Alteration in the chloroplastic metabolism leads to ROS accumulation in pea plants in response to plum pox virus

Cold atmospheric plasma enhances morphological and biochemical attributes of tomato seedlings

Cold atmospheric plasma (CAP) is a physical technology with notable effects on living organisms. In the present study, tomato seeds (Solanum lycopersicum var. Bassimo Mill.) were exposed to CAP for various time intervals, ranging from 1 to 5 min, in both continuous and intermittent periods, and were compared with a control group that received no CAP treatment. Seedlings grown from treated seeds exhibited improvements in levels of growth traits, photosynthetic pigments, and metabolite contents when compared to the control group. Seedlings from seeds treated with S04 displayed significant increases in shoot and root lengths, by 32.45% and 20.60% respectively, compared to the control group. Moreover, seedlings from seeds treated with S01 showed a 101.90% increase in total protein, whereas those treated with S02 experienced a 119.52% increase in carbohydrate content. These findings highlight the substantial improvements in growth characteristics, photosynthetic pigments, and metabolite levels in seedlings from treated seeds relative to controls. Total antioxidant capacity was boosted by CAP exposure. The activities of enzymes including superoxide dismutase, catalase, and peroxidases were stimulated by S02 and exceeded control treatment by (177.48%, 137.41%, and 103.32%), respectively. Additionally, exposure to S04 increased the levels of non-enzymatic antioxidants like flavonoids, phenolics, saponins, and tannins over the control group (38.08%, 30.10%, 117.19%, and 94.44%), respectively. Our results indicate that CAP-seed priming is an innovative and cost-effective approach to enhance the growth, bioactive components, and yield of tomato seedlings.

A viral movement protein targets host catalases for 26S proteasome-mediated degradation to facilitate viral infection and aphid transmission in wheat

The infection of host plants by many different viruses causes reactive oxygen species (ROS) accumulation and yellowing symptoms, but the mechanisms through which plant viruses counteract ROS-mediated immunity to facilitate infection and symptom development have not been fully elucidated. Most plant viruses are transmitted by insect vectors in the field, but the molecular mechanisms underlying virus‒host-insect interactions are unclear. In this study, we investigated the interactions among wheat, barley yellow dwarf virus (BYDV), and its aphid vector and found that the BYDV movement protein (MP) interacts with both wheat catalases (CATs) and the 26S proteasome ubiquitin receptor non-ATPase regulatory subunit 2 homolog (PSMD2) to facilitate the 26S proteasome-mediated degradation of CATs, promoting viral infection, disease symptom development, and aphid transmission. Overexpression of the BYDV MP gene in wheat enhanced the degradation of CATs, which leading to increased accumulation of ROS and thereby enhanced viral infection. Interestingly, transgenic wheat lines overexpressing BYDV MP showed significantly reduced proliferation of wingless aphids and an increased number of winged aphids. Consistent with this observation, silencing of CAT genes also enhanced viral accumulation and reduced the proliferation of wingless aphids but increased the occurrence of winged aphids. In contrast, transgenic wheat plants overexpressing TaCAT1 exhibited the opposite changes and showed increases in grain size and weight upon infection with BYDV. Biochemical assays demonstrated that BYDV MP interacts with PSMD2 and promotes 26S proteasome-mediated degradation of TaCAT1 likely in a ubiquitination-independent manner. Collectively, our study reveals a molecular mechanism by which a plant virus manipulates the ROS production system of host plants to facilitate viral infection and transmission, shedding new light on the sophisticated interactions among viruses, host plants, and insect vectors.

Physiological and Biochemical Responses Induced by Plum Pox Virus and Plum Bark Necrosis Steam Pitting Associated Virus in Tuscany Autochthonous Plum cv. Coscia di Monaca

The present study focused on trees of Tuscany autochthonous plum cv. Coscia di Monaca in order to evaluate the presence of viruses and elucidate the physiological and biochemical responses to virus infections under real field conditions. Among the several investigated viruses, plums tested positive only to plum pox virus (PPV) and plum bark necrosis steam pitting associated virus (PBNSPaV), occurring as both singular and co-infections. This is the first report of PBNSPaV in a Tuscany orchard. Furthermore, the present study not only confirmed the detrimental effects of PPV on the carbon dioxide assimilation rate due to both stomatal limitations and mesophyll impairments, but also showed that although PBNSPaV did not induce such photosynthetic impairments when occurring as singular infection, it enhanced this damaging effect when present as a co-infection with PPV, as confirmed by a severe decrease in the chlorophyll content. Infection-specific responses in terms of accessory pigments (i.e., carotenoids and xanthophylls), as well as sugars and organic acids, were also reported, these being likely related to photoprotective mechanisms and osmotic regulations under virus-induced oxidative stress. Overall, the results here presented represent an important step to fill knowledge gaps about the interaction of plant viruses and autochthonous Prunus cultivars.

Host range and molecular and ultrastructural analyses of Asparagus virus 1 pathotypes isolated from garden asparagus Asparagus officinalis L

Asparagus samples were examined from growing areas of Germany and selected European as well as North, Central and South American countries. Overall, 474 samples were analyzed for Asparagus virus 1 (AV1) using DAS-ELISA. In our survey, 19 AV1 isolates were further characterized. Experimental transmission to 11 species belonging to Aizoaceae, Amarantaceae, Asparagaceae, and Solanaceae succeeded. The ultrastructure of AV1 infection in asparagus has been revealed and has been compared with the one in indicator plants. The cylindrical inclusion (CI) protein, a core factor in viral replication, localized within the cytoplasm and in systemic infections adjacent to the plasmodesmata. The majority of isolates referred to pathotype I (PI). These triggered a hypersensitive resistance in inoculated leaves of Chenopodium spp. and were incapable of infecting Nicotiana spp. Only pathotype II (PII) and pathotype III (PIII) infected Nicotiana benthamiana systemically but differed in their virulence when transmitted to Chenopodium spp. The newly identified PIII generated amorphous inclusion bodies and degraded chloroplasts during systemic infection but not in local lesions of infected Chenopodium spp. PIII probably evolved via recombination in asparagus carrying a mixed infection by PI and PII. Phylogeny of the coat protein region recognized two clusters, which did not overlap with the CI-associated grouping of pathotypes. These results provide evidence for ongoing modular evolution of AV1.

Comparative metabolomic analysis between tomato and halophyte plants under intercropping conditions

Halophyte-based intercropping appears nowadays as a valuable approach in soil remediation and agriculture. In this work, intercropping between the halophyte Arthrocaulon macrostachyum and tomato (Solanum lycopersicum var. Sargento) was studied in both plant species using comparative mass spectrometry-based metabolomics coupled to metabolic pathway predictions. A significant number of changes in metabolites was observed in the halophyte. In terms of alteration of specific metabolic pathways, intercropping conditions stimulated sugar and starch metabolisms in tomato, whereas in the halophyte, intercropping mainly altered amino acid-related pathways. In addition, arginine and proline metabolism were commonly affected in both tomato and halophyte plants. Moreover, metabolomic changes were associated with physiological alterations in tomato. In this sense, mild oxidative stress was induced in intercropped tomato plants, which, in turn, could trigger signaling events leading to plant adjustment to intercropping conditions. This study represents the first approach toward understanding intercropping interactions at the metabolome level and its effect on plant physiology, opening up prospects for further characterization of this crop cultivation strategy.

Compositional biases and evolution of the largest plant RNA virus order Patatavirales

Patatavirales is the largest order of plant RNA viruses and exclusively contains the family Potyviridae, accounting for 30 % of all known plant viruses. The composition bias of animal RNA viruses and several plant RNA viruses has been determined. However, the comprehensive nucleic acid composition, codon pair usage patterns, dinucleotide preference and codon pair preference of plant RNA viruses have not been investigated to date. In this study, integrated analysis and discussion of the nucleic acid composition, codon usage patterns, dinucleotide composition and codon pair bias of potyvirids were performed using 3732 complete genome coding sequences. The nucleic acid composition of potyvirids was significantly enriched in A/U. Interestingly, the A/U-rich nucleotide composition of Patatavirales is essential for determining the preferred A-ended and U-ended codons and the overexpression of UpG and CpA dinucleotides. The codon usage patterns and codon pair bias of potyvirids were significantly correlated with their nucleic acid composition. Additionally, the codon usage pattern, dinucleotide composition and codon-pair bias of potyvirids are more dependent on the classification of the virus compared with their hosts. Our analysis provides a better understanding of future research on the origin and evolution patterns of the order Patatavirales.

Glutathione Contribution in Interactions between Turnip mosaic virus and Arabidopsis thaliana Mutants Lacking Respiratory Burst Oxidase Homologs D and F

Respiratory burst oxidase homologs (Rbohs) play crucial and diverse roles in plant tissue-mediated production of reactive oxygen species during the development, growth, and response of plants to abiotic and biotic stress. Many studies have demonstrated the contribution of RbohD and RbohF in stress signaling in pathogen response differentially modulating the immune response, but the potential role of the Rbohs-mediated response in plant-virus interactions remains unknown. The present study analyzed, for the first time, the metabolism of glutathione in rbohD-, rbohF-, and rbohD/F-transposon-knockout mutants in response to Turnip mosaic virus (TuMV) infection. rbohD-TuMV and Col-0-TuMV interactions were characterized by susceptible reaction to TuMV, associated with significant activity of GPXLs (glutathione peroxidase-like enzymes) and induction of lipid peroxidation in comparison to mock-inoculated plants, with reduced total cellular and apoplastic glutathione content observed at 7-14 dpi and dynamic induction of apoplast GSSG (oxidized glutathione) at 1-14 dpi. Systemic virus infection resulted in the induction of AtGSTU1 and AtGSTU24, which was highly correlated with significant downregulation of GSTs (glutathione transferases) and cellular and apoplastic GGT (γ-glutamyl transferase) with GR (glutathione reductase) activities. On the contrary, resistant rbohF-TuMV reactions, and especially enhanced rbohD/F-TuMV reactions, were characterized by a highly dynamic increase in total cellular and apoplastic glutathione content, with induction of relative expression of AtGGT1, AtGSTU13, and AtGSTU19 genes. Moreover, virus limitation was highly correlated with the upregulation of GSTs, as well as cellular and apoplastic GGT with GR activities. These findings clearly indicate that glutathione can act as a key signaling factor in not only susceptible rbohD reaction but also the resistance reaction presented by rbohF and rbohD/F mutants during TuMV interaction. Furthermore, by actively reducing the pool of glutathione in the apoplast, GGT and GR enzymes acted as a cell first line in the Arabidopsis-TuMV pathosystem response, protecting the cell from oxidative stress in resistant interactions. These dynamically changed signal transductions involved symplast and apoplast in mediated response to TuMV.

Tomato SlGSTU38 interacts with the PepMV coat protein and promotes viral infection

Pepino mosaic virus (PepMV) is pandemic in tomato crops, causing important economic losses world-wide. No PepMV-resistant varieties have been developed yet. Identification of host factors interacting with PepMV proteins is a promising source of genetic targets to develop PepMV-resistant varieties. The interaction between the PepMV coat protein (CP) and the tomato glutathione S-transferase (GST) SlGSTU38 was identified in a yeast two-hybrid (Y2H) screening and validated by directed Y2H and co-immunoprecipitation assays. SlGSTU38-knocked-out Micro-Tom plants (gstu38) generated by the CRISPR/Cas9 technology together with live-cell imaging were used to understand the role of SlGSTU38 during infection. The transcriptomes of healthy and PepMV-infected wild-type (WT) and gstu38 plants were profiled by RNA-seq analysis. SlGSTU38 functions as a PepMV-specific susceptibility factor in a cell-autonomous manner and relocalizes to the virus replication complexes during infection. Besides, knocking out SlGSTU38 triggers reactive oxygen species accumulation in leaves and the deregulation of stress-responsive genes. SlGSTU38 may play a dual role: On the one hand, SlGSTU38 may exert a proviral function depending on its specific interaction with the PepMV CP; and on the other hand, SlGSTU38 may delay PepMV-infection sensing by participating in the redox intracellular homeostasis in a nonspecific manner.

Alpha-momorcharin preserves catalase activity to inhibit viral infection by disrupting the 2b-CAT interaction in Solanum lycopersicum

Many host factors of plants are used by viruses to facilitate viral infection. However, little is known about how alpha-momorcharin (αMMC) counters virus-mediated attack strategies in tomato. Our present research revealed that the 2b protein of cucumber mosaic virus (CMV) directly interacted with catalases (CATs) and inhibited their activities. Further analysis revealed that transcription levels of catalase were induced by CMV infection and that virus accumulation increased in CAT-silenced or 2b-overexpressing tomato plants compared with that in control plants, suggesting that the interaction between 2b and catalase facilitated the accumulation of CMV in hosts. However, both CMV accumulation and viral symptoms were reduced in αMMC transgenic tomato plants, indicating that αMMC engaged in an antiviral role in the plant response to CMV infection. Molecular experimental analysis demonstrated that αMMC interfered with the interactions between catalases and 2b in a competitive manner, with the expression of αMMC inhibited by CMV infection. We further demonstrated that the inhibition of catalase activity by 2b was weakened by αMMC. Accordingly, αMMC transgenic plants exhibited a greater ability to maintain redox homeostasis than wild-type plants when infected with CMV. Altogether, these results reveal that αMMC retains catalase activity to inhibit CMV infection by subverting the interaction between 2b and catalase in tomato.

AMF species do matter: Rhizophagus irregularis and Funneliformis mosseae affect healthy and PVY-infected Solanum tuberosum L. in a different way

Arbuscular mycorrhizal fungi (AMF) were documented to positively influence plant growth and yield, which is extremely important for the production of many crops including potato. However, the nature of the interaction between arbuscular mycorrhiza and plant virus that share the same host is not well characterized. In this study, we examined the effect of different AMF, Rhizophagus irregularis and Funneliformis mosseae, on healthy and potato virus Y (PVY)-infected Solanum tuberosum L. The analyses conducted included the measurement of potato growth parameters, oxidative stress indicators, and photosynthetic capacity. Additionally, we evaluated both the development of AMF in plant roots and the virus level in mycorrhizal plants. We found that two AMF species colonized plant roots to varying degrees (ca. 38% for R. irregularis vs. 20% for F. mosseae). Rhizophagus irregularis had a more positive effect on potato growth parameters, causing a significant increase in the total fresh and dry weight of tubers, along with virus-challenged plants. Furthermore, this species lowered hydrogen peroxide levels in PVY-infected leaves and positively modulated the levels of nonenzymatic antioxidants, i.e., ascorbate and glutathione in leaves and roots. Finally, both fungal species contributed to reduced lipid peroxidation and alleviation of virus-induced oxidative damage in plant organs. We also confirmed an indirect interaction between AMF and PVY inhabiting the same host. The two AMF species seemed to have different abilities to colonize the roots of virus-infected hosts, as R. irregularis showed a stronger drop in mycorrhizal development in the presence of PVY. At the same time, arbuscular mycorrhiza exerted an effect on virus multiplication, causing increased PVY accumulation in plant leaves and a decreased concentration of virus in roots. In conclusion, the effect of AMF-plant interactions may differ depending on the genotypes of both symbiotic partners. Additionally, indirect AMF-PVY interactions occur in host plants, diminishing the establishment of arbuscular mycorrhiza while changing the distribution of viral particles in plants.

Responses of the growth, photosynthetic characteristics, endogenous hormones and antioxidant activity of Carpinus betulus L. seedlings to different light intensities

Light is an important ecological factor that affects plant growth, survival and distribution. Carpinus betulus L. is native to central Europe and is used as an ornamental plant with strong adaptability. It is an important tree species for landscaping and timber use. What's more, the antioxidant- and anticancer-related properties of C. betulus leaf extracts are remarkable, that make it a possible raw material for medicine. Light intensity is an important environmental factor affecting the growth and physicochemical changes of C. betulus, but the mechanism of its effect on this species still remains unknown. In this study, the growth, photosynthetic characteristics, endogenous hormones and antioxidant activity responses of C. betulus seedlings to four light intensity gradients (T0: normal light; T1: 75%; T2: 50%; T3: 25% of normal light) were studied after 60 days of shading treatments. The results showed a significant effect of low light intensity on the values of the growth and physiological parameters of C. betulus. The low light intensity caused the inhibition of plant biomass accumulation and the degradation of photosynthetic capacity and stomatal behavior and aggravated the cell membrane lipid peroxidation. However, the plant height growth, leaf area, specific leaf area, photosynthetic pigment content, and contents of GA₃ and ABA of C. betulus increased with decreasing light intensity. We found that C. betulus can tolerate mild (T1) and moderate (T2) shading stress by developing photoprotective mechanisms and maintaining relatively high concentrations of organic osmolytes and high antioxidant enzyme activities (superoxide dismutase, peroxidase, catalase and ascorbate peroxidase), but the ability of C. betulus to synthesize osmotic substances and enzymatic antioxidants was impaired under severe shading conditions (T3). Our results suggest that C. betulus can make effective use of low light resources by adjusting its morphology, material distribution, photosynthetic rate and antioxidant enzyme system in suitable low-light environments (50%~75% of normal light); however, light intensity levels that are too low (25% of normal light) will have adverse effects on plant growth. The results of this study provide not only new insights into the response mechanisms of C. betulus to light intensity but also a scientific basis for the cultivation and application of C. betulus in China.

Effect of light intensities on the photosynthesis, growth and physiological performances of two maple species

Photoinhibition decreases photosynthetic capacity and can therefore affect the plant survival, growth, and distribution, but little is known about how it affects on kindred tree species. We conducted field experiments to measure the photosynthetic, growth and physiological performances of two maple species (Acer mono and A. pseudosieboldianum) seedlings at four light intensities (100%, 75%, 55%, and 20% of full light) and evaluated the adaptability of seedlings. We found that: (1) A. mono seedlings have larger light saturated photosynthetic rates (A _max), the light saturation point (LSP), and lower light compensation point (LCP) than A. pseudosieboldianum seedlings, thus indicating that the former has a stronger light utilization ability. (2) A. mono seedlings under 75% light intensity and had higher seedling height (SH), basal stem diameter (BSD), leaf number (LN), leaf area per plant (LAPP) and total dry weight (TDW), while A. pseudosieboldianum seedling at 55% light intensity displayed greater growth advantages, which agreed with their response of light saturated photosynthetic rate. Morphological plasticity adjustments such as decreased root shoot ratio (RSR) and increased specific leaf area (SLA) showed how seedlings adapt to weak light environments. (3) 100% and 20% light intensities increased the malondialdehyde (MDA) content of two maple seedlings, indicating that very strong or very weak light could lead to the imbalance of reactive oxygen species (ROS) metabolism. The regulation of antioxidant enzyme activities such as superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT), as well as the content of osmoregulation substances such as free proline and soluble protein, are the main mechanisms of plant adaptation to light stress. Although both A. mono and A. pseudosieboldianum are highly shade tolerant, subtle differences in the photosynthetic, morphological and physiological traits underpinning their shade tolerance suggest A. pseudosieboldianum has the advantage to deal with the light threat. Future studies should focus on the expression level of photosynthesis-related genes and cell, to better understand the adaptation mechanism of plants to light variation which facilitates forest development, either natural or via silvicultural practices. This information expands our understanding of the light-regulating mechanism of trees, which contributes to develop management practices to support natural forest regeneration.

Detecting free radicals post viral infections

Free radical generation plays a key role in viral infections. While free radicals have an antimicrobial effect on bacteria or fungi, their interplay with viruses is complicated and varies greatly for different types of viruses as well as different radical species. In some cases, radical generation contributes to the defense against the viruses and thus reduces the viral load. In other cases, radical generation induces mutations or damages the host tissue and can increase the viral load. This has led to antioxidants being used to treat viral infections. Here we discuss the roles that radicals play in virus pathology. Furthermore, we critically review methods that facilitate the detection of free radicals in vivo or in vitro in viral infections.

AtGSTU19 and AtGSTU24 as Moderators of the Response of Arabidopsis thaliana to Turnip mosaic virus

Plants produce glutathione as a response to the intercellular redox state. Glutathione actively participates in the reactive oxygen species (ROS)-dependent signaling pathway, especially under biotic stress conditions. Most of the glutathione S-transferases (GSTs) are induced in cells during the defense response of plants not only through highly specific glutathione-binding abilities but also by participating in the signaling function. The tau class of GSTs has been reported to be induced as a response under stress conditions. Although several studies have focused on the role of the tau class of GSTs in plant–pathogen interactions, knowledge about their contribution to the response to virus inoculation is still inadequate. Therefore, in this study, the response of Atgstu19 and Atgstu24 knockout mutants to mechanical inoculation of Turnip mosaic virus (TuMV) was examined. The systemic infection of TuMV was more dynamically promoted in Atgstu19 mutants than in wild-type (Col-0) plants, suggesting the role of GSTU19 in TuMV resistance. However, Atgstu24 mutants displayed virus limitation and downregulation of the relative expression of TuMV capsid protein, accompanied rarely by TuMV particles only in vacuoles, and ultrastructural analyses of inoculated leaves revealed the lack of virus cytoplasmic inclusions. These findings indicated that Atgstu24 mutants displayed a resistance-like reaction to TuMV, suggesting that GSTU24 may suppress the plant resistance. In addition, these findings confirmed that GSTU1 and GSTU24 are induced and contribute to the susceptible reaction to TuMV in the Atgstu19–TuMV interaction. However, the upregulation of GSTU19 and GSTU13 highly correlated with virus limitation in the resistance-like reaction in the Atgstu24–TuMV interaction. Furthermore, the highly dynamic upregulation of GST and glutathione reductase (GR) activities resulted in significant induction (between 1 and 14 days post inoculation [dpi]) of the total glutathione pool (GSH + GSSG) in response to TuMV, which was accompanied by the distribution of active glutathione in plant cells. On the contrary, in Atgstu19, which is susceptible to TuMV interaction, upregulation of GST and GR activity only up to 7 dpi symptom development was reported, which resulted in the induction of the total glutathione pool between 1 and 3 dpi. These observations indicated that GSTU19 and GSTU24 are important factors in modulating the response to TuMV in Arabidopsis thaliana. Moreover, it was clear that glutathione is an important component of the regulatory network in resistance and susceptible response of A. thaliana to TuMV. These results help achieve a better understanding of the mechanisms regulating the Arabidopsis–TuMV pathosystem.

Untangling the Physio-Chemical and Transcriptional Changes of Black Gram Cultivars After Infection With Urdbean Leaf Crinkle Virus

Black gram (Vigna mungo) is an important pulse crop of India. The leaf crinkle disease caused by the urdbean leaf crinkle virus (ULCV) is a severe threat to black gram production. Black gram plants infected by ULCV show a considerable decline in plant growth and yield. However, detailed information about the interactions between the host, black gram, and ULCV is unclear. This study investigated the responses of two cultivars VBN (Bg) 6 and CO 5 to ULCV infection by physiological, biochemical, and transcriptional analyses. Virus symptoms were mild in VBN (Bg) 6 but were serious in CO 5. Upon the viral infection, VBN (Bg) 6 exhibited a low reduction in chlorophyll content than CO 5. The levels of sugar, protein, phenol, hydrogen peroxide (H2O2), and malondialdehyde (MDA) contents were altered by a viral infection in both cultivars. Although, the activities of antioxidant enzymes [Ascorbate peroxidase (APX), superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT)] were increased by ULCV infection. Following the viral infection, the expression level of the salicylic acid (SA), jasmonic acid (JA), and ethylene (ET) defense pathway-related genes was recorded higher in the VBN (Bg) 6 than that recorded in CO 5, indicating a positive correlation between resistance and these indicative indices. This dynamic physio-biochemical and transcriptional profiles of two black gram cultivars on ULCV infection augment our understanding of the complex interaction response between this crop and its pathogen. Additionally, it offers an inventory of potential indicators for future black gram screening and breeding to enhance resistance.

Exploring New Routes for Genetic Resistances to Potyviruses: The Case of the Arabidopsis thaliana Phosphoglycerates Kinases (PGK) Metabolic Enzymes

The development of recessive resistance by loss of susceptibility is a consistent strategy to combat and limit damages caused by plant viruses. Susceptibility genes can be turned into resistances, a feat that can either be selected among the plant’s natural diversity or engineered by biotechnology. Here, we summarize the current knowledge on the phosphoglycerate kinases (PGK), which have emerged as a new class of susceptibility factors to single-stranded positive RNA viruses, including potyviruses. PGKs are metabolic enzymes involved in glycolysis and the carbon reduction cycle, encoded by small multigene families in plants. To fulfil their role in the chloroplast and in the cytosol, PGKs genes encode differentially addressed proteins. Here, we assess the diversity and homology of chloroplastic and cytosolic PGKs sequences in several crops and review the current knowledge on their redundancies during plant development, taking Arabidopsis as a model. We also show how PGKs have been shown to be involved in susceptibility—and resistance—to viruses. Based on this knowledge, and drawing from the experience with the well-characterized translation initiation factors eIF4E, we discuss how PGKs genes, in light of their subcellular localization, function in metabolism, and susceptibility to viruses, could be turned into efficient genetic resistances using genome editing techniques.

The regulatory role of γ-aminobutyric acid in chickpea plants depends on drought tolerance and water scarcity level

γ-Aminobutyric acid (GABA) is a non-protein amino acid with multifunctional roles in dynamic plant responses. To determine the effects of exogenous GABA application (0, 25 and 50 µM) on drought response, two chickpea cultivars with contrasting tolerance to water deficit were examined. Plants were exposed to four irrigation levels (irrigation to 100, 60, 40 and 20% field capacity). Water deficit decreased growth, chlorophyll content, and photosynthetic efficiency. It increased electrolyte leakage and lipid peroxidation owing to both higher ROS accumulation and lower antioxidant enzyme activity. These negative effects of water deficit and the alleviating role of GABA application were more prominent in the sensitive, as compared to the tolerant cultivar. Water deficit also increased proline and GABA contents more in the tolerant cultivar, whereas their content was more enhanced by GABA application in the sensitive one. This may confer an additional level of regulation that results in better alleviation of drought damage in tolerant chickpea cultivars. In conclusion, the stimulatory effect of GABA on growth and physiological modulation depends on both the water stress severity and the cultivar sensitivity to it, implying a probable unknown GABA-related mechanism established by tolerant chickpea cultivars; a lost or not gained mechanism in susceptible ones.

MiR398-regulated antioxidants contribute to Bamboo mosaic virus accumulation and symptom manifestation

Virus infections that cause mosaic or mottling in leaves commonly also induce increased levels of reactive oxygen species (ROS). However, how ROS contributes to symptoms is less well documented. Bamboo mosaic virus (BaMV) causes chlorotic mosaic symptoms in both Brachypodium distachyon and Nicotiana benthamiana. The BaMV △CPN35 mutant with an N-terminal deletion of its coat protein gene exhibits asymptomatic infection independently of virus titer. Histochemical staining of ROS in mock-, BaMV-, and BaMV△CPN35-infected leaves revealed that hydrogen peroxide (H2O2) accumulated solely in BaMV-induced chlorotic spots. Moreover, exogenous H2O2 treatment enhanced yellowish chlorosis in BaMV-infected leaves. Both BaMV and BaMV△CPN35 infection could induce the expression of Cu/Zu superoxide dismutase (CSD) antioxidants at messenger RNA and protein level. However, BaMV triggered the abundant accumulation of full-length NbCSD2 preprotein (prNbCSD2, without transit peptide cleavage), whereas BaMV△CPN35 induced a truncated prNbCSD2. Confocal microscopy showed that majority of NbCSD2-green fluorescent protein (GFP) predominantly localized in the cytosol upon BaMV infection, but BaMV△CPN35 infection tended to cause NbCSD2-GFP to remain in chloroplasts. By 5'-RNA ligase-mediated rapid amplification of cDNA ends, we validated CSDs are the targets of miR398 in vivo. Furthermore, BaMV infection increased the level of miR398, while the level of BaMV titer was regulated positively by miR398 but negatively by CSD2. In contrast, overexpression of cytosolic form NbCSD2, impairing the transport into chloroplasts, greatly enhanced BaMV accumulation. Taken together, our results indicate that induction of miR398 by BaMV infection may facilitate viral titer accumulation, and cytosolic prNbCSD2 induction may contribute to H2O2 accumulation, resulting in the development of BaMV chlorotic symptoms in plants.

Three-dimensional quantitative imaging of Tobacco mosaic virus and Zucchini yellow mosaic virus induced ultrastructural changes

Two-dimensional ultrastructural changes of Tobacco mosaic virus (TMV) and Zucchini yellow mosaic virus (ZYMV) in tobacco and pumpkin plants, respectively, are well studied. To provide 3D data, representative control and infected cells were reconstructed using serial sectioning and transmission electron microscopy. Quantitative data of 3D ultrastructural changes were then extracted from the cytosol and organelles by image analysis. While TMV induced the accumulation of an average of 40 virus inclusion bodies in the cytosol, which covered about 13% of the cell volume, ZYMV caused the accumulation of an average of 1752 cylindrical inclusions in the cytosol, which covered about 2.7% of the total volume of the cell. TMV infection significantly decreased the number and size of mitochondria (- 49 and - 20%) and peroxisomes (- 62 and - 28%) of the reconstructed cell. The reconstructed ZYMV-infected cell contained more (105%) and larger (109%) mitochondria when compared to the control cell. While the reconstructed TMV-infected cell contained larger (20%) and the ZYMV-infected smaller (19%) chloroplasts, both contained less chloroplasts (- 40% for TMV and - 23% for ZYMV). In chloroplasts, the volume of starch and plastoglobules increased (664% and 150% for TMV and 1324% and 1300% for ZYMV) when compared to the control. The latter was correlated with a decrease in the volume of thylakoids in the reconstructed ZYMV-infected cell (- 31%) indicating that degradation products from thylakoids are transported and stored in plastoglobules. Summing up, the data collected in this study give a comprehensive overview of 3D changes induced by TMV and ZYMV in plants.

Blue Light Improves Photosynthetic Performance and Biomass Partitioning toward Harvestable Organs in Saffron (Crocus sativus L.)

Saffron is a valuable plant and one of the most expensive spices worldwide. Nowadays, there is a tendency to produce this crop in indoor plant production systems. However, the production of saffron is restricted by the need for the reproduction of high-quality corms. In this study, we investigated the effect of different ratios of red (R) and blue (B) light spectra (including 100% B (monochromatic B), 75%, 50%, 40%, 25% B, and 0% B (monochromatic R) on the photosynthetic performance and biomass partitioning as well as morphological and biochemical characteristics of saffron. The growth of flower, root, and corm was improved by increasing the proportion of B to R light. B-grown plants were characterized by the highest photosynthetic functionality with efficient electron transport and lower energy dissipation when compared to R-grown plants. B light directed biomass toward the corms and floral organs, while R light directed it toward the leaves. In saffron, the weight of a daughter corm is of great importance since it determines the yield of the next year. As the ratio of B to R light increased, the daughter corms also became heavier, at the cost of reducing their number, though increasing the proportion of B-enhanced antioxidant capacity as well as the activity of ascorbate peroxidase and catalase while superoxide dismutase activity was enhanced in R-grown plants. In conclusion, B light increased the production of high-quality daughter corms and altered biomass partitioning towards harvestable organs (corms and flowers) in saffron plants.

Healthy Photosynthetic Mechanism Suggests ISR Elicited by Bacillus spp. in Capsicum chinense Plants Infected with PepGMV

The aim of this study was to evaluate the effect of inoculation with Bacillus spp. isolates on the photosynthetic apparatus of Capsicum chinense plants infected with PepGMV. In vitro and greenhouse experiments were performed to evaluate whether the inoculation improved plants’ performance through the increase in photosynthetic efficiency to control PepGMV. The results showed that despite PepGMV infection, the plants inoculated with some isolates of Bacillus spp. had a healthy photosynthetic mechanism, as the photochemical parameters and gas exchange increased. The maximum photochemical quantum yield of PSII (Fv/Fm) of plants with PepGMV and inoculated with Bacillus isolates (M9, K46, and K47) increased (7.85, 7.09, and 7.77%, respectively) with respect to uninoculated controls. In inoculated plants, the CO₂ assimilation rate increased and the transpiration rate decreased, therefore indicating an increased water use efficiency. This effect was reflected by the less severe symptoms caused by PepGMV in the plants obtained from seeds inoculated with different Bacillus spp. Plants inoculated with K47 isolates showed an increase in fruit yield and quality. This study suggests that it is possible to protect, at the greenhouse level, C. chinense plants from PepGMV through selected rhizobacteria inoculation.

Sugarcane mosaic virus mediated changes in cytosine methylation pattern and differentially transcribed fragments in resistance-contrasting sugarcane genotypes

Sugarcane mosaic virus (SCMV) is the causal agent of sugarcane mosaic disease (SMD) in Brazil; it is mainly controlled by using resistant cultivars. Studies on the changes in sugarcane transcriptome provided the first insights about the molecular basis underlying the genetic resistance to SMD; nonetheless, epigenetic modifications such as cytosine methylation is also informative, considering its roles in gene expression regulation. In our previous study, differentially transcribed fragments (DTFs) were obtained using cDNA-amplified fragment length polymorphism by comparing mock- and SCMV-inoculated plants from two sugarcane cultivars with contrasting responses to SMD. In this study, the identification of unexplored DTFs was continued while the same leaf samples were used to evaluate SCMV-mediated changes in the cytosine methylation pattern by using methylation-sensitive amplification polymorphism. This analysis revealed minor changes in cytosine methylation in response to SCMV infection, but distinct changes between the cultivars with contrasting responses to SMD, with higher hypomethylation events 24 and 72 h post-inoculation in the resistant cultivar. The differentially methylated fragments (DMFs) aligned with transcripts, putative promoters, and genomic regions, with a preponderant distribution within CpG islands. The transcripts found were associated with plant immunity and other stress responses, epigenetic changes, and transposable elements. The DTFs aligned with transcripts assigned to stress responses, epigenetic changes, photosynthesis, lipid transport, and oxidoreductases, in which the transcriptional start site is located in proximity with CpG islands and tandem repeats. Real-time quantitative polymerase chain reaction results revealed significant upregulation in the resistant cultivar of aspartyl protease and VQ protein, respectively, selected from DMF and DTF alignments, suggesting their roles in genetic resistance to SMD and supporting the influence of cytosine methylation in gene expression. Thus, we identified new candidate genes for further validation and showed that the changes in cytosine methylation may regulate important mechanisms underlying the genetic resistance to SMD.

Effects of Exogenous Putrescine on Delaying Senescence of Cut Foliage of Nephrolepis cordifolia

Senescence is the main limitation for cut foliage display in vase. Naturally occurring polyamines such as putrescine (Put) have been considered effective anti-senescence agents. However, effect of Put on cut foliage in vase in a realistic indoor environment has not yet been revealed. In the present study, effects of Put spraying on the postharvest performance of cut foliage of Nephrolepis cordifolia L. were investigated. Cut fronds sprayed with deionized water (Put0) showed visible injuries after 10 days in vase. Meanwhile, chlorophyll (Chl), soluble protein (Sp), and proline (Pro) content were decreased by 60.15, 57.93, and 73.09% respectively, photochemical activity reflected by Chl fluorescence parameters was inhibited, whereas electrolyte leakage (EL), contents of soluble sugar (Ss), malondialdehyde (MDA), and hydrogen peroxide (H₂O₂) were increased (+194.29, +44.83, +34.06, and +178.01%, respectively). Put spraying extended the vase life of the cut foliage and the 2.0 mM Put had a longer vase life (21 days) than 0.2 mM (15 days). Leaf spraying of 2.0 mM Put for 10 days significantly ameliorated the losses of Chl, Sp, and Pro content (-10.72, -26.29, and -42.64%, respectively), followed by 0.2 mM Put (-27.36, -36.24, and -60.55%, respectively). Put spraying also improved photochemical capability and prevented membrane impairment as well as visible injury in comparison with Put0. In addition, 2.0 mM Put had a better mitigating ability than that of 0.2 mM. Leaf spraying of 2.0 mM Put greatly reduced the decline of the effective quantum yield of photochemical energy conversion in PSII (ΦPSII), the maximal quantum yield of PSII photochemistry measured in the dark-adapted state (Fv/Fm) and electron transport rate (ETR) (-7.89, -12.91, and -10.06%, respectively), and also inhibited the increases of EL, MDA, Ss, and H₂O₂ (+31.87, +6.43, +16.22, and +49.40%, respectively). Overall, Put played important roles in deterring the degradation of Chl, Ss, and Pro, detoxifying the H₂O₂, weakening the sugar signaling, mitigating the decline of photochemical activity, and eventually postponing the leaf senescence. The present study gives new insights into effects of Put on leaf senescence and provides a strategy for preserving post-harvest cut foliage.

Alpha-momorcharin enhances Nicotiana benthamiana resistance to tobacco mosaic virus infection through modulation of reactive oxygen species

Alpha-momorcharin (α-MMC), a member of the plant ribosomal inactivating proteins (RIPs) family, has been proven to exhibit important biological properties in animals, including antiviral, antimicrobial, and antitumour activities. However, the mechanism by which α-MMC increases plant resistance to viral infections remains unclear. To study the effect of α-MMC on plant viral defence and how α-MMC increases plant resistance to viruses, recombinant DNA and transgenic technologies were employed to investigate the role of α-MMC in Nicotiana benthamiana resistance to tobacco mosaic virus (TMV) infection. Treatment with α-MMC produced through DNA recombinant technology or overexpression of α-MMC mediated by transgenic technology alleviated TMV-induced oxidative damage and reduced the accumulation of reactive oxygen species (ROS) during TMV-green fluorescent protein infection of N. benthamiana. There was a significant decrease in TMV replication in the upper leaves following local α-MMC treatment and in α-MMC-overexpressing plants relative to control plants. These results suggest that application or overexpression of α-MMC in N. benthamiana increases resistance to TMV infection. Finally, our results showed that overexpression of α-MMC up-regulated the expression of ROS scavenging-related genes. α-MMC confers resistance to TMV infection by means of modulating ROS homeostasis through controlling the expression of antioxidant enzyme-encoding genes. Overall, our study revealed a new crosstalk mechanism between α-MMC and ROS during resistance to viral infection and provides a framework to understand the molecular mechanisms of α-MMC in plant defence against viral pathogens.

Subcellular Roles of Glutathione in Mediating Plant Defense during Biotic Stress

Glutathione and reactive oxygen species (ROS) play important roles, within different cell compartments, in activating plant defense and the development of resistance. In mitochondria, the accumulation of ROS and the change of glutathione towards its oxidized state leads to mitochondrial dysfunction, activates cell death, and triggers resistance. The accumulation of glutathione in chloroplasts and peroxisomes at the early stages of plant pathogen interactions is related to increased tolerance and resistance. The collapse of the antioxidative system in these two cell compartments at the later stages leads to cell death through retrograde signaling. The cytosol can be considered to be the switchboard during biotic stress where glutathione is synthesized, equally distributed to, and collected from different cell compartments. Changes in the redox state of glutathione and the accumulation of ROS in the cytosol during biotic stress can initiate the activation of defense genes in nuclei through pathways that involve salicylic acid, jasmonic acid, auxins, and abscisic acid. This review dissects the roles of glutathione in individual organelles during compatible and incompatible bacterial, fungal, and viral diseases in plants and explores the subcelluar roles of ROS, glutathione, ascorbate, and related enzymes in the development of resistance.

Potential Role of Photosynthesis in the Regulation of Reactive Oxygen Species and Defence Responses to Blumeria graminis f. sp. tritici in Wheat

Photosynthesis is not only a primary generator of reactive oxygen species (ROS) but also a component of plant defence. To determine the relationships among photosynthesis, ROS, and defence responses to powdery mildew in wheat, we compared the responses of the Pm40-expressing wheat line L658 and its susceptible sister line L958 at 0, 6, 12, 24, 48, and 72 h post-inoculation (hpi) with powdery mildew via analyses of transcriptomes, cytology, antioxidant activities, photosynthesis, and chlorophyll fluorescence parameters. The results showed that H₂O₂ accumulation in L658 was significantly greater than that in L958 at 6 and 48 hpi, and the enzymes activity and transcripts expression of peroxidase and catalase were suppressed in L658 compared with L958. In addition, the inhibition of photosynthesis in L658 paralleled the global downregulation of photosynthesis-related genes. Furthermore, the expression of the salicylic acid-related genes non-expressor of pathogenesis related genes 1 (NPR1), pathogenesis-related 1 (PR1), and pathogenesis-related 5 (PR5) was upregulated, while the expression of jasmonic acid- and ethylene-related genes was inhibited in L658 compared with L958. In conclusion, the downregulation of photosynthesis-related genes likely led to a decline in photosynthesis, which may be combined with the inhibition of peroxidase (POD) and catalase (CAT) to generate two stages of H₂O₂ accumulation. The high level of H₂O_2, salicylic acid and PR1 and PR5 in L658 possible initiated the hypersensitive response.

Nuclear proteome of virus-infected and healthy potato leaves

BACKGROUND

Infection of plants by viruses interferes with expression and subcellular localization of plant proteins. Potyviruses comprise the largest and most economically damaging group of plant-infecting RNA viruses. In virus-infected cells, at least two potyviral proteins localize to nucleus but reasons remain partly unknown.

RESULTS

In this study, we examined changes in the nuclear proteome of leaf cells from a diploid potato line (Solanum tuberosum L.) after infection with potato virus A (PVA; genus Potyvirus; Potyviridae) and compared the data with that acquired for healthy leaves. Gel-free liquid chromatography-coupled to tandem mass spectrometry was used to identify 807 nuclear proteins in the potato line v2-108; of these proteins, 370 were detected in at least two samples of healthy leaves. A total of 313 proteins were common in at least two samples of healthy and PVA-infected leaves; of these proteins, 8 showed differential accumulation. Sixteen proteins were detected exclusively in the samples from PVA-infected leaves, whereas other 16 proteins were unique to healthy leaves. The protein Dnajc14 was only detected in healthy leaves, whereas different ribosomal proteins, ribosome-biogenesis proteins, and RNA splicing-related proteins were over-represented in the nuclei of PVA-infected leaves. Two virus-encoded proteins were identified in the samples of PVA-infected leaves.

CONCLUSIONS

Our results show that PVA infection alters especially ribosomes and splicing-related proteins in the nucleus of potato leaves. The data increase our understanding of potyvirus infection and the role of nucleus in infection. To our knowledge, this is the first study of the nuclear proteome of potato leaves and one of the few studies of changes occurring in nuclear proteomes in response to plant virus infection.

Modulation of disease severity by plant positive-strand RNA viruses: The complex interplay of multifunctional viral proteins, subviral RNAs and virus-associated RNAs with plant signaling pathways and defense responses

Plant viruses induce a range of symptoms of varying intensity, ranging from severe systemic necrosis to mild or asymptomatic infection. Several evolutionary constraints drive virus virulence, including the dependence of viruses on host factors to complete their infection cycle, the requirement to counteract or evade plant antiviral defense responses and the mode of virus transmission. Viruses have developed an array of strategies to modulate disease severity. Accumulating evidence has highlighted not only the multifunctional role that viral proteins play in disrupting or highjacking plant factors, hormone signaling pathways and intracellular organelles, but also the interaction networks between viral proteins, subviral RNAs and/or other viral-associated RNAs that regulate disease severity. This review focusses on positive-strand RNA viruses, which constitute the majority of characterized plant viruses. Using well-characterized viruses with different genome types as examples, recent advances are discussed as well as knowledge gaps and opportunities for further research.

Interactions Between Microorganisms and a Seaweed-Derived Biostimulant on the Growth and Biochemical Composition of Amaranthus hybridus L

Natural biostimulants such as plant growth-promoting rhizobacteria (PGPRs) and seaweed extracts are used in agriculture to improve crop yield in an environmentally friendly approach. However, interaction effects between different biostimulants are seldom investigated. This study aimed to determine the combined effect of PGPRs and Kelpak® (KEL), a seaweed-derived extract, on the growth and biochemical composition of Amaranthus hybridus, a traditional leafy vegetable of South Africa. A pot trial was conducted with 6 treatments—control (distilled water), Bacillus licheniformis (BL) inoculum, Pseudomonas fluorescens (PF) inoculum, 1% KEL, and combination treatments of KEL + BL and KEL + PF. These were applied 3 times to A. hybridus seedlings at 2 weekly intervals prior to harvesting after 6 weeks. Growth parameters and biochemical content were quantified in the harvested material. Kelpak® significantly improved growth (leaf number and area, shoot and root length, and fresh weight) and chlorophyll and carotenoid content. Treatments with 2 microorganisms had a significant negative effect on growth and pigment content. However, the combination treatments significantly improved growth and photosynthetic pigment content to similar levels as the KEL treatment. The mineral content was significantly increased for most minerals when treated with PF and decreased when treated with KEL and KEL + BL. Treatment with 2 bacterial strains and KEL caused a significant decrease in superoxidase dismutase activity with an additive effect when applied in combination. This suggests stress reduction in A. hybridus. Combined use of PGPR and seaweed extracts promises to be an eco-friendly strategy to improve the production and mineral content of traditional leafy vegetables such as A. hybridus.

Low-temperature tolerance of the Antarctic species Deschampsia antarctica: A complex metabolic response associated with nutrient remobilization

The species Deschampsia antarctica (DA) is one of the only two native vascular species that live in Antarctica. We performed ecophysiological, biochemical, and metabolomic studies to investigate the responses of DA to low temperature. In parallel, we assessed the responses in a non-Antarctic reference species (Triticum aestivum [TA]) from the same family (Poaceae). At low temperature (4°C), both species showed lower photosynthetic rates (reductions were 70% and 80% for DA and TA, respectively) and symptoms of oxidative stress but opposite responses of antioxidant enzymes (peroxidases and catalase). We employed fused least absolute shrinkage and selection operator statistical modelling to associate the species-dependent physiological and antioxidant responses to primary metabolism. Model results for DA indicated associations with osmoprotection, cell wall remodelling, membrane stabilization, and antioxidant secondary metabolism (synthesis of flavonols and phenylpropanoids), coordinated with nutrient mobilization from source to sink tissues (confirmed by elemental analysis), which were not observed in TA. The metabolic behaviour of DA, with significant changes in particular metabolites, was compared with a newly compiled multispecies dataset showing a general accumulation of metabolites in response to low temperatures. Altogether, the responses displayed by DA suggest a compromise between catabolism and maintenance of leaf functionality.

Enhanced bioactive compound production in broccoli cells due to coronatine and methyl jasmonate is linked to antioxidative metabolism

Elicited broccoli suspension-cultured cells (SCC) provide a useful system for obtaining bioactive compounds, including glucosinolates (GS) and phenolic compounds (PCs). In this work, coronatine (Cor) and methyl jasmonate (MJ) were used to increase the bioactive compound production in broccoli SCC. Although the use of Cor and MJ in secondary metabolite production has already been described, information concerning how elicitors affect cell metabolism is scarce. It has been suggested that Cor and MJ trigger defence reactions affecting the antioxidative metabolism. In the current study, the concentration of 0.5 μM Cor was the most effective treatment for increasing both the total antioxidant capacity (measured as ferulic acid equivalents) and glucosinolate content in broccoli SCC. The elicited broccoli SCC also showed higher polyphenol oxidase activity than the control cells. Elicitation altered the antioxidative metabolism of broccoli SCC, which displayed biochemical changes in antioxidant enzymes, a decrease in the glutathione redox state and an increase in lipid peroxidation levels. Furthermore, we studied the effect of elicitation on the protein profile and observed an induction of defence-related proteins. All of these findings suggest that elicitation not only increases bioactive compound production, but it also leads to mild oxidative stress in broccoli SCC that could be an important factor triggering the production of these compounds.

Biochemical study of the effect of stress conditions on the mandelonitrile-associated salicylic acid biosynthesis in peach

Salicylic acid (SA) plays a central role in plant responses to environmental stresses. In a recent study, we suggested a third pathway for SA biosynthesis from mandelonitrile (MD) in peach plants. This pathway is an alternative to the phenylalanine ammonia-lyase pathway and links SA biosynthesis and cyanogenesis. In the present work, using biochemical approaches, we studied the effect of salt stress and Plum pox virus (PPV) infection on this proposed SA biosynthetic pathway from MD. Peach plants were submitted to salt stress and Plum pox virus (PPV) infection. We studied the levels of SA and its intermediates/precursors (phenylalanine, MD, amygdalin and benzoic acid) in in vitro shoots. Moreover, in peach seedlings, we analysed the content of H₂ O₂ -related enzymes, SA and the stress-related hormones abscisic acid and jasmonic acid. We showed that the contribution of this SA biosynthetic pathway from MD to the total SA pool does not seem to be important under the stress conditions assayed. Nevertheless, MD treatment not only affected the SA content, but also had a pleiotropic effect on abscisic acid and jasmonic acid levels. Furthermore, MD modulates the antioxidative metabolism via SA-dependent or -independent redox-related signalling pathways. Even though the proposed SA biosynthetic pathway seems to be functional under stress conditions, MD, and hence cyanogenic glycosides, may be operating more broadly than by influencing SA pathways and signalling. Thus, the physiological function of the proposed SA biosynthetic pathway remains to be elucidated.

γ-Aminobutyric acid confers cadmium tolerance in maize plants by concerted regulation of polyamine metabolism and antioxidant defense systems

Gamma-Aminobutyric acid (GABA) accumulates in plants following exposure to heavy metals. To investigate the role of GABA in cadmium (Cd) tolerance and elucidate the underlying mechanisms, GABA (0, 25 and 50 µM) was applied to Cd-treated maize plants. Vegetative growth parameters were improved in both Cd-treated and control plants due to GABA application. Cd uptake and translocation were considerably inhibited by GABA. Antioxidant enzyme activity was enhanced in plants subjected to Cd. Concurrently GABA caused further increases in catalase and superoxide dismutase activities, which led to a significant reduction in hydrogen peroxide, superoxide anion and malondealdehyde contents under stress conditions. Polyamine biosynthesis-responsive genes, namely ornithine decarboxylase and spermidine synthase, were induced by GABA in plants grown under Cd shock. GABA suppressed polyamine oxidase, a gene related to polyamine catabolism, when plants were exposed to Cd. Consequently, different forms of polyamines were elevated in Cd-exposed plants following GABA application. The maximum quantum efficiency of photosystem II (Fv/Fm) was decreased by Cd-exposed plants, but was completely restored by GABA to the same value in the control. These results suggest a multifaceted contribution of GABA, through regulation of Cd uptake, production of reactive oxygen species and polyamine metabolism, in response to Cd stress.

Transcriptome analysis of Luffa cylindrica (L.) Roem response to infection with Cucumber mosaic virus (CMV)

Cucumber mosaic virus (CMV) can cause serious losses in Luffa cylindrica (L.) Roem. Chemical application to control CMV is ineffective and environmentally unfriendly. The development of resistant hybrids is the best way to control CMV disease. Elucidating the virus-host interaction of CMV and molecular basis underlying Luffa spp. resistance against CMV would undoubtedly facilitate breeding for resistance against CMV disease. Transcriptome sequencing was used to analyze differentially expressed genes (DEGs) caused by CMV infection. A total of 138,336 unigenes were assembled, and 74,525 unigenes were annotated. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis indicated that the three major enrichment pathways (according to the p-values) were flavonoid biosynthesis, sulfur metabolism, and photosynthesis. Genes involved in basal defenses, probably R genes, were determined to be related to CMV resistance. Using quantitative real-time PCR, we validated the differential expression of 8 genes. A number of genes associated with CMV resistance were found in this study. This study provides transcriptomic information regarding CMV-Luffa spp. interactions and will shed light on our understanding of host-virus interactions.

Dynamic Transcriptional Profiles of Arabidopsis thaliana Infected by Tomato spotted wilt virus

Tomato spotted wilt virus (TSWV) is a negative-stranded RNA virus that infects hundreds of plant species, causing great economic loss. Infected Arabidopsis thaliana plants develop symptoms including chlorosis and wilt, which can lead to cell death. From 9 to 15 days after TSWV infection, symptoms progress through a three-stage process of appearance, severity, and death. In this study, deep sequencing technology was first used to explore gene expression in response to TSWV infection in model plant A. thaliana at different symptom development stages. We found that plant immune defense and protein degradation are induced by TSWV infection and that both inductions became stronger over time. The photosynthesis pathway was attenuated with TSWV infection. Cell wall metabolism had a large extent of downregulation while some genes were upregulated. These results illustrate the dynamic nature of TSWV infection in A. thaliana at the whole-transcriptome level. The link between biological processes and subpathway metabolism was further analyzed. Our study provides new insight into host regulatory networks and dynamic processes in response to TSWV infection.

Cytochrome respiration pathway and sulphur metabolism sustain stress tolerance to low temperature in the Antarctic species Colobanthus quitensis

Understanding the strategies employed by plant species that live in extreme environments offers the possibility to discover stress tolerance mechanisms. We studied the physiological, antioxidant and metabolic responses to three temperature conditions (4, 15, and 23°C) of Colobanthus quitensis (CQ), one of the only two native vascular species in Antarctica. We also employed Dianthus chinensis (DC), to assess the effects of the treatments in a non-Antarctic species from the same family. Using fused LASSO modelling, we associated physiological and biochemical antioxidant responses with primary metabolism. This approach allowed us to highlight the metabolic pathways driving the response specific to CQ. Low temperature imposed dramatic reductions in photosynthesis (up to 88%) but not in respiration (sustaining rates of 3.0-4.2 μmol CO₂  m^-2  s^-1 ) in CQ, and no change in the physiological stress parameters was found. Its notable antioxidant capacity and mitochondrial cytochrome respiratory activity (20 and two times higher than DC, respectively), which ensure ATP production even at low temperature, was significantly associated with sulphur-containing metabolites and polyamines. Our findings potentially open new biotechnological opportunities regarding the role of antioxidant compounds and respiratory mechanisms associated with sulphur metabolism in stress tolerance strategies to low temperature.

Molecular Plant-Plum Pox Virus Interactions

Plum pox virus, the agent that causes sharka disease, is among the most important plant viral pathogens, affecting Prunus trees across the globe. The fabric of interactions that the virus is able to establish with the plant regulates its life cycle, including RNA uncoating, translation, replication, virion assembly, and movement. In addition, plant-virus interactions are strongly conditioned by host specificities, which determine infection outcomes, including resistance. This review attempts to summarize the latest knowledge regarding Plum pox virus-host interactions, giving a comprehensive overview of their relevance for viral infection and plant survival, including the latest advances in genetic engineering of resistant species.

Contrasting growth, physiological and gene expression responses of Clematis crassifolia and Clematis cadmia to different irradiance conditions

Clematis crassifolia and Clematis cadmia Buch.-Ham. ex Hook.f. & Thomson are herbaceous vine plants native to China. C. crassifolia is distributed in shaded areas, while C. cadmia mostly grows in bright, sunny conditions in mountainous and hilly landscapes. To understand the potential mechanisms involved in the irradiance responses of C. crassifolia and C. cadmia, we conducted a pot experiment under three irradiance treatments with natural irradiation and two different levels of shading. Various growth, photosynthetic, oxidative and antioxidative parameters and the relative expression of irradiance-related genes were examined. In total, 15 unigenes were selected for the analysis of gene expression. The exposure of C. crassifolia to high irradiance resulted in growth inhibition coupled with increased levels of chlorophyll, increased catalase, peroxidase, and superoxide dismutase activity and increased expression of c144262_g2, c138393_g1 and c131300_g2. In contrast, under high irradiance conditions, C. cadmia showed an increase in growth and soluble protein content accompanied by a decrease in the expression of c144262_g2, c133872_g1, and c142530_g1, suggesting their role in the acclimation of C. cadmia to a high-irradiance environment. The 15 unigenes were differentially expressed in C. crassifolia and C. cadmia under different irradiance conditions. Thus, our study revealed that there are essential differences in the irradiance adaptations of C. crassifolia and C. cadmia due to the differential physiological and molecular mechanisms underlying their irradiance responses, which result from their long-term evolution in contrasting habitats.

Differential expression of structural and functional proteins during bean common mosaic virus-host plant interaction

Bean common mosaic virus (BCMV), the most common seed-borne pathogen in Phaseolus vulgaris L. is known to cause severe loss in productivity across the globe. In the present study, proteomic analyses were performed for leaf samples from control (healthy) and susceptible BCMV infected plants. The differential expression of proteins was evaluated using two-dimensional gel electrophoresis (2-DE). Approximately, 1098 proteins were spotted, amongst which 107 proteins were observed to be statistically significant with differential expression. The functional categorization of the differential proteins illustrated that they were involved in biotic/abiotic stress (18%), energy and carbon metabolism (11%), photosynthesis (46%), protein biosynthesis (10%), chaperoning (5%), chlorophyll (5%) and polyunsaturated fatty acid biosynthesis (5%). This is the first report on the comparative proteome study of compatible plant-BCMV interactions in P. vulgaris which contributes largely to the understanding of protein-mediated disease resistance/susceptible mechanisms.

The apoplastic antioxidant system and altered cell wall dynamics influence mesophyll conductance and the rate of photosynthesis

Mesophyll conductance (gm ), the diffusion of CO2 from substomatal cavities to the carboxylation sites in the chloroplasts, is a highly complex trait driving photosynthesis (net CO2 assimilation, AN ). However, little is known concerning the mechanisms by which it is dynamically regulated. The apoplast is considered as a 'key information bridge' between the environment and cells. Interestingly, most of the environmental constraints affecting gm also cause apoplastic responses, cell wall (CW) alterations and metabolic rearrangements. Since CW thickness is a key determinant of gm , we hypothesize that other changes in this cellular compartiment should also influence gm . We study the relationship between the antioxidant apoplastic system and CW metabolism and the gm responses in tobacco plants (Nicotiana sylvestris L.) under two abiotic stresses (drought and salinity), combining in vivo gas-exchange measurements with analyses of antioxidant activities, CW composition and primary metabolism. Stress treatments imposed substantial reductions in AN (58-54%) and gm (59%), accompanied by a strong antioxidant enzymatic response at the apoplastic and symplastic levels. Interestingly, apoplastic but not symplastic peroxidases were positively related to gm . Leaf anatomy remained mostly stable; however, the stress treatments significantly affected the CW composition, specifically pectins, which showed significant relationships with AN and gm . The treatments additionally promoted a differential primary metabolic response, and specific CW-related metabolites including galactose, glucosamine and hydroxycinnamate showed exclusive relationships with gm independent of the stress. These results suggest that gm responses can be attributed to specific changes in the apoplastic antioxidant system and CW metabolism, opening up more possibilities for improving photosynthesis using breeding/biotechnological strategies.

Soybean Cytochrome b5 Is a Restriction Factor for Soybean Mosaic Virus

Soybean mosaic virus (SMV) is one of the most destructive viral diseases in soybeans (Glycine max). In this study, an interaction between the SMV P3 protein and cytochrome b5 was detected by yeast two-hybrid assay, and bimolecular fluorescence complementation assay showed that the interaction took place at the cell periphery. Further, the interaction was confirmed by co-immunoprecipitation analysis. Quantitative real-time polymerase chain reaction analysis revealed that GmCYB5 gene was differentially expressed in resistant and susceptible soybean plants after inoculation with SMV-SC15 strain. To test the involvement of this gene in SMV resistance, the GmCYB5 was silenced using a bean pod mottle virus (BPMV)-based vector construct. Results showed that GmCYB5-1 was 83% and 99% downregulated in susceptible (NN1138-2) and resistant (RN-9) cultivars, respectively, compared to the empty vector-treated plants. Silencing of GmCYB5 gene promotes SMV replication in soybean plants. Our results suggest that during SMV infection, the host CYB5 protein targets P3 protein to inhibit its proliferation. Taken together, these results suggest that CYB5 is an important factor in SMV infection and replication in soybeans, which could help soybean breeders develop SMV resistant soybean cultivars.

The Respiratory Burst Oxidase Homolog D (RbohD) Cell and Tissue Distribution in Potato-Potato Virus Y (PVYNTN) Hypersensitive and Susceptible Reactions

The respiratory burst oxidase homolog D (RbohD) acts as a central driving force of reactive oxygen species signaling in plant cells by integrating many different signal transduction pathways in plants, including incompatible interactions with pathogens. This study demonstrated the localization and distribution of RbohD in two types of potato–potato virus Y (PVY) interactions: Compatible and incompatible (resistant). The results indicated a statistically significant induction of the RbohD antigen signal in both interaction types. In the hypersensitive response (resistant reaction) of potato with a high level of resistance to the potato tuber necrotic strain of PVY (PVY^NTN), RbohD localization followed by hydrogen peroxide (H₂O₂) detection was concentrated in the apoplast. In contrast, in the hypersensitive response of potato with a low resistance level to PVY^NTN, the distribution of RbohD was concentrated more in the plant cell organelles than in the apoplast, resulting in the virus particles being present outside the inoculation area. Moreover, when compared to mock-inoculated plants and to the hypersensitive response, the PVY^NTN-compatible potato interaction triggered high induction in the RbohD distribution, which was associated with necrotization. Our findings indicated that RbohD and hydrogen peroxide deposition was associated with the hypersensitive response, and both were detected in the vascular tissues and chloroplasts. These results suggest that the RbohD distribution is actively dependent on different types of PVY ^NTN-potato plant interactions. Additionally, the RbohD may be involved in the PVY^NTN tissue limitation during the hypersensitive response, and it could be an active component of the systemic signal transduction in the susceptible host reaction.

Aphid-borne Viral Spread Is Enhanced by Virus-induced Accumulation of Plant Reactive Oxygen Species

Most known plant viruses are spread from plant to plant by insect vectors. There is strong evidence that nonpersistently transmitted viruses manipulate the release of plant volatiles to attract insect vectors, thereby promoting virus spread. The mechanisms whereby aphid settling and feeding is altered on plants infected with these viruses, however, are unclear. Here we employed loss-of-function mutations in cucumber mosaic virus (CMV) and one of its host plants, tobacco (Nicotiana tabacum), to elucidate such mechanisms. We show that, relative to a CMVΔ2b strain with a deletion of the viral suppressor of RNAi 2b protein in CMV, plants infected with wild-type CMV produce higher concentrations of the reactive oxygen species (ROS) H₂O₂ in plant tissues. Aphids on wild-type CMV-infected plants engage in shorter probes, less phloem feeding, and exhibit other changes, as detected by electrical penetration graphing technology, relative to CMVΔ2b-infected plants. Therefore, the frequency of virus acquisition and the virus load per aphid were greater on CMV-infected plants than on CMVΔ2b-infected plants. Aphids also moved away from initial feeding sites more frequently on wild-type CMV infected versus CMVΔ2b-infected plants. The role of H₂O₂ in eliciting these effects on aphids was corroborated using healthy plants infused with H₂O₂ Finally, H₂O₂ levels were not elevated, and aphid behavior was unchanged, on CMV-infected RbohD-silenced tobacco plants, which are deficient in the induction of ROS production. These results suggest that CMV uses its viral suppressor of RNAi protein to increase plant ROS levels, thereby enhancing its acquisition and transmission by vector insects.

Glutathione S-Transferase Enzymes in Plant-Pathogen Interactions

Plant glutathione S-transferases (GSTs) are ubiquitous and multifunctional enzymes encoded by large gene families. A characteristic feature of GST genes is their high inducibility by a wide range of stress conditions including biotic stress. Early studies on the role of GSTs in plant biotic stress showed that certain GST genes are specifically up-regulated by microbial infections. Later numerous transcriptome-wide investigations proved that distinct groups of GSTs are markedly induced in the early phase of bacterial, fungal and viral infections. Proteomic investigations also confirmed the accumulation of multiple GST proteins in infected plants. Furthermore, functional studies revealed that overexpression or silencing of specific GSTs can markedly modify disease symptoms and also pathogen multiplication rates. However, very limited information is available about the exact metabolic functions of disease-induced GST isoenzymes and about their endogenous substrates. The already recognized roles of GSTs are the detoxification of toxic substances by their conjugation with glutathione, the attenuation of oxidative stress and the participation in hormone transport. Some GSTs display glutathione peroxidase activity and these GSTs can detoxify toxic lipid hydroperoxides that accumulate during infections. GSTs can also possess ligandin functions and participate in the intracellular transport of auxins. Notably, the expression of multiple GSTs is massively activated by salicylic acid and some GST enzymes were demonstrated to be receptor proteins of salicylic acid. Furthermore, induction of GST genes or elevated GST activities have often been observed in plants treated with beneficial microbes (bacteria and fungi) that induce a systemic resistance response (ISR) to subsequent pathogen infections. Further research is needed to reveal the exact metabolic functions of GST isoenzymes in infected plants and to understand their contribution to disease resistance.

Responses of Morphology, Gas Exchange, Photochemical Activity of Photosystem II, and Antioxidant Balance in Cyclocarya paliurus to Light Spectra

Light quality is a critical factor regulating photosynthetic capacity which directly affects the final yield of plants. Cyclocarya paliurus is a multiple function tree species and its leaves are widely used as tea production and ingredient in functional foods in China. However, the effects of varying light quality on photosynthetic process and the photoprotective mechanisms remains unexplored in-depth. In this study, the biomass accumulation, morphology changes, photosynthetic capacity, stomata ultrastructure, pigments content, PSII activity, reactive oxygen species production, antioxidant enzymes, and phenolic content of C. paliurus plants under different light-emitting diodes (LED) light treatments were investigated to test a hypothesis that the difference in photosynthetic efficiency of C. paliurus plants under differential light quality is related to the degree of photoinhibition and the activation of photoprotection. We found that C. paliurus plants performed better under the treatments of WL (white light, 445 and 560 nm) and BL (blue light, 456 nm) than the treatment of GL (green light, 514 nm) and RL (red light, 653 nm). The better performances were characterized by higher values of photosynthetic capacity, total biomass, pigments content, specific leaf mass per area, seeding height increment, leaf thickness and palisade length. In contrast, plants under the treatments of GL and RL suffered significant photoinhibition but effectively developed photoprotective mechanisms. Results of this study provide not only some insights of the response mechanisms of plant photosynthesis to light quality but also a scientific basis for improving the cultivation of C. paliurus plantations.

The effect of mandelonitrile, a recently described salicylic acid precursor, on peach plant response against abiotic and biotic stresses

In a previous work, we observed that mandelonitrile (MD), which controls cyanogenic glycoside turnover, is involved in salicylic acid (SA) biosynthesis in peach plants. In order to gain knowledge about the possible roles of this SA biosynthetic pathway, this current study looks at the effect of MD and phenylalanine (Phe; MD precursor) treatments on peach plant performance from an agronomic point of view. Abiotic (2 g·l^-1 NaCl) and biotic (Plum pox virus, PPV) stresses were assayed. We recorded the following chlorophyll fluorescence parameters: quantum yield of photochemical energy conversion in PSII [Y(II)], photochemical quenching (qP) and quantum yield of regulated non-photochemical energy loss in PSII and its coefficient [Y(NPQ) and qN]. In addition, considering that environmental stresses lead to nutritional disorders, we determined the soluble K⁺ , Ca²⁺ , Na⁺ and Cl^- concentrations in NaCl-stressed seedlings. In PPV-infected seedlings, we recorded the Ca²⁺ level, which has been suggested to play critical roles in regulating SA-related plant defence responses against pathogens. The MD treatment lessened the effect of both stresses on plant development. In addition, an increase in non-photochemical quenching parameters was observed in MD-treated seedlings, suggesting a safer dissipation of excess energy under stress conditions. In NaCl-stressed peach seedlings both treatments stimulated the accumulation of phytotoxic ions in roots, whereas in PPV-infected seedlings MD increased Ca²⁺ content. Our results suggest that MD and Phe influence the response of peach seedlings to the deleterious effects of salt and PPV infection stresses.

Effects of growth under different light spectra on the subsequent high light tolerance in rose plants

Photosynthesis is defined as a light-dependent process; however, it is negatively influenced by high light (HL) intensities. To investigate whether the memory of growth under monochromatic or combinational lights can influence plant responses to HL, rose plants were grown under different light spectra [including red (R), blue (B), 70:30 % red:blue (RB) and white (W)] and were exposed to HL (1500 μmol m-2 s-1) for 12 h. Polyphasic chlorophyll a fluorescence (OJIP) transients revealed that although monochromatic R- and B-grown plants performed well under control conditions, the functionality of their electron transport system was more sensitive to HL than that of the RB- and W-grown plants. Before exposure to HL, the highest anthocyanin concentration was observed in R- and B-grown plants, while exposure to HL reduced anthocyanin concentration in both R- and B-grown plants. Ascorbate peroxidase and catalase activities decreased, while superoxide dismutase activity was increased after exposure to HL. This caused an increase in H2O2 concentration and malondialdehyde content following HL exposure. Soluble carbohydrates were decreased by exposure to HL, and this decrease was more emphasized in R- and B-grown plants. In conclusion, growing plants under monochromatic light reduced the plants ability to cope with HL stress.

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.

Title: Enhanced salt tolerance and photosynthetic performance: Implication of ɤ-amino butyric acid application in salt-exposed lettuce (Lactuca sativa L.) plants

Gamma-Amino Butyric Acid (GABA) is a substantial component of the free amino acid pool with low concentration in plant tissues. Enhanced GABA content occurs during plant growth and developmental processes like seed germination. GABA level, basically, alters in response to many endogenous and exogenous stimuli. In the current study, GABA effects were studied on germination, photosynthetic performance and oxidative damages in salt-exposed lettuce plants. Three NaCl (0, 40 and 80 mM) and two GABA (0 and 25 μM) concentrations were applied on lettuce during two different developmental (seed germination and seedlings growth) stages. Negative effects of salinity on germination and plant growth were removed by GABA application. GABA significantly reduced mean germination time (MGT) in salt-exposed lettuce seeds. Although, salinity caused a significant decline in maximum quantum yield of photosystem II (Fv/Fm) during distinct steps of plant growth, GABA application improved Fv/Fm particularly on high salinity level. GABA decreased specific energy fluxes per reaction center (RC) for energy absorption and dissipation, while enhanced-electron transport flux in photosynthetic apparatus of lettuce plants was observed in GABA-supplemented plants. Moreover, decline in non-photochemical quenching (NPQ) and quenching coefficients (qP, qL, qN) by salt stress were recovered by GABA application. Elevated electrolyte leakage considerably decreased by GABA exposure on salt-treated plants. Although, proline level increased by NaCl treatments in a concentration dependent manner, combined application of salt with GABA caused a significant reduction in proline content. Catalase; EC 1.11.1.6 (CAT), l-ascorbate peroxidase; EC 1.11.1.11 (APX), and superoxide dismutase; EC 1.15.1.1 (SOD) activities were increased by GABA exposure in salt-supplemented plants that resulted in regulated hydrogen peroxide level. In conclusion, a multifaceted role for GABA is suggested for minimizing detrimental effects of salinity on lettuce through improvement of photosynthetic functionality and regulation of oxidative stress.