Plant responses to UV radiation and links to pathogen resistance

Microgreens and novel non-thermal seed germination techniques for sustainable food systems: a review

There are a number of cutting-edge techniques implemented in the germination process, including high pressure processing, ultrasonic, ultraviolet, light, non-thermal plasma, magnetic field, microwave radiation, electrolyzed oxidizing water, and plasma activated water. The influence of these technological advances on seed germination procedure is addressed in this review. The use of these technologies has several benefits, including the enhancement of plant growth rate and the modulation of bioactive chemicals like ABA, protein, and peroxidase concentrations, as well as the suppression of microbial development. Microgreens' positive health effects, such as their antioxidant, anticancer, antiproliferative/pro-oxidant, anti-obesity, and anti-inflammatory properties are extensively reviewed. The phytochemical and bioactive components of microgreens were investigated, including the concentrations of vitamin K, vitamin C, vitamin E, micro and macro nutrients, pro-vitamin A, polyphenols, and glucosinolates. Furthermore, the potential commercial uses of microgreens, as well as the current market transformation and prospects for the future are explored.

The MRE11-ATM-SOG1 DNA damage signaling pathway confers rice immunity to Xanthomonas oryzae

Plants are constantly exposed to microbial pathogens in the environment. One branch of innate plant immunity is mediated by cell-membrane-localized receptors, but less is known about associations between DNA damage and plant immune responses. Here, we show that rice (Oryza sativa) mesophyll cells are prone to DNA double-stranded breaks (DSBs) in response to ZJ173, a strain of Xanthomonas oryzae pv. oryzae (Xoo). The DSB signal transducer ataxia telangiectasia mutated (ATM), but not the ATM and Rad3-related branch, confers resistance against Xoo. Mechanistically, the MRE11-ATM module phosphorylates suppressor of gamma response 1 (SOG1), which activates several phenylpropanoid pathway genes and prompts downstream phytoalexin biosynthesis during Xoo infection. Intriguingly, overexpression of the topoisomerase gene TOP6A3 causes a switch from the classic non-homologous end joining (NHEJ) pathway to the alternative NHEJ and homologous recombination pathways at Xoo-induced DSBs. The enhanced ATM signaling of the alternative NHEJ pathway strengthens the SOG1-regulated phenylpropanoid pathway and thereby boosts Xoo-induced phytoalexin biosynthesis in TOP6A3-OE1 overexpression lines. Overall, the MRE11-ATM-SOG1 pathway serves as a prime example of plant-pathogen interactions that occur via host non-specific recognition. The function of TOP6-facilitated ATM signaling in the defense response makes it a promising target for breeding of rice germplasm that exhibits resistance to bacterial blight disease without a growth penalty.

The recent relationship between ultraviolet-B radiation and biotic resistance in plants: a novel non-chemical strategy for managing biotic stresses

Ultraviolet-B radiation (UVB; 280-315 nm) is a significant environmental factor that alters plant development, changes interactions between species, and reduces the prevalence of pests and diseases. While UVB radiation has negative effects on plant growth and performance at higher doses, at lower and ambient doses, UVB radiation acts as a non-chemical method for managing biotic stresses by having positive effects on disease resistance and genes that protect plants from pests. Understanding the recent relationship between UVB radiation and plants' biotic stresses is crucial for the development of crops that are resistant to UVB and biotic stresses. However, little is known about the recent interactions between UVB radiation and biotic stresses in plants. This review discusses the most recent connections between UVB radiation and biotic stresses in crops, including how UVB radiation affects a plant's resistance to disease and pests. The interaction of UVB radiation with pathogens and herbivores has been the subject of the most extensive research of these. This review also discusses additional potential strategies for conferring multiple UVB-biotic stress resistance in crop plants, such as controlling growth inhibition, miRNA 396 and 398 modulations, and MAP kinase. This study provides crucial knowledge and methods for scientists looking to develop multiple resistant crops that will improve global food security.

Ultraviolet radiation promotes the production of hispidin polyphenols by medicinal mushroom Inonotus obliquus

Production of hispidin polyphenols in Inonotus obliquus is a stress-induced response triggered by environmental factors. As one of the important environmental factors, ultraviolet (UV) radiation plays regulatory roles in fungal growth and development. However, whether UV radiation regulates the formation of hispidin polyphenols remains to be established. In this study, we cultivated I. obliquus on solid medium and imposed intermittent UV radiation. We showed that UV exposure inhibited the growth of mycelia but increased the production of polyphenols. Further bioassays revealed that UV radiation also increased the catalytic activities of phenylalanine ammonia-lyase (PAL) and chalcone isomerase (CHI), up-regulated expression of genes related to redox, transcriptional regulation, and metabolism. In addition, the total extracts from the UV-irradiated group were more capable of scavenging DPPH and ABTS⁺ free radicals, especially at the later stage of culture. Thus, UV radiation, acting as one of the environmental factors, stimulated the accumulation of polyphenols in I. obliquus by regulating the activities of enzymes and the expression of genes related to growth and metabolism, and can be tentatively used as a feasible strategy to enhance the production of polyphenols in I. obliquus.

UVA and UVB Radiation as Innovative Tools to Biofortify Horticultural Crops with Nutraceuticals

The consumption of fruits and vegetables is related to the prevention and treatment of chronic–degenerative diseases due to the presence of secondary metabolites with pharmaceutical activity. Most of these secondary metabolites, also known as nutraceuticals, are present in low concentrations in the plant tissue. Therefore, to improve the health benefits of horticultural crops, it is necessary to increase their nutraceutical content before reaching consumers. Applying ultraviolet radiation (UVR) to fruits and vegetables has been a simple and effective technology to biofortify plant tissue with secondary metabolites. This review article describes the physiological and molecular basis of stress response in plants. Likewise, current literature on the mechanisms and effects of UVA and UVB radiation on the accumulation of different bioactive phytochemicals are reviewed. The literature shows that UVR is an effective tool to biofortify horticultural crops to enhance their nutraceutical content.

Effects of Defoliation at Fruit Set on Vine Physiology and Berry Composition in Cabernet Sauvignon Grapevines

Grapevine canopy defoliation is a fundamentally important technique for the productivity and quality of grapes. Leaf removal is a pivotal operation on high-density vines which aims to improve air circulation, light exposure, and leaf gas exchange. The effects of leaf removal (LR) on vine physiology and berry composition in Cabernet Sauvignon grapevines were studied during the 2018–2019 growing season in the Bolgheri area, Tuscany, Italy. The basal leaves were removed at fruit set at two severity levels (removal of four basal leaves of each shoot (LR4) and removal of eight basal leaves (LR8)). The two treatments were compared with the not defoliated control (CTRL). The following physiological parameters of vines were measured: leaf gas exchange, leaf water potential, chlorophyll fluorescence and indirect chlorophyll content. The results showed that defoliation increased single leaf photosynthesis. In addition, qualitative grape parameters (phenolic and technological analyses) and daytime and night-time berry temperature were studied. The results showed that leaf removal had an impact on total soluble solids (°Brix), titratable acidity, and pH. The LR8-treated grapes had higher titratable acidity, while those in the LR4 treatment had higher °Brix and extractable anthocyanin and polyphenol content. Berry weight was not significantly influenced by the timing and severity of basal defoliation. Therefore, this research aims to investigate the effects of defoliation at the fruit set on vines performance.

A Review of Strawberry Photobiology and Fruit Flavonoids in Controlled Environments

Rapid technology development in controlled environment (CE) plant production has been applied to a large variety of plants. In recent years, strawberries have become a popular fruit for CE production because of their high economic and nutritional values. With the widespread use of light-emitting diode (LED) technology in the produce industry, growers can manipulate strawberry growth and development by providing specific light spectra. Manipulating light intensity and spectral composition can modify strawberry secondary metabolism and highly impact fruit quality and antioxidant properties. While the impact of visible light on secondary metabolite profiles for other greenhouse crops is well documented, more insight into the impact of different light spectra, from UV radiation to the visible light spectrum, on strawberry plants is required. This will allow growers to maximize yield and rapidly adapt to consumer preferences. In this review, a compilation of studies investigating the effect of light properties on strawberry fruit flavonoids is provided, and a comparative analysis of how light spectra influences strawberry's photobiology and secondary metabolism is presented. The effects of pre-harvest and post-harvest light treatments with UV radiation and visible light are considered. Future studies and implications for LED lighting configurations in strawberry fruit production for researchers and growers are discussed.

Impact of UV-C Radiation Applied during Plant Growth on Pre- and Postharvest Disease Sensitivity and Fruit Quality of Strawberry

Ultraviolet-C (UV-C) radiation is efficient in reducing the development of diseases in many species, including strawberry (Fragaria × ananassa). Several studies suggest that UV-C radiation is effective not only because of its disinfecting effect but also because it may stimulate plant defenses. In this study, the effect of preharvest UV-C radiation applied during strawberry cultivation on plant growth, fruit quality, and susceptibility to major fungal diseases such as gray mold, powdery mildew, and soft rot was evaluated. UV-C treatments had an impact on flowering initiation and fruit development. Flowering occurred earlier for UV-C-treated plants than for nontreated plants. At harvest, a larger amount of fruit was produced by treated plants despite their slight decrease in leaf area. UV-C treatment did not improve strawberry shelf life but did not alter the physical integrity of strawberry fruit. Natural infection of leaves to powdery mildew and of fruit to Rhizopus spp. strongly decreased in response to UV-C treatment.

Effect of ultraviolet treatment on shelf life of fresh lotus root

The potential use of ultraviolet (UV)-C (254 nm) to extend postharvest shelf life of fresh unprocessed lotus root (Nelumbo nucifera G.) was determined. UV treatment for 30 and 60 min effectively reduced weight loss, improved moisture, color retention, and soluble solids of samples when stored at 25°C for 15 days. Microbial growth inhibition of UV was evidenced by 1.8 and 1.0 log reductions in the 30 and 60 min-treated samples. Phenylalanine ammonia lyase (PAL) activity and total phenol contents (TPCs) detected in lotus root were higher, while oxidative enzymes peroxidase (POD) and polyphenol oxidase (PPO) were inhibited by UV treatment. Gallic acid, gallocatechin, and catechin levels were increased in 30 min-treated samples by about 0.9, 13.4, 8.0 mg/100 g. The results suggest that extension of postharvest storage life by UV-C is most likely through the protective roles exerted from stimulation of the phenylpropanoid pathway in the treated roots. PRACTICAL APPLICATIONS: Unlike previous studies that are mainly focused on shelf life extension of processed products of the rhizome, this study determines the potential use of a nonchemical and ecologically friendly ultraviolet (UV-C) treatment to extend shelf life of intact uncut fresh lotus root. Our results demonstrated that UV-C treatment significantly prolonged the shelf life of lotus root. Use of this method is promising as a treatment to improve postharvest storage life of fresh lotus root, to improve its export potential and help to address unmet local demands for the crop.

Differential expression after UV-B radiation and characterization of chalcone synthase from the Patagonian hairgrass Deschampsia antarctica

Deschampsiaantarctica inhabits the maritime territory of Antarctica and South Patagonia. It grows under very harsh environmental conditions. The survival of this species in low freezing temperatures and under high levels of UV-B radiation may constitute some of the most remarkable adaptive plant responses and suggests that this plant possesses genes associated with cold and UV tolerance. Frequently, increased levels of flavonoids have been linked to highly UV-B irradiated plants. Studies examining the biosynthesis of flavonoids in D. antarctica may provide clues to its success in this extreme environment. In this study, we characterized the family of genes encoding chalcone synthase, a key enzyme of the flavonoid biosynthetic pathway. DaCHS was cloned, sequenced and characterized by using software tools. CHS contains two domains, the N-terminal domain ranges from amino acid 8 to 231 and the C-terminal domain ranges from amino acid 241 to 391. Sequence analysis of the three family members revealed a high degree of identity after comparison with other monocotyledons such as Oryza sativa L., Zea mays L. and Hordeum vulgare L. According to these results, DaCHS can be grouped together with H. vulgare CHS1 in the same branch. The phylogenetic tree was built using MEGA software and the neighbour join method with 1000 bootstrap replicates. A model of DaCHS was constructed by way of structural tools and key amino acid residues were identified at the active motif site.

UVA, UVB Light Doses and Harvesting Time Differentially Tailor Glucosinolate and Phenolic Profiles in Broccoli Sprouts

Broccoli sprouts contain health-promoting glucosinolate and phenolic compounds that can be enhanced by applying ultraviolet light (UV). Here, the effect of UVA or UVB radiation on glucosinolate and phenolic profiles was assessed in broccoli sprouts. Sprouts were exposed for 120 min to low intensity and high intensity UVA (UVAL, UVAH) or UVB (UVBL, UVBH) with UV intensity values of 3.16, 4.05, 2.28 and 3.34 W/m², respectively. Harvest occurred 2 or 24 h post-treatment; and methanol/water or ethanol/water (70%, v/v) extracts were prepared. Seven glucosinolates and 22 phenolics were identified. Ethanol extracts showed higher levels of certain glucosinolates such as glucoraphanin, whereas methanol extracts showed slight higher levels of phenolics. The highest glucosinolate accumulation occurred 24 h after UVBH treatment, increasing 4-methoxy-glucobrassicin, glucobrassicin and glucoraphanin by ~170, 78 and 73%, respectively. Furthermore, UVAL radiation and harvest 2 h afterwards accumulated gallic acid hexoside I (~14%), 4-O-caffeoylquinic acid (~42%), gallic acid derivative (~48%) and 1-sinapoyl-2,2-diferulolyl-gentiobiose (~61%). Increases in sinapoyl malate (~12%), gallotannic acid (~48%) and 5-sinapoyl-quinic acid (~121%) were observed with UVBH Results indicate that UV-irradiated broccoli sprouts could be exploited as a functional food for fresh consumption or as a source of bioactive phytochemicals with potential industrial applications.

Involvement of Inositol Biosynthesis and Nitric Oxide in the Mediation of UV-B Induced Oxidative Stress

The involvement of NO-signaling in ultraviolet B (UV-B) induced oxidative stress (OS) in plants is an open question. Inositol biosynthesis contributes to numerous cellular functions, including the regulation of plants tolerance to stress. This work reveals the involvement of inositol-3-phosphate synthase 1 (IPS1), a key enzyme for biosynthesis of myo-inositol and its derivatives, in the response to NO-dependent OS in Arabidopsis. Homozygous mutants deficient for IPS1 (atips1) and wild-type plants were transformed with a reduction- grx1-rogfp2 and used for the dynamic measurement of UV-B-induced and SNP (sodium nitroprusside)-mediated oxidative stresses by confocal microscopy. atips1 mutants displayed greater tissue-specific resistance to the action of UV-B than the wild type. SNP can act both as an oxidant or repairer depending on the applied concentration, but mutant plants were more tolerant than the wild type to nitrosative effects of high concentration of SNP. Additionally, pretreatment with low concentrations of SNP (10, 100 μM) before UV-B irradiation resulted in a tissue-specific protective effect that was enhanced in atips1. We conclude that the interplay between nitric oxide and inositol signaling can be involved in the mediation of UV-B-initiated oxidative stress in the plant cell.

Reference gene validation for quantitative RT-PCR during biotic and abiotic stresses in Vitis vinifera

Grapevine is one of the most cultivated fruit crop worldwide with Vitis vinifera being the species with the highest economical importance. Being highly susceptible to fungal pathogens and increasingly affected by environmental factors, it has become an important agricultural research area, where gene expression analysis plays a fundamental role. Quantitative reverse transcription polymerase chain reaction (qRT-PCR) is currently amongst the most powerful techniques to perform gene expression studies. Nevertheless, accurate gene expression quantification strongly relies on appropriate reference gene selection for sample normalization. Concerning V. vinifera, limited information still exists as for which genes are the most suitable to be used as reference under particular experimental conditions. In this work, seven candidate genes were investigated for their stability in grapevine samples referring to four distinct stresses (Erysiphe necator, wounding and UV-C irradiation in leaves and Phaeomoniella chlamydospora colonization in wood). The expression stability was evaluated using geNorm, NormFinder and BestKeeper. In all cases, full agreement was not observed for the three methods. To provide comprehensive rankings integrating the three different programs, for each treatment, a consensus ranking was created using a non-weighted unsupervised rank aggregation method. According to the last, the three most suitable reference genes to be used in grapevine leaves, regardless of the stress, are UBC, VAG and PEP. For the P. chlamydospora treatment, EF1, CYP and UBC were the best scoring genes. Acquaintance of the most suitable reference genes to be used in grapevine samples can contribute for accurate gene expression quantification in forthcoming studies.

Study of leaf metabolome modifications induced by UV-C radiations in representative Vitis, Cissus and Cannabis species by LC-MS based metabolomics and antioxidant assays

UV-C radiation is known to induce metabolic modifications in plants, particularly to secondary metabolite biosynthesis. To assess these modifications from a global and untargeted perspective, the effects of the UV-C radiation of the leaves of three different model plant species, Cissus antarctica Vent. (Vitaceae), Vitis vinifera L. (Vitaceae) and Cannabis sativa L. (Cannabaceae), were evaluated by an LC-HRMS-based metabolomic approach. The approach enabled the detection of significant metabolite modifications in the three species studied. For all species, clear modifications of phenylpropanoid metabolism were detected that led to an increased level of stilbene derivatives. Interestingly, resveratrol and piceid levels were strongly induced by the UV-C treatment of C. antarctica leaves. In contrast, both flavonoids and stilbene polymers were upregulated in UV-C-treated Vitis leaves. In Cannabis, important changes in cinnamic acid amides and stilbene-related compounds were also detected. Overall, our results highlighted phytoalexin induction upon UV-C radiation. To evaluate whether UV-C stress radiation could enhance the biosynthesis of bioactive compounds, the antioxidant activity of extracts from control and UV-C-treated leaves was measured. The results showed increased antioxidant activity in UV-C-treated V. vinifera extracts.

NLR-associating transcription factor bHLH84 and its paralogs function redundantly in plant immunity

In plants and animals, nucleotide-binding and leucine-rich repeat domain containing (NLR) immune receptors are utilized to detect the presence or activities of pathogen-derived molecules. However, the mechanisms by which NLR proteins induce defense responses remain unclear. Here, we report the characterization of one basic Helix-loop-Helix (bHLH) type transcription factor (TF), bHLH84, identified from a reverse genetic screen. It functions as a transcriptional activator that enhances the autoimmunity of NLR mutant snc1 (suppressor of npr1-1, constitutive 1) and confers enhanced immunity in wild-type backgrounds when overexpressed. Simultaneously knocking out three closely related bHLH paralogs attenuates RPS4-mediated immunity and partially suppresses the autoimmune phenotypes of snc1, while overexpression of the other two close paralogs also renders strong autoimmunity, suggesting functional redundancy in the gene family. Intriguingly, the autoimmunity conferred by bHLH84 overexpression can be largely suppressed by the loss-of-function snc1-r1 mutation, suggesting that SNC1 is required for its proper function. In planta co-immunoprecipitation revealed interactions between not only bHLH84 and SNC1, but also bHLH84 and RPS4, indicating that bHLH84 associates with these NLRs. Together with previous finding that SNC1 associates with repressor TPR1 to repress negative regulators, we hypothesize that nuclear NLR proteins may interact with both transcriptional repressors and activators during immune responses, enabling potentially faster and more robust transcriptional reprogramming upon pathogen recognition.

In plants and animals, NLR immune receptors are utilized to detect pathogen-derived molecules and activate immunity. However, the mechanisms of plant NLR activation remain unclear. Here, we report on bHLH84, which functions as a transcriptional activator. Simultaneously knocking out three closely related bHLH paralogs partially suppresses the autoimmunity of snc1 and compromises RPS4-mediated defense, while overexpression of these close paralogs renders strong autoimmunity, suggesting functional redundancy in the gene family. In planta co-immunoprecipitation revealed interactions between not only bHLH84 and SNC1, but also bHLH84 and RPS4. Therefore bHLH84 family transcription factors associate with these NLRs to activate defense responses, enabling potentially faster and more robust transcriptional reprogramming upon pathogen recognition.

Genome stability in the uvh6 mutant of Arabidopsis thaliana

Plant XPD homolog UVH6 is the protein involved in the repair of strand breaks, and the excision repair and uvh6 mutant is not impaired in transgenerational increase in HRF. While analyzing the transgenerational response to stress in plants, we found that the promoter and gene body of Arabidopsis thaliana (Arabidopsis) XPD homolog UVH6 underwent hypomethylation and showed an increase in the level of transcript. Here, we analyzed the mutant of this gene, uvh6-1, by crossing it to two different reporter lines: one which allows for analysis of homologous recombination frequency (HRF) and another which makes it possible to analyze the frequency of point mutations. We observed that uvh6-1 plants exhibited lower rate of spontaneous homologous recombination but higher frequencies of spontaneous point mutations. The analysis of strand breaks using ROPS and Comet assays showed that the mutant had a much higher level of strand breaks at non-induced conditions. Exposure to stresses such as UVC, heat, cold, flood and drought showed that the mutant was not impaired in an increase in somatic HRF. The analysis of spontaneous HRF in the progeny of control plants compared to that of the progeny of stressed plants demonstrated that uvh6-1 was mildly affected in response to temperature, UV and drought. Our data suggest that UVH6 may be involved in the repair of strand breaks and excision repair, but it is unlikely that UVH6 is required for transgenerational increase in HRF.

Microbial pathogens trigger host DNA double-strand breaks whose abundance is reduced by plant defense responses

Immune responses and DNA damage repair are two fundamental processes that have been characterized extensively, but the links between them remain largely unknown. We report that multiple bacterial, fungal and oomycete plant pathogen species induce double-strand breaks (DSBs) in host plant DNA. DNA damage detected by histone γ-H2AX abundance or DNA comet assays arose hours before the disease-associated necrosis caused by virulent Pseudomonas syringae pv. tomato. Necrosis-inducing paraquat did not cause detectable DSBs at similar stages after application. Non-pathogenic E. coli and Pseudomonas fluorescens bacteria also did not induce DSBs. Elevation of reactive oxygen species (ROS) is common during plant immune responses, ROS are known DNA damaging agents, and the infection-induced host ROS burst has been implicated as a cause of host DNA damage in animal studies. However, we found that DSB formation in Arabidopsis in response to P. syringae infection still occurs in the absence of the infection-associated oxidative burst mediated by AtrbohD and AtrbohF. Plant MAMP receptor stimulation or application of defense-activating salicylic acid or jasmonic acid failed to induce a detectable level of DSBs in the absence of introduced pathogens, further suggesting that pathogen activities beyond host defense activation cause infection-induced DNA damage. The abundance of infection-induced DSBs was reduced by salicylic acid and NPR1-mediated defenses, and by certain R gene-mediated defenses. Infection-induced formation of γ-H2AX still occurred in Arabidopsis atr/atm double mutants, suggesting the presence of an alternative mediator of pathogen-induced H2AX phosphorylation. In summary, pathogenic microorganisms can induce plant DNA damage. Plant defense mechanisms help to suppress rather than promote this damage, thereby contributing to the maintenance of genome integrity in somatic tissues.

Multicellular organisms are continuously exposed to microbes and have developed sophisticated defense mechanisms to counter attack by microbial pathogens. Organisms also encounter many types of DNA damage and have evolved multiple mechanisms to maintain their genomic integrity. Even though these two fundamental responses have been characterized extensively, the relationship between them remains largely unclear. Our study demonstrates that microbial plant pathogens with diverse life styles, including bacteria, oomycete and fungal pathogens, induce double-strand breaks (DSBs) in the genomes of infected host plant cells. DSB induction is apparently a common feature during plant-pathogen interactions. DSBs are the most deleterious form of DNA damage and can lead to chromosomal aberrations and gene mutations. In response to pathogen infection, plant immune responses are activated and contribute to suppressing pathogen-induced DSBs, thereby maintaining better genome integrity and stability. The findings identify important ways that the plant immune and DNA damage repair responses are interconnected. Awareness of the above phenomena may foster future development of disease management approaches that improve crop productivity under biotic stress.

Ultra-weak photon emission as a non-invasive tool for the measurement of oxidative stress induced by UVA radiation in Arabidopsis thaliana

All living organisms emit ultra-weak photon emission as a result of oxidative processes caused by the physical or chemical stress factors. In the present study, the effect of oxidative stress induced by the exposure of the plant model Arabidopsis thaliana to ultraviolet A (UVA) radiation was studied using ultra-weak photon emission. When Arabidopsis plants and leaves were exposed to UVA radiation, two kinetically distinguished phases in the ultra-weak photon emission decay were observed: the fast decay phase (τ1=0.805±0.024 min) and slow decay phase (τ2=4.321±0.166 min). The spectral analysis of the UVA radiation-induced ultra-weak photon emission showed that the photon emission during the fast decay phase is from both blue-green and red regions of the spectrum, whereas the photon emission during the slow decay phase is solely from the blue-green region of the spectrum. These observations reveal that triplet excited carbonyls contribute to ultra-weak photon emission during both fast and slow decay phases, whereas chlorophylls participate in the ultra-weak photon emission solely during the fast decay phase. It is illustrated here that the ultra-weak photon emission serves as a non-invasive method for the monitoring of oxidative stress in plants caused by UVA radiation.

Genetic interactions of Arabidopsis thaliana damaged DNA binding protein 1B (DDB1B) with DDB1A, DET1, and COP1

Damaged DNA Binding protein 1 (DDB1)–CULLIN4 E3 ubiquitin ligase complexes have been implicated in diverse biological processes in a range of organisms. Arabidopsis thaliana encodes two homologs of DDB1, DDB1A, and DDB1B. In this study we use a viable partial loss of function allele of DDB1B, ddb1b-2, to examine genetic interactions with DDB1A, DET1 and COP1. Although the ddb1b-2 ddb1a double mutant is lethal, ddb1a ddb1b-2/+ and ddb1b-2 ddb1a/+ heterozygotes exhibit few developmental phenotypes but do exhibit decreased tolerance of ultraviolet light. In addition, germination in ddb1a and ddb1a ddb1b-2/+ was found to be sensitive to salt and mannitol, and both DDB1 single mutants as well as the heterozygotes exhibited heat sensitivity. DE-ETIOLATED1 (DET1) and CONSTITUTIVE PHOTOMORPHOGENIC1 (COP1) are negative regulators of light development which interact with DDB1-CUL4 complexes. Although ddb1a strongly enhances det1 phenotypes in both dark- and light-grown seedlings, ddb1b-2 weakly enhanced the det1 short hypocotyl phenotype in the dark, as well as enhancing anthocyanin levels and suppressing the det1 low chlorophyll phenotype in light-grown seedlings. In adults, ddb1a suppresses det1 early flowering and enhances the det1 dwarf phenotype. A similar trend was observed in ddb1b-2 det1 double mutants, although the effects were smaller in magnitude. In cop1 mutants, ddb1b-2 enhanced the cop1-4 short hypocotyl phenotype in dark and light, enhanced anthocyanin levels in cop1-1 in the light, but had no effect in adults. Thus the requirement for DDB1B varies in the course of development, from COP1-specific effects in hypocotyls to DET1-specific in adults.

Measurement and analysis of broadband UVB solar radiation in Spain

Measurements of broadband UVB irradiance (290-315 nm) at 14 locations in Spain for the period 2000-2009 have been used to generate instantaneous, hourly and daily values of irradiance (W m(-2)) and radiant exposure (kJ m(-2)). These measurements, and its statistical indices, have been analyzed. For the UVB irradiance, the values corresponding to July (maximum) and December (minimum) have been analyzed as representative of the year during the whole period for all locations. For the UVB radiant exposure, the temporal evolution of daily values has been evaluated for all locations to estimate an average yearly behavior. The accumulated radiant exposure for an average year has also been studied for each location. Finally, to determine possible trends in the evolution of the UVB levels, the linear regressions for the mean daily values for all locations have been determined.

Transcriptomic and proteomic profiling of maize embryos exposed to camptothecin

BACKGROUND

Camptothecin is a plant alkaloid that specifically binds topoisomerase I, inhibiting its activity and inducing double stranded breaks in DNA, activating the cell responses to DNA damage and, in response to severe treatments, triggering cell death.

RESULTS

Comparative transcriptomic and proteomic analyses of maize embryos that had been exposed to camptothecin were conducted. Under the conditions used in this study, camptothecin did not induce extensive degradation in the genomic DNA but induced the transcription of genes involved in DNA repair and repressed genes involved in cell division. Camptothecin also affected the accumulation of several proteins involved in the stress response and induced the activity of certain calcium-dependent nucleases. We also detected changes in the expression and accumulation of different genes and proteins involved in post-translational regulatory processes.

CONCLUSIONS

This study identified several genes and proteins that participate in DNA damage responses in plants. Some of them may be involved in general responses to stress, but others are candidate genes for specific involvement in DNA repair. Our results open a number of new avenues for researching and improving plant resistance to DNA injury.

Tobacco mosaic virus infection results in an increase in recombination frequency and resistance to viral, bacterial, and fungal pathogens in the progeny of infected tobacco plants

Our previous experiments showed that infection of tobacco (Nicotiana tabacum) plants with Tobacco mosaic virus (TMV) leads to an increase in homologous recombination frequency (HRF). The progeny of infected plants also had an increased rate of rearrangements in resistance gene-like loci. Here, we report that tobacco plants infected with TMV exhibited an increase in HRF in two consecutive generations. Analysis of global genome methylation showed the hypermethylated genome in both generations of plants, whereas analysis of methylation via 5-methyl cytosine antibodies demonstrated both hypomethylation and hypermethylation. Analysis of the response of the progeny of infected plants to TMV, Pseudomonas syringae, or Phytophthora nicotianae revealed a significant delay in symptom development. Infection of these plants with TMV or P. syringae showed higher levels of induction of PATHOGENESIS-RELATED GENE1 gene expression and higher levels of callose deposition. Our experiments suggest that viral infection triggers specific changes in progeny that promote higher levels of HRF at the transgene and higher resistance to stress as compared with the progeny of unstressed plants. However, data reported in these studies do not establish evidence of a link between recombination frequency and stress resistance.

Variation in natural plant products and the attraction of bodyguards involved in indirect plant defenseThe present review is one in the special series of reviews on animal–plant interactions

Plants can respond to feeding or egg deposition by herbivorous arthropods by changing the volatile blend that they emit. These herbivore-induced plant volatiles (HIPVs) can attract carnivorous natural enemies of the herbivores, such as parasitoids and predators, a phenomenon that is called indirect plant defense. The volatile blends of infested plants can be very complex, sometimes consisting of hundreds of compounds. Most HIPVs can be classified as terpenoids (e.g., (E)-β-ocimene, (E,E)-α-farnesene, (E)-4,8-dimethyl-1,3,7-nonatriene), green leaf volatiles (e.g., hexanal, (Z)-3-hexen-1-ol, (Z)-3-hexenyl acetate), phenylpropanoids (e.g., methyl salicylate, indole), and sulphur- or nitrogen-containing compounds (e.g., isothiocyanates or nitriles, respectively). One highly intriguing question has been which volatiles out of the complex blend are the most important ones for the carnivorous natural enemies to locate "suitable host plants. Here, we review the methods and techniques that have been used to elucidate the carnivore-attracting compounds. Electrophysiological methods such as electroantennography have been used with parasitoids to elucidate which compounds can be perceived by the antennae. Different types of elicitors and inhibitors have widely been applied to manipulate plant volatile blends. Furthermore, transgenic plants that were genetically modified in specific steps in one of the signal transduction pathways or biosynthetic routes have been used to find steps in HIPV emission crucial for indirect plant defense. Furthermore, we provide an overview on biotic and abiotic factors that influence the emission of HIPVs and how this can affect the interactions between members of different trophic levels. Consequently, we review the progress that has been made in this exciting research field during the past 30 years since the first studies on HIPVs emerged and we highlight important issues to be addressed in the future.

Cloning and validation of novel miRNA from basmati rice indicates cross talk between abiotic and biotic stresses

Most of the physiological processes are controlled by the small RNAs in several organisms including plants. A huge database exists on one type of small RNA, i.e., microRNAs (miRs) identified from diverse species. However, the processes of data-mining of miRs in most of the species are still incomplete. Rice feeds the hungry trillions and hence understanding its developmental processes as well as its stress biology, which might be largely controlled by the small RNA pathways, is certainly a worthwhile task. Here, we report the cloning and identification of approximately 40 new putative miRs from local basmati rice variety in accordance to the annotation suggested by Meyers et al. (Plant Cell 20:3186-3190, 2008). About 23 sequences were derived from rice exposed to salt stress while 18 were derived from rice infected with tungro virus. A few of these putative miRs were common to both. Our data showed that at least two of these miRs were up-regulated in response to both abiotic and biotic stresses. The miR target predictions indicate that most of the putative miRs target specific metabolic processes. The up-regulation of similar miRs in response to two entirely different types of stresses suggests a converging functional role of miRs in managing various stresses. Our findings suggest that more rice miRs need to be identified and a thorough understanding of the function of such miRs will help unravel the mysteries of rice stress biology.

Transgenerational stress memory is not a general response in Arabidopsis

Adverse conditions can trigger DNA damage as well as DNA repair responses in plants. A variety of stress factors are known to stimulate homologous recombination, the most accurate repair pathway, by increasing the concentration of necessary enzymatic components and the frequency of events. This effect has been reported to last into subsequent generations not exposed to the stress. To establish a basis for a genetic analysis of this transgenerational stress memory, a broad range of treatments was tested for quantitative effects on homologous recombination in the progeny. Several Arabidopsis lines, transgenic for well-established recombination traps, were exposed to 10 different physical and chemical stress treatments, and scored for the number of somatic homologous recombination (SHR) events in the treated generation as well as in the two subsequent generations that were not treated. These numbers were related to the expression level of genes involved in homologous recombination and repair. SHR was enhanced after the majority of treatments, confirming previous data and adding new effective stress types, especially interference with chromatin. Compounds that directly modify DNA stimulated SHR to values exceeding previously described induction rates, concomitant with an induction of genes involved in SHR. In spite of the significant stimulation in the stressed generations, the two subsequent non-treated generations only showed a low and stochastic increase in SHR that did not correlate with the degree of stimulation in the parental plants. Transcripts coding for SHR enzymes generally returned to pre-treatment levels in the progeny. Thus, transgenerational effects on SHR frequency are not a general response to abiotic stress in Arabidopsis and may require special conditions.