive plant viruses, causing severe losses in many important crops worldwide. The non-structural protein NSm of TSWV is a viral movement protein that induces viral symptoms. However, the molecular mechanisms by which NSm contributes to symptom development are unclear. Here, we present evidence that NSm directly interacts with Nicotiana benthamiana chloroplast thylakoid membrane protein TMP14 (NbTMP14) by yeast two-hybrid and bimolecular fluorescence complementation (BiFC) assays. The interaction between NSm and NbTMP14 led to the translocation of the NbTMP14 protein from the chloroplast to the cytoplasm in TSWV-infected plants, and overexpressing NSm decreased NbTMP14 mRNA accumulation. In addition, abnormal chloroplasts and starch accumulation were observed in TSWV-infected plants. Silencing of NbTMP14 by TRV VIGS also showed similar results to those of TSWV-infected plants. Overexpressing NbTMP14 in transgenic N. benthamiana plants impeded TSWV infection, and silencing NbTMP14 in N. benthamiana plants increased disease symptom severity and virus accumulation. To our knowledge, this is the first report showing that the plant chloroplast TMP14 protein is involved in viral infection. Knowledge of the interaction between NSm and NbTMP14 advances our understanding of the molecular mechanisms underlying TSWV symptom development and infection.

Artificial miRNA mediated resistance in tobacco against Jatropha leaf curl Gujarat virus by targeting RNA silencing suppressors

The leaf curl disease of Jatropha caused by geminiviruses results in heavy economic losses. In the present study, we report the identification of a new strain of a Jatropha leaf curl Gujarat virus (JLCuGV), which encodes six ORFs with each one having RNA silencing suppressor activity. Therefore, three artificial microRNAs (amiRNAs; C1/C4, C2/C3 and V1/V2) were designed employing overlapping regions, each targeting two ORFs of JLCuGV genomic DNA and transformed in tobacco. The C1/C4 and C2/C3 amiRNA transgenics were resistant while V1/V2 amiRNA transgenics were tolerant against JLCuGV. The relative level of amiRNA inversely related to viral load indicating a correlation with disease resistance. The assessment of photosynthetic parameters suggests that the transgenics perform significantly better in response to JLCuGV infiltration as compared to wild type (WT). The metabolite contents were not altered remarkably in amiRNA transgenics, but sugar metabolism and tricarboxylic acid (TCA) cycle showed noticeable changes in WT on virus infiltration. The overall higher methylation and demethylation observed in amiRNA transgenics correlated with decreased JLCuGV accumulation. This study demonstrates that amiRNA transgenics showed enhanced resistance to JLCuGV while efficiently maintaining normalcy in their photosynthesis and metabolic pathways as well as homeostasis in the methylation patterns.

Phenotyping viral infection in sweetpotato using a high-throughput chlorophyll fluorescence and thermal imaging platform

BACKGROUND

Virus diseases caused by co-infection with Sweet potato feathery mottle virus (SPFMV) and Sweetpotato chlorotic stunt virus (SPCSV) are a severe problem in the production of sweetpotato (Ipomoea batatas L.). Traditional molecular virus detection methods include nucleic acid-based and serological tests. In this study, we aimed to validate the use of a non-destructive imaging-based plant phenotype platform to study plant-virus synergism in sweetpotato by comparing four virus treatments with two healthy controls.

RESULTS

By monitoring physiological and morphological effects of viral infection in sweetpotato over 29 days, we quantified photosynthetic performance from chlorophyll fluorescence (ChlF) imaging and leaf thermography from thermal infrared (TIR) imaging among sweetpotatoes. Moreover, the differences among different treatments observed from ChlF and TIR imaging were related to virus accumulation and distribution in sweetpotato. These findings were further validated at the molecular level by related gene expression in both photosynthesis and carbon fixation pathways.

CONCLUSION

Our study validated for the first time the use of ChlF- and TIR-based imaging systems to distinguish the severity of virus diseases related to SPFMV and SPCSV in sweetpotato. In addition, we demonstrated that the operating efficiency of PSII and photochemical quenching were the most sensitive parameters for the quantification of virus effects compared with maximum quantum efficiency, non-photochemical quenching, and leaf temperature.

Phenotyping Plant Responses to Biotic Stress by Chlorophyll Fluorescence Imaging

Photosynthesis is a pivotal process in plant physiology, and its regulation plays an important role in plant defense against biotic stress. Interactions with pathogens and pests often cause alterations in the metabolism of sugars and sink/source relationships. These changes can be part of the plant defense mechanisms to limit nutrient availability to the pathogens. In other cases, these alterations can be the result of pests manipulating the plant metabolism for their own benefit. The effects of biotic stress on plant physiology are typically heterogeneous, both spatially and temporarily. Chlorophyll fluorescence imaging is a powerful tool to mine the activity of photosynthesis at cellular, leaf, and whole-plant scale, allowing the phenotyping of plants. This review will recapitulate the responses of the photosynthetic machinery to biotic stress factors, from pathogens (viruses, bacteria, and fungi) to pests (herbivory) analyzed by chlorophyll fluorescence imaging both at the lab and field scale. Moreover, chlorophyll fluorescence imagers and alternative techniques to indirectly evaluate photosynthetic traits used at field scale are also revised.

Transcriptional reprogramming caused by the geminivirus Tomato yellow leaf curl virus in local or systemic infections in Nicotiana benthamiana

BACKGROUND

Viruses have evolved to create a cellular environment permissive for viral replication in susceptible hosts. Possibly both enabling and resulting from these virus-triggered changes, infected hosts undergo a dramatic transcriptional reprogramming, the analysis of which can shed light on the molecular processes underlying the outcome of virus-host interactions. The study of the transcriptional changes triggered by the plant DNA viruses geminiviruses is potentially hampered by the low representation of infected cells in the total population, a situation that becomes extreme in those cases, like that of Tomato yellow leaf curl virus (TYLCV), in which the virus is restricted to phloem companion cells.

RESULTS

In order to gain insight into how different the transcriptional landscapes of TYLCV-infected cells or whole tissues of TYLCV-infected plants might be, here we compare the transcriptional changes in leaf patches infected with TYLCV by agroinfiltration or in systemic leaves of TYLCV-infected plants in Nicotiana benthamiana. Our results show that, in agreement with previous works, infection by TYLCV induces a dramatic transcriptional reprogramming; the detected changes, however, are not equivalent in local and systemic infections, with a much larger number of genes differentially expressed locally, and some genes responding in an opposite manner. Interestingly, a transcriptional repression of the auxin signalling pathway and a transcriptional activation of the ethylene signalling pathway were detected in both local and systemically infected samples. A transcriptional activation of defence was also detectable in both cases. Comparison with the transcriptional changes induced by systemic infection by the geminivirus Tobacco curly shoot virus (TbSV) shows common subsets of up- and down-regulated genes similarly affected by both viral species, unveiling a common transcriptional repression of terpenoid biosynthesis, a process also suppressed by the geminivirus Tomato yellow leaf curl China virus.

CONCLUSIONS

Taken together, the results presented here not only offer insight into the transcriptional changes derived from the infection by TYLCV in N. benthamiana, but also demonstrate that the resolution provided by local and systemic infection approaches largely differs, highlighting the urge to come up with a better system to gain an accurate view of the molecular and physiological changes caused by the viral invasion.

Photosynthetic and Stress Responsive Proteins Are Altered More Effectively in Nicotiana benthamiana Infected with Plum pox virus Aggressive PPV-CR versus Mild PPV-C Cherry-Adapted Isolates

Plum pox virus (PPV, family Potyviridae) is one of the most important viral pathogens of Prunus spp. causing considerable damage to stone-fruit industry worldwide. Among the PPV strains identified so far, only PPV-C, PPV-CR, and PPV-CV are able to infect cherries under natural conditions. Herein, we evaluated the pathogenic potential of two viral isolates in herbaceous host Nicotiana benthamiana. Significantly higher accumulation of PPV capsid protein in tobacco leaves infected with PPV-CR (RU-30sc isolate) was detected in contrast to PPV-C (BY-101 isolate). This result correlated well with the symptoms observed in the infected plants. To further explore the host response upon viral infection at the molecular level, a comprehensive proteomic profiling was performed. Using reverse-phase ultra-high-performance liquid chromatography followed by label-free mass spectrometry quantification, we identified 38 unique plant proteins as significantly altered due to the infection. Notably, the abundances of photosynthesis-related proteins, mainly from the Calvin-Benson cycle, were found more aggressively affected in plants infected with PPV-CR isolate than those of PPV-C. This observation was accompanied by a significant reduction in the amount of photosynthetic pigments extracted from the leaves of PPV-CR infected plants. Shifts in the abundance of proteins that are involved in stimulation of photosynthetic capacity, modification of amino acid, and carbohydrate metabolism may affect plant growth and initiate energy formation via gluconeogenesis in PPV infected N. benthamiana. Furthermore, we suggest that the higher accumulation of H2O2 in PPV-CR infected leaves plays a crucial role in plant defense and development by activating the glutathione synthesis.

Blue Native/SDS-PAGE and iTRAQ-Based Chloroplasts Proteomics Analysis of Nicotiana tabacum Leaves Infected with M Strain of Cucumber Mosaic Virus Reveals Several Proteins Involved in Chlorosis Symptoms

Virus infection in plants involves necrosis, chlorosis, and mosaic. The M strain of cucumber mosaic virus (M-CMV) has six distinct symptoms: vein clearing, mosaic, chlorosis, partial green recovery, complete green recovery, and secondary mosaic. Chlorosis indicates the loss of chlorophyll which is highly abundant in plant leaves and plays essential roles in photosynthesis. Blue native/SDS-PAGE combined with mass spectrum was performed to detect the location of virus, and proteomic analysis of chloroplast isolated from virus-infected plants was performed to quantify the changes of individual proteins in order to gain a global view of the total chloroplast protein dynamics during the virus infection. Among the 438 proteins quantified, 33 showed a more than twofold change in abundance, of which 22 are involved in the light-dependent reactions and five in the Calvin cycle. The dynamic change of these proteins indicates that light-dependent reactions are down-accumulated, and the Calvin cycle was up-accumulated during virus infection. In addition to the proteins involved in photosynthesis, tubulin was up-accumulated in virus-infected plant, which might contribute to the autophagic process during plant infection. In conclusion, this extensive proteomic investigation on intact chloroplasts of virus-infected tobacco leaves provided some important novel information on chlorosis mechanisms induced by virus infection.

Biochemical changes in the leaves of mungbean (Vigna radiata) plants infected by phytoplasma

Objective:

Phyllody disease caused by phytoplasma is an emerging problem in mungbean worldwide. However, the alterations in the host physiology and its associated biochemical components induced by the infection with phytoplasma in mungbean plant remain unknown. Hence the present study was performed with the diseased plants in order to determine the patho-physiological changes that take place.

Methods:

Under present study, the changes in total phenolic compounds, total soluble proteins, peroxidase (POD), catalase (CAT), polyphenol oxidase (PPO), Chlorophyll a, Chlorophyll b, and total chlorophyll were studied in leaves of phytoplasma-infected and healthy plants of six mungbean genotypes.

Results:

Total phenols were decreased significantly in four but increased in one genotype. Protein contents were increased significantly in two genotypes, POD in four, PPO in one and PAL in two genotypes. However, activity of CAT and amount of

Conclusion:

These results suggest that phytoplasma can interfere with host metabolism and photosynthesis to induce disease. In conclusion, this study provides new insights into the mungbean response to phytoplasma infection.

Characterization and assessment of two biocontrol bacteria against Pseudomonas syringae wilt in Solanum lycopersicum and its genetic responses

Pseudomonas and Bacillus species are attractive due to their potential bio-control application against plant bacterial pathogens. Pseudomonas aeruginosa strain D4 and Bacillus stratosphericus strain FW3 were isolated from mine tailings in South Korea. In these potent bacterial strains, we observed improved antagonistic activity against Pseudomonas syringae DC3000. These strains produced biocatalysts for plant growth promotion, and in vivo examination of Solanum lycopersicum included analysis of disease severity, ion leakage, chlorophyll content, and H₂O₂ detection. In addition, regulation of the defense genes pathogen-related protein 1a (PR1a) and phenylalanine ammonia lyase (PAL) was compared with treated plants and untreated control plants. The results suggest that these two bacterial strains provide protection against plant pathogens via direct and indirect modes of action and could be used as a bio-control agent.

Inducible expression of magnesium protoporphyrin chelatase subunit I (CHLI)-amiRNA provides insights into cucumber mosaic virus Y satellite RNA-induced chlorosis symptoms

Recent studies with Y satellite RNA (Y-sat) of cucumber mosaic virus have demonstrated that Y-sat modifies the disease symptoms in specific host plants through the silencing of the magnesium protoporphyrin chelatase I subunit (CHLI), which is directed by the Y-sat derived siRNA. Along with the development of peculiar yellow phenotypes, a drastic decrease in CHLI-transcripts and a higher accumulation of Y-sat derived siRNA were observed. To investigate the molecular mechanisms underlying the Y-sat-induced chlorosis, especially whether or not the reduced expression of CHLI causes the chlorosis simply through the reduced production of chlorophyll or it triggers some other mechanisms leading to the chlorosis, we have established a new experimental system with an inducible silencing mechanism. This system involves the expression of artificial microRNAs targeting of Nicotiana tabacum CHLI gene under the control of chemically inducible promoter. The CHLI mRNA levels and total chlorophyll content decreased significantly in 2 days, enabling us to analyze early events in induced chlorosis and temporary changes therein. This study revealed that the silencing of CHLI did not only result in the decreased chlorophyll content but also lead to the downregulation of chloroplast and photosynthesis-related genes expression and the upregulation of defense-related genes. Based on these results, we propose that the reduced expression of CHLI could activate unidentified signaling pathways that lead plants to chlorosis.

Chlorophyll fluorescence lifetime imaging provides new insight into the chlorosis induced by plant virus infection

KEY MESSAGE

Leaf chlorosis induced by plant virus infection has a short fluorescence lifetime, which reflects damaged photosynthetic complexes and degraded chloroplasts. Plant viruses often induce chlorosis and necrosis, which are intimately related to photosynthetic functions. Chlorophyll fluorescence lifetime measurement is a valuable noninvasive tool for analyzing photosynthetic processes and is a sensitive indicator of the environment surrounding the fluorescent molecules. In this study, our central goal was to explore the effect of viral infection on photosynthesis by employing chlorophyll fluorescence lifetime imaging (FLIM), steady-state fluorescence, non-photochemical quenching (NPQ), transmission electron microscopy (TEM), and pigment analysis. The data indicated that the chlorophyll fluorescence lifetime of chlorotic leaves was significantly shorter than that of healthy control leaves, and the fitted short lifetime component of chlorophyll fluorescence of chlorotic leaves was dominant. This dominant short lifetime component may result from damage to the structure of thylakoid, which was confirmed by TEM. The NPQ value of chlorotic leaves was slightly higher than that of healthy green leaves, which can be explained by increased neoxanthin, lutein and violaxanthin content relative to chlorophyll a. The difference in NPQ is slight, but FLIM can provide simple and direct characterization of PSII structure and photosynthetic function. Therefore, this technique shows great potential as a simple and rapid method for studying mechanisms of plant virus infection.

Quantification of Pea enation mosaic virus 1 and 2 during infection of Pisum sativum by one step real-time RT-PCR

Pea enation mosaic virus 1 (PEMV1) and Pea enation mosaic virus 2 (PEMV2) are two viruses in an obligate symbiosis that cause pea enation mosaic disease mainly in plants in the Fabaceae family. This virus system is a valuable model to investigate plant virus replication, movement and vector transmission. Thus, here we describe growth conditions, virus detection methods, and virus accumulation behavior. To measure the accumulation and movement of PEMV1 and PEMV2 in plants during the course of infection, we developed a quantitative real-time one-step reverse transcription PCR procedure using the SYBR-green® technology. Viral primers were designed that anneal to conserved but distinct regions in the RNA-dependent RNA polymerase gene of each virus. Moreover, the normalization of viral accumulation was performed to correct for sample-to-sample variation by designing primers to two different Pisum sativum housekeeping genes: actin and β-tubulin. Transcript levels for these housekeeping genes did not change significantly in response to PEMV infection. Conditions were established for maximum PCR efficiency for each gene, and quantification using QuBit® technology. Both viruses reached maximum accumulation around 21days post-inoculation of pea plants. These results provide valuable tools and knowledge to allow reproducible studies of this emerging model virus system virus complex.

Picturing pathogen infection in plants

Several imaging techniques have provided valuable tools to evaluate the impact of biotic stress on host plants. The use of these techniques enables the study of plant-pathogen interactions by analysing the spatial and temporal heterogeneity of foliar metabolism during pathogenesis. In this work we review the use of imaging techniques based on chlorophyll fluorescence, multicolour fluorescence and thermography for the study of virus, bacteria and fungi-infected plants. These studies have revealed the impact of pathogen challenge on photosynthetic performance, secondary metabolism, as well as leaf transpiration as a promising tool for field and greenhouse management of diseases. Images of standard chlorophyll fluorescence (Chl-F) parameters obtained during Chl-F induction kinetics related to photochemical processes and those involved in energy dissipation, could be good stress indicators to monitor pathogenesis. Changes on UV-induced blue (F440) and green fluorescence (F520) measured by multicolour fluorescence imaging in pathogen-challenged plants seem to be related with the up-regulation of the plant secondary metabolism and with an increase in phenolic compounds involved in plant defence, such as scopoletin, chlorogenic or ferulic acids. Thermal imaging visualizes the leaf transpiration map during pathogenesis and emphasizes the key role of stomata on innate plant immunity. Using several imaging techniques in parallel could allow obtaining disease signatures for a specific pathogen. These techniques have also turned out to be very useful for presymptomatic pathogen detection, and powerful non-destructive tools for precision agriculture. Their applicability at lab-scale, in the field by remote sensing, and in high-throughput plant phenotyping, makes them particularly useful. Thermal sensors are widely used in crop fields to detect early changes in leaf transpiration induced by both air-borne and soil-borne pathogens. The limitations of measuring photosynthesis by Chl-F at the canopy level are being solved, while the use of multispectral fluorescence imaging is very challenging due to the type of light excitation that is used.

The Plant Immunity Regulating F-Box Protein CPR1 Supports Plastid Function in Absence of Pathogens

The redox imbalanced 6 mutant (rimb6) of Arabidopsis thaliana was isolated in a genetic screening approach for mutants with defects in chloroplast-to-nucleus redox signaling. It has an atypically low activation status of the 2-Cys peroxiredoxin-A promoter in the seedling stage. rimb6 shows wildtype-like germination, seedling development and greening, but slower growth and reduced biomass in the rosette stage. Mapping of the casual mutation revealed that rimb6 carries a single nucleotide polymorphism in the gene encoding CONSTITUTIVE EXPRESSER OF PATHOGENESIS RELATED (PR) GENES 1, CPR1 (At4g12560), leading to a premature stop codon. CPR1 is known as a repressor of pathogen signaling and regulator of microtubule organization. Allelism of rimb6 and cpr1 revealed a function of CPR1 in chloroplast stress protection. Expression studies in pathogen signaling mutants demonstrated that CPR1-mediated activation of genes for photosynthesis and chloroplast antioxidant protection is, in contrast to activation of pathogen responses, regulated independently from PAD4-controlled salicylic acid (SA) accumulation. We conclude that the support of plastid function is a basic, SA-independent function of CPR1.

Chloroplast in Plant-Virus Interaction

In plants, the chloroplast is the organelle that conducts photosynthesis. It has been known that chloroplast is involved in virus infection of plants for approximate 70 years. Recently, the subject of chloroplast-virus interplay is getting more and more attention. In this article we discuss the different aspects of chloroplast-virus interaction into three sections: the effect of virus infection on the structure and function of chloroplast, the role of chloroplast in virus infection cycle, and the function of chloroplast in host defense against viruses. In particular, we focus on the characterization of chloroplast protein-viral protein interactions that underlie the interplay between chloroplast and virus. It can be summarized that chloroplast is a common target of plant viruses for viral pathogenesis or propagation; and conversely, chloroplast and its components also can play active roles in plant defense against viruses. Chloroplast photosynthesis-related genes/proteins (CPRGs/CPRPs) are suggested to play a central role during the complex chloroplast-virus interaction.

Chloroplast in Plant-Virus Interaction

In plants, the chloroplast is the organelle that conducts photosynthesis. It has been known that chloroplast is involved in virus infection of plants for approximate 70 years. Recently, the subject of chloroplast-virus interplay is getting more and more attention. In this article we discuss the different aspects of chloroplast-virus interaction into three sections: the effect of virus infection on the structure and function of chloroplast, the role of chloroplast in virus infection cycle, and the function of chloroplast in host defense against viruses. In particular, we focus on the characterization of chloroplast protein-viral protein interactions that underlie the interplay between chloroplast and virus. It can be summarized that chloroplast is a common target of plant viruses for viral pathogenesis or propagation; and conversely, chloroplast and its components also can play active roles in plant defense against viruses. Chloroplast photosynthesis-related genes/proteins (CPRGs/CPRPs) are suggested to play a central role during the complex chloroplast-virus interaction.

Silicon nanoparticles (SiNp) alleviate chromium (VI) phytotoxicity in Pisum sativum (L.) seedlings

The present study was aimed to investigate the effect of silicon nanoparticles (SiNp) against Cr (VI) phytotoxicity in pea seedlings. Results show that Cr(VI, 100 μM) significantly (P < 0.05) declined growth of pea which was accompanied by the enhanced level of Cr. Additionally, photosynthetic pigments and chlorophyll fluorescence parameters like F(v)/F(m), F(v)/F0 and qP were decreased while NPQ significantly (P < 0.05) increased under Cr(VI) treatment. Superoxide radical, hydrogen peroxide and malondialdehyde (MDA-lipid peroxidation) contents were enhanced by Cr(VI). Activities of antioxidant enzymes like superoxide dismutase and ascorbate peroxidase were increased by Cr (VI) while activities of catalase, glutathione reductase and dehydroascorbate reductase were inhibited significantly (P < 0.05). Micro and macronutrients also show decreasing trends (except S) under Cr(VI) treatment. However, addition of SiNp together with Cr(VI) protects pea seedlings against Cr(VI) phytotoxicity hence improved growth was noticed. In conclusion, the results of this study show that Cr(VI) causes negative impact on pea seedlings, however; SiNp protects pea seedlings against Cr(VI) phytotoxicity by reducing Cr accumulation and oxidative stress, and up-regulating antioxidant defense system and nutrient elements.

Interaction between PVY HC-Pro and the NtCF1β-subunit reduces the amount of chloroplast ATP synthase in virus-infected tobacco

The photosynthetic rate of virus-infected plants is always reduced. However, the molecular mechanism underlying this phenomenon remains unclear. The helper component-proteinase (HC-Pro) of Potato virus Y (PVY) was found in the chloroplasts of PVY-infected tobacco, indicating some new function of HC-Pro in the chloroplasts. We generated HC-Pro transgenic plants with a transit peptide to target the protein to chloroplast. The HC-Pro transgenic tobacco showed a decreased photosynthetic rate by 25% at the light intensity of 600 μmol m(-2) s(-1). Using a yeast two-hybrid screening assay to search for chloroplast proteins interacting with HC-Pro, we identified that PVY HC-Pro can interact with the chloroplast ATP synthase NtCF1β-subunit. This interaction was confirmed by GST pull-down and co-immunoprecipitation assays. HC-Pro didn't interfere with the activity of assembled ATP synthase in vitro. The HC-Pro/NtCF1β-subunit interaction might affect the assembly of ATP synthase complex. Quantitative western blot and immunogold labeling of the ATP synthase indicated that the amount of ATP synthase complex was decreased in both the HC-Pro transgenic and the PVY-infected tobacco. These results demonstrate that HC-Pro plays an important role in reducing the photosynthetic rate of PVY-infected plants, which is a completely new role of HC-Pro besides its multiple known functions.

Grapevine leafroll disease and associated viruses: a unique pathosystem

Grapevine leafroll is the most complex and intriguing viral disease of grapevine (Vitis spp.). Several monopartite closteroviruses (family Closteroviridae) from grapevines have been molecularly characterized, yet their role in disease etiology is not completely resolved. Hence, these viruses are currently designated under the umbrella term of Grapevine leafroll-associated viruses (GLRaVs). This review examines our current understanding of the genetically divergent GLRaVs and highlights the emerging picture of several unique aspects of the leafroll disease pathosystem. A systems biology approach using contemporary technologies in molecular biology, -omics, and cell biology aids in exploring the comparative molecular biology of GLRaVs and deciphering the complex network of host-virus-vector interactions to bridge the gap between genomics and phenomics of leafroll disease. In addition, grapevine-infecting closteroviruses have a great potential as designer viruses to pursue functional genomics and for the rational design of novel disease intervention strategies in this agriculturally important perennial fruit crop.

Water Balance, Hormone Homeostasis, and Sugar Signaling Are All Involved in Tomato Resistance to Tomato Yellow Leaf Curl Virus

Vacuolar water movement is largely controlled by membrane channels called tonoplast-intrinsic aquaporins (TIP-AQPs). Some TIP-AQP genes, such as TIP2;2 and TIP1;1, are up-regulated upon exposure to biotic stress. Moreover, TIP1;1 transcript levels are higher in leaves of a tomato (Solanum lycopersicum) line resistant to Tomato yellow leaf curl virus (TYLCV) than in those of a susceptible line with a similar genetic background. Virus-induced silencing of TIP1;1 in the tomato resistant line and the use of an Arabidopsis (Arabidopsis thaliana) tip1;1 null mutant showed that resistance to TYLCV is severely compromised in the absence of TIP1:1. Constitutive expression of tomato TIP2;2 in transgenic TYLCV-susceptible tomato and Arabidopsis plants was correlated with increased TYLCV resistance, increased transpiration, decreased abscisic acid levels, and increased salicylic acid levels at the early stages of infection. We propose that TIP-AQPs affect the induction of leaf abscisic acid, which leads to increased levels of transpiration and gas exchange, as well as better salicylic acid signaling.

Response of bean (Vicia faba L.) plants to low sink demand by measuring the gas exchange rates and chlorophyll a fluorescence kinetics

Background

The decline of photosynthesis in plants under low sink demand is well known. Previous studies focused on the relationship between stomatal conductance (g_s) and net photosynthetic rate (P_n). These studies investigated the effect of changes in Photosystem II (PSII) function on the P_n decline under low sink demand. However, little is known about its effects on different limiting steps of electron transport chain in PSII under this condition.

Methodology/Principal Finding

Two-month-old bean plants were processed by removing pods and flowers (low sink demand). On the 1^st day after low sink demand treatment, a decline of P_n was accompanied by a decrease in g_s and internal-to-ambient CO₂ concentration ratio (C_i/C_a). From the 3^rd to 9^th day, P_n and g_s declined continuously while C_i/C_a ratio remained stable in the treatment. Moreover, these values were lower than that of control. W_k (a parameter reflecting the damage to oxygen evolving complex of the donor side of PSII) values in the treatment were significantly higher than their corresponding control values. However, RC_QA (a parameter reflecting the number of active RCs per excited cross-section of PSII) values in the treatment were significantly lower than control from the 5^th day. From the 11^th to 21^st day, P_n and g_s of the treatment continued to decline and were lower than control. This was accompanied by a decrease of RC_QA, and an increase of W_k. Furthermore, the quantum yield parameters φ_Po, φ_Eo and ψ_Eo in the treatment were lower than in control; however, C_i/C_a values in the treatment gradually increased and were significantly higher than control on the 21^st day.

Conclusions

Stomatal limitation during the early stage, whereas a combination of stomatal and non-stomatal limitation during the middle stage might be responsible for the reduction of P_n under low sink demand. Non-stomatal limitation during the late stages after the removal of the sink of roots and pods may also cause P_n reduction. The non-stomatal limitation was associated with the inhibition of PSII electron transport chain. Our data suggests that the donor side of PSII was the most sensitive to low sink demand followed by the reaction center of PSII. The acceptor side of PSII may be the least sensitive.

The chlorotic symptom induced by Sunflower chlorotic mottle virus is associated with changes in redox-related gene expression and metabolites

Systemic infections are commonly associated with changes in host metabolism and gene expression. Sunflower chlorotic mottle virus (SuCMoV) causes systemic infection with sugar increase, photoinhibition and increase in antioxidant enzyme activities before chlorotic symptom appearance in sunflower leaves. The aim of this study was to determine if chlorotic symptom development induced by SuCMoV infection is accompanied by changes in different redox-related metabolites and transcripts. Symptom development was analyzed in the second pair of leaves (systemic infection) at different post-inoculation times: before symptom appearance (BS, 4 dpi), and at an early (ES, 7 dpi) and later stage (LS, 12 dpi) of symptom expression. The results showed that the virus reaches the second pair of leaves at 4 dpi. A positive correlation between chlorotic symptom and number of viral copies was also observed. Changes in hydrogen peroxide, glutathione, pyridine nucleotides and ATP content were observed since symptom appearance (ES, 7 dpi). The expression of some of the genes analyzed was also strongly affected by SuCMoV infection. Specifically, down-regulation of both chloroplast-encoded genes and chloroplast-targeted genes: psbA, rbcS, Cu/Zn sod, Fe sod, phosphoglycolate phosphatase, psbO, psaH and fnr was present, whereas the expression of cytoplasmic-targeted genes, apx1, and Cu/Zn sod was up-regulated. Mitochondrial Mn sod decreased at BS stage and aox decreased only at ES stage. Peroxisomal catalase (cat-2) was lower at BS and LS stages. All these results suggest that SuCMoV infection induces progressive changes in determinants of redox homeostasis associated with chlorotic symptom development.

Risk-taking plants: anisohydric behavior as a stress-resistance trait

Water scarcity is a critical limitation for agricultural systems. Two different water management strategies have evolved in plants: an isohydric strategy and an anisohydric strategy. Isohydric plants maintain a constant midday leaf water potential (Ψleaf) when water is abundant, as well as under drought conditions, by reducing stomatal conductance as necessary to limit transpiration. Anisohydric plants have more variable Ψleaf and keep their stomata open and photosynthetic rates high for longer periods, even in the presence of decreasing leaf water potential. This risk-taking behavior of anisohydric plants might be beneficial when water is abundant, as well as under moderately stressful conditions. However, under conditions of intense drought, this behavior might endanger the plant. We will discuss the advantages and disadvantages of these two water-usage strategies and their effects on the plant's ability to tolerate abiotic and biotic stress. The involvement of plant tonoplast AQPs in this process will also be discussed.