S-Nitrosoglutathion Reductase Activity Modulates the Thermotolerance of Seeds Germination by Controlling ABI5 Stability under High Temperature

Seed germination or dormancy status is strictly controlled by endogenous phytohormone and exogenous environment signals. Abscisic acid (ABA) is the important phytohormone to suppress seed germination. Ambient high temperature (HT) also suppressed seed germination, or called as secondary seed dormancy, through upregulating ABI5, the essential component of ABA signal pathway. Previous result shows that appropriate nitric oxide (NO) breaks seed dormancy through triggering S-nitrosoglutathion reductase (GSNOR1)-dependent S-nitrosylation modification of ABI5 protein, subsequently inducing the degradation of ABI5. Here we found that HT induced the degradation of GSNOR1 protein and reduced its activity, thus accumulated more reactive nitrogen species (RNS) to damage seeds viability. Furthermore, HT increased the S-nitrosylation modification of GSNOR1 protein, and triggered the degradation of GSNOR1, therefore stabilizing ABI5 to suppress seed germination. Consistently, the ABI5 protein abundance was lower in the transgenic line overexpressing GSNOR1, but higher in the gsnor mutant after HT stress. Genetic analysis showed that GSNOR1 affected seeds germination through ABI5 under HT. Taken together, our data reveals a new mechanism by which HT triggers the degradation of GSNOR1, and thus stabilizing ABI5 to suppress seed germination, such mechanism provides the possibility to enhance seed germination tolerance to HT through genetic modification of GNSOR1.     

Effects of Nano-Cerium Oxide on Seed Germination and Seedling Growth of <i>Vitex negundo</i>

Cerium oxide nanoparticles (CeO₂NPs) are likely to have dramatic impacts on plant performances, yet the effects of CeO₂NPs on seed germination and seedling growth have not been fully explored. In this study, the seed germination and seedling growth of subshrub species Vitex negundo under different concentrations of CeO₂NPs (low-1 mg/L, medium-100 mg/L, high-500 mg/L) have been discussed. Results showed that: (1) The seed germination rate reduces by 11.25% and 2.5% under the low and medium concentrations of CeO₂NPs, respectively, but increased by 7.08% under the high concentration; (2) CeO₂NPs had significant effects on the growth traits (root length, shoot height and biomass) of seedlings, being the highest under the medium concentration and the lowest under the highest concentration; (3) The superoxide dismutase activity was the maximum (355.91 U/g), but the protein concentration was the minimum (3.85 ug/mL) under the high concentration of CeO₂NPs. Our results indicated that the effects of CeO₂NPs on seed germination and seedling growth are concentrationdependency, i.e., low and medium concentrations inhibited while high concentration promoted seed germination, however, seedling growth showed opposite responses. Therefore, appropriate CeO₂NPs concentrations are beneficial to the seed germination and seedling growth of Vitex negundo and improve the physiological performance of seedlings and enhance their adaptability to environmental adversity.     

Allantoin Alleviates Seed Germination Thermoinhibition in <i>Arabidopsis</i>

Allantoin as the metabolite of purine catabolism can store and remobilize nitrogen for plant growth and development. However, emerging evidence suggests it also contributes to plant tolerance to stress response through altering abscisic acid (ABA) and reducing reactive oxygen species (ROS) level. 1-CYS PEROXIREDOXIN (PER1) is a seed-specific antioxidant that enhances seed longevity through scavenging ROS over-accumulation. High temperature (HT) suppresses seed germination and induces seed secondary dormancy, called as seed germination thermoinhibition. However, the mechanism that allantoin and PER1 regulate seed germination thermoinhibition remains unknown. In this study, we reported that allantoin treatment enhances seed germination under HT stress. Consistently, the aln mutants displayed higher seed germination, as well as more accumulation of endogenous allantoin, than that of wild-type control. Further biochemical and genetic analyses showed that allantoin reduces ABA content under HT, and allantoin targets PER1 to efficiently scavenge HT-induced ROS accumulation, meanwhile, the function of allantoin requires PER1 during seed gemination thermotolerance. Collectively, our finding proposes a novel function of allantoin in enhancing seed germination tolerance to HT, and uncovers the underlying mechanism by which allantoin regulates seed germination through altering ABA metabolism and PER1-mediated ROS level under HT stress.     

Differential Responses of <i>NHX1</i> and <i>SOS1</i> Gene Expressions to Salinity in two <i>Miscanthus sinensis</i> Anderss. Accessions with Different Salt Tolerance

The lignocellulosic crop Miscanthus spp. has been identified as a good candidate for biomass production. The responses of Miscanthus sinensis Anderss. to salinity were studied to satisfy the needs for high yields in marginal areas and to avoid competition with food production. The results indicated that the relative advantages of the tolerant accession over the sensitive one under saline conditions were associated with restricted Na⁺ accumulation in shoots. Seedlings of two accessions (salt-tolerant ‘JM0119’ and salt-sensitive ‘JM0099’) were subjected to 0 (control), 100, 200, and 300 mM NaCl stress to better understand the salt-induced biochemical responses of genes involved in Na⁺ accumulation in M. sinensis. The adaptation responses of genes encoding for Na⁺ /H⁺ antiporters, NHX1 and SOS1 to NaCl stress were examined in JM0119 and JM0099.The cDNA sequences of genes examined were highly conserved among the relatives of M. sinensis based on the sequencing on approximate 600 bp-long cDNA fragments obtained from degenerate PCR. These salt-induced variations of gene expression investigated by quantitative real-time PCR provided evidences for insights of the molecular mechanisms of salt tolerance in M. sinensis. The expression of NHX1 was up-regulated by salt stress in JM0119 shoot and root tissues. However, it was hardly affected in JM0099 shoot tissue except for a significant increase at the 100 mM salt treatment, and it was salt-suppressed in the JM0099 root tissue. In the root tissue, the expression of SOS1 was induced by the high salt treatment in JM0119 but repressed by all salt treatments in JM0099. Thus, the remarkably higher expression of NHX1 and SOS1 were associated with the resistance to Na⁺ toxicity by regulation of the Na⁺ influx, efflux, and sequestration under different salt conditions.     

Identification and Expression Analysis of Abscisic Acid Signal Transduction Genes in Hemp Seeds

Abscisic acid (ABA) is involved in regulating diverse biological processes, but its signal transduction genes and roles in hemp seed germination are not well known. Here, the ABA signaling pathway members, PYL, PP2C and SnRK2 gene families, were identified from the hemp reference genome, including 7 CsPYL (pyrab-actin resistance1-like, ABA receptor), 8 CsPP2CA (group A protein phosphatase 2c), and 7 CsSnRK2 (sucrose nonfermenting1-related protein kinase 2). The content of ABA in hemp seeds in germination stage is lower than that in non-germination stage. Exogenous ABA (1 or 10 μM) treatment had a significant regulatory effect on the selected PYL, PP2C, SnRK2 gene families. CsAHG3 and CsHAI1 were most significantly affected by exogenous ABA treatment. Yeast two-hybrid experiments were performed to reveal that CsPYL5, CsSnRK2.2, and CsSnRK2.3 could interact with CsPP2CA7 and demonstrate that this interaction was ABA-independent. Our results indicated that CsPYL5, CsSnRK2.2, CsSnRK2.3 and CsPP2CA7 might involve in the ABA signaling transduction pathway of hemp seeds during the hemp seed germination stages. This study suggested that novel genetic views can be brought into investigation of ABA signaling pathway in hemp seeds and lay the foundation for further exploration of the mechanism of hemp seed germination.     

A histone methyltransferase inhibits seed germination by increasing PIF1 mRNA expression in imbibed seeds

Phytochrome‐interacting factor 1 (PIF1) inhibits light‐dependent seed germination. The specific function of PIF1 in seed germination is partly due to its high level of expression in imbibed seeds, but the associated regulatory factors have not been identified. Here we show that mutation of the early flowering in short days (EFS) gene, encoding an H3K4 and H3K36 methyltransferase, decreases the level of H3K36me2 and H3K36me3 but not H3K4me3 at the PIF1 locus, reduces the targeting of RNA polymerase II to the PIF1 locus, and reduces mRNA expression of PIF1 in imbibed seeds. Consistently, the efs mutant geminated even under the phyB_off condition, and had an expression profile of PIF1 target genes similar to that of the pif1 mutant. Introduction of an EFS transgene into the efs mutant restored the level of H3K36me2 and H3K36me3 at the PIF1 locus, the high‐level expression of PIF1 mRNA, the expression pattern of PIF1 target genes, and the light‐dependent germination of these seeds. Introduction of a PIF1 transgene into the efs mutant also restored the expression pattern of PIF1 target genes and light‐dependent germination in imbibed seeds, but did not restore the flowering phenotype. Taken together, our results indicate that EFS is necessary for high‐level expression of PIF1 mRNA in imbibed seeds.     

Substrate,Hormone, Winnowing,and Stratification Influence the Seed Germination of <i>Ilex asprella</i> (Hook. et Arn.) Champ. ex Benth

Ilex asprella (Hook. et Arn.) Champ. ex Benth is one of the most important traditional Chinese medicines in southern China. The seeds of Ilex asprella usually have extremely low germination due to their dormancy characteristics, which severely impacts the efficiency of seedling raising and increases labor costs. In this study, to improve the seed germination of I. asprella, the effects of germination substrate, hormone, winnowing, and stratification treatments on the seed germination of I. asprella were investigated. The results of the germination matrix showed that the highest germination percentage of 45.2% was achieved under the 20°C/10°C day/night temperature and vermiculite germination medium conditions. The results of hormone treatments revealed that 100–400 mg/L of gibberellin (GA) and 50–100 mg/L of salicylic acid (SA) were found to be effective in releasing the dormancy of I. asprella seeds. Moreover, winnowing could effectively eliminate unsaturated seeds and impurities, thus improving the seed germination of I. asprella. Furthermore, warm temperature (15°C) stratification could expand the temperature range of I. asprella’s seed germination, which was beneficial for seed germination of I. asprella and for seed nursery at room temperature in production practice. The present study obtained a method to break dormancy and increase seed germination in I. asprella, thereby forming a groundwork for improving the efficiency of large-scale planting of I. asprella.     

Estimation of Growth and Photosynthetic Performance of Two C₄ Species (<i>Pennisetum spicatum</i> (L.) Körn. and <i>Zea mays</i> L.) under a Low Temperature Treatment

Pearl millet (Pennisetum spicatum (L.) Körn.) and maize (Zea mays L.) are C₄ grass species grown for feeding humans and animals in Almadinah Almunawwarah, which is in the western part of Saudi Arabia. During the winter, the mean temperature, which drops to 14°C, represents a major problem for the growth of these species in this region. Therefore, the objectives of this research were to investigate the growth response and the photosynthetic performance of P. spicatum and Z. mays under a low temperature stress. The treatments involved daytime and nighttime temperatures of 14/12°C (low temperature) and 24/22°C (optimum temperature). The results indicated that low temperature significantly reduced all growth and physiological parameters, including seed germination, leaf expansion, leaf area, shoot length and root length of the two species compared to those of the control. Additionally, the low temperature significantly decreased the light-saturated assimilation rate (A_sat), quantum yield (ϕ), saturated rate of carbon dioxide uptake (A_max) and efficiency of carboxylation on both species compared to those of the control. Moreover, the values of Fv/Fm and the chlorophyll contents of both species were significantly reduced by low temperature compared to those of the control. It can be concluded that both species had little tolerance to low temperatures.     

Characterization and Expression of Ammonium Transporter in Peach (<i>Prunus persica</i>) and Regulation Analysis in Response to External Ammonium Supply

As the preferred nitrogen (N) source, ammonium (NH₄⁺ ) contributes to plant growth and development and fruit quality. In plants, NH₄⁺ uptake is facilitated by a family of NH₄⁺ transporters (AMT). However, the molecular mechanisms and functional characteristics of the AMT genes in peach have not been mentioned yet. In this present study, excess NH₄⁺ stress severely hindered shoot growth and root elongation, accompanied with reduced mineral accumulation, decreased leaf chlorophyll concentration, and stunned photosynthetic performance. In addition, we identified 14 putative AMT genes in peach (PpeAMT). Expression analysis showed that PpeAMT genes were differently expressed in peach leaves, stems and roots, and were distinctly regulated by external NH₄⁺ supplies. Putative cis-elements involved in abiotic stress adaption, Ca²⁺ response, light and circadian rhythms regulation, and seed development were observed in the promoters of the PpeAMT family genes. Phosphorylation analysis of residues within the C-terminal of PpeAMT proteins revealed many conserved phosphorylation residues in both the AMT1 and AMT2 subfamily members, which could potentially play roles in controlling the NH₄⁺ transport activities. This study provides gene resources to study the biological function of AMT proteins in peach, and reveals molecular basis for NH₄⁺ uptake and N nutrition mechanisms of fruit trees.     

Overexpression of <i>IbSINA5</i> Increases Cold Tolerance through a CBF SINA-COR Mediated Module in Sweet Potato

Seven in absentia (SINA) family proteins play a central role in plant growth, development and resistance to abiotic stress. However, their biological function in plant response to cold stress is still largely unknown. In this work, a seven in absentia gene IbSINA5 was isolated from sweet potato. Quantitative real-time polymerase chain reaction (qRT-PCR) analyses demonstrated that IbSINA5 was ubiquitously expressed in various tissues and organs of sweet potato, with a predominant expression in fibrous roots, and was remarkably induced by cold, drought and salt stresses. Subcellular localization assays revealed that IbSINA5-GFP fusion protein was mainly localized in cytoplasm and nucleus. Overexpression of IbSINA5 in sweet potato led to dramatically improved resistance to cold stress in transgenic plants, which was associated with the up-regulated expression of IbCOR (cold-regulated) genes, increased proline production, and decreased malondialdehyde (MDA) and H₂O₂ accumulation in the leaves of transgenic plants. Furthermore, transient expression of IbCBF3, a C-repeat binding factor (CBF) gene, in the leaf protoplasts of wild type sweet potato plants up-regulated the expression of both IbSINA5 and IbCOR genes. Our results suggest that IbSINA5 could function as a positive regulator in the cold signaling pathway through a CBF-SINA-COR mediated module in sweet potato, and have a great potential to be used as a candidate gene for the future breeding of new plant species with improved cold resistance.