The TFIIS and TFIIS-like genes from Medicago truncatula are involved in oxidative stress response

Molecular dynamics of seed priming at the crossroads between basic and applied research

The potential of seed priming is still not fully exploited. Our limited knowledge of the molecular dynamics of seed pre-germinative metabolism is the main hindrance to more effective new-generation techniques. Climate change and other recent global crises are disrupting food security. To cope with the current demand for increased food, feed, and biofuel production, while preserving sustainability, continuous technological innovation should be provided to the agri-food sector. Seed priming, a pre-sowing technique used to increase seed vigor, has become a valuable tool due to its potential to enhance germination and stress resilience under changing environments. Successful priming protocols result from the ability to properly act on the seed pre-germinative metabolism and stimulate events that are crucial for seed quality. However, the technique still requires constant optimization, and researchers are committed to addressing some key open questions to overcome such drawbacks. In this review, an update of the current scientific and technical knowledge related to seed priming is provided. The rehydration-dehydration cycle associated with priming treatments can be described in terms of metabolic pathways that are triggered, modulated, or turned off, depending on the seed physiological stage. Understanding the ways seed priming affects, either positively or negatively, such metabolic pathways and impacts gene expression and protein/metabolite accumulation/depletion represents an essential step toward the identification of novel seed quality hallmarks. The need to expand the basic knowledge on the molecular mechanisms ruling the seed response to priming is underlined along with the strong potential of applied research on primed seeds as a source of seed quality hallmarks. This route will hasten the implementation of seed priming techniques needed to support sustainable agriculture systems.

SK, Sheoran S, K. UB, K. BN, Kumar S, Singh AN, Singh HV. Seed Longevity in Legumes: Deeper Insights Into Mechanisms and Molecular Perspectives

Sustainable agricultural production largely depends upon the viability and longevity of high-quality seeds during storage. Legumes are considered as rich source of dietary protein that helps to ensure nutritional security, but associated with poor seed longevity that hinders their performance and productivity in farmer's fields. Seed longevity is the key determinant to assure proper seed plant value and crop yield. Thus, maintenance of seed longevity during storage is of prime concern and a pre-requisite for enhancing crop productivity of legumes. Seed longevity is significantly correlated with other seed quality parameters such as germination, vigor, viability and seed coat permeability that affect crop growth and development, consequently distressing crop yield. Therefore, information on genetic basis and regulatory networks associated with seed longevity, as well as molecular dissection of traits linked to longevity could help in developing crop varieties with good storability. Keeping this in view, the present review focuses towards highlighting the molecular basis of seed longevity, with special emphasis on candidate genes and proteins associated with seed longevity and their interplay with other quality parameters. Further, an attempt was made to provide information on 3D structures of various genetic loci (genes/proteins) associated to seed longevity that could facilitate in understanding the interactions taking place within the seed at molecular level. This review compiles and provides information on genetic and genomic approaches for the identification of molecular pathways and key players involved in the maintenance of seed longevity in legumes, in a holistic manner. Finally, a hypothetical fast-forward breeding pipeline has been provided, that could assist the breeders to successfully develop varieties with improved seed longevity in legumes.

Plant Recovery after Metal Stress-A Review

Contamination of the environment with metals, their adverse impact on plant performance and transmission to the human food chain through crops and vegetables are important concerns worldwide. Although the literature on metal contamination, toxicity and plant response to this stress factor is quite abundant, there are very limited reports on the phenomenon of plant recovery after metal stress. The present article reviews available literature on the recovery process examined in various plant species, in response to several metals (Al, Cd, Cu, Ni, Pb, Zn), applied at different concentrations and treatment duration. The reviewed studies have been carried out in laboratory conditions. However, it should be highlighted that although metal stress is not as transient as most of other stress factors (e.g., drought, heat, chilling), metal concentration in the soil may still decrease due to, e.g., leaching to lower soil layers or uptake by organisms. Thus, in natural conditions, plants may be subjected to post-metal-stress conditions. The review also discusses the mechanism behind efficient recovery and the impact of post metal stress on future plant performance-possible acquisition of stress memory, adaptation to unfavorable conditions and cross-tolerance towards other stress factors.

Growth and development of AtMSH7 mutants in Arabidopsis thaliana

DNA mismatch repair (MMR) is a highly conserved biological pathway that improves the fidelity of DNA replication and recombination. MMR is initiated when MutS proteins recognize mismatches and small loops of unpaired nucleotides. Arabidopsis thaliana and other plants encode MutS protein homologs (MSH) conserved among other eukaryotic organisms, but also encode an extra MSH polypeptide (MSH7). In order to better understand the role of MSH7 in vivo, a full set of phenotypic parameters that covered the development of the plant from seed imbibition to flowering and seed maturation was analyzed in A. thaliana harboring two different msh7 alleles. Plants deficient in MSH7 show statistically significant faster germination rates, longer primary roots during the juvenile vegetative phase, and higher cauline leaf and axillary and lateral inflorescence numbers compared with wild type. We also quantified number, length and area of siliques and seed number per silique. Disruption of MSH7 resulted in a higher number of smaller siliques than wild type. There were no differences in seed number per silique between genotypes. These findings suggest that mutant plant growth appears to be caused by an impaired cell cycle checkpoint that allows cell division without adequate DNA repair. This increase in proliferation activity demonstrates a functional and temporal link between DNA repair and cell cycle regulation.

Beneficial contribution of the arbuscular mycorrhizal fungus, Rhizophagus irregularis, in the protection of Medicago truncatula roots against benzo[a]pyrene toxicity

Arbuscular mycorrhizal fungi are able to improve plant establishment in polluted soils but little is known about the genes involved in the plant protection against pollutant toxicity by mycorrhization, in particular in the presence of polycyclic aromatic hydrocarbons (PAH). The present work aims at studying in both symbiotic partners, Medicago truncatula and Rhizophagus irregularis: (i) expression of genes putatively involved in PAH tolerance (MtSOD, MtPOX, MtAPX, MtGST, MtTFIIS, and MtTdp1α), (ii) activities of antioxidant (SOD, POX) and detoxification (GST) enzymes, and (iii) H₂O₂ and the heavy PAH, benzo[a]pyrene (B[a]P) accumulation. In the presence of B[a]P, whereas induction of the enzymatic activities was detected in R. irregularis and non-mycorrhizal roots as well as upregulation of the gene expressions in the non-mycorrhizal roots, downregulation of the gene expressions and decrease of enzyme activities were observed in mycorrhizal roots. Moreover, B[a]P increased H₂O₂ production in non-mycorrhizal roots and in R. irregularis but not in mycorrhizal roots. In addition, a lower B[a]P bioaccumulation in mycorrhizal roots was measured in comparison with non-mycorrhizal roots. Being less affected by pollutant toxicity, mycorrhizal roots did not activate any defense mechanism either at the gene expression regulation level or at the enzymatic level.

Systems biology and genome-wide approaches to unveil the molecular players involved in the pre-germinative metabolism: implications on seed technology traits

The pre-germinative metabolism is among the most fascinating aspects of seed biology. The early seed germination phase, or pre-germination, is characterized by rapid water uptake (imbibition), which directs a series of dynamic biochemical events. Among those are enzyme activation, DNA damage and repair, and use of reserve storage compounds, such as lipids, carbohydrates and proteins. Industrial seedling production and intensive agricultural production systems require seed stocks with high rate of synchronized germination and low dormancy. Consequently, seed dormancy, a quantitative trait related to the activation of the pre-germinative metabolism, is probably the most studied seed trait in model species and crops. Single omics, systems biology, QTLs and GWAS mapping approaches have unveiled a list of molecules and regulatory mechanisms acting at transcriptional, post-transcriptional and post-translational levels. Most of the identified candidate genes encode for regulatory proteins targeting ROS, phytohormone and primary metabolisms, corroborating the data obtained from simple molecular biology approaches. Emerging evidences show that epigenetic regulation plays a crucial role in the regulation of these mentioned processes, constituting a still unexploited strategy to modulate seed traits. The present review will provide an up-date of the current knowledge on seed pre-germinative metabolism, gathering the most relevant results from physiological, genetics, and omics studies conducted in model and crop plants. The effects exerted by the biotic and abiotic stresses and priming are also addressed. The possible implications derived from the modulation of pre-germinative metabolism will be discussed from the point of view of seed quality and technology.

Transcriptomic and physiological analyses of Medicago sativa L. roots in response to lead stress

Lead (Pb) is one of the nonessential and toxic metals that threaten the environment and human health. Medicago sativa L. is a legume with high salt tolerance and high biomass production. It is not only a globally important forage crop but is also an ideal plant for phytoremediation. However, the biological and molecular mechanisms that respond to heavy metals are still not well defined in M. sativa. In this study, de novo and strand-specific RNA-sequencing was performed to identify genes involved in the Pb stress response in M. sativa roots. A total of 415,350 unigenes were obtained from the assembled cDNA libraries, among which 5,416 were identified as significantly differentially expressed genes (DEGs) (false discovery rate < 0.005) between cDNA libraries from control and Pb-treated plants. Gene ontology and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses of the DEGs showed they mainly clustered with terms associated with binding, transport, membranes, and the pathways related to signal and energy metabolism. Moreover, a number of candidate genes included antioxidant enzymes, metal transporters, and transcription factors involved in heavy metal response were upregulated under Pb stress. Quantitative real-time PCR(qRT-PCR) validation of the expression patterns of 10 randomly selected candidate DEGs were consistent with the transcriptome analysis results. Thus, this study offers new information towards the investigation of biological changes and molecular mechanisms related to Pb stress response in plants.

Genetic Modification for Improving Seed Vigor Is Transitioning from Model Plants to Crop Plants

Although seed vigor is a complex physiological trait controlled by quantitative trait loci, technological advances in the laboratory are being translated into applications for enhancing seed vigor in crop plants. In this article, we summarize and discuss pioneering work in the genetic modification of seed vigor, especially through the over-expression of protein L-isoaspartyl methyltransferase (PIMT, EC 2.1.1.77) in seeds. The impressive success in improving rice seed vigor through the over-expression of PIMT provides a valuable reference for engineering high-vigor seeds for crop production. In recent decades, numerous genes/proteins associated with seed vigor have been identified. It is hoped that such potential candidates may be used in the development of genetically edited crops for a high and stable yield potential in crop production. This possibility is very valuable in the context of a changing climate and increasing world population.

Molecular processes induced in primed seeds-increasing the potential to stabilize crop yields under drought conditions

Environmental stress factors such as drought, salinity, temperature extremes and rising CO₂ negatively affect crop growth and productivity. Faced with the scarcity of water resources, drought is the most critical threat to world food security. This is particularly important in the context of climate change and an increasing world population. Seed priming is a very promising strategy in modern crop production management. Although it has been known for several years that seed priming can enhance seed quality and the effectiveness of stress responses of germinating seeds and seedlings, the molecular mechanisms involved in the acquisition of stress tolerance by primed seeds in the germination process and subsequent plant growth remain poorly understood. This review provides an overview of the metabolic changes modulated by priming, such as the activation of DNA repair and the antioxidant system, accumulation of aquaporins and late embryogenesis abundant proteins that contribute to enhanced drought stress tolerance. Moreover, the phenomenon of "priming memory," which is established during priming and can be recruited later when seeds or plants are exposed to stress, is highlighted.

Analysis of the transgenerational iron deficiency stress memory in Arabidopsis thaliana plants

We investigated the existence of the transgenerational memory of iron (Fe) deficiency stress, in Arabidopsis thaliana. Plants were grown under Fe deficiency/sufficiency, and so were their offspring. The frequency of somatic homologous recombination (SHR) events, of DNA strand breaks as well as the expression of the transcription elongation factor TFIIS-like gene increase when plants are grown under Fe deficiency. However, SHR frequency, DNA strand break events, and TFIIS-like gene expression do not increase further when plants are grown for more than one generation under the same stress, and furthermore, they decrease back to control values within two succeeding generations grown under control conditions, regardless of the Fe deficiency stress history of the mother plants. Seedlings produced from plants grown under Fe deficiency evolve more oxygen than control seedlings, when grown under Fe sufficiency: however, this trait is not associated with any change in the protein profile of the photosynthetic apparatus and is not transmitted to more than one generation. Lastly, plants grown for multiple generations under Fe deficiency produce seeds with greater longevity: however, this trait is not inherited in offspring generations unexposed to stress. These findings suggest the existence of multiple-step control of mechanisms to prevent a genuine and stable transgenerational transmission of Fe deficiency stress memory, with the tightest control on DNA integrity.

Seed priming: state of the art and new perspectives

Priming applied to commercial seed lots is widely used by seed technologists to enhance seed vigour in terms of germination potential and increased stress tolerance. Priming can be also valuable to seed bank operators who need improved protocols of ex situ conservation of germplasm collections (crop and native species). Depending on plant species, seed morphology and physiology, different priming treatments can be applied, all of them triggering the so-called 'pre-germinative metabolism'. This physiological process takes place during early seed imbibition and includes the seed repair response (activation of DNA repair pathways and antioxidant mechanisms), essential to preserve genome integrity, ensuring proper germination and seedling development. The review provides an overview of priming technology, describing the range of physical-chemical and biological treatments currently available. Optimised priming protocols can be designed using the 'hydrotime concept' analysis which provides the theoretical bases for assessing the relationship between water potential and germination rate. Despite the efforts so far reported to further improve seed priming, novel ideas and cutting-edge investigations need to be brought into this technological sector of agri-seed industry. Multidisciplinary translational research combining digital, bioinformatic and molecular tools will significantly contribute to expand the range of priming applications to other relevant commercial sectors, e.g. the native seed market.

Copper-mediated genotoxic stress is attenuated by the overexpression of the DNA repair gene MtTdp2α (tyrosyl-DNA phosphodiesterase 2) in Medicago truncatula plants

Our study highlights the use of the DNA repair gene MtTdp2α as a tool for improving the plant response to heavy metal stress. Tyrosyl-DNA phosphodiesterase 2 (Tdp2), involved in the removal of DNA topoisomerase II-mediated DNA damage and cell proliferation/differentiation signalling in animal cells, is still poorly characterised in plants. The Medicago truncatula lines Tdp2α-13c and Tdp2α-28 overexpressing the MtTdp2α gene and control (CTRL) line were exposed to 0.2 mM CuCl2. The DNA diffusion assay revealed a significant reduction in the percentage of necrosis caused by copper in the aerial parts of the Tdp2α-13c and Tdp2α-28 plants while neutral single cell gel electrophoresis highlighted a significant decrease in double strand breaks (DSBs), compared to CTRL. In the copper-treated Tdp2α-13c and Tdp2α-28 lines there was up-regulation (up to 4.0-fold) of genes encoding the α and β isoforms of Tyrosyl-DNA phosphodiesterase 1, indicating the requirement for Tdp1 function in the response to heavy metals. As for DSB sensing, the MtMRE11, MtRAD50 and MtNBS1 genes were also significantly up-regulated (up to 2.3-fold) in the MtTdp2α-overexpressing plants grown under physiological conditions, compared to CTRL line, and then further stimulated in response to copper. The basal antioxidant machinery was always activated in all the tested lines, as indicated by the concomitant up-regulation of MtcytSOD and MtcpSOD genes (cytosolic and chloroplastic Superoxide Dismutase), and MtMT2 (type 2 metallothionein) gene. The role of MtTdp2α gene in enhancing the plant response to genotoxic injury under heavy metal stress is discussed.

Synergistic exposure of rice seeds to different doses of γ-ray and salinity stress resulted in increased antioxidant enzyme activities and gene-specific modulation of TC-NER pathway

Recent reports have underlined the potential of gamma (γ)-rays as tools for seed priming, a process used in seed industry to increase seed vigor and to enhance plant tolerance to biotic/abiotic stresses. However, the impact of γ -rays on key aspects of plant metabolism still needs to be carefully evaluated. In the present study, rice seeds were challenged with different doses of γ -rays and grown in absence/presence of NaCl to assess the impact of these treatments on the early stages of plant life. Enhanced germination efficiency associated with increase in radicle and hypocotyl length was observed, while at later stages no increase in plant tolerance to salinity stress was evident. APX, CAT, and GR were enhanced at transcriptional level and in terms of enzyme activity, indicating the activation of antioxidant defence. The profiles of DNA damage accumulation were obtained using SCGE and the implication of TC-NER pathway in DNA damage sensing and repair mechanisms is discussed. OsXPB2, OsXPD, OsTFIIS, and OsTFIIS-like genes showed differential modulation in seedlings and plantlets in response to γ -irradiation and salinity stress. Altogether, the synergistic exposure to γ -rays and NaCl resulted in enhanced oxidative stress and proper activation of antioxidant mechanisms, thus being compatible with plant survival.

Plant hormone signaling and modulation of DNA repair under stressful conditions

The role played by phytohormone signaling in the modulation of DNA repair gene and the resulting effects on plant adaptation to genotoxic stress are poorly investigated. Information has been gathered using the Arabidopsis ABA (abscisic acid) overly sensitive mutant abo4-1, defective in the DNA polymerase ε function that is required for DNA repair and recombination. Similarly, phytohormone-mediated regulation of the Ku genes, encoding the Ku heterodimer protein involved in DNA repair, cell cycle control and telomere homeostasis has been demonstrated, highlighting a scenario in which hormones might affect genome stability by modulating the frequency of homologous recombination, favoring plant adaptation to genotoxic stress. Within this context, the characterisation of Arabidopsis AtKu mutants allowed disclosing novel connections between DNA repair and phytohormone networks. Another intriguing aspect deals with the emerging correlation between plant defense response and the mechanisms responsible for genome stability. There is increasing evidence that systemic acquired resistance (SAR) and homologous recombination share common elements represented by proteins involved in DNA repair and chromatin remodeling. This hypothesis is supported by the finding that volatile compounds, such as methyl salicylate (MeSA) and methyl jasmonate (MeJA), participating in the plant-to-plant communication can trigger genome instability in response to genotoxic stress agents. Phytohormone-mediated control of genome stability involves also chromatin remodeling, thus expanding the range of molecular targets. The present review describes the most significant advances in this specific research field, in the attempt to provide a better comprehension of how plant hormones modulate DNA repair proteins as a function of stress.

γ irradiation with different dose rates induces different DNA damage responses in Petunia x hybrida cells

In plants, there is evidence that different dose rate exposures to gamma (γ) rays can cause different biological effects. The dynamics of DNA damage accumulation and molecular mechanisms that regulate recovery from radiation injury as a function of dose rate are poorly explored. To highlight dose-rate dependent differences in DNA damage, single cell gel electrophoresis was carried out on regenerating Petunia x hybrida leaf discs exposed to LDR (total dose 50 Gy, delivered at 0.33 Gy min(-1)) and HDR (total doses 50 and 100 Gy, delivered at 5.15 Gy min(-1)) γ-ray in the 0-24h time period after treatments. Significant fluctuations of double strand breaks and different repair capacities were observed between treatments in the 0-4h time period following irradiation. Dose-rate-dependent changes in the expression of the PhMT2 and PhAPX genes encoding a type 2 metallothionein and the cytosolic isoform of ascorbate peroxidase, respectively, were detected by Quantitative RealTime-Polymerase Chain Reaction. The PhMT2 and PhAPX genes were significantly up-regulated (3.0- and 0.7-fold) in response to HDR. The results are discussed in light of the potential practical applications of LDR-based treatments in mutation breeding.

DNA profiling, telomere analysis and antioxidant properties as tools for monitoring ex situ seed longevity

BACKGROUND AND AIMS

The germination test currently represents the most used method to assess seed viability in germplasm banks, despite the difficulties caused by the occurrence of seed dormancy. Furthermore, seed longevity can vary considerably across species and populations from different environments, and studies related to the eco-physiological processes underlying such variations are still limited in their depth. The aim of the present work was the identification of reliable molecular markers that might help in monitoring seed deterioration.

METHODS

Dry seeds were subjected to artificial ageing and collected at different time points for molecular/biochemical analyses. DNA damage was measured using the RAPD (random amplified polymorphic DNA) approach while the seed antioxidant profile was obtained using both the DPPH (1,1-diphenyl, 2-picrylhydrazyl) assay and the Folin-Ciocalteu reagent method. Electron paramagnetic resonance (EPR) provided profiles of free radicals. Quantitative real-time polymerase chain reaction (QRT-PCR) was used to assess the expression profiles of the antioxidant genes MT2 (type 2 metallothionein) and SOD (superoxide dismutase). A modified QRT-PCR protocol was used to determine telomere length.

KEY RESULTS

The RAPD profiles highlighted different capacities of the two Silene species to overcome DNA damage induced by artificial ageing. The antioxidant profiles of dry and rehydrated seeds revealed that the high-altitude taxon Silene acaulis was characterized by a lower antioxidant specific activity. Significant upregulation of the MT2 and SOD genes was observed only in the rehydrated seeds of the low-altitude species. Rehydration resulted in telomere lengthening in both Silene species.

CONCLUSIONS

Different seed viability markers have been selected for plant species showing inherent variation of seed longevity. RAPD analysis, quantification of redox activity of non-enzymatic antioxidant compounds and gene expression profiling provide deeper insights to study seed viability during storage. Telomere lengthening is a promising tool to discriminate between short- and long-lived species.

Spectroscopic determination of the toxicity, absorption, reduction, and translocation of Cr(VI) in two Magnoliopsida species

Hexavalent chromium is a contaminant highly mobile in the environment that is toxic for plants at low concentrations. In this work, the physiological response of Convolvulus arvensis and Medicago truncatula plants to Cr(VI) treatments was compared. C. arvensis is a potential Cr hyperaccumulator well adapted to semiarid conditions that biotransform Cr(VI) to the less toxic Cr(III). M. truncatula is a model plant well adapted to semiarid conditions with a well studied genetic response to heavy metal stress. The results demonstrated that C. arvensis is more tolerant to Cr toxicity and has a higher Cr translocation to the leaves. The inductively coupled plasma optical emission spectroscopy results showed that C. arvensis plants treated with 10 mg Cr(VI) L(-1) accumulated 1512, 210, and 131 mg Cr kg(-1) in roots, stems, and leaves, respectively. While M. truncatula plants treated with the same Cr(VI) concentration accumulated 1081, 331, and 44 (mg Cr kg(-1)) in roots, stems, and leaves, respectively. Enzymatic assays demonstrated that Cr(VI) decreased ascorbate peroxidase activity and increased catalase activity in M. truncatula, while an opposite response was found in C. arvensis. The x-ray absorption spectroscopy studies showed that both plant species reduced Cr(VI) to the less toxic Cr(III).

Understanding the molecular pathways associated with seed vigor

Farmers and growers are constantly looking for high quality seeds able to ensure uniform field establishment and increased production. Seed priming is used to induce pre-germinative metabolism and then enhance germination efficiency and crop yields. It has been hypothesized that priming treatments might also improve stress tolerance in germinating seeds, leaving a sort of 'stress memory'. However, the molecular bases of priming still need to be clarified and the identification of molecular indicators of seed vigor is nowadays a relevant goal for the basic and applied research in seed biology. It is generally acknowledged that enhanced seed vigor and successful priming depend on DNA repair mechanisms, activated during imbibition. The complexity of the networks of DNA damage control/repair functions has been only partially elucidated in plants and the specific literature that address seeds remains scanty. The DNA repair pathways hereby described (Nucleotide and Base Excision Repair, Non-Homologous End Joining, Homologous Recombination) play specific roles, all of them being critical to ensure genome stability. This review also focuses on some novel regulatory mechanisms of DNA repair (chromatin remodeling and small RNAs) while the possible use of telomere sequences as markers of aging in seed banks is discussed. The significant contribution provided by Electron Paramagnetic Resonance in elucidating the kinetics of seed aging, in terms of free radical profiles and membrane integrity is reported.

New insights on the barrel medic MtOGG1 and MtFPG functions in relation to oxidative stress response in planta and during seed imbibition

In plants, 8-oxoguanine DNA glycosylase/lyase (OGG1) and formamidopyrimidine-DNA glycosylase (FPG) play similar roles within the base excision repair (BER) pathway involved in the removal of oxidized bases, e.g. 7,8-dihydro-8-oxoguanine (8-oxo-dG) and formamidopyrimidine (FAPy) lesions. To date, it is not clear why plants have retained both the OGG1 and FPG functions. In the present work, we have investigated the possible roles played in planta by MtOGG1 and MtFPG genes from Medicago truncatula Gaertn. (barrel medic). Bioinformatic investigation revealed the presence of putative mitochondrial and nuclear localization signals in the MtOGG1 and MtFPG amino acid sequences, respectively, thus suggesting for different subcellular fates. The expression profiles of both genes were evaluated by Quantitative Real-Time PCR (QRT-PCR) in barrel medic plantlets grown in vitro under oxidative stress conditions induced by copper (CuCl(2), 0.05, 0.1 and 0.2 mM) and polyethylene glycol (PEG6000, 50, 100 and 150 g L(-1)). The MtOGG1 and MtFPG genes were up-regulated in response to stress agents, at different levels, depending on treatment and tissue. As for copper, MtOGG1 showed significant up-regulation (up to 1.2- and 1.7-fold) only in roots while the MtFPG mRNA significantly increased (up to 1.3- and 2.8-fold, respectively) in roots and aerial parts. In response to PEG, the MtOGG1 expression was significantly enhanced in aerial parts (up to 1.3-fold) while the MtFPG showed significant (1.2-fold) up-regulation in roots. The expression profiles of MtOGG1 and MtFPG genes were also evaluated during seed imbibition, a physiological process which is characterized by Reactive Oxygen Species (ROS) accumulation and requires active DNA repair.

Genotoxic stress and DNA repair in plants: emerging functions and tools for improving crop productivity

Crop productivity is strictly related to genome stability, an essential requisite for optimal plant growth/development. Genotoxic agents (e.g., chemical agents, radiations) can cause both chemical and structural damage to DNA. In some cases, they severely affect the integrity of plant genome by inducing base oxidation, which interferes with the basal processes of replication and transcription, eventually leading to cell death. The cell response to oxidative stress includes several DNA repair pathways, which are activated to remove the damaged bases and other lesions. Information concerning DNA repair in plants is still limited, although results from gene profiling and mutant analysis suggest possible differences in repair mechanisms between plants and other eukaryotes. The present review focuses on the base- and nucleotide excision repair (BER, NER) pathways, which operate according to the most common DNA repair rule (excision of damaged bases and replacement by the correct nucleotide), highlighting the most recent findings in plants. An update on DNA repair in organelles, chloroplasts and mitochondria is also provided. Finally, it is generally acknowledged that DNA repair plays a critical role during seed imbibition, preserving seed vigor. Despite this, only a limited number of studies, described here, dedicated to seeds are currently available.