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

Piriformospora indica suppresses the symptoms produced by Banana bract mosaic virus by inhibiting its replication and manipulating chlorophyll and carotenoid biosynthesis and degradation in banana

Banana bract mosaic virus (BBrMV) infection results in characteristic reddish streaks on pseudostem and chlorotic spindle lesions on leaves leading to traveler's palm appearance and complete crop loss depending on the stage of infection in banana plants. Here, we discuss the influence of P. indica colonization (a beneficial fungal root endophyte) on BBrMV infection, specific viral component genes responsible for symptom development, chlorophyll and carotenoid biosynthesis, and degradation in BBrMV-infected banana plants. P. indica colonization significantly and substantially reduced the severity of Banana bract mosaic disease (BBrMD) in addition to increased growth, development and yield of banana plants. The percent disease incidence (PDI) of BBrMV ranges from 50 to 70 per cent in plants raised from suckers and from 58 to 92 per cent in TC plants under artificial inoculation. P. indica-colonized plants inoculated with BBrMV resulted in an enhanced plant height, root length, leaf width, and leaf length of 72, 88, 90, and 60 per cent, respectively, compared to BBrMV alone-infected banana plants along with the reduced disease severity. BBrMV infection showed a drastic decrease of chlorophyll a, chlorophyll b, and total chlorophyll contents by down-regulating chlorophyll biosynthesis (Chlorophyll synthase-CHLG) and upregulating chlorophyll degradation (Chlorophyllase-CLH1 and CLH2 and Pheophytin pheophorbide hydrolase-PPH) genes; and by up-regulating carotenoids biosynthesis (Phytoene synthases-PSY1 and PSY2) and down-regulating its degradation (Phytoene desaturase-PDS) genes compared to P. indica-colonized banana plants challenge inoculated with BBrMV. P. indica also inhibited the expression of the viral genes (P3 and HC-Pro) involved in symptom development. P. indica-colonized banana plants reduced the BBrMV symptoms severity by enhancing chlorophyll biosynthesis; and decreasing chlorophyll degradation and carotenoid biosynthesis and degradation; and inhibiting the viral genes responsible for symptom development in addition to enhanced growth and yield of banana plants.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-024-03983-y.

Integrated transcriptome and microRNA sequencing analyses reveal gene responses in poplar leaves infected by the novel pathogen bean common mosaic virus (BCMV)

Recently, a novel poplar mosaic disease caused by bean common mosaic virus (BCMV) was investigated in Populus alba var. pyramidalis in China. Symptom characteristics, physiological performance of the host, histopathology, genome sequences and vectors, and gene regulation at the transcriptional and posttranscriptional levels were analyzed and RT-qPCR (quantitative reverse transcription PCR) validation of expression was performed in our experiments. In this work, the mechanisms by which the BCMV pathogen impacts physiological performance and the molecular mechanisms of the poplar response to viral infection were reported. The results showed that BCMV infection decreased the chlorophyll content, inhibited the net photosynthesis rate (Pn) and stomatal conductance (Gs), and significantly changed chlorophyll fluorescence parameters in diseased leaves. Transcriptome analysis revealed that the expression of the majority of DEGs (differentially expressed genes) involved in the flavonoid biosynthesis pathway was promoted, but the expression of all or almost all DEGs associated with photosynthesis-antenna proteins and the photosynthesis pathway was inhibited in poplar leaves, suggesting that BCMV infection increased the accumulation of flavonoids but decreased photosynthesis in hosts. Gene set enrichment analysis (GSEA) illustrated that viral infection promoted the expression of genes involved in the defense response or plant-pathogen interaction. MicroRNA-seq analysis illustrated that 10 miRNA families were upregulated while 6 families were downregulated in diseased poplar leaves; moreover, miR156, the largest family with the most miRNA members and target genes, was only differentially upregulated in long-period disease (LD) poplar leaves. Integrated transcriptome and miRNA-seq analyses revealed 29 and 145 candidate miRNA-target gene pairs; however, only 17 and 76 pairs, accounting for 2.2% and 3.2% of all DEGs, were authentically negatively regulated in short-period disease (SD) and LD leaves, respectively. Interestingly, 4 miR156/SPL (squamosa promoter-binding-like protein) miRNA-target gene pairs were identified in LD leaves: the miR156 molecules were upregulated, but SPL genes were downregulated. In conclusion, BCMV infection significantly changed transcriptional and posttranscriptional gene expression in poplar leaves, inhibited photosynthesis, increased the accumulation of flavonoids, induced systematic mosaic symptoms, and decreased physiological performance in diseased poplar leaves. This study elucidated the fine-tuned regulation of poplar gene expression by BCMV; moreover, the results also suggested that miR156/SPL modules played important roles in the virus response and development of viral systematic symptoms in plant virus disease.

Activated malate circulation contributes to the manifestation of light-dependent mosaic symptoms

Mosaic symptoms are commonly observed in virus-infected plants. However, the underlying mechanism by which viruses cause mosaic symptoms as well as the key regulator(s) involved in this process remain unclear. Here, we investigate maize dwarf mosaic disease caused by sugarcane mosaic virus (SCMV). We find that the manifestation of mosaic symptoms in SCMV-infected maize plants requires light illumination and is correlated with mitochondrial reactive oxidative species (mROS) accumulation. The transcriptomic and metabolomic analyses results together with the genetic and cytopathological evidence indicate that malate and malate circulation pathways play essential roles in promoting mosaic symptom development. Specifically, at the pre-symptomatic infection stage or infection front, SCMV infection elevates the enzymatic activity of pyruvate orthophosphate dikinase by decreasing the phosphorylation of threonine527 under light, resulting in malate overproduction and subsequent mROS accumulation. Our findings indicate that activated malate circulation contributes to the manifestation of light-dependent mosaic symptoms via mROS.

OsAPX1 Positively Contributes to Rice Blast Resistance

Ascorbate peroxidases (APXs) maintain cellular reactive oxygen species (ROS) homeostasis through their peroxidase activity. Here, we report that OsAPX1 also promotes ROS production such that a delicate cellular ROS homeostasis is achieved temporally after Magnaporthe oryzae infection. OsAPX1 specifically induces ROS production through increasing respiratory burst oxidase homologs (OsRBOHs) expression and can be inhibited by DPI, a ROS inhibitor. The time-course experiment data show that the simultaneous induction of OsAPX1 and OsRBOHs leads to ROS accumulation at an early stage; whereas a more durable expression of OsAPX1 leads to ROS scavenging at a later stage. By the temporal switching between ROS inducer and eliminator, OsAPX1 triggers an instant ROS burst upon M. oryzae infection and then a timely elimination of ROS toxicity. We find that OsAPX1 is under the control of the miR172a-OsIDS1 regulatory module. OsAPX1 also affects salicylic acid (SA) synthesis and signaling, which contribute to blast resistance. In conclusion, we show that OsAPX1 is a key factor that connects the upstream gene silencing and transcription regulatory routes with the downstream phytohormone and redox pathway, which provides an insight into the sophisticated regulatory network of rice innate immunity.

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.

Interactions between soybean, Bradyrhizobium japonicum and Soybean mosaic virus: the effects depend on the interaction sequence

The symbiotic interaction between soybean and nitrogen-fixing rhizobia can lead to plant growth promotion and induced systemic responses. Symbiotic interactions may increase tolerance/resistance to abiotic/biotic stress conditions, but are also sensitive to environmental conditions. Soybean mosaic virus (SMV), which is transmitted by seed and aphids, severely affects crop yields in many areas of the world, consequently virus infection may precede rhizobium infection or vice versa in the field. With the hypothesis that sequence of interaction is a key determinant of the resulting responses; growth, primary metabolism and defence responses were evaluated in different interaction sequences. Results showed that vegetative growth was promoted by Bradyrhizobium japonicum (Bj) inoculation and drastically impaired by SMV infection. The negative effect of SMV single infection on soybean growth parameters was correlated with photosynthesis decrease, sugar accumulation, oxidative damage, and increases in salicylic acid levels. Bj inoculation partially reversed virus-induced symptoms, mainly at Bj-SMV sequence. However, this symptom attenuation did not correlate with less virus accumulation. Nodulation was negatively affected by SMV, particularly when virus infection was previous to Bj inoculation (SMV-Bj). Defence related hormones (salicylic acid (SA)/jasmonic acid (JA)) and the expression of defence-related genes were dependent on the sequence of tripartite interaction. The present study showed that the sequence of the tripartite interaction among soybean, Bj and SMV determinates the tolerance/susceptibility to SMV infection, through changes in the defence mechanism and metabolic alteration.

Suppression of nbe-miR166h-p5 attenuates leaf yellowing symptoms of potato virus X on Nicotiana benthamiana and reduces virus accumulation

MicroRNAs (miRNAs) play essential roles in plant development. There is increasing evidence that changed expression of miRNAs in virus-infected plants contributes to the development of viral symptoms. Here, we analysed the altered expression of miRNAs of Nicotiana benthamiana in response to Potato virus X (PVX) by Illumina Solexa sequencing. One of the 21 miRNAs significantly affected, nbe-miR166h-p5, was closely associated with viral symptoms. Using the Tobacco rattle virus-based miRNA suppression (VbMS) system, we found that the suppression of nbe-miR166h-p5 in plants caused leaves to turn dark green with increased chlorophyll. When PVX was inoculated on nbe-miR166h-p5-suppressed plants, the leaf yellowing symptom of PVX was largely attenuated with less reduction in chlorophyll content, and the accumulation of PVX was decreased. nbe-miR166h-p5 was also up-regulated in plants infected by Turnip mosaic virus (TuMV), and its suppression attenuated the leaf yellowing symptom of TuMV and decreased viral accumulation. Three potential targets of nbe-miR166h-p5 were identified. The results indicate the association of nbe-miR166h-p5 with symptoms of PVX and also with those of TuMV, providing useful information on the relationship between miRNA and viral infection.

Molecular Basis Underlying Leaf Variegation of a Moth Orchid Mutant (Phalaenopsis aphrodite subsp. formosana)

Leaf variegation is often the focus of plant breeding. Here, we studied a variegated mutant of Phalaenopsis aphrodite subsp. formosana, which is usually used as a parent of horticultural breeding, to understand its anatomic and genetic regulatory mechanisms in variegation. Chloroplasts with well-organized thylakoids and starch grains were found only in the mesophyll cells of green sectors but not of yellow sectors, confirming that the variegation belongs to the chlorophyll type. The two-dimensional electrophoresis and LC/MS/MS also reveal differential expressions of PsbP and PsbO between the green and yellow leaf sectors. Full-length cDNA sequencing revealed that mutant transcripts were caused by intron retention. When conditioning on the total RNA expression, we found that the functional transcript of PsbO and mutant transcript of PsbP are higher expressed in the yellow sector than in the green sector, suggesting that the post-transcriptional regulation of PsbO and PsbP differentiates the performance between green and yellow sectors. Because PsbP plays an important role in the stability of thylakoid folding, we suggest that the negative regulation of PsbP may inhibit thylakoid development in the yellow sectors. This causes chlorophyll deficiency in the yellow sectors and results in leaf variegation. We also provide evidence of the link of virus CymMV and the formation of variegation according to the differential expression of CymMV between green and yellow sectors.

Label-free Proteomic Reveals that Cowpea Severe Mosaic Virus Transiently Suppresses the Host Leaf Protein Accumulation During the Compatible Interaction with Cowpea (Vigna unguiculata [L.] Walp.)

Viruses are important plant pathogens that threaten diverse crops worldwide. Diseases caused by Cowpea severe mosaic virus (CPSMV) have drawn attention because of the serious damages they cause to economically important crops including cowpea. This work was undertaken to quantify and identify the responsive proteins of a susceptible cowpea genotype infected with CPSMV, in comparison with mock-inoculated controls, using label-free quantitative proteomics and databanks, aiming at providing insights on the molecular basis of this compatible interaction. Cowpea leaves were mock- or CPSMV-inoculated and 2 and 6 days later proteins were extracted and analyzed. More than 3000 proteins were identified (data available via ProteomeXchange, identifier PXD005025) and 75 and 55 of them differentially accumulated in response to CPSMV, at 2 and 6 DAI, respectively. At 2 DAI, 76% of the proteins decreased in amount and 24% increased. However, at 6 DAI, 100% of the identified proteins increased. Thus, CPSMV transiently suppresses the synthesis of proteins involved particularly in the redox homeostasis, protein synthesis, defense, stress, RNA/DNA metabolism, signaling, and other functions, allowing viral invasion and spread in cowpea tissues.

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.

The detection of hydrogen peroxide involved in plant virus infection by fluorescence spectroscopy

The production of reactive oxygen species (ROS) forms part of the defense reaction of plants against invading pathogens. ROS have multifaceted signaling functions in mediating the establishment of multiple responses. To verify whether hydrogen peroxide (H2 O2 ) contributes to plant virus infection and the development of induced symptoms, we used fluorescence to monitor the generation of H2 O2 and confocal laser scanning microscopy (CLSM) to investigate the subcellular distribution of H2 O2 in leaves. In this study, the M strain of Cucumber mosaic virus (M-CMV) induced heavy chlorotic symptoms in Nicotiana tabacum cv. white burley during systemic infection. Compared with mock-inoculated leaves, H2 O2 accumulation in inoculated leaves increased after inoculation, then decreased after 4 days. For systemically infected leaves that showed chlorotic symptoms, H2 O2 accumulation was always higher than in healthy leaves. Subcellular H2 O2 localization observed using CLSM showed that H2 O2 in inoculated leaves was generated mainly in the chloroplasts and cell wall, whereas in systemically infected leaves H2 O2 was generated mainly in the cytosol. The levels of coat protein in inoculated and systemically infected leaves might be associated with changes in the level of H2 O2 and symptom development. Further research is needed to elucidate the generation mechanism and the relationship between coat protein and oxidative stress during infection and symptom development. Copyright © 2016 John Wiley & Sons, Ltd.

Barley yellow dwarf virus infection and elevated CO2 alter the antioxidants ascorbate and glutathione in wheat

Plant antioxidants ascorbate and glutathione play an important role in regulating potentially harmful reactive oxygen species produced in response to virus infection. Barley yellow dwarf virus is a widespread viral pathogen that systemically infects cereal crops including wheat, barley and oats. In addition, rising atmospheric CO₂ will alter plant growth and metabolism, including many potential but not well understood effects on plant-virus interactions. In order to better understand the wheat-BYDV interaction and any potential changes under elevated CO₂, the total concentration and oxidised fraction of ascorbate and glutathione was measured in leaves of a susceptible wheat cultivar (Triticum aestivum L. 'Yitpi') infected with Barley yellow dwarf virus-PAV (Padi Avenae virus) and grown under elevated CO₂ in controlled environment chambers. Virus infection decreased total leaf ascorbate and glutathione concentrations and increased the fraction of oxidised ascorbate (dehydroascorbate). Elevated CO₂ decreased the fraction of oxidised ascorbate. In this work, we demonstrate that systemic infection by a phloem-restricted virus weakens the antioxidant pools of ascorbate and glutathione. In addition, elevated CO₂ may decrease oxidative stress, for example, from virus infection, but there was no direct evidence for an interactive effect between treatments.

Identification and regulation of host genes related to Rice stripe virus symptom production

Viral infections cause plant chlorosis, stunting, necrosis or other symptoms. The down-regulation of chloroplast-related genes (ChRGs) is assumed to be responsible for chlorosis. We identified the differentially expressed genes (DEGs) in Rice stripe virus (RSV)-infected Nicotiana benthamiana, and examined the contribution of 75 down-regulated DEGs to RSV symptoms by silencing them one by one using Tobacco rattle virus (TRV)-induced gene silencing. Silencing of 11 of the 75 down-regulated DEGs caused plant chlorosis, and nine of the 11 were ChRGs. Silencing of a down-regulated DEG encoding the eukaryotic translation initiation factor 4A (eIF4A) caused leaf-twisting and stunting that were visible on RSV-infected N. benthamiana. A region of RSV RNA4 was complementary to part of eIF4A mRNA and virus-derived small interfering (vsiRNAs) from that region were present in infected N. benthamiana. When expressed as artificial microRNAs, those vsiRNAs could target NbeIF4A mRNA for regulation. We provide experimental evidence supporting the association of ChRGs with chlorosis and show that eIF4A is involved in RSV symptom development. This is also the first report demonstrating that siRNA derived directly from a plant virus can target a host gene for regulation.

Primary Metabolism, Phenylpropanoids and Antioxidant Pathways Are Regulated in Potato as a Response to Potato virus Y Infection

Potato production is one of the most important agricultural sectors, and it is challenged by various detrimental factors, including virus infections. To control losses in potato production, knowledge about the virus—plant interactions is crucial. Here, we investigated the molecular processes in potato plants as a result of Potato virus Y (PVY) infection, the most economically important potato viral pathogen. We performed an integrative study that links changes in the metabolome and gene expression in potato leaves inoculated with the mild PVY^N and aggressive PVY^NTN isolates, for different times through disease development. At the beginning of infection (1 day post-inoculation), virus-infected plants showed an initial decrease in the concentrations of metabolites connected to sugar and amino-acid metabolism, the TCA cycle, the GABA shunt, ROS scavangers, and phenylpropanoids, relative to the control plants. A pronounced increase in those metabolites was detected at the start of the strong viral multiplication in infected leaves. The alterations in these metabolic pathways were also seen at the gene expression level, as analysed by quantitative PCR. In addition, the systemic response in the metabolome to PVY infection was analysed. Systemic leaves showed a less-pronounced response with fewer metabolites altered, while phenylpropanoid-associated metabolites were strongly accumulated. There was a more rapid onset of accumulation of ROS scavengers in leaves inoculated with PVY^N than those inoculated with PVY^NTN. This appears to be related to the lower damage observed for leaves of potato infected with the milder PVY^N strain, and at least partially explains the differences between the phenotypes observed.

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.

A geminivirus betasatellite damages the structural and functional integrity of chloroplasts leading to symptom formation and inhibition of photosynthesis

Geminivirus infection often causes severe vein clearing symptoms in hosts. Recently a betasatellite has emerged as a key regulator of symptom induction. To understand the host-betasatellite interactions in the process of symptom development, a systematic study was carried out involving symptoms induced by a betasatellite associated with radish leaf curl disease (RaLCB) in Nicotiana benthamiana. It has been found that βC1 protein localized to chloroplasts of host cells, and RaLCB lacking βC1, which failed to produce symptoms, had no effect on chloroplast ultrastructure. Vein flecking induced by transiently expressed βC1 was associated with chloroplast ultrastructure. In addition, the betasatellite down-regulates expression of genes involved in chlorophyll biosynthesis as well as genes involved in chloroplast development and plastid translocation. Interestingly, the expression of key host genes involved in chlorophyll degradation remains unaffected. Betasatellite infection drastically reduced the numbers of active reaction centres and the plastoquinol pool size in leaves exhibiting vein clearing symptoms. Betasatellite-mediated impediments at different stages of chloroplast functionality affect the photosynthetic efficiency of N. benthamiana. To the best of the authors' knowledge, this is the first evidence of a chloroplast-targeting protein encoded by a DNA virus which induces vein clearing and structurally and functionally damages chloroplasts in plants.

Molecular biology of potyviruses

Potyvirus is the largest genus of plant viruses causing significant losses in a wide range of crops. Potyviruses are aphid transmitted in a nonpersistent manner and some of them are also seed transmitted. As important pathogens, potyviruses are much more studied than other plant viruses belonging to other genera and their study covers many aspects of plant virology, such as functional characterization of viral proteins, molecular interaction with hosts and vectors, structure, taxonomy, evolution, epidemiology, and diagnosis. Biotechnological applications of potyviruses are also being explored. During this last decade, substantial advances have been made in the understanding of the molecular biology of these viruses and the functions of their various proteins. After a general presentation on the family Potyviridae and the potyviral proteins, we present an update of the knowledge on potyvirus multiplication, movement, and transmission and on potyvirus/plant compatible interactions including pathogenicity and symptom determinants. We end the review providing information on biotechnological applications of potyviruses.

Quantitative transcriptional changes associated with chlorosis severity in mosaic leaves of tobacco plants infected with Cucumber mosaic virus

Cucumber mosaic virus (CMV) causes mosaic disease in inoculated tobacco plants. Coat protein (CP) is one of the major virulence determinants of CMV, and an amino acid substitution at residue 129 in CP alters the severity of chlorosis, such as pale green chlorosis and white chlorosis, in symptomatic tissues of mosaic leaves of infected tobacco. In this study, we compared the transcriptomes of chlorotic tissues infected with the wild-type pepo strain of CMV and two strains carrying CP mutants with diverse chlorosis severity. Differential gene expression analysis showed that CMV inoculation appeared to have similar effects on the transcriptional expression profiles of the symptomatic chlorotic tissues, and only the magnitude of expression differed among the different CMVs. Gene ontology analysis with biological process and cellular component terms revealed that many nuclear genes related to abiotic stress responses, including responses to cadmium, heat, cold and salt, were up-regulated, whereas chloroplast- and photosynthesis-related genes (CPRGs) were down-regulated, in the chlorotic tissues. Interestingly, the level of CPRG down-regulation was correlated with the severity of chlorosis. These results indicate that CP mutation governs the repression level and mRNA accumulation of CPRGs, which are closely associated with the induction of chlorosis.

Redox-related metabolites and gene expression modulated by sugar in sunflower leaves: similarities with Sunflower chlorotic mottle virus-induced symptom

Sugars are part of an integrated redox system, since they are key regulators of respiration and photosynthesis, and therefore of the levels of reducing power, ATP and ROS. These elements are major determinants of the cellular redox state, which is involved in the perception and regulation of many endogenous and environmental stimuli. Our previous findings suggested that early sugar increase produced during compatible Sunflower chlorotic mottle virus (SuCMoV) infection might modulate chlorotic symptom development through redox state alteration in sunflower. The purpose of this work was to characterize redox-related metabolites and gene expression changes associated with high sugar availability and symptom development induced by SuCMoV. The results show that sugar caused an increase in glutathione, ascorbate, pyridine nucleotides, and ATP. In addition, higher sugar availability reduced hydrogen peroxide and ΦPSII. This finding suggests that high sugar availability would be associated with cellular redox alteration and photoinhibitory process. The expression of the genes analyzed was also strongly affected by sugar, such as the down-regulation of psbA and up-regulation of psbO and cp29. The expression level of cytoplasmic (apx-1 and gr)- and chloroplastic (Fe-sod)-targeted genes was also significantly enhanced in sugar-treated leaves. Therefore, all these responses suggest that sugars induce chloroplastic redox state alteration with photoinhibition process that could be contributing to chlorotic symptom development during SuCMoV infection.