Gene expression programs during Brassica oleracea seed maturation, osmopriming, and germination are indicators of progression of the germination process and the stress tolerance level

Moving forward to understand the alteration of physiological mechanism by seed priming with different halo-agents under salt stress

Soil salinity hampers the survival and productivity of crops. To minimize salt-associated damages in plant, better salt management practices in agriculture have become a prerequisite. Seed priming with different halo-agents is a technique, which improves the primed plant's endurance to tackle sodium. Salt tolerance is achieved in tolerant plants through fundamental physiological mechanisms- ion-exclusion and tissue tolerance, and salt-tolerant plants may (Na+ accumulators) or may not (Na+ excluders) allow sodium movement to leaves. While Na+ excluders depend on ion exclusion in roots, Na+ accumulators are proficient Na+ managers that can compartmentalize Na+ in leaves and use them beneficially as inexpensive osmoticum. Salt-sensitive plants are Na+ accumulators, but their inherent tissue tolerance ability and ion-exclusion process are insufficient for tolerance. Seed priming with different halo-agents aids in 'rewiring' of the salt tolerance mechanisms of plants. The resetting of the salt tolerance mechanism is not universal for every halo-agent and might vary with halo-agents. Here, we review the physiological mechanisms that different halo-agents target to confer enhanced salt tolerance in primed plants. Calcium and potassium-specific halo-agents trigger Na+ exclusion in roots, thus ensuring a low amount of Na+ in leaves. In contrast, Na+-specific priming agents favour processes for Na+ inclusion in leaves, improve plant tissue tolerance or vacuolar sequestration, and provide the greatest benefit to salt-sensitive and sodium accumulating plants. Overall, this review will help to understand the underlying mechanism behind plant's inherent nature towards salt management and its amelioration with different halo-agents, which helps to optimize crop stress performance.

Climate-resilient crops: Lessons from xerophytes

Developing climate-resilient crops is critical for future food security and sustainable agriculture under current climate scenarios. Of specific importance are drought and soil salinity. Tolerance traits to these stresses are highly complex, and the progress in improving crop tolerance is too slow to cope with the growing demand in food production unless a major paradigm shift in crop breeding occurs. In this work, we combined bioinformatics and physiological approaches to compare some of the key traits that may differentiate between xerophytes (naturally drought-tolerant plants) and mesophytes (to which the majority of the crops belong). We show that both xerophytes and salt-tolerant mesophytes have a much larger number of copies in key gene families conferring some of the key traits related to plant osmotic adjustment, abscisic acid (ABA) sensing and signalling, and stomata development. We show that drought and salt-tolerant species have (i) higher reliance on Na for osmotic adjustment via more diversified and efficient operation of Na+ /H+ tonoplast exchangers (NHXs) and vacuolar H+ - pyrophosphatase (VPPases); (ii) fewer and faster stomata; (iii) intrinsically lower ABA content; (iv) altered structure of pyrabactin resistance/pyrabactin resistance-like (PYR/PYL) ABA receptors; and (v) higher number of gene copies for protein phosphatase 2C (PP2C) and sucrose non-fermenting 1 (SNF1)-related protein kinase 2/open stomata 1 (SnRK2/OST1) ABA signalling components. We also show that the past trends in crop breeding for Na+ exclusion to improve salinity stress tolerance are counterproductive and compromise their drought tolerance. Incorporating these genetic insights into breeding practices could pave the way for more drought-tolerant and salt-resistant crops, securing agricultural yields in an era of climate unpredictability.

Seed priming with gas plasma-activated water in Ethiopia's "orphan" crop tef (Eragrostis tef)

MAIN CONCLUSION

Seed priming with gas plasma-activated water results in an increased ageing resilience in Eragrostis tef grains compared to a conventional hydropriming protocol. Tef (Eragrostis tef) is a cereal grass and a major staple crop of Ethiopia and Eritrea. Despite its significant importance in terms of production, consumption, and cash crop value, tef has been understudied and its productivity is low. In this study, tef grains have undergone different priming treatments to enhance seed vigour and seedling performance. A conventional hydropriming and a novel additive priming technology with gas plasma-activated water (GPAW) have been used and tef grains were then subjected to germination performance assays and accelerated ageing. Tef priming increases the germination speed and vigour of the grains. Priming with GPAW retained the seed storage potential after ageing, therefore, presenting an innovative environmental-friendly seed technology with the prospect to address variable weather conditions and ultimately food insecurity. Seed technology opens new possibilities to increase productivity of tef crop farming to achieve a secure and resilient tef food system and economic growth in Ethiopia by sustainable intensification of agriculture beyond breeding.

Changes in Medicago truncatula seed proteome along the rehydration-dehydration cycle highlight new players in the genotoxic stress response

Introduction

Several molecular aspects underlying the seed response to priming and the resulting vigor profile are still poorly understood. Mechanisms involved in genome maintenance deserve attention since the balance between stimulation of germination and DNA damage accumulation versus active repair is a key determinant for designing successful seed priming protocols.

Methods

Changes in the Medicago truncatula seed proteome were investigated in this study, using discovery mass spectrometry and label-free quantification, along the rehydration-dehydration cycle of a standard vigorization treatment (hydropriming plus dry-back), and during post-priming imbibition.

Resuts and discussion

From 2056 to 2190 proteins were detected in each pairwise comparison, among which six were differentially accumulated and 36 were detected only in one condition. The following proteins were selected for further investigation: MtDRP2B (DYNAMIN-RELATED PROTEIN), MtTRXm4 (THIOREDOXIN m4), and MtASPG1 (ASPARTIC PROTEASE IN GUARD CELL 1) showing changes in seeds under dehydration stress; MtITPA (INOSINE TRIPHOSPHATE PYROPHOSPHORYLASE), MtABA2 (ABSCISIC ACID DEFICIENT 2), MtRS2Z32 (SERINE/ARGININE-RICH SPLICING FACTOR RS2Z32), and MtAQR (RNA HELICASE AQUARIUS) that were differentially regulated during post-priming imbibition. Changes in the corresponding transcript levels were assessed by qRT-PCR. In animal cells, ITPA hydrolyses 2'-deoxyinosine triphosphate and other inosine nucleotides, preventing genotoxic damage. A proof of concept was performed by imbibing primed and control M. truncatula seeds in presence/absence of 20 mM 2'-deoxyinosine (dI). Results from comet assay highlighted the ability of primed seeds to cope with dI-induced genotoxic damage. The seed repair response was assessed by monitoring the expression profiles of MtAAG (ALKYL-ADENINE DNA GLYCOSILASE) and MtEndoV (ENDONUCLEASE V) genes that participate in the repair of the mismatched I:T pair in BER (base excision repair) and AER (alternative excision repair) pathways, respectively.

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.

Seed priming can enhance and retain stress tolerance in ensuing generations by inducing epigenetic changes and trans-generational memory

The significance of priming in enhancing abiotic stress tolerance is well-established in several important crops. Priming positively impacts plant growth and improves stress tolerance at multiple developmental stages, and seed priming is one of the most used methods. Seed priming influences the pre-germinative metabolism that ensures proper germination, early seedling establishment, enhanced stress tolerance and yield, even under unfavourable environmental conditions. Seed priming involves pre-exposure of seeds to mild stress, and this pre-treatment induces specific changes at the physiological and molecular levels. Interestingly, priming can improve the efficiency of the DNA repair mechanism, along with activation of specific signalling proteins and transcription factors for rapid and efficient stress tolerance. Notably, such acquired stress tolerance may be retained for longer duration, namely, later developmental stages or even subsequent generations. Epigenetic and chromatin-based mechanisms such as DNA methylation, histone modifications, and nucleosome positioning are some of the key molecular changes involved in priming/stress memory. Further, the retention of induced epigenetic changes may influence the priming-induced trans-generational stress memory. This review discusses known and plausible seed priming-induced molecular mechanisms that govern germination and stress memory within and across generations, highlighting their role in regulating the plant response to abiotic stresses. Understanding the molecular mechanism for activation of stress-responsive genes and the epigenetic changes resulting from seed priming will help to improve the resiliency of the crops for enhanced productivity under extreme environments.

Transcriptomic insights into the effects of abscisic acid on the germination of Magnolia sieboldii K. Koch seed

Magnolia sieboldii K. Koch is a deciduous tree species. However, the wild resource of M. sieboldii has been declining due to excessive utilization and seed dormancy. In our previous research, M. sieboldii seeds have morphophysiological dormancy and low germination rates under natural conditions. The aim of the present study was to identify the genes involved in dormancy maintenance. In this study, the germination percentage of M. sieboldii seeds negatively correlated with the content of endogenous abscisic acid (ABA). The hydration of seeds for germination showed three distinct phases. Five key time points were identified: 0 h imbibition (dry seed, GZ), 0 day after imbibition (DAI), 16 DAI, 40 DAI, and 56 DAI. The comprehensive transcript profiles of M. sieboldii seeds treated with ABA and water at the five key germinating stages were obtained. A total of 9641 differentially expressed genes (DEGs) were identified, and 208 and 197 common DEGs were found throughout the ABA and water treatments, respectively. Compared with that in the GZ, 518, 696, 2133, and 1535 DEGs were identified in the SH group at 0, 16, 40 and 56 DAI, respectively. 666, 1725, 1560 and 1415 DEGs were identified in the ABA group at 0, 16, 40, and 56 DAI, respectively. Among the identified DEGs, 12 722 were annotated with GO terms, the top three enriched GO terms were different among the DEGs at 56 DAI in the ABA vs. SH treatments. KEGG pathway enrichment analysis for DEGs indicated that oxidative phosphorylation, protein processing in endoplasmic reticulum, starch and sucrose metabolism play an important role in seed response to ABA. 1926 TFs are obtained and classified into 72 families from the M. sieboldii transcriptome. Results of differential gene expression analysis together with qRT-PCR indicated that phase II is crucial for rapid and successful seed germination. This study is the first to present the global expression patterns of ABA-regulated transcripts in M. sieboldii seeds at different germinating phases.

Bacillus subtilis biofilm matrix components target seed oil bodies to promote growth and anti-fungal resistance in melon

Beneficial microorganisms are used to stimulate the germination of seeds; however, their growth-promoting mechanisms remain largely unexplored. Bacillus subtilis is commonly found in association with different plant organs, providing protection against pathogens or stimulating plant growth. We report that application of B. subtilis to melon seeds results in genetic and physiological responses in seeds that alter the metabolic and developmental status in 5-d and 1-month-old plants upon germination. We analysed mutants in different components of the extracellular matrix of B. subtilis biofilms in interaction with seeds and found cooperation in bacterial colonization of seed storage tissues and growth promotion. Combining confocal microscopy with fluorogenic probes, we found that two specific components of the extracellular matrix, amyloid protein TasA and fengycin, differentially increased the concentrations of reactive oxygen species inside seeds. Further, using electron and fluorescence microscopy and metabolomics, we showed that both TasA and fengycin targeted the oil bodies in the seed endosperm, resulting in specific changes in lipid metabolism and accumulation of glutathione-related molecules. In turn, this results in two different plant growth developmental programmes: TasA and fengycin stimulate the development of radicles, and fengycin alone stimulate the growth of adult plants and resistance in the phylloplane to the fungus Botrytis cinerea. Understanding mechanisms of bacterial growth promotion will enable the design of bespoke growth promotion strains.

Mechanisms of growth promotion of Bacillus subtilis on melon seeds are identified using a combination of multi-omics and microscopy.

Changes in genotoxic stress response, ribogenesis and PAP (3'-phosphoadenosine 5'-phosphate) levels are associated with loss of desiccation tolerance in overprimed Medicago truncatula seeds

Re-establishment of desiccation tolerance is essential for the survival of germinated seeds facing water deficit in the soil. The molecular and ultrastructural features of desiccation tolerance maintenance and loss within the nuclear compartment are not fully resolved. In the present study, the impact of desiccation-induced genotoxic stress on nucleolar ultrastructure and ribogenesis was explored along the rehydration-dehydration cycle applied in standard seed vigorization protocols. Primed and overprimed Medicago truncatula seeds, obtained through hydropriming followed by desiccation (dry-back), were analysed. In contrast to desiccation-tolerant primed seeds, overprimed seeds enter irreversible germination and do not survive dry-back. Reactive oxygen species, DNA damage and expression profiles of antioxidant/DNA Damage Response genes were measured, as main hallmarks of the seed response to desiccation stress. Nuclear ultrastructural features were also investigated. Overprimed seeds subjected to dry-back revealed altered rRNA accumulation profiles and up-regulation of genes involved in ribogenesis control. The signal molecule PAP (3'-phosphoadenosine 5'-phosphate) accumulated during dry-back only in primed seeds, as a distinctive feature of desiccation tolerance. The presented results show the molecular and ultrastructural landscapes of the seed desiccation response, including substantial changes in nuclear organization.

Priming With Silicon: A Review of a Promising Tool to Improve Micronutrient Deficiency Symptoms

Priming consists of a short pretreatment or preconditioning of seeds or seedlings with different types of primers (biological, chemical, or physical), which activates various mechanisms that improve plant vigor. In addition, stress responses are also upregulated with priming, obtaining plant phenotypes more tolerant to stress. As priming is thought to create a memory in plants, it is impairing a better resilience against stress situations. In today's world and due to climatic change, almost all plants encounter stresses with different severity. Lots of these stresses are relevant to biotic phenomena, but lots of them are also relevant to abiotic ones. In both these two conditions, silicon application has strong and positive effects when used as a priming agent. Several Si seed priming experiments have been performed to cope with several abiotic stresses (drought, salinity, alkaline stress), and Si primers have been used in non-stress situations to increase seed or seedlings vigor, but few has been done in the field of plant recovery with Si after a stress situation, although promising results have been referenced in the scarce literature. This review pointed out that Si could be successfully used in seed priming under optimal conditions (increased seed vigor), to cope with several stresses and also to recover plants from stressful situations more rapidly, and open a promising research topic to investigate, as priming is not an expensive technique and is easy to introduce by growers.

Dynamics of seed dormancy and germination at high temperature stress is affected by priming and phytohormones in rapeseed (Brassica napus L.)

High temperature stress (HTS) imposes secondary dormancy (SD) also known as thermo-dormancy in many seeds. Priming by soil moisture however, may improve germination though under HTS it may compromise seed longevity. Knowledge of how HTS and priming affect dormancy status/viability loss of a particular crop seed species is essential in agriculture. Accordingly, control non-primed and hydro-primed seeds from Dk-xpower and Traper rapeseed cultivars with low and high potential for SD induction, respectively, were compared for germination behavior, response to GA and some phytohormone effectors under HTS. HTS reduced germination in non-primed Dk-xpower and Traper seeds mainly through the induction of thermo-inhibition/death and thermo-dormancy, respectively. Under HTS, GA₃ application reduced thermo-dormancy in favor of thermo-inhibition only in Traper but the GA inhibitor paclobutrazol intensified thermo-dormancy in both cultivars. The ABA inhibitor, fluridone also reduced thermo-dormancy in favor of thermo-inhibition only in Traper. Thus, under HTS, GA biosynthesis is determinant in seed thermo-dormancy/thermo-inhibition dynamics. Hydropriming improved germination under HTS through reduced thermo-inhibition/death (Dk-xpower) and thermo-dormancy (Traper). Here, GA₃ application increased death and compromised germination mainly in Dk-xpower. Paclubutrazol application however, increased thermo-dormancy by compromising thermo-inhibition/death in Traper. Overall, hydro-priming weakened seed phytohormonal germination responses. Controlled deterioration resulted in decreased longevity of hydro-primed seeds but induced SD in non-primed Traper seeds. Thus, down-regulation of GA biosynthesis may control differential induction of SD in rapeseed seeds under HTS while hydro-priming stimulates seed germination possibly through overcoming limitations in GA biosynthesis. The agricultural importance of these findings at the ecosystem scale is discussed.

Seed priming with proline improved photosystem II efficiency and growth of wheat (Triticum aestivum L.)

BACKGROUND

Proline can promote growth of plants by increasing photosynthetic activity under both non-stress and abiotic stress conditions. However, its role in non-stressed conditions is least studied. An experiment was conducted to assess as to whether increase in growth of wheat due to seed priming with proline under non-stress condition was associated with proline-induced changes in photosystem II (PSII) activity. Seeds of four wheat varieties (S-24, Sehar-06, Galaxy-13, and Pasban-90) were primed with different concentrations of proline (0, 5, 15 and 25 mM) for 12 h and allowed to grow under normal conditions. Biomass accumulation and photosynthetic performance, being two most sensitive features/indicators of plant growth, were selected to monitor proline modulated changes.

RESULTS

Seed priming with proline increased the fresh and dry weights of shoots and roots, and plant height of all four wheat varieties. Maximum increase in growth attributes was observed in all four wheat varieties at 15 mM proline. Maximum growth improvement due to proline was found in var. Galaxy-13, whereas the reverse was true for S-24. Moreover, proline treatment changed the Fo, Fm, Fv/Fo, PI_ABS, PI_Tot in wheat varieties indicating changes in PSII activity. Proline induced changes in energy fluxes for absorption, trapping, electron transport and heat dissipation per reaction center indicated that var. Galaxy-13 had better ability to process absorbed light energy through photosynthetic machinery. Moreover, lesser PSII efficiency in var. S-24 was due to lower energy flux for electron transport and greater energy flux for heat dissipation. This was further supported by the fact that var. S-24 had disturbance at acceptor side of PSI as reflected by reduction in ΔV_IP, probability and energy flux for electron transport at the PSI end electron acceptors.

CONCLUSION

Seed priming with proline improved the growth of wheat varieties, which depends on type of variety and concentration of proline applied. Seed priming with proline significantly changed the PSII activity in wheat varieties, however, its translation in growth improvement depends on potential of processing of absorbed light energy by electron acceptors of electron transport chain, particularly those present at PSI end.

Ageing beautifully: can the benefits of seed priming be separated from a reduced lifespan trade-off?

Germination performance is affected following seed exposure to a combination of temperature fluctuations and cycles of hydration and dehydration. This has long been exploited in a seed technology termed priming, which increases germination speed and seedling vigour, but these benefits have often been associated with effects on seed lifespan, or longevity, with conflicting evidence for positive and negative effects. Seed longevity is a key seed trait influencing not only the storage of commercial stocks but also in situ and ex situ seed conservation. In the context of increasingly variable environmental conditions faced by both crops and wild species, this has led to renewed interest in understanding the molecular factors that underlie priming. Here, we provide an overview of the literature relating to the effect of priming on seed lifespan, and catalogue the different parameters used for priming treatments and their consequences on longevity for a range of species. Our current limited understanding of the molecular basis for priming effects is also outlined, with an emphasis on recent advances and promising approaches that should lead towards the application and monitoring of the priming process in a less empirical manner.

Matrix-Assisted Laser Desorption/Ionization-Mass Spectrometry Imaging of Metabolites during Sorghum Germination

Dhurrin is the most abundant cyanogenic glucoside found in sorghum (Sorghum bicolor) where it plays a key role in chemical defense by releasing toxic hydrogen cyanide upon tissue disruption. Besides this well-established function, there is strong evidence that dhurrin plays additional roles, e.g. as a transport and storage form of nitrogen, released via endogenous recycling pathways. However, knowledge about how, when and why dhurrin is endogenously metabolized is limited. We combined targeted metabolite profiling with matrix-assisted laser desorption/ionization-mass spectrometry imaging to investigate accumulation of dhurrin, its recycling products and key general metabolites in four different sorghum lines during 72 h of grain imbibition, germination and early seedling development, as well as the spatial distribution of these metabolites in two of the lines. Little or no dhurrin or recycling products were present in the dry grain, but their de novo biosynthesis started immediately after water uptake. Dhurrin accumulation increased rapidly within the first 24 h in parallel with an increase in free amino acids, a key event in seed germination. The trajectories and final concentrations of dhurrin, the recycling products and free amino acids reached within the experimental period were dependent on genotype. Matrix-assisted laser desorption/ionization-mass spectrometry imaging demonstrated that dhurrin primarily accumulated in the germinating embryo, confirming its function in protecting the emerging tissue against herbivory. The dhurrin recycling products, however, were mainly located in the scutellum and/or pericarp/seed coat region, suggesting unknown key functions in germination.

Overview of the Role of Cell Wall DUF642 Proteins in Plant Development

The DUF642 protein family is found exclusively in spermatophytes and is represented by 10 genes in Arabidopsis and in most of the 24 plant species analyzed to date. Even though the primary structure of DUF642 proteins is highly conserved in different spermatophyte species, studies of their expression patterns in Arabidopsis have shown that the spatial-temporal expression pattern for each gene is specific and consistent with the phenotypes of the mutant plants studied so far. Additionally, the regulation of DUF642 gene expression by hormones and environmental stimuli was specific for each gene, showing both up- and down-regulation depending of the analyzed tissue and the intensity or duration of the stimuli. These expression patterns suggest that the DUF642 genes are involved throughout the development and growth of plants. In general, changes in the expression patterns of DUF642 genes can be related to changes in pectin methyl esterase activity and/or to changes in the degree of methyl-esterified homogalacturonans during plant development in different cell types. Thus, the regulation of pectin methyl esterases mediated by DUF642 genes could contribute to the regulation of the cell wall properties during plant growth.

Comprehensive dissection of transcript and metabolite shifts during seed germination and post-germination stages in poplar

BACKGROUND

Seed germination, a complex, physiological-morphogenetic process, is a critical stage in the life cycle of plants. Biological changes in germinating seeds have not been investigated in poplar, a model woody plant.

RESULTS

In this study, we exploited next-generation sequencing and metabolomics analysis and uncovered a series of significantly different genes and metabolites at various stages of seed germination and post germination. The K-means method was used to identify multiple transcription factors, including AP2/EREBP, DOF, and YABBY, involved in specific seed germination and post-germination stages. A weighted gene coexpression network analysis revealed that cell wall, amino acid metabolism, and transport-related pathways were significantly enriched during stages 3 and 5, with no significant enrichment observed in primary metabolic processes such as glycolysis and the tricarboxylic acid cycle. A metabolomics analysis detected significant changes in intermediate metabolites in these primary metabolic processes, while a targeted correlation network analysis identified the gene family members most relevant to these changing metabolites.

CONCLUSIONS

Taken together, our results provide important insights into the molecular networks underlying poplar seed germination and post-germination processes. The targeted correlation network analysis approach developed in this study can be applied to search for key candidate genes in specific biochemical reactions and represents a new strategy for joint multiomics analyses.

Regulation of α-expansins genes in Arabidopsis thaliana seeds during post-osmopriming germination

Seed osmopriming is a pre-sowing treatment that involves limitation of the seed water imbibition, so that pre-germinative metabolic activities proceed without radicular protrusion. This technique is used for improving germination rate, uniformity of seedling growth and hastening the time to start germination. In Arabidopsis thaliana, seed germination has been associated with the induction of enzymes involved in cell wall modifications, such as expansins. The α-expansins (EXPAs) are involved in cell wall relaxation and extension during seed germination. We used online tools to identify AtEXPA genes with preferential expression during seed germination and RT-qPCR to study the expression of five EXPA genes at different germination stages of non-primed and osmoprimed seeds. In silico promoter analysis of these genes showed that motifs similar to cis-acting elements related to abiotic stress, light and phytohormone responses are the most overrepresented in promoters of these AtEXPA genes, showing that their expression is likely be regulated by intrinsic developmental and environmental signals during Arabidopsis seed germination. The osmopriming conditioning had a decreased time and mean to 50% germination without affecting the percentage of final seed germination. The dried PEG-treated seeds showed noticeable high mRNA levels earlier at the beginning of water imbibition (18 h), showing that transcripts of all five EXPA isoforms were significantly produced during the osmopriming process. The strong up-regulation of these AtEXPA genes, mainly AtEXPA2, were associated with the earlier germination of the osmoprimed seeds, which qualifies them to monitor osmopriming procedures and the advancement of germination.

New Insight on Water Status in Germinating Brassica napus Seeds in Relation to Priming-Improved Germination

Seed priming is a pre-sowing method successfully used to improve seed germination. Since water plays a crucial role in germination, the aim of this study was to investigate the relationship between better germination performances of osmoprimed Brassica napus seeds and seed water status during germination. To achieve this goal, a combination of different kinds of approaches was used, including nuclear magnetic resonance (NMR) spectroscopy, TEM, and SEM as well as semi-quantitative PCR (semi-qPCR). The results of this study showed that osmopriming enhanced the kinetics of water uptake and the total amount of absorbed water during both the early imbibition stage and in the later phases of seed germination. The spin⁻spin relaxation time (T₂) measurement suggests that osmopriming causes faster water penetration into the seed and more efficient tissue hydration. Moreover, factors potentially affecting water relations in germinating primed seeds were also identified. It was shown that osmopriming (i) changes the microstructural features of the seed coat, e.g., leads to the formation of microcracks, (ii) alters the internal structure of the seed by the induction of additional void spaces in the seed, (iii) increases cotyledons cells vacuolization, and (iv) modifies the expression pattern of aquaporin genes.

Identification of a seed maturation protein gene from Coffea arabica (CaSMP) and analysis of its promoter activity in tomato

A seed maturation protein gene (CaSMP) from Coffea arabica is expressed in the endosperm of yellow/green fruits. The CaSMP promoter drives reporter expression in the seeds of immature tomato fruits. In this report, an expressed sequence tag-based approach was used to identify a seed-specific candidate gene for promoter isolation in Coffea arabica. The tissue-specific expression of the cognate gene (CaSMP), which encodes a yet uncharacterized coffee seed maturation protein, was validated by RT-qPCR. Additional expression analysis during coffee fruit development revealed higher levels of CaSMP transcript accumulation in the yellow/green phenological stage. Moreover, CaSMP was preferentially expressed in the endosperm and was down-regulated during water imbibition of the seeds. The presence of regulatory cis-elements known to be involved in seed- and endosperm-specific expression was observed in the CaSMP 5'-upstream region amplified by genome walking (GW). Additional histochemical analysis of transgenic tomato (cv. Micro-Tom) lines harboring the GW-amplified fragment (~ 1.4 kb) fused to uidA reporter gene confirmed promoter activity in the ovule of immature tomato fruits, while no activity was observed in the seeds of ripening fruits and in the other organs/tissues examined. These results indicate that the CaSMP promoter can be used to drive transgene expression in coffee beans and tomato seeds, thus representing a promising biotechnological tool.

Gene expression patterns regulating the seed metabolism in relation to deterioration/ageing of primed mung bean (Vigna radiata L.) seeds

We are proposing mechanisms to account for the loss of viability (seed deterioration/ageing) and enhancement in seed quality (post-storage priming treatment). In order to understand the regulatory mechanism of these traits, we conducted controlled deterioration (CD) test for up to 8 d using primed mung bean seeds and examined how CD effects the expression of many genes, regulating the seed metabolism in relation to CD and priming. Germination declined progressively with increased duration of CD, and the priming treatment completely/partially reversed the inhibition depending on the duration of CD. The loss of germination capacity by CD was accompanied by a reduction in total RNA content and RNA integrity, indicating that RNA quantity and quality impacts seed longevity. Expression analysis revealed that biosynthesis genes of GA, ethylene, ABA and ROS-scavenging enzymes were differentially affected in response to duration of CD and priming, suggesting coordinately regulated mechanisms for controlling the germination capacity of seeds by modifying the permeability characteristics of biological membranes and activities of different enzymes. ABA genes were highly expressed when germination was delayed and inhibited by CD. Whereas, GA and ethylene genes were more highly expressed when germination was enhanced and permitted by priming under similar conditions. GSTI, a well characterized enzyme family involved in stress tolerance, was expressed in primed seeds over the period of CD, suggesting an additional protection against deterioration. The results are discussed in light of understanding the mechanisms underlying longevity/priming which are important issues economically and ecologically.

Transient Heat Stress During Early Seed Development Primes Germination and Seedling Establishment in Rice

Rice yield is highly sensitive to increased temperature. Given the trend of increasing global temperatures, this sensitivity to higher temperatures poses a challenge for achieving global food security. Early seed development in rice is highly sensitive to unfavorable environmental conditions. Heat stress (HS) during this stage decreases seed size and fertility, thus reducing yield. Here, we explore the transgenerational phenotypic consequences of HS during early seed development on seed viability, germination, and establishment. To elucidate the impact of HS on the developmental events in post-zygotic rice seeds, we imposed moderate (35°C) and severe (39°C) HS treatments initiated 1 day after fertilization and maintained for 24, 48, or 72 h. The transient HS treatments altered the initiation of endosperm (ED) cellularization, seed size and/or the duration of spikelet ripening. Notably, seeds exposed to 24 and 48 h moderate HS exhibited higher germination rate compared to seeds derived from plants grown under control or severe HS. A short-term HS resulted in altered expression of Gibberellin (GA) and ABA biosynthesis genes during early seed development, and GA and ABA levels and starch content at maturity. The increased germination rate after 24 of moderate HS could be due to altered ABA sensitivity and/or increased starch level. Our findings on the impact of transient HS on hormone homeostasis provide an experimental framework to elucidate the underlying molecular and metabolic pathways.

Analysis of the lipid body proteome of the oleaginous alga Lobosphaera incisa

BACKGROUND

Lobosphaera incisa (L. incisa) is an oleaginous microalga that stores triacylglycerol (TAG) rich in arachidonic acid in lipid bodies (LBs). This organelle is gaining attention in algal research, since evidence is accumulating that proteins attached to its surface fulfill important functions in TAG storage and metabolism.

RESULTS

Here, the composition of the LB proteome in L incisa was investigated by comparing different cell fractions in a semiquantitative proteomics approach. After applying stringent filters to the proteomics data in order to remove contaminating proteins from the list of possible LB proteins (LBPs), heterologous expression of candidate proteins in tobacco pollen tubes, allowed us to confirm 3 true LBPs: A member of the algal Major Lipid Droplet Protein family, a small protein of unknown function and a putative lipase. In addition, a TAG lipase that belongs to the SUGAR DEPENDENT 1 family of TAG lipases known from oilseed plants was identified. Its activity was verified by functional complementation of an Arabidopsis thaliana mutant lacking the major seed TAG lipases.

CONCLUSIONS

Here we describe 3 LBPs as well as a TAG lipase from the oleaginous microalga L. incisa and discuss their possible involvement in LB metabolism. This study highlights the importance of filtering LB proteome datasets and verifying the subcellular localization one by one, so that contaminating proteins can be recognized as such. Our dataset can serve as a valuable resource in the identification of additional LBPs, shedding more light on the intriguing roles of LBs in microalgae.

AhDGR2, an amaranth abiotic stress-induced DUF642 protein gene, modifies cell wall structure and composition and causes salt and ABA hyper-sensibility in transgenic Arabidopsis

An amaranth DGR gene, induced under abiotic stress, modifies cell wall structure and causes hypersensitivity to ABA and salt when overexpressed in Arabidopsis. DUF642 is a highly conserved plant-specific family of unknown cell wall-associated proteins. The AhDGR2 gene, coding for a DUF642 protein, was significantly induced in grain amaranth (Amaranthus hypochondriacus) plants subjected to water-deficit and salinity stress, thereby suggesting its participation in abiotic stress tolerance in this plant. A role in development was also inferred from the higher AhDGR2 expression rates detected in young tissues. Subsequent overexpression of AhDGR2 in transgenic Arabidopsis plants (OE-AhDGR2) supported its possible role in development processes. Thus, OE-AhDGR2 plants generated significantly longer roots when grown in normal MS medium. However, they showed a hypersensitivity to increasing concentrations of abscisic acid or NaCl in the medium, as manifested by shorter root length, smaller and slightly chlorotic rosettes, as well as highly reduced germination rates. Contrary to expectations, OE-AhDGR2 plants were intolerant to abiotic stress. Moreover, cell walls in transgenic plants were thinner, in leaves, and more disorganized, in roots, and had significantly modified pectin levels. Lower pectin methylesterase activity detected in leaves of OE-AhDGR2 plants, but not in roots, was contrary to previous reports associating DUF642 proteins and decreased pectin esterification levels in cell walls. Nonetheless, microarray data identified candidate genes whose expression levels explained the phenotypes observed in leaves of OE-AhDGR2 plants, including several involved in cell wall integrity and extension, growth and development, and resistance to abiotic stress. These results support the role of DUF642 proteins in cell wall-related processes and offer novel insights into their possible role(s) in plants.

Seed priming alleviated salt stress effects on rice seedlings by improving Na+/K+ and maintaining membrane integrity

The potential of seed priming by different chemicals on alleviation of growth inhibition of rice (<em>Oryza</em> <em>sativa</em> L.) seedlings under salt stress was investigated. A preliminary experiment using 10 seed-priming chemicals including NaCl, KCl, CaCl2, KNO3, ascorbic acid (AsA), mannitol, polyethylene glycol (PEG6000), sorbitol, wood vinegar and distilled water revealed that mannitol, KNO3 and wood vinegar were more effective than the others in alleviating salt-induced growth inhibition of 10- day-old seedlings. Various concentrations of mannitol (1, 2 and 3%), KNO3 (0.25, 0.5 and 0.75%) and wood vinegar (1:1000, 1:300 and 1:100 dilutions) were subsequently used to prime rice seeds to investigate the effects on mitigation of salt-induced growth inhibition and modulation of physiological responses of 4-week-old rice plants grown in a hydroponic solution. All tested concentrations of mannitol, KNO3 and wood vinegar resulted in seedlings with significantly higher dry weights than those grown from non-primed and hydroprimed seeds under both controlled and saltstressed (150 mM NaCl, 7 days) conditions. Under salt stress, enhanced growth of seedlings raised from seeds primed with all three chemicals was attributable to greater membrane stability, higher chlorophyll content and lower Na+/K+ ratio.

Transcriptome Analysis of Taxillusi chinensis (DC.) Danser Seeds in Response to Water Loss

BACKGROUND

Taxillus chinensis (DC.) Danser, the official species of parasitic loranthus that grows by parasitizing other plants, is used in various traditional Chinese medicine prescriptions. ABA-dependent and ABA-independent pathways are two major pathways in response to drought stress for plants and some genes have been reported to play a key role during the dehydration including dehydration-responsive protein RD22, late embryogenesis abundant (LEA) proteins, and various transcription factors (TFs) like MYB and WRKY. However, genes responding to dehydration are still unknown in loranthus.

METHODS AND RESULTS

Initially, loranthus seeds were characterized as recalcitrant seeds. Then, biological replicates of fresh loranthus seeds (CK), and seeds after being dehydrated for 16 hours (Tac-16) and 36 hours (Tac-36) were sequenced by RNA-Seq, generating 386,542,846 high quality reads. A total of 164,546 transcripts corresponding to 114,971 genes were assembled by Trinity and annotated by mapping them to NCBI non-redundant (NR), UniProt, GO, KEGG pathway and COG databases. Transcriptome profiling identified 60,695, 56,027 and 66,389 transcripts (>1 FPKM) in CK, Tac-16 and Tac-36, respectively. Compared to CK, we obtained 2,102 up-regulated and 1,344 down-regulated transcripts in Tac-16 and 1,649 up-regulated and 2,135 down-regulated transcripts in Tac-36 by using edgeR. Among them some have been reported to function in dehydration process, such as RD22, heat shock proteins (HSP) and various TFs (MYB, WRKY and ethylene-responsive transcription factors). Interestingly, transcripts encoding ribosomal proteins peaked in Tac-16. It is indicated that HSPs and ribosomal proteins may function in early response to drought stress. Raw sequencing data can be accessed in NCBI SRA platform under the accession number SRA309567.

CONCLUSIONS

This is the first time to profile transcriptome globally in loranthus seeds. Our findings provide insights into the gene regulations of loranthus seeds in response to water loss and expand our current understanding of drought tolerance and germination of seeds.

Environmental and genetic effects on tomato seed metabolic balance and its association with germination vigor

BACKGROUND

The metabolite content of a seed and its ability to germinate are determined by genetic makeup and environmental effects during development. The interaction between genetics, environment and seed metabolism and germination was studied in 72 tomato homozygous introgression lines (IL) derived from Solanum pennelli and S. esculentum M82 cultivar. Plants were grown in the field under saline and fresh water irrigation during two consecutive seasons, and collected seeds were subjected to morphological analysis, gas chromatograph-mass spectrometry (GC-MS) metabolic profiling and germination tests.

RESULTS

Seed weight was under tight genetic regulation, but it was not related to germination vigor. Salinity significantly reduced seed number but had little influence on seed metabolites, affecting only 1% of the statistical comparisons. The metabolites negatively correlated to germination were simple sugars and most amino acids, while positive correlations were found for several organic acids and the N metabolites urea and dopamine. Germination tests identified putative loci for improved germination as compared to M82 and in response to salinity, which were also characterized by defined metabolic changes in the seed.

CONCLUSIONS

An integrative analysis of the metabolite and germination data revealed metabolite levels unambiguously associated with germination percentage and rate, mostly conserved in the different tested seed development environments. Such consistent relations suggest the potential for developing a method of germination vigor prediction by metabolic profiling, as well as add to our understanding of the importance of primary metabolic processes in germination.

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.

Comparative Transcriptional Profiling of Primed and Non-primed Rice Seedlings under Submergence Stress

Submergence stress is a limiting factor for direct-seeded rice systems in rainfed lowlands and flood-prone areas of South and Southeast Asia. The present study demonstrated that submergence stress severely hampered the germination and seedling growth of rice, however, seed priming alleviated the detrimental effects of submergence stress. To elucidate the molecular basis of seed priming-induced submergence tolerance, transcriptome analyses were performed using 4-day-old primed (selenium-Se and salicylic acid-SA priming) and non-primed rice seedlings under submergence stress. Genomewide transcriptomic profiling identified 2371 and 2405 transcripts with Se- and SA-priming, respectively, that were differentially expressed in rice compared with non-priming treatment under submergence. Pathway and gene ontology term enrichment analyses revealed that genes involved in regulation of secondary metabolism, development, cell, transport, protein, and metal handling were over-represented after Se- or SA-priming. These coordinated factors might have enhanced the submergence tolerance and maintained the better germination and vigorous seedling growth of primed rice seedlings. It was also found that many genes involved in cellular and metabolic processes such as carbohydrate metabolism, cellular, and metabolic biosynthesis, nitrogen compound metabolic process, transcription, and response to oxidative stress were induced and overlapped in seed priming treatments, a finding which reveals the common mechanism of seed priming-induced submergence tolerance. Taken together, these results may provide new avenues for understanding and advancing priming-induced responses to submergence tolerance in crop plants.

Comparative Transcriptional Profiling of Primed and Non-primed Rice Seedlings under Submergence Stress

Submergence stress is a limiting factor for direct-seeded rice systems in rainfed lowlands and flood-prone areas of South and Southeast Asia. The present study demonstrated that submergence stress severely hampered the germination and seedling growth of rice, however, seed priming alleviated the detrimental effects of submergence stress. To elucidate the molecular basis of seed priming-induced submergence tolerance, transcriptome analyses were performed using 4-day-old primed (selenium-Se and salicylic acid-SA priming) and non-primed rice seedlings under submergence stress. Genomewide transcriptomic profiling identified 2371 and 2405 transcripts with Se- and SA-priming, respectively, that were differentially expressed in rice compared with non-priming treatment under submergence. Pathway and gene ontology term enrichment analyses revealed that genes involved in regulation of secondary metabolism, development, cell, transport, protein, and metal handling were over-represented after Se- or SA-priming. These coordinated factors might have enhanced the submergence tolerance and maintained the better germination and vigorous seedling growth of primed rice seedlings. It was also found that many genes involved in cellular and metabolic processes such as carbohydrate metabolism, cellular, and metabolic biosynthesis, nitrogen compound metabolic process, transcription, and response to oxidative stress were induced and overlapped in seed priming treatments, a finding which reveals the common mechanism of seed priming-induced submergence tolerance. Taken together, these results may provide new avenues for understanding and advancing priming-induced responses to submergence tolerance in crop plants.

Proteomics analysis reveals distinct involvement of embryo and endosperm proteins during seed germination in dormant and non-dormant rice seeds

Seed germination is a complex trait which is influenced by many genetic, endogenous and environmental factors, but the key event(s) associated with seed germination are still poorly understood. In present study, the non-dormant cultivated rice Yannong S and the dormant Dongxiang wild rice seeds were used as experimental materials, we comparatively investigated the water uptake, germination time course, and the differential proteome of the effect of embryo and endosperm on germination of these two types of seeds. A total of 231 and 180 protein spots in embryo and endosperm, respectively, showed a significant change in abundance during germination. We observed that the important proteins associated with seed germination included those involved in metabolism, energy production, protein synthesis and destination, storage protein, cell growth and division, signal transduction, cell defense and rescue. The contribution of embryo and endosperm to seed germination is different. In embryo, the proteins involved in amino acid activation, sucrose cleavage, glycolysis, fermentation and protein synthesis increased; in endosperm, the proteins involved in sucrose cleavage and glycolysis decreased, and those with ATP and CoQ synthesis and proteolysis increased. Our results provide some new knowledge to understand further the mechanism of seed germination.

Effect of osmopriming on germination and initial growth of Physalis angulata L. under salt stress and on expression of associated genes

ABSTRACT This study aimed to evaluate the effects of priming on seed germination under salt stress and gene expression in seeds and seedlings of P. angulata L. After priming for 10 days, seed germination was tested in plastic trays containing 15 ml of water (0 dS m-1 - control) or 15 ml of NaCl solution (2, 4, 6, 8, 10, 12, 14 and 16 dS m-1). Fresh and dry weight of shoots and roots of seedlings were evaluated at 0, 2, 4, 6, 8 dS m-1. Total RNA was extracted from whole seeds and seedlings followed by RT-qPCR. The target genes selected for this study were: ascorbate peroxidase (APX), glutathione-S-transferase (GST), thioredoxin (TXN), high affinity potassium transporter protein 1 (HAK1) and salt overly sensitive 1 (SOS1). At an electroconductivity of 14 dS m-1 the primed seeds still germinated to 72%, in contrast with the non-primed seeds which did not germinate. The relative expression of APX was higher in primed seeds and this may have contributed to the maintenance of high germination in primed seeds at high salt concentrations. GST and TXN displayed increased transcript levels in shoots and roots of seedlings from primed seeds. Priming improved seed germination as well as salt tolerance and this is correlated with increased expression of APX in seeds and SOS1, GST and TXN in seedlings.

Seed priming to alleviate salinity stress in germinating seeds

Salinity is one of the major abiotic stresses that affect crop production in arid and semiarid areas. Seed germination and seedling growth are the stages most sensitive to salinity. Salt stress causes adverse physiological and biochemical changes in germinating seeds. It can affect the seed germination and stand establishment through osmotic stress, ion-specific effects and oxidative stress. The salinity delays or prevents the seed germination through various factors, such as a reduction in water availability, changes in the mobilization of stored reserves and affecting the structural organization of proteins. Various techniques can improve emergence and stand establishment under salt conditions. One of the most frequently utilized is seed priming. The process of seed priming involves prior exposure to an abiotic stress, making a seed more resistant to future exposure. Seed priming stimulates the pre-germination metabolic processes and makes the seed ready for radicle protrusion. It increases the antioxidant system activity and the repair of membranes. These changes promote seed vigor during germination and emergence under salinity stress. The aim of this paper is to review the recent literature on the response of plants to seed priming under salinity stress. The mechanism of the effect of salinity on seed germination is discussed and the seed priming process is summarized. Physiological, biochemical and molecular changes induced by priming that lead to seed enhancement are covered. Plants' responses to some priming agents under salinity stress are reported based on the best available data. For a great number of crops, little information exists and further research is needed.

Different Modes of Hydrogen Peroxide Action During Seed Germination

Hydrogen peroxide was initially recognized as a toxic molecule that causes damage at different levels of cell organization and thus losses in cell viability. From the 1990s, the role of hydrogen peroxide as a signaling molecule in plants has also been discussed. The beneficial role of H2O2 as a central hub integrating signaling network in response to biotic and abiotic stress and during developmental processes is now well established. Seed germination is the most pivotal phase of the plant life cycle, affecting plant growth and productivity. The function of hydrogen peroxide in seed germination and seed aging has been illustrated in numerous studies; however, the exact role of this molecule remains unknown. This review evaluates evidence that shows that H2O2 functions as a signaling molecule in seed physiology in accordance with the known biology and biochemistry of H2O2. The importance of crosstalk between hydrogen peroxide and a number of signaling molecules, including plant phytohormones such as abscisic acid, gibberellins, and ethylene, and reactive molecules such as nitric oxide and hydrogen sulfide acting on cell communication and signaling during seed germination, is highlighted. The current study also focuses on the detrimental effects of H2O2 on seed biology, i.e., seed aging that leads to a loss of germination efficiency. The dual nature of hydrogen peroxide as a toxic molecule on one hand and as a signal molecule on the other is made possible through the precise spatial and temporal control of its production and degradation. Levels of hydrogen peroxide in germinating seeds and young seedlings can be modulated via pre-sowing seed priming/conditioning. This rather simple method is shown to be a valuable tool for improving seed quality and for enhancing seed stress tolerance during post-priming germination. In this review, we outline how seed priming/conditioning affects the integrative role of hydrogen peroxide in seed germination and aging.

Proteome analysis of dormancy-released seeds of Fraxinus mandshurica Rupr. in response to re-dehydration under different conditions

Desiccation tolerance is the ability of orthodox seeds to achieve equilibrium with atmospheric relative humidity and to survive in this state. Understanding how orthodox seeds respond to dehydration is important for improving quality and long-term storage of seeds under low temperature and drought stress conditions. Long-term storage of seeds is an artificial situation, because in most natural situations a seed that has been shed may not remain in a desiccated state for very long, and if dormant it may undergo repeated cycles of hydration. Different types of seeds are differentially sensitive to desiccation and this directly affects long-term storage. For these reasons, many researchers are investigating loss of desiccation tolerance during orthodox seed development to understand how it is acquired. In this study, the orthodox seed proteome response of Fraxinus mandshurica Rupr. to dehydration (to a relative water content of 10%, which mimics seed dehydration) was investigated under four different conditions viz. 20 °C; 20 °C with silica gel; 1 °C; and 1 °C after pretreatment with Ca2+. Proteins from seeds dehydrated under different conditions were extracted and separated by two-dimensional difference gel electrophoresis (2D-DIGE). A total of 2919 protein spots were detected, and high-resolution 2D-DIGE indicated there were 27 differentially expressed. Seven of these were identified using MALDI TOF/TOF mass spectrometry. Inferences from bioinformatics annotations of these proteins established the possible involvement of detoxifying enzymes, transport proteins, and nucleotide metabolism enzymes in response to dehydration. Of the seven differentially abundant proteins, the amounts of six were down-regulated and one was up-regulated. Also, a putative acyl-coenzyme A oxidase of the glyoxylate cycle increased in abundance. In particular, the presence of kinesin-1, a protein important for regulation and cargo interaction, was up-regulated in seeds exposed to low temperature dehydration. Kinesin-1 is present in all major lineages, but it is rarely detected in seed desiccation tolerance of woody species. These observations provide new insight into the proteome of seeds in deep dormancy under different desiccation conditions.

Deciphering priming-induced improvement of rapeseed (Brassica napus L.) germination through an integrated transcriptomic and proteomic approach

Rape seeds primed with -1.2 MPa polyethylene glycol 6000 showed improved germination performance. To better understand the beneficial effect of osmopriming on seed germination, a global expression profiling method was used to compare, for the first time, transcriptomic and proteomic data for osmoprimed seeds at the crucial phases of priming procedure (soaking, drying), whole priming process and subsequent germination. Brassica napus was used here as a model to dissect the process of osmopriming into its essential components. A total number of 952 genes and 75 proteins were affected during the main phases of priming and post-priming germination. Transcription was not coordinately associated with translation resulting in a limited correspondence between mRNAs level and protein abundance. Soaking, drying and final germination of primed seeds triggered distinct specific pathways since only a minority of genes and proteins were involved in all phases of osmopriming while a vast majority was involved in only one single phase. A particular attention was paid to genes and proteins involved in the transcription, translation, reserve mobilization, water uptake, cell cycle and oxidative stress processes.

BIIDXI, the At4g32460 DUF642 gene, is involved in pectin methyl esterase regulation during Arabidopsis thaliana seed germination and plant development

BACKGROUND

DUF642 proteins constitute a highly conserved family of proteins that are associated with the cell wall and are specific to spermatophytes. Transcriptome studies have suggested that members of this family are involved in seed development and germination processes. Previous in vitro studies have revealed that At4g32460- and At5g11420-encoded proteins interact with the catalytic domain of pectin methyl esterase 3 (AtPME3, which is encoded by At3g14310). PMEs play an important role in plant development, including seed germination. The aim of this study was to evaluate the function of the DUF642 gene At4g32460 during seed germination and plant development and to determine its relation to PME activity regulation.

RESULTS

Our results indicated that the DUF642 proteins encoded by At4g32460 and At5g11420 could be positive regulators of PME activity during several developmental processes. Transgenic lines overexpressing these proteins showed increased PME activity during seed germination, and improved seed germination performance. In plants expressing At4g32460 antisense RNA, PME activity was decreased in the leaves, and the siliques were very short and contained no seeds. This phenotype was also present in the SALK_142260 and SALK_054867 lines for At4g32460.

CONCLUSIONS

Our results suggested that the DUF642 family contributes to the complexity of the methylesterification process by participating in the fine regulation of pectin status during plant development.

Transcription factors and glyoxylate cycle genes prominent in the transition of soybean cotyledons to the first functional leaves of the seedling

During early seedling growth, the cotyledons transition from a storage tissue to become effectively the first leaf-like structures of the plant. In this programmed developmental process, they likely undergo a massive change in gene expression to redirect their metabolism and physiological processes. To define the developmental shifts in gene expression and begin to understand the gene regulatory networks that set this transition in motion, we carried out high-throughput RNA sequencing of cotyledons from seven developmental stages of soybean seedlings. We identified 154 gene models with high expression exclusively in the early seedling stages. A significant number (about 25 %) of those genes with known annotations were involved in carbohydrate metabolism. A detailed examination of glyoxylate cycle genes revealed the upregulation of their expression in the early stages of development. A total of approximately 50 % of the highly expressed genes whose expression peaked in the mid-developmental stages encoded ribosomal family proteins. Our analysis also identified 219 gene models with high expression at late developmental stages. The majority of these genes are involved in photosynthesis, including photosystem I- and II-associated genes. Additionally, the advantage of RNA-Seq to detect genes expressed at low levels revealed approximately 460 transcription factors with notable expression in at least one stage of the developing soybean seedling. Relatively over-represented transcription factor genes encode AP2, zinc finger, NAC, WRKY, and MYB families. These transcription factor genes may lead to the transcriptional reprogramming during the transition of seedling cotyledons from storage tissue to metabolically active organs that serve as the first functional leaves of the plant.

Effect of desiccation on the dynamics of genome-wide DNA methylation in orthodox seeds of Acer platanoides L

5-methylcytosine, an abundant epigenetic mark, plays an important role in the regulation of plant growth and development, but there is little information about stress-induced changes in DNA methylation in seeds. In the present study, changes in a global level of m5C were measured in orthodox seeds of Acer platanoides L. during seed desiccation from a WC of 1.04 to 0.05-0.06 g H2O g g(-1) dry mass (g g(-1)). Changes in the level of DNA methylation were measured using 2D TLC e based method. Quality of desiccated seeds was examined by germination and seedling emergence tests. Global m5C content (R2)increase was observed in embryonic axes isolated from seeds collected at a high WC of 1.04 g g(-1) after their desiccation to significantly lower WC of 0.17 and 0.19 g g(-1). Further desiccation of these seeds to a WC of 0.06 g g(-1), however, resulted in a significant DNA demethylation to R2 ¼ 11.52-12.22%. Similar m5C decrease was observed in seeds which undergo maturation drying on the tree and had four times lower initial WC of 0.27 g g(-1) at the time of harvest, as they were dried to a WC of 0.05 g g(-1). These data confirm that desiccation induces changes in seed m5C levels. Results were validated by seed lots derived from tree different A. platanoides provenances. It is plausible that sine wave-like alterations in m5C amount may represent a specific response of orthodox seeds to drying and play a relevant role in desiccation tolerance in seeds.

Dehydrin expression in seeds and maturation drying: a paradigm change

Dehydrins are well known for being expressed in leaves during the course of developmental processes as well as under drought stress, being part of the protective machinery. Moreover, in seed physiology, dehydrins are classified as late embryogenesis-related proteins (LEA protein), where they are thought to be responsible for persistence and longevity of seeds. Although both topics are a focus of modern plant biology, a direct linkage between these both areas is generally lacking. Based on an alignment of the chain of events, this paper will help to generate understanding that the occurrence of dehydrins in maturing seeds and leaves suffering drought stress is part of the same basic principle: basic principle: dehydrins are expressed in response to water shortage. Unfortunately, the related developmental process in seeds, i.e. maturation drying, has not been adequately considered as a part of this process. As a corresponding implication, the chain of events must be adjusted: the differences in dehydrin expression in orthodox, intermediate and recalcitrant seeds could be directly attributed to the occurrence or absence of maturation drying. The differences in dehydrin expression in orthodox, intermediate and recalcitrant seeds, and thus the differences in longevity, could be attributed to the occurrence or absence of a maturation drying.

The Dormancy Marker DRM1/ARP Associated with Dormancy but a Broader Role In Planta

Plants must carefully regulate their development in order to survive a wide range of conditions. Of particular importance to this is dormancy release, deciding when to grow and when not to, given these varying conditions. In order to better understand the growth release mechanism of dormant tissue at the molecular and physiological levels, molecular markers can be used. One gene family that has a long association with dormancy, which is routinely used as a marker for dormancy release, is DRM1/ARP (dormancy-associated gene-1/auxin-repressed protein). This plant-specific gene family has high sequence identity at the protein level throughout several plant species, but its function in planta remains undetermined. This review brings together and critically analyzes findings on the DRM1/ARP family from a number of species. We focus on the relevance of this gene as a molecular marker for dormancy, raising questions of what its role might actually be in the plant.

Seed storage at elevated partial pressure of oxygen, a fast method for analysing seed ageing under dry conditions

BACKGROUND AND AIMS

Despite differences in physiology between dry and relative moist seeds, seed ageing tests most often use a temperature and seed moisture level that are higher than during dry storage used in commercial practice and gene banks. This study aimed to test whether seed ageing under dry conditions can be accelerated by storing under high-pressure oxygen. methods: Dry barley (Hordeum vulgare), cabbage (Brassica oleracea), lettuce (Lactuca sativa) and soybean (Glycine max) seeds were stored between 2 and 7 weeks in steel tanks under 18 MPa partial pressure of oxygen. Storage under high-pressure nitrogen gas or under ambient air pressure served as controls. The method was compared with storage at 45 °C after equilibration at 85 % relative humidity and long-term storage at the laboratory bench. Germination behaviour, seedling morphology and tocopherol levels were assessed.

KEY RESULTS

The ageing of the dry seeds was indeed accelerated by storing under high-pressure oxygen. The morphological ageing symptoms of the stored seeds resembled those observed after ageing under long-term dry storage conditions. Barley appeared more tolerant of this storage treatment compared with lettuce and soybean. Less-mature harvested cabbage seeds were more sensitive, as was the case for primed compared with non-primed lettuce seeds. Under high-pressure oxygen storage the tocopherol levels of dry seeds decreased, in a linear way with the decline in seed germination, but remained unchanged in seeds deteriorated during storage at 45 °C after equilibration at 85 % RH.

CONCLUSIONS

Seed storage under high-pressure oxygen offers a novel and relatively fast method to study the physiology and biochemistry of seed ageing at different seed moisture levels and temperatures, including those that are representative of the dry storage conditions as used in gene banks and commercial practice.

At3g08030 transcript: a molecular marker of seed ageing

BACKGROUND AND AIMS

Prolonged storage generally reduces seed viability and vigour, although the rate of deterioration varies among species and environmental conditions. Here, we suggest a possible ageing molecular marker: At3g08030 mRNA. At3g08030 is a member of the DUF642 highly conserved family of cell-wall-associated proteins that is specific for spermatophytes.

METHODS

At3g08030 expression was performed by RT-PCR and qRT-PCR analysis in seed samples differing in their rate of germination and final germination following a matrix priming and/or controlled deterioration (rapid ageing) treatment.

KEY RESULTS

The At3g08030 gene transcript was present during the entire Arabidopsis thaliana plant life cycle and in seeds, during maturation, the ripening period and after germination. Matrix priming treatment increased the rate of germination of control seeds and seeds aged by controlled deterioration. Priming treatments also increased At3g08030 expression. To determine whether the orthologues of this gene are also age markers in other plant species, At3g08030 was cloned in two wild species, Ceiba aesculifolia and Wigandia urens. As in A. thaliana, the At3g08030 transcript was not present in aged seeds of the tested species but was present in recently shed seeds. A reduction in germination performance of the aged seeds under salt stress was determined by germination assays.

CONCLUSIONS

At3g08030 mRNA detection in a dry seed lot has potential for use as a molecular marker for germination performance in a variety of plant species.

Altered levels of the Taraxacum kok-saghyz (Russian dandelion) small rubber particle protein, TkSRPP3, result in qualitative and quantitative changes in rubber metabolism

Several proteins have been identified and implicated in natural rubber biosynthesis, one of which, the small rubber particle protein (SRPP), was originally identified in Hevea brasiliensis as an abundant protein associated with cytosolic vesicles known as rubber particles. While previous in vitro studies suggest that SRPP plays a role in rubber biosynthesis, in vivo evidence is lacking to support this hypothesis. To address this issue, a transgene approach was taken in Taraxacum kok-saghyz (Russian dandelion or Tk) to determine if altered SRPP levels would influence rubber biosynthesis. Three dandelion SRPPs were found to be highly abundant on dandelion rubber particles. The most abundant particle associated SRPP, TkSRPP3, showed temporal and spatial patterns of expression consistent with patterns of natural rubber accumulation in dandelion. To confirm its role in rubber biosynthesis, TkSRPP3 expression was altered in Russian dandelion using over-expression and RNAi methods. While TkSRPP3 over-expressing lines had slightly higher levels of rubber in their roots, relative to the control, TkSRPP3 RNAi lines showed significant decreases in root rubber content and produced dramatically lower molecular weight rubber than the control line. Not only do results here provide in vivo evidence of TkSRPP proteins affecting the amount of rubber in dandelion root, but they also suggest a function in regulating the molecular weight of the cis-1, 4-polyisoprene polymer.

Molecular and physiological dissection of enhanced seed germination using short-term low-concentration salt seed priming in tomato

Seed germination is the initial step of plant development. Seed priming with salt promotes seed germination in tomato (Solanum lycopersicum L.); however, the molecular and physiological mechanisms underlying the enhancement of seed germination by priming remain to be elucidated. In this study, we examined the following in seeds both during and after priming treatment: the endogenous abscisic acid (ABA) and gibberellin (GA) concentrations; the expression of genes encoding ABA catabolic and GA biosynthesis enzymes, including 8'-hydroxylase (CYP707A), copalyl diphosphate synthase (CPS), GA 20-oxidase (GA20ox) and GA 3-oxidase (GA3ox); and endosperm cap weakening enzymes, including expansin (EXP), class I β-1,3-glucanase (GulB), endo-β-mannanase (MAN) and xyloglucan endotransglucosylase (XTH). Tomato seeds were soaked for 24 h at 25 °C in the dark in 300 mM NaCl (NaCl-priming) or distilled water (hydro-priming). For both priming treatments, the ABA content in the seeds increased during treatment but rapidly decreased after sowing. Both during and after the priming treatments, the ABA levels in the hydro-primed seeds and NaCl-primed seeds were not significantly different. The expression levels of SlGA20ox1, SlGA3ox1 and SlGA3ox2 were significantly enhanced in the NaCl-primed seeds compared to the hydro-primed seeds. The GA(4) content was quantifiable after both types of priming, indicating that GA(4) is the major bioactive GA molecule involved in tomato seed germination. The GA(4) content was significantly higher in the NaCl-primed seeds than in the hydro-primed seeds 12 h after sowing and thereafter. Additionally, the peak expression levels of SlEXP4, SlGulB, SlMAN2 and SlXTH4 occurred earlier and were significantly higher in the NaCl-primed seeds than in the hydro-primed seeds. These results suggest that the observed effect of NaCl-priming on tomato seed germination is caused by an increase of the GA(4) content via GA biosynthetic gene activation and a subsequent increase in the expression of genes related to endosperm cap weakening.

The highly conserved spermatophyte cell wall DUF642 protein family: phylogeny and first evidence of interaction with cell wall polysaccharides in vitro

The evolution of spermatophyte plants involved fundamental changes in cell wall structure and function which resulted from diversification of carbohydrates and proteins. Cell wall proteomic analyses identified a novel family of proteins of yet unknown function, the DUF642 (Domain of Unknown Function 642) proteins. To investigate the evolution of the DUF642 gene family, 154 gene sequences from 24 plant species were analyzed, and phylogenetic inferences were conducted using the Maximum Likelihood and Bayesian Inference methods. Orthologous genes were detected in spermatophyte species and absent in non-seed known plant genomes. Protein sequences shared conserved motifs that defined the signature of the family. Distribution of conserved motifs indicated an ancestral intragenic duplication event. Gene phylogeny documented paleoduplication events originating three or four clades, depending on root position. When based on mid-point rooting, it retrieved four monophyletic clades: A, B, C, and D. A glycosylphosphatidylinositol (GPI)-anchor site and one or two galactose-binding domains-like (GBDLs) could be predicted for some DUF642 proteins. The B, C, and D clades grouped the predicted GPI-anchored proteins. First evidence of in vitro interaction of a DUF642 protein with a cell wall polysaccharide fraction is provided. A competition assay with cellulose prevented this interaction. The degree of diversification and the conservation of the family suggested that DUF642 proteins are key components in seed plant evolution.