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

Seed Longevity and Ageing: A Review on Physiological and Genetic Factors with an Emphasis on Hormonal Regulation

Upon storage, seeds inevitably age and lose their viability over time, which determines their longevity. Longevity correlates with successful seed germination and enhancing this trait is of fundamental importance for long-term seed storage (germplasm conservation) and crop improvement. Seed longevity is governed by a complex interplay between genetic factors and environmental conditions experienced during seed development and after-ripening that will shape seed physiology. Several factors have been associated with seed ageing such as oxidative stress responses, DNA repair enzymes, and composition of seed layers. Phytohormones, mainly abscisic acid, auxins, and gibberellins, have also emerged as prominent endogenous regulators of seed longevity, and their study has provided new regulators of longevity. Gaining a thorough understanding of how hormonal signalling genes and pathways are integrated with downstream mechanisms related to seed longevity is essential for formulating strategies aimed at preserving seed quality and viability. A relevant aspect related to research in seed longevity is the existence of significant differences between results depending on the seed equilibrium relative humidity conditions used to study seed ageing. Hence, this review delves into the genetic, environmental and experimental factors affecting seed ageing and longevity, with a particular focus on their hormonal regulation. We also provide gene network models underlying hormone signalling aimed to help visualize their integration into seed longevity and ageing. We believe that the format used to present the information bolsters its value as a resource to support seed longevity research for seed conservation and crop improvement.

Genomic Identification and Expression Profiling of Lesion Simulating Disease Genes in Alfalfa (Medicago sativa) Elucidate Their Responsiveness to Seed Vigor

Seed aging, a common physiological phenomenon during forage seed storage, is a crucial factor contributing to a loss of vigor, resulting in delayed seed germination and seedling growth, as well as limiting the production of hay. Extensive bodies of research are dedicated to the study of seed aging, with a particular focus on the role of the production and accumulation of reactive oxygen species (ROS) and the ensuing oxidative damage during storage as a primary cause of decreases in seed vigor. To preserve optimal seed vigor, ROS levels must be regulated. The excessive accumulation of ROS can trigger programmed cell death (PCD), which causes the seed to lose vigor permanently. LESION SIMULATING DISEASE (LSD) is one of the proteins that regulate PCD, encodes a small C2C2 zinc finger protein, and plays a molecular function as a transcriptional regulator and scaffold protein. However, genome-wide analysis of LSD genes has not been performed for alfalfa (Medicago sativa), as one of the most important crop species, and, presently, the molecular regulation mechanism of seed aging is not clear enough. Numerous studies have also been unable to explain the essence of seed aging for LSD gene regulating PCD and affecting seed vigor. In this study, we obtained six MsLSD genes in total from the alfalfa (cultivar Zhongmu No. 1) genome. Phylogenetic analysis demonstrated that the MsLSD genes could be classified into three subgroups. In addition, six MsLSD genes were unevenly mapped on three chromosomes in alfalfa. Gene duplication analysis demonstrated that segmental duplication was the key driving force for the expansion of this gene family during evolution. Expression analysis of six MsLSD genes in various tissues and germinating seeds presented their different expressions. RT-qPCR analysis revealed that the expression of three MsLSD genes, including MsLSD2, MsLSD5, and MsLSD6, was significantly induced by seed aging treatment, suggesting that they might play an important role in maintaining seed vigor. Although this finding will provide valuable insights into unveiling the molecular mechanism involved in losing vigor and new strategies to improve alfalfa seed germinability, additional research must comprehensively elucidate the precise pathways through which the MsLSD genes regulate seed vigor.

Transcription factor TERF1 promotes seed germination through HEXOKINASE 1 (HXK1)-mediated signaling pathway

Seed germination, a vital process for plant growth and development, is regulated by ethylene. Previously, we showed that Tomato Ethylene Responsive Factor 1 (TERF1), an ethylene-responsive factor (ERF) transcription factor, could significantly promote seed germination by increasing glucose content. As glucose can function as a signaling molecule to regulate plant growth and development through HEXOKINASE 1 (HXK1), we aim to illustrate how TERF1 promotes seed germination through the HXK1-mediated signaling pathway. We showed that seeds overexpressing TERF1 exhibited more resistance to N-acetylglucosamine (NAG), an inhibitor of the HXK1- mediated signaling pathway. We identified genes regulated by TERF1 through HXK1 based on transcriptome analysis. Gene expression and phenotype analysis demonstrated that TERF1 repressed the ABA signaling pathway through HXK1, which promoted germination through activating the plasma membrane (PM) H+-ATPase. TERF1 also alleviated the endoplasmic reticulum (ER) stress to accelerate germination by maintaining reactive oxygen species (ROS) homeostasis through HXK1. Our findings provide new insights into the mechanism regulated by ethylene through the glucose-HXK1 signaling pathway during seed germination.

Comparative Seeds Storage Transcriptome Analysis of Astronium fraxinifolium Schott, a Threatened Tree Species from Brazil

Astronium fraxinifolium Schott (Anacardiaceae), also known as a 'gonçalo-alves', is a tree of the American tropics, with distribution in Mexico, part of Central America, Argentina, Bolivia, Brazil and Paraguay. In Brazil it is an endangered species that occurs in the Cerrado, Caatinga and in the Amazon biomes. In support of ex situ conservation, this work aimed to study two accessions with different longevity (p50) of A. fraxinifolium collected from two different geographic regions, and to evaluate the transcriptome during aging of the seeds in order to identify genes related to seed longevity. Artificial ageing was performed at a constant temperature of 45 °C and 60% relative humidity. RNA was extracted from 100 embryonic axes exposed to control and aging conditions for 21 days. The transcriptome analysis revealed differentially expressed genes such as Late Embryogenesis Abundant (LEA) genes, genes involved in the photosystem, glycine rich protein (GRP) genes, and several transcription factors associated with embryo development and ubiquitin-conjugating enzymes. Thus, these results contribute to understanding which genes play a role in seed ageing, and may serve as a basis for future functional characterization of the seed aging process in A. fraxinifolium.

Volatile signature indicates viability of dormant orthodox seeds

All seeds eventually die even under optimal storage conditions. The moment of viability loss is difficult to predict and detect. In order to differentiate between dead and viable dormant orthodox seeds, GC-MS analysis was used to non-invasively evaluate the volatile signature of seeds of Pyrus communis L. and Sorbus aucuparia L. Dormant seeds are capable of extended metabolic depression. However, their low metabolic rate remains largely unquantified, and there are no measurements of metabolites, i.e. volatile organic compounds (VOC) for physiologically dormant seeds during storage. Therefore, to address this issue, seeds were stored at a broad range of moisture content (MC) ranging from 2 to 30% under cryogenic (-196°C), cool (5°C) and elevated (40°C) temperatures. Volatile emission was highly dependent on seed MC and storage temperature and was higher under conditions associated with seed viability loss. However, changes in the emission of volatiles entrapped in seeds and released during 24 h after storage were detected for all conditions, providing insight into the processes occurring in dry dormant seeds. Among the 36 volatiles identified, three (acetaldehyde, ethanol, ethyl acetate) were highly correlated with seed germinability and show potential for the non-invasive screening of viability. Significantly, all three VOC are derived mostly from glycolysis and peroxidation and were detected even under very low moisture and temperature storage conditions. This is the first study to report on VOC accumulation and emission from physiologically dormant seeds and provide a broader view into their viability.

A Critical Review of the Current Global Ex Situ Conservation System for Plant Agrobiodiversity. II. Strengths and Weaknesses of the Current System and Recommendations for Its Improvement

In this paper, we review gene bank operations that have an influence on the global conservation system, with the intention to identify critical aspects that should be improved for optimum performance. We describe the role of active and base collections and the importance of linking germplasm conservation and use, also in view of new developments in genomics and phenomics that facilitate more effective and efficient conservation and use of plant agrobiodiversity. Strengths, limitations, and opportunities of the existing global ex situ conservation system are discussed, and measures are proposed to achieve a rational, more effective, and efficient global system for germplasm conservation and sustainable use. The proposed measures include filling genetic and geographic gaps in current ex situ collections; determining unique accessions at the global level for long-term conservation in virtual base collections; intensifying existing international collaborations among gene banks and forging collaborations with the botanic gardens community; increasing investment in conservation research and user-oriented supportive research; improved accession-level description of the genetic diversity of crop collections; improvements of the legal and policy framework; and oversight of the proposed network of global base collections.

Exogenous antioxidants on quality of cabbage seeds

Abstract During seed germination there is production of reactive oxygen species, which, in a controlled way, are important to cell signaling and protection against pathogens, but, in excess, impair germination. Therefore, the objective of this study was to assess the action of different compounds on antioxidant mechanisms and enzymatic activation in cabbage seeds. Compounds like kojic acid, thymol and tyrosol were used to imbibe the cabbage seeds together with distilled water, and a control treatment without imbibition was used as well, with subsequent assessment by means of germination test, endosperm rupture, vigor, radicle protrusion, and assessment of seedling biochemical analyses by the activity of enzymes ascorbate peroxidase, catalase, superoxide dismutase and α-amylase. Data were subjected to analysis of variance and to the LSD means comparison test. Seeds treated with tyrosol presented higher results on the rupture of the endosperm, germination and vigor, and root development increased with use antioxidants. For the activity of antioxidant enzymes in seedlings, only kojic acid showed increase in the superoxide dismutase activity. There was also a reduction in the catalase activity with the use of thymol and tyrosol compounds compared to dry-seed assessments. After tyrosol treatment, ascorbate peroxidase enzyme was not detected, and water-imbibed seeds showed higher α-amylase activity. The use of antioxidant compounds has beneficial effects on cabbage seeds, and soaking with tyrosol led to better physiological quality, with activation of antioxidant defense mechanisms during germination.

Why Seed Physiology Is Important for Genebanking

Genebank management is a field in its own right; it is multifaceted, requiring a diverse set of skills and knowledge. Seed physiology is one area that is critical to the successful operation of seed genebanks, requiring understanding of seed quality during development and maturation, seed dormancy and germination, and seed longevity in storage of the target species. Careful management of the workflow between these activities, as seeds move from harvest to storage, and the recording and management of all relevant associated data, is key to ensuring the effective conservation of plant genetic resources. This review will discuss various aspects of seed physiology that genebank managers should be aware of, to ensure appropriate decisions are made about the handling and management of their seed collections.

Genetic and Epigenetic Stability in Rye Seeds under Different Storage Conditions: Ageing and Oxygen Effect

Seed ageing is a complex process and can be described as the loss of viability or quality with time. It is important to elucidate whether genetic and epigenetic stability is altered in stored seeds and in seedlings produced from them. Non-stored and stored rye seeds at different stages of ageing were compared, as well as the seedlings obtained from them. Seeds were stored at 35 °C and 15% water content, under vacuum or air atmosphere. DNA of seeds and seedlings was isolated at three stages of the deterioration curve: P75 (13 days), P20 (29 days), and P0 (36 days). Genetic stability was assessed by RAPD technique, and epigenetic changes by MSAP markers. While seeds showed genetic stability after storage, the similarity of seedlings obtained from seeds stored for 29 days was lower (95%) when compared to seedlings from control seeds. Epigenetic changes were between 15% and 30% (both de novo methylation and demethylation) in the stored seeds compared to control seeds, with no differences between 13 and 29 days of storage with either air or vacuum atmospheres. In seedlings, epigenetic changes significantly increased with storage time. In conclusion, ageing increased epigenetic instability in both seeds and seedlings, when compared to controls.

Heteromorphic seeds of wheat wild relatives show germination niche differentiation

Crop wild relatives are fundamental genetic resources for crop improvement. Wheat wild relatives often produce heteromorphic seeds that differ in morphological and physiological traits. Several Aegilops and Triticum species possess, within the same spikelet, a dimorphic seed pair, with one seed being larger than the other. A comprehensive analysis is needed to understand which traits are involved in seed dimorphism and if these aspects of variation in dimorphic pairs are functionally related. To this end, dispersal units of Triticum urartu and five Aegilops species were X-rayed and the different seed morphs weighed. Germination tests were carried out on seeds, both dehulled and left in their dispersal units. Controlled ageing tests were performed to detect differences in seed longevity among seed morphs, and the antioxidant profile was assessed in terms of antioxidant compounds equipment and expression of selected antioxidant genes. We used PCA to group seed morphs sharing similar patterns of germination traits, longevity estimates and antioxidant profile. Different seed morphs differed significantly in terms of mass, final germination, germination timing, longevity estimates and antioxidant profile in most of the tested species. Small seeds germinated slower, had lower germination when left in their dispersal units, a higher antioxidant potential and were longer-lived than large seeds. The antioxidant gene expression varied between morphs, with different patterns across species but not clearly reflecting the phenotypic observations. The results highlight different trait trade-offs in dimorphic seeds of Aegilops and T. urartu, affecting their germination phenology and longevity, thereby resulting in recruitment niche differentiation.

Hydropriming and Biopriming Improve Medicago truncatula Seed Germination and Upregulate DNA Repair and Antioxidant Genes

Seed germination is a critical parameter for the successful development of sustainable agricultural practices. While seed germination is impaired by environmental constraints emerging from the climate change scenario, several types of simple procedures, known as priming, can be used to enhance it. Seed priming is defined as the process of regulating seed germination by managing a series of parameters during the initial stages of germination. Hydropriming is a highly accessible and economic technique that involves soaking of seeds in water followed by drying. Biopriming refers to the inoculation of seeds with beneficial microorganism. The present study aims to investigate whether hydropriming and biopriming could enhance seed germination. Thereby, the germination of Medicago truncatula seeds exposed to hydropriming and/or Bacillus spp. isolates was monitored for two-weeks. The seeds were sown in trays containing two types of in situ agricultural soils collected from Northern India (Karsara, Varanasi). This region is believed to be contaminated by solid waste from a nearby power plant. Phenotypic parameters had been monitored and compared to find the most appropriate combination of treatments. Additionally, qRT-PCR was used to evaluate the expression levels of specific genes used as molecular indicators of seed quality. The results show that, while hydropriming significantly enhanced seed germination percentage, biopriming resulted in improved seedling development, represented by increased biomass rather than seedling length. At a molecular level, this is reflected by the upregulation of genes involved in DNA damage repair and antioxidant defence. In conclusion, hydropriming and biopriming are efficient to improve seed germination and seedling establishment in soils collected from damaged sites of Northern India; this is reflected by morphological parameters and molecular hallmarks of seed quality.

Aspergillus fumigatus and Aspergillosis in 2019

Aspergillus fumigatus is a saprotrophic fungus; its primary habitat is the soil. In its ecological niche, the fungus has learned how to adapt and proliferate in hostile environments. This capacity has helped the fungus to resist and survive against human host defenses and, further, to be responsible for one of the most devastating lung infections in terms of morbidity and mortality. In this review, we will provide (i) a description of the biological cycle of A. fumigatus; (ii) a historical perspective of the spectrum of aspergillus disease and the current epidemiological status of these infections; (iii) an analysis of the modes of immune response against Aspergillus in immunocompetent and immunocompromised patients; (iv) an understanding of the pathways responsible for fungal virulence and their host molecular targets, with a specific focus on the cell wall; (v) the current status of the diagnosis of different clinical syndromes; and (vi) an overview of the available antifungal armamentarium and the therapeutic strategies in the clinical context. In addition, the emergence of new concepts, such as nutritional immunity and the integration and rewiring of multiple fungal metabolic activities occurring during lung invasion, has helped us to redefine the opportunistic pathogenesis of A. fumigatus.

Loss of genetic integrity in artificially aged seed lots of rice (Oryza sativa L.) and common bean (Phaseolus vulgaris L.)

Loss of genetic integrity can occur during the long-term conservation of seeds. We have studied these effects in seeds of rice (Oryza sativa L.) and common bean (Phaseolus vulgaris L.) exposed to accelerated aging (elevated temperature and moisture) conditions. Tests of first count, germination, and germination speed index were performed to measure physiological quality; cytogenetic tests and comet assay were used to evaluate genetic integrity. With aging, we observed a decrease in mitotic index and an increase in the frequency of chromosomal alterations in root cells of imbibed seeds, as well as increased DNA damage (comet assay) in dry and imbibed seed embryos of both species. The comet assay can be a useful technique for measuring genetic integrity in seed conservation programs.

Hydrogen peroxide signaling integrates with phytohormones during the germination of magnetoprimed tomato seeds

Seeds of tomato were magnetoprimed at 100 mT for 30 min followed by imbibition for 12 and 24 h, respectively, at 20 °C, to examine the biochemical and molecular changes involved in homeostasis of hydrogen peroxide (H₂O₂) and its signaling associated with hormone interactions for promoting vigor. The relative transcript profiles of genes involved in the synthesis of H₂O₂ like Cu-amine oxidase (AO), receptor for activated C kinase 1 (RACK1) homologue (ArcA2) and superoxide dismutase (SOD1 and SOD9) increased in magnetoprimed tomato seeds as compared to unprimed ones with a major contribution (21.7-fold) from Cu-amine oxidase. Amongst the genes involved in the scavenging of H₂O₂ i.e, metallothionein (MT1, MT3 and MT4), catalase (CAT1) and ascorbate peroxidase (APX1 and APX2), MT1 and MT4 exhibited 14.4- and 15.4-fold increase respectively, in the transcript abundance, in primed seeds compared to the control. We report in our study that metallothionein and RACK1 play a vital role in the reactive oxygen species mediated signal transduction pathway to enhance the speed of germination in magnetoprimed tomato seeds. Increased enzymatic activities of catalase and ascorbate peroxidase were observed at 12 h of imbibition in the magnetoprimed seeds indicating their roles in maintaining H₂O₂ levels in the primed seeds. The upregulation of ABA 8′-hydroxylase and GA3 oxidase1 genes eventually, lead to the decreased abscisic acid/gibberellic acid (ABA/GA₃) ratio in the primed seeds, suggesting the key role of H₂O₂ in enhancing the germination capacity of magnetoprimed tomato seeds.

Metabolic and gene expression hallmarks of seed germination uncovered by sodium butyrate in Medicago truncatula

Because high-quality seeds are essential for successful crop production in challenging environments, understanding the molecular bases of seed vigour will lead to advances in seed technology. Histone deacetylase inhibitors, promoting histone hyperacetylation, are used as tools to explore aspects still uncovered of the abiotic stress response in plants. The aim of this work was to investigate novel signatures of seed germination in Medicago truncatula, using the histone deacetylase inhibitor sodium butyrate (NaB) as stress agent. NaB-treated and untreated seeds collected at 2 and 8 hr of imbibition and at the radicle protrusion stage underwent molecular phenotyping and nontargeted metabolome profiling. Quantitative enrichment analysis revealed the influence of NaB on seed nucleotide, amino acid, lipid, and carbohydrate metabolism. Up-regulation of antioxidant and polyamine biosynthesis genes occurred in response to NaB. DNA damage evidenced in NaB-treated seeds correlated with up-regulation of base-excision repair genes. Changes in N¹ -methyladenosine and N¹ -methylguanine were associated with up-regulation of MtALKBH1 (alkylation repair homolog) gene. N² ,N² -dimethylguanosine and 5-methylcytidine, tRNA modifications involved in the post-transcriptional regulation of DNA damage response, were also accumulated in NaB-treated seeds at the radicle protrusion stage. The observed changes in seed metabolism can provide novel potential metabolic hallmarks of germination.

Improving soil seed bank management

Problems associated with simplified weed management motivate efforts for diversification. Integrated weed management uses the fundamentals of weed biology and applied ecology to provide a framework for diversified weed management programs; the soil seed bank comprises a necessary part of this framework. By targeting seeds, growers can inhibit the propagule pressure on which annual weeds depend for agricultural invasion. Some current management practices affect weed seed banks, such as crop rotation and tillage, but these tools are often used without specific intention to manage weed seeds. Difficulties quantifying the weed seed bank, understanding seed bank phenology, and linking seed banks to emerged weed communities challenge existing soil seed bank management practices. Improved seed bank quantification methods could include DNA profiling of the soil seed bank, mark and recapture, or 3D LIDAR mapping. Successful and sustainable soil seed bank management must constrain functionally diverse and changing weed communities. Harvest weed seed controls represent a step forward, but over-reliance on this singular technique could make it short-lived. Researchers must explore tools inspired by other pest management disciplines, such as gene drives or habitat modification for predatory organisms. Future weed seed bank management will combine multiple complementary practices that enhance diverse agroecosystems. © 2018 Society of Chemical Industry.

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.

The Seed Repair Response during Germination: Disclosing Correlations between DNA Repair, Antioxidant Response, and Chromatin Remodeling in Medicago truncatula

This work provides novel insights into the effects caused by the histone deacetylase inhibitor trichostatin A (TSA) during Medicago truncatula seed germination, with emphasis on the seed repair response. Seeds treated with H₂O and TSA (10 and 20 μM) were collected during imbibition (8 h) and at the radicle protrusion phase. Biometric data showed delayed germination and impaired seedling growth in TSA-treated samples. Comet assay, performed on radicles at the protrusion phase and 4-days old M. truncatula seedlings, revealed accumulation of DNA strand breaks upon exposure to TSA. Activation of DNA repair toward TSA-mediated genotoxic damage was evidenced by the up-regulation of MtOGG1(8-OXOGUANINE GLYCOSYLASE/LYASE) gene involved in the removal of oxidative DNA lesions, MtLIGIV(LIGASE IV) gene, a key determinant of seed quality, required for the rejoining of DNA double strand breaks and TDP(TYROSYL-DNA PHOSPHODIESTERASE) genes encoding the multipurpose DNA repair enzymes tyrosyl-DNA phosphodiesterases. Since radical scavenging can prevent DNA damage, the specific antioxidant activity (SAA) was measured by DPPH (1,1-diphenyl-2-picrylhydrazyl) and Folin-Ciocalteu reagent assays. Fluctuations of SAA were observed in TSA-treated seeds/seedlings concomitant with the up-regulation of antioxidant genes MtSOD(SUPEROXIDE DISMUTASE, MtAPX(ASCORBATE PEROXIDASE) and MtMT2(TYPE 2 METALLOTHIONEIN). Chromatin remodeling, required to facilitate the access of DNA repair enzymes at the damaged sites, is also part of the multifaceted seed repair response. To address this aspect, still poorly explored in plants, the MtTRRAP(TRANSFORMATION/TRANSACTIVATION DOMAIN-ASSOCIATED PROTEIN) gene was analyzed. TRRAP is a transcriptional adaptor, so far characterized only in human cells where it is needed for the recruitment of histone acetyltransferase complexes to chromatin during DNA repair. The MtTRRAP gene and the predicted interacting partners MtHAM2 (HISTONE ACETYLTRANSFERASE OF THE MYST FAMILY) and MtADA2A (TRANSCRIPTIONAL ADAPTOR) showed tissue- and dose-dependent fluctuations in transcript levels. PCA (Principal Component Analysis) and correlation analyses suggest for a new putative link between DNA repair and chromatin remodeling that involves MtOGG1 and MtTRRAP genes, in the context of seed germination. Interesting correlations also connect DNA repair and chromatin remodeling with antioxidant players and proliferation markers.

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 birth to death: dual functions of reactive oxygen species in seed physiology

BACKGROUND

Reactive oxygen species (ROS) are considered to be detrimental to seed viability. However, recent studies have demonstrated that ROS have key roles in seed germination particularly in the release of seed dormancy and embryogenesis, as well as in protection from pathogens.

SCOPE

This review considers the functions of ROS in seed physiology. ROS are present in all cells and at all phases of the seed life cycle. ROS accumulation is important in breaking seed dormancy, and stimulating seed germination and protection from pathogens. However, excessive ROS accumulation can be detrimental. Therefore, knowledge of the mechanisms by which ROS influence seed physiology will provide insights that may not only allow the development of seed quality markers but also help us understand how dormancy can be broken in several recalcitrant species.

CONCLUSIONS

Reactive oxygen species have a dual role in seed physiology. Understanding the relative importance of beneficial and detrimental effects of ROS provides great scope for the improvement and maintenance of seed vigour and quality, factors that may ultimately increase crop yields.

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.

Towards a better monitoring of seed ageing under ex situ seed conservation

Long-term conservation of 7.4 million ex situ seed accessions held in agricultural genebanks and botanic gardens worldwide is a challenging mission for human food security and ecosystem services. Recent advances in seed biology and genomics may have opened new opportunities for effective management of seed germplasm under long-term storage. Here, we review the current development of tools for assessing seed ageing and research advances in seed biology and genomics, with a focus on exploring their potential as better tools for monitoring of seed ageing. Seed ageing is found to be associated with the changes reflected in reactive oxygen species and mitochondria-triggered programmed cell deaths, expression of antioxidative genes and DNA and protein repair genes, chromosome telomere lengths, epigenetic regulation of related genes (microRNA and methylation) and altered organelle and nuclear genomes. Among these changes, the signals from mitochondrial and nuclear genomes may show the most promise for use in the development of tools to predict seed ageing. Non-destructive and non-invasive analyses of stored seeds through calorimetry or imaging techniques are also promising. It is clear that research into developing advanced tools for monitoring seed ageing to supplement traditional germination tests will be fruitful for effective conservation of ex situ seed germplasm.

Functional analysis of the new barley gene HvKu80 indicates that it plays a key role in double-strand DNA break repair and telomere length regulation

Genotoxic stress causes a reduced stability of the plant genome and has a detrimental effect on plant growth and productivity. Double-strand breaks (DSBs) are the most harmful of all DNA lesions because they cause the loss of genetic information on both strands of the DNA helix. In the presented study the coding and genomic sequences of the HvKu80 gene were determined. A mutational analysis of two fragments of HvKu80 using TILLING (Targeting Induced Local Lesions IN Genomes) allowed 12 mutations to be detected, which resulted in identification of 11 alleles. Multidirectional analyses demonstrated that the HvKu80 gene is involved in the elimination of DSBs in Hordeum vulgare. The barley mutants carrying the identified ku80.c and ku80.j alleles accumulated bleomycin-induced DSBs to a much greater extent than the parent cultivar 'Sebastian'. The altered reaction of the mutants to DSB-inducing agent and the kinetics of DNA repair in these genotypes are associated with a lower expression level of the mutated gene. The study also demonstrated the significant role of the HvKu80 gene in the regulation of telomere length in barley.

Alleles of newly identified barley gene HvPARP3 exhibit changes in efficiency of DNA repair

Genome integrity is constantly challenged by endo- and exogenous DNA-damaging factors. The influence of genotoxic agents causes an accumulation of DNA lesions, which if not repaired, become mutations that can cause various abnormalities in a cell metabolism. The main pathway of DSB repair, which is based on non-homologous recombination, is canonical non-homologous end joining (C-NHEJ). It has been shown that this mechanism is highly conserved in both Pro- and Eukaryotes. The mechanisms that underlie DSB repair through C-NHEJ have mainly been investigated in mammalian systems, and therefore our knowledge about this process is much more limited as far as plants, and crop plants in particular, are concerned. Recent studies have demonstrated that PARP3 is an important response factor to the presence of DSB in a genome. The aims of this study were to identify the sequence of the barley PARP3 gene, to perform a mutational analysis of the sequence that was identified using the TILLING (Targeting Induced Local Lesions IN Genomes) method and to phenotype the mutants that were identified through their exposure to mutagenic treatment with the DSB-inducing chemical--bleomycin. A functional analysis led to the identification of a series of parp3 alleles. The mutants were characterized using several different approaches, including quantifying the DSB and γH2AX foci, which validated the function of the HvPARP3 gene in DSB repair in barley. The potential involvement of the HvPARP3 gene in the regulation of telomere length in barley was also analyzed.

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.

Environmentally induced transgenerational changes in seed longevity: maternal and genetic influence

BACKGROUND AND AIMS

Seed longevity, a fundamental plant trait for ex situ conservation and persistence in the soil of many species, varies across populations and generations that experience different climates. This study investigates the extent to which differences in seed longevity are due to genetic differences and/or modified by adaptive responses to environmental changes.

METHODS

Seeds of two wild populations of Silene vulgaris from alpine (wA) and lowland (wL) locations and seeds originating from their cultivation in a lowland common garden for two generations (cA1, cL1, cA2 and cL2) were exposed to controlled ageing at 45 °C, 60 % relative humidity and regularly sampled for germination and relative mRNA quantification (SvHSP17.4 and SvNRPD12).

KEY RESULTS

The parental plant growth environment affected the longevity of seeds with high plasticity. Seeds of wL were significantly longer lived than those of wA. However, when alpine plants were grown in the common garden, longevity doubled for the first generation of seeds produced (cA1). Conversely, longevity was similar in all lowland seed lots and did not increase in the second generation of seeds produced from alpine plants grown in the common garden (cA2). Analysis of parental effects on mRNA seed provisioning indicated that the accumulation of gene transcripts involved in tolerance to heat stress was highest in wL, cL1 and cL2, followed by cA1, cA2 and wA.

CONCLUSIONS

Seed longevity has a genetic basis, but may show strong adaptive responses, which are associated with differential accumulation of mRNA via parental effects. Adaptive adjustments of seed longevity due to transgenerational plasticity may play a fundamental role in the survival and persistence of the species in the face of future environmental challenges. The results suggest that regeneration location may have important implications for the conservation of alpine plants held in seed banks.

Advances in seed conservation of wild plant species: a review of recent research

Seed banking is now widely used for the ex situ conservation of wild plant species. Many seed banks that conserve wild species broadly follow international genebank guidelines for seed collection, processing, storage, and management. However, over the last 10-20 years, problems and knowledge gaps have been identified, which have led to more focused seed conservation research on diverse species. For example, there is now greater ecogeographic understanding of seed storage behaviour and of the relative longevity of orthodox seeds, and we are therefore able to predict which species should be conserved using cryostorage techniques; seed development studies have identified when seeds should be harvested for maximal tolerance of desiccation and longevity in storage, as well as highlighting how seed development can vary between species; and there is now a wealth of literature on the dormancy-breaking and germination requirements of wild species which, as well as enabling better management of accessions, will also mean that their use in restoration, species reintroduction, or for evaluation for other applications is possible. Future research may be focused, for example, on nursery and plant production systems for wild plant species that maximize genetic diversity, so that introduced seeds and plant materials have the resilience to cope with future environmental stresses.