Delay In Germination Research Articles

Characterization of Arabidopsis thaliana Promoter Bidirectionality and Antisense RNAs by Inactivation of Nuclear RNA Decay Pathways.

In animals, RNA polymerase II initiates transcription bidirectionally from gene promoters to produce pre-mRNAs on the forward strand and promoter upstream transcripts (PROMPTs) on the reverse strand. PROMPTs are degraded by the nuclear exosome. Previous studies based on nascent RNA approaches concluded that Arabidopsis (Arabidopsis thaliana) does not produce PROMPTs. Here, we used steady-state RNA sequencing in mutants defective in nuclear RNA decay including the exosome to reassess the existence of Arabidopsis PROMPTs. While they are rare, we identified ∼100 cases of exosome-sensitive PROMPTs in Arabidopsis. Such PROMPTs are sources of small interfering RNAs in exosome-deficient mutants, perhaps explaining why plants have evolved mechanisms to suppress PROMPTs. In addition, we found ∼200 long, unspliced and exosome-sensitive antisense RNAs that arise from transcription start sites within parts of the genome encoding 3'-untranslated regions on the sense strand. The previously characterized noncoding RNA that regulates expression of the key seed dormancy regulator, DELAY OF GERMINATION1, is a typical representative of this class of RNAs. Transcription factor genes are overrepresented among loci with exosome-sensitive antisense RNAs, suggesting a potential for widespread control of gene expression via this class of noncoding RNAs. Lastly, we assess the use of alternative promoters in Arabidopsis and compare the accuracy of existing TSS annotations.

Seed treatment with the fungicide fluopyram limits cotyledon infection by Leptosphaeria maculans and reduces blackleg of canola

Blackleg, caused by Leptosphaeria maculans, is a serious disease on canola or rapeseed in Canada, Australia and Europe. Disease levels have increased in western Canada recently and additional tools are needed to improve blackleg management. Seed treatment can be a cost-effective approach against blackleg, but there is currently no registered seed-treatment product targeting aboveground blackleg infection. In this study, a range of fungicides was evaluated for control of cotyledon infection by L. maculans and blackleg of canola. Under controlled environmental conditions, fluopyram showed greater efficacy than fluquinconazole (used against blackleg in Australia) in limiting cotyledon infection, while Prosper® EverGol and Helix® Vibrance (industry standards) were ineffective. Fluopyram at a rate of 30–150 g/100 kg seed generally inhibited cotyledon infection and this efficacy was not affected by delayed soil moisture for 3 weeks after planting. This indicates that the efficacy will unlikely be affected by a slight delay in germination due to a soil moisture deficit after seeding. In addition to typical mechanisms of succinate dehydrogenase inhibitor fungicides, fluopyram also induced expression of the indicator gene coding PR-1 proteins substantially, indicating the potential for inducing disease resistance. In field trials at 75 and 150 g/100 kg seed, fluopyram reduced the infection on cotyledons resulting from pricking inoculation on both susceptible and resistant canola cultivars, potentially limiting the infection into the stem. These seed treatment rates reduced the disease severity index (DSI) substantially on the susceptible cultivar, while DSI was low on a resistant cultivar with or without fluopyram treatment.

Wheat PP2C-a10 regulates seed germination and drought tolerance in transgenic Arabidopsis

Key messageA wheat protein phosphatase PP2C-a10, which interacted with TaDOG1L1 and TaDOG1L4, promoted seed germination and decreased drought tolerance of transgenic Arabidopsis.Seed dormancy and germination are critical to plant fitness. DELAY OF GERMINATION 1 (DOG1) is a quantitative trait locus for dormancy in Arabidopsis thaliana. Some interactions between DOG1 and the type 2C protein phosphatases (PP2Cs) have been reported in Arabidopsis. However, the research on molecular functions and regulations of DOG1Ls and group A PP2Cs in wheat (Triticum aestivum. L), an important crop plant, is rare. In this study, the whole TaDOG1L family was identified. Expression analysis revealed that TaDOG1L2, TaDOG1L4 and TaDOG1L-N2 specially expressed in wheat grains, while others displayed distinct expression patterns. Yeast two-hybrid analysis of TaDOG1Ls and group A TaPP2Cs revealed interaction patterns differed from those in Arabidopsis, and TaDOG1L1 and TaDOG1L4 interacted with TaPP2C-a10. The qRT-PCR analysis showed that TaPP2C-a10 exhibited the highest transcript level in wheat grains. Further investigation showed that ectopic expression of TaPP2C-a10 in Arabidopsis promoted seed germination and decreased sensitivity to ABA during germination stage. Additionally, TaPP2C-a10 transgenic Arabidopsis exhibited decreased tolerance to drought stress. Finally, the phylogenetic analysis indicated that TaPP2C-a10 gene was conserved in angiosperm during evolutionary process. Overall, our results reveal the role of TaPP2C-a10 in seed germination and abiotic stress response, as well as the functional diversity of TaDOG1L family.

Dormancy cycling: translation-related transcripts are the main difference between dormant and non-dormant seeds in the field.

SummaryPrimary seed dormancy is a mechanism that orchestrates the timing of seed germination in order to prevent out‐of‐season germination. Secondary dormancy can be induced in imbibed seeds when they encounter prolonged unfavourable conditions. Secondary dormancy is not induced during dry storage, and therefore the mechanisms underlying this process have remained largely unexplored. Here, a 2‐year seed burial experiment in which dormancy cycling was studied at the physiological and transcriptional level is presented. For these analyses six different Arabidopsis thaliana genotypes were used: Landsberg erecta (Ler) and the dormancy associated DELAY OF GERMINATION (DOG) near‐isogenic lines 1, 2, 3, 6 and 22 (NILDOG1, 2, 3, 6 and 22). The germination potential of seeds exhumed from the field showed that these seeds go through dormancy cycling and that the dynamics of this cycling is genotype dependent. RNA‐seq analysis revealed large transcriptional changes during dormancy cycling, especially at the time points preceding shifts in dormancy status. Dormancy cycling is driven by soil temperature and the endosperm is important in the perception of the environment. Genes that are upregulated in the low‐ to non‐dormant stages are enriched for genes involved in translation, indicating that the non‐dormant seeds are prepared for rapid seed germination.

Teaching an Old Dog a New Trick: Multifaceted Strategies to Control Primary Seed Germination by DELAY OF GERMINATION 1 (DOG1)

Primary seed dormancy is a critical trait for sustainable agricultural development, ensuring seed germination under favorable conditions. The induction, maintenance and release of seed dormancy is a complicated physiological process that is strictly controlled by a variety of endogenous signals and environmental factors. In Arabidopsis, DOG1 (DELAY OF GERMINATION 1) is identi- fied as the main quantitative trait locus (QTL) of seed dormancy, which contributes to deep dormancy in the Cvi ecotype. In recent years, considerable progress has been made to elucidate the molecular regulatory mechanism by which DOG1 controls seed dormancy. In this review, we describe a series of findings on the role of DOG1 in controlling primary seed dormancy, ranging from transcriptional and posttranslational regulation, epigenetic modification, and protein stability to biochemical functions during environmental perception and adaptation. We propose that the DOG1-based regulatory network is a good model for elucidating the basic biological mechanism governing seed dormancy and providing valuable information to genetically engineer crops for quality improvement.

In vitro efficacy of two commercial products of Metarhizium anisopliae s.l. for controlling the cattle tick Rhipicephalus microplus

The effects of two different products - Metarril® SP Organic (dry conidia) and Metarril® SC Organic (emulsifiable concentrated conidia in vegetable oil) - on eggs, larvae and Rhipicephalus microplus engorged females were here explored. Three concentrations (108, 107, and 106 conidia mL-1) for both products were prepared in water + 0.1% Tween® 80 (v/v); afterward, bioassays were carried out for all R. microplus stages by immersion in suspensions (Metarril® SP) or formulations (Metarril® SC). Metarril® SP suspensions showed low efficacy and did not affect biological parameters of treated engorged females; for eggs and larvae, only slight decreases in hatchability and larvae population were observed. Despite a delay in germination, Metarril® SC presented better results; for females, reductions in Egg Mass Weight (EMW) and Egg Production Index (EPI) were reported. On eggs, 108 conidia mL-1 increased Incubation Period (IP), shortened Hatching Period (HP) and decreased hatchability by up to 61%; for larvae, 107 and 108 conidia mL-1 reached 99.6 and 100% larval mortality respectively, 10 days after fungal exposure. Thus, further studies involving the use of oil-based formulations for ticks such as Metarril® SC need to be performed, especially to control the most susceptible stages (eggs and larvae).

The Evening Complex and the Chromatin-Remodeling Factor PICKLE Coordinately Control Seed Dormancy by Directly Repressing DOG1 in Arabidopsis

Primary seed dormancy is acquired during seed development and maturation, which is important for plant fitness and survival. DELAY OF GERMINATION1 (DOG1) plays a critical role in inducing seed dormancy. DOG1 expression increases rapidly during seed development, but the precise mechanism underlying this process remains elusive. In this study, we showed that mutants with a loss or reduced function of the chromatin-remodeling factor PICKLE (PKL) exhibit increased seed dormancy. PKL associates with DOG1 chromatin and inhibits its transcription. We found that PKL physically interacts with LUX ARRHYTHMO (LUX), a member of the evening complex (EC) of the circadian clock. Furthermore, LUX directly binds to a specific coding sequence of DOG1, and DOG1 acts genetically downstream of PKL and LUX. Mutations in either LUX or EARLY FLOWERING3 (ELF3) encoding another member of the EC led to increased DOG1 expression and enhanced seed dormancy. Surprisingly, these phenotypes were abolished when the parent plants were grown under continuous light. In addition, we observed that loss of function of either PKL or LUX decreased H3K27me3 levels at the DOG1 locus. Taken together, our study reveals a regulatory mechanism in which EC proteins coordinate with PKL to transmit circadian signals for directly regulating DOG1 expression and seed dormancy during seed development.

The specific molecular architecture of plant 3-hydroxy-3-methylglutaryl-CoA lyase

3-Hydroxy-3-methylglutaryl-CoA (HMG-CoA) lyase (HMGL) is involved in branched-chain amino acid catabolism leading to acetyl-CoA production. Here, using bioinformatics analyses and protein sequence alignments, we found that in Arabidopsis thaliana a single gene encodes two HMGL isoforms differing in size (51 kDa, HMGL51 and 46 kDa, HMGL46). Similar to animal HMGLs, both isoforms comprised a C-terminal type 1 peroxisomal retention motif, and HMGL51 contained a mitochondrial leader peptide. We observed that only a shortened HMGL (35 kDa, HMGL35) is conserved across all kingdoms of life. Most notably, all plant HMGLs also contained a specific N-terminal extension (P100) that is located between the N-terminal mitochondrial targeting sequence TP35 and HMGL35 and is absent in bacteria and other eukaryotes. Interestingly, using HMGL enzyme assays, we found that rather than HMGL46, homodimeric recombinant HMGL35 is the active enzyme catalyzing acetyl-CoA and acetoacetate synthesis when incubated with (S)-HMG-CoA. This suggested that the plant-specific P100 peptide may inactivate HMGL according to specific physiological requirements. Therefore, we investigated whether the P100 peptide in HMGL46 alters its activity, possibly by modifying the HMGL46 structure. We found that induced expression of a cytosolic HMGL35 version in A. thaliana delays germination and leads to rapid wilting and chlorosis in mature plants. Our results suggest that in plants, P100-mediated HMGL inactivation outside of peroxisomes or mitochondria is crucial, protecting against potentially cytotoxic effects of HMGL activity while it transits to these organelles.

Arabidopsis thaliana SEED DORMANCY 4-LIKE regulates dormancy and germination by mediating the gibberellin pathway.

The molecular mechanisms underlying seed dormancy and germination are not fully understood. Here, we show that Arabidopsis thaliana SEED DORMANCY 4-LIKE (AtSdr4L) is a novel specific regulator of dormancy and germination. AtSdr4L encodes a protein with an unknown biochemical function that is localized in the nucleus and is expressed specifically in seeds. Loss of function of AtSdr4L results in increased seed dormancy. The germination of freshly harvested seeds of the Atsdr4l mutant is insensitive to gibberellin (GA). After-ripened mutant seeds are hypersensitive to the GA biosynthesis-inhibitor paclobutrazol but show unaltered sensitivity to abscisic acid. Several GA biosynthesis genes and GA-regulated cell wall remodeling genes are down-regulated in the mutant in both dormant and after-ripened seeds. These results suggest that the Atsdr4l mutation causes both decreased GA biosynthesis and reduced responses. In addition, a genetic analysis indicated that AtSdr4L is epistatic to DELAY OF GERMINATION1 (DOG1) for dormancy and acts upstream of RGA-LIKE 2 (RGL2) in the GA pathway. We propose that AtSdr4L regulates seed dormancy and germination by mediating both the DOG1 and GA pathways.

DELAY OF GERMINATION1-LIKE4 acts as an inducer of seed reserve accumulation.

More than 70% of global food supply depends on seeds. The major seed reserves, such as proteins, lipids, and polysaccharides, are produced during seed maturation. Here, we report that DELAY OF GERMINATION1-LIKE4 (DOGL4) is a major inducer of reserve accumulation during seed maturation. The DOGL family proteins are plant-specific proteins of largely unknown biochemical function. DOGL4 shares only limited homology in amino acid sequence with DOG1, a major regulator of seed dormancy. DOGL4 was identified as one of the outstanding abscisic acid (ABA)-induced genes in our RNA sequencing analysis, whereas DOG1 was not induced by ABA. Induction of DOGL4 caused the expression of 70 seed maturation-specific genes, even in germinating seeds, including the major seed reserves ALBUMIN, CRUCIFERIN and OLEOSIN. Although DOG1 affects the expression of many seed maturation genes, the major seed reserve genes induced by DOGL4 are not altered by the dog1 mutation. Furthermore, the reduced dormancy and longevity phenotypes observed in the dog1 seeds were not observed in the dogl4 mutants, suggesting that these two genes have limited functional overlap. Taken together, these results suggest that DOGL4 is a central factor mediating reserve accumulation in seeds, and that the two DOG1 family proteins have diverged over the course of evolution into independent regulators of seed maturation, but retain some overlapping function.

AoStuA, an APSES transcription factor, regulates the conidiation, trap formation, stress resistance and pathogenicity of the nematode-trapping fungus Arthrobotrys oligospora.

The APSES protein family comprises a conserved class of fungus-specific transcriptional regulators. Some members have been identified in partial ascomycetes. In this study, the APSES protein StuA (AoStuA) of the nematode-trapping fungus Arthrobotrys oligospora was characterized. Compared with the wild-type (WT) strain, three ΔAoStuA mutants grew relatively slowly, displayed a 96% reduction in sporulation capacity and a delay in conidial germination. The reduced sporulation capacity correlated with transcriptional repression of several sporulation-related genes. The mutants were also more sensitive to chemical stressors than the WT strain. Importantly, the mutants were unable to produce mycelial traps for nematode predation. Moreover, peroxisomes and Woronin bodies were abundant in the WT cells but hardly found in the cells of those mutants. The lack of such organelles correlated with transcriptional repression of some genes involved in the biogenesis of peroxisomes and Woronin bodies. The transcript levels of several genes involved in the cAMP/PKA signalling pathway were also significantly reduced in the mutants versus the WT strain, implicating a regulatory role of AoStuA in the transcription of genes involved in the cAMP/PKA signalling pathway that regulates an array of cellular processes and events. In particular, AoStuA is indispensable for A. oligospora trap formation and virulence.

Synergistic Inhibition of Mycotoxigenic Fungi and Mycotoxin Production by Combination of Pomegranate Peel Extract and Azole Fungicide.

Fungal plant pathogens cause considerable losses in yield and quality of field crops worldwide. In addition, under specific environmental conditions, many fungi, including such as some Fusarium and Aspergillus spp., are further able to produce mycotoxins while colonizing their host, which accumulate in human and animal tissues, posing a serious threat to consumer health. Extensive use of azole fungicides in crop protection stimulated the emergence of acquired azole resistance in some plant and human fungal pathogens. Combination treatments, which become popular in clinical practice, offer an alternative strategy for managing potentially resistant toxigenic fungi and reducing the required dosage of specific drugs. In the current study we tested the effect of pomegranate peel extract (PPE) on the growth and toxin production of the mycotoxigenic fungi Aspergillus flavus and Fusarium proliferatum, both alone and in combination with the azole fungicide prochloraz (PRZ). Using time-lapse microscopy and quantitative image analysis we demonstrate significant delay of conidial germination and hyphal elongation rate in both fungi following PPE treatment in combination with PRZ. Moreover, PPE treatment reduced aflatoxin production by A. flavus up to 97%, while a combined treatment with sub-inhibitory doses of PPE and PRZ resulted in complete inhibition of toxin production over a 72 h treatment. These findings were supported by qRT-PCR analysis, showing down-regulation of key genes involved in the aflatoxin biosynthetic pathway under combined PPE/PRZ treatment al low concentrations. Our results provide first evidence for synergistic effects between the commercial drug PRZ and natural compound PPE. Future application of these findings may allow to reduce the required dosage of PRZ, and possibly additional azole drugs, to inhibit mycotoxigenic fungi, ultimately reducing potential concerns over exposure to high doses of these potentially harmful fungicides.

The Long-Standing Paradox of Seed Dormancy Unfolded?

There has been a long-standing question in seed research, why cyanide, a respiration inhibitor, breaks seed dormancy. While the alternative respiratory pathway and reactive oxygen species have been suggested to be part of the mechanism, the cell biological and mechanistic significance of this paradox remains unclear. The outcomes of recent research on mitochondrial RNA processing for the subunits of the electron transport chain complexes seem to offer a logical explanation. This opinion article attempts to integrate the accumulating evidence of mitochondrial involvement in ABA signaling with the frontier of seed research on DELAY OF GERMINATION1, a master regulator of dormancy, to present a coherent model for ABA signaling in seeds, which could also address the old paradox in seed research.

Overexpression of NtabDOG1L promotes plant growth and enhances drought tolerance in Nicotiana tabacum

Drought is one of the major environmental stresses limiting crop growth and production. It is very important to exploit and utilize drought-tolerance genes to improve crop drought-resistance. In this study, we identified two homoeologs of a Nicotiana tabacum (Ntab) DELAY OF GERMINATION (DOG) 1 like gene, named as NtabDOG1L-T and NtabDOG1L-S, respectively. The NtabDOG1L genes were preferentially expressed in roots and their expression levels were induced by polyethylene glycol, high salt, cold, and abscisic acid treatments. Subcellular localization results indicated that NtabDOG1L-T was localized in the nucleus, cytoplasm and cell membrane. Overexpression of NtabDOG1L-T in tobacco resulted in roots growth enhancement in transgenic plants. Furthermore, overexpression of NtabDOG1L-T enhanced drought stress tolerance in transgenic tobacco. The transgenic tobacco lines exhibited lower leaf water loss and electrolyte leakage, lower content of malondialdehyde and reactive oxygen species (ROS), and higher antioxidant enzymes activities after drought treatment when compared with wild type (WT) plants. In addition, the expression levels of several genes encoding key antioxidant enzymes and drought-related proteins were higher in the transgenic plants than in the WT plants under drought stress. Taken together, our results showed that NtabDOG1L functions as a novel regulator that improves plant growth and drought tolerance in tobacco.

Arabidopsis Histone Methyltransferase SUVH5 Is a Positive Regulator of Light-Mediated Seed Germination.

Plant lifecycle starts from seed germination, which is regulated by various environmental cues and endogenous hormones. Light promotes seed germination mainly by phytochrome B (PHYB) during the initial phase of imbibition, which involves genome-wide light-responsive transcription changes. Recent studies indicated an involvement of multiple epigenetic factors in the control of seed germination. However, few studies have been reported about the role of a histone methyltransferase in light-mediated seed germination process. Here, we identified SUVH5, a histone H3 lysine 9 methyltransferase, as a positive regulator in light-mediated seed germination in Arabidopsis. Loss of function of SUVH5 leads to decreased PHYB-dependent seed germination. RNA-sequencing analysis displayed that SUVH5 regulates 24.6% of light-responsive transcriptome in imbibed seeds, which mainly related to hormonal signaling pathways and developmental processes. Furthermore, SUVH5 represses the transcription of ABA biosynthesis and signal transduction-related genes, as well as a family of DELAY OF GERMINATION (DOG) genes via dimethylation of histone H3 at lysine 9 (H3K9me2) in imbibed seeds. Taken together, our findings revealed that SUVH5 is a novel positive regulator of light-mediated seed germination in Arabidopsis.

Coumarin-Induced Delay of Rice Seed Germination Is Mediated by Suppression of Abscisic Acid Catabolism and Reactive Oxygen Species Production.

Abscisic acid (ABA) is a crucial phytohormone for the regulation of seed germination. The ABA content of seeds is regulated by synthesis and catabolic pathways. Coumarin, an important plant allelochemical, can inhibit seed germination effectively, although whether it is involved in the regulation of ABA content during seed germination has not been elucidated. For the study reported herein, we show that coumarin effectively inhibits rice seed germination and vivipary. We found that the ABA content gradually decreased in water-imbibed rice seeds and that the content and activity of the Oryza sativa 9-cis epoxycarotenoid dioxygenases (OsNCEDs), which are ABA synthases, decreased during seed germination. At the transcription level, the expression of OsNCED1–3 appeared to decrease, whereas the expression of the ABA 8′-hydroxylase 2 and 3 genes (OsABA8’ox2/3) first appeared to increase and then decrease. Samples of rice seeds were also imbibed in water containing coumarin, which increased their ABA content but did not significantly increase the activity or content of their OsNCEDs or OsNCED1–3 transcription. Interestingly, coumarin imbibition remarkably reduced OsABA8’ox2/3 expression in rice embryos, which partially explained how coumarin increased the ABA content of germinating rice embryos. Coumarin also inhibited the accumulation of reactive oxygen species (ROS) in rice embryos and increased the activity of superoxide dismutase and catalase, which are indispensable for seed germination. These results indicate that coumarin delays seed germination by inhibiting ABA catabolism, particularly by decreasing the expression of OsABA8’ox2/3 rather than by increasing ABA synthesis. Moreover, coumarin increases the ABA content while decreasing the ROS content in rice embryos. Our results enhance our understanding of the regulation of ABA and ROS during seed germination and provide theoretical support for application of coumarin to prevent sprouting before crop harvesting.

PERKECAMBAHAN BIJI DAN TIPE-TIPE FUNGSIONAL SEMAI PADA JENIS-JENIS SUKU ANNONACEAE

Annonaceae produces small to large seeds. The size of seeds is closely related to the amount of food reserves that directly affect germination process. Cotyledons of the Annonaceae vary according to its exposure, position, or texture/function. This research aimed to determine the seed germination characters of 21 species of Annonaceae in Bogor Botanic Gardens. Twenty five to thirty seeds of each species were planted in a sand medium. First germination, germination rate and seedling functional types were observed and recorded. The result confirmed that Annonaceae seeds required varied time to germinate, i.e. fast, slow and delay germination. There were seven species included in the fast germination, 11 species slow germination and three species delayed germination. The earliest seed germination occurred at 24 days after sowing (DAS) ( Cananga odorata ), whereas the longest occurred at 212 DAS ( Platymitra macrocarpa ). The number of species with cryptocotylar cotyledon type was more than those of phanerocotylar cotyledons type (14 species and seven species, respectively). The epigeal cotyledons type found in 17 species that is higher than hypogeal cotyledon type (four species). Species with cotyledon reserve type were more than foliar cotyledons type (14 species and seven species, respectively). The proportion of seedling types PEF ( phanerocotylar-epigeal-foliaceous ), CER ( crypto-cotylar-epigeal-reservoir ) and CHR ( crypto-cotylar-hypogeal-reservoir ) were 33.33%, 47.62%, 19.05% respectively

Assessment of Effects of Soil Allelotoxicity and Toxicity of Fungicides on the Development of Grain Crops

Allelotoxicity of soils has a negative effect on plant growth, which was evident in the delay of germination under field conditions, namely, a time shift in the development of crops. The technique for determining the time shift under laboratory conditions has been developed. It has been possible to assess the impact of soil allelotoxicity on the yield by comparing the results obtained with the available literature data on the effect of sowing time on yield reduction. For this purpose, a time delay in seed germination and the development of seedlings in soils was compared with the time required for the same development stages for crops sown on the quartz sand, which does not contain toxins. It was found out that the dependence of time shift, expressed in percentage of the value of soil allelotoxicity, has an exponential character. Therefore, time shift may at times exceed the period of seeds development on an inert substrate in case of high soil allelotoxicity. It has been shown that the pre-sowing seed treatment with fungicides in some cases greatly increased the joint inhibition effect of soils and fungicides on seed germination and development of seedlings. Hence, in order to prevent a decrease in yield before application of fungicides for specific crops (varieties) and soils, it is necessary to check up the possibility of their application with developed laboratory technique.

Basic LEUCINE ZIPPER TRANSCRIPTION FACTOR67 Transactivates DELAY OF GERMINATION1 to Establish Primary Seed Dormancy in Arabidopsis.

Seed dormancy governs the timing of germination, one of the most important developmental transitions in a plant's life cycle. The DELAY OF GERMINATION1 (DOG1) gene is a key regulator of seed dormancy and a major quantitative trait locus in Arabidopsis (Arabidopsis thaliana). DOG1 expression is under tight developmental and environmental regulation, but the transcription factors involved are not known. Here we show that basic LEUCINE ZIPPER TRANSCRIPTION FACTOR67 (bZIP67) acts downstream of the central regulator of seed development, LEAFY COTYLEDON1, to transactivate DOG1 during maturation and help to establish primary dormancy. We show that bZIP67 overexpression enhances dormancy and that bZIP67 protein (but not transcript) abundance is increased in seeds matured in cool conditions, providing a mechanism to explain how temperature regulates DOG1 expression. We also show that natural allelic variation in the DOG1 promoter affects bZIP67-dependent transactivation, providing a mechanism to explain ecotypic differences in seed dormancy that are controlled by the DOG1 locus.

Microplastics accumulate on pores in seed capsule and delay germination and root growth of the terrestrial vascular plant Lepidium sativum

The impacts of nano- and microplastics (<100 nm and <5 mm, respectively) on terrestrial systems is to the present largely unexplored. Plastic particles are likely to accumulate in these systems primarily by the application of sewage sludge. The aim of the current study was to investigate the effects of three sizes of plastic particles (50, 500, and 4800 nm) on a terrestrial plant (cress; Lepidium sativum), using a standardized 72 h bioassay. Cress seeds were exposed to five different concentrations of plastics, ranging from 103 to 107 particles mL−1. Germination rate was significantly reduced after 8 h of exposure for all three sizes of plastics, with increased adverse effect with increasing plastic sizes. Seeds exposed to 4800 nm microplastics showed a germination rate decline from 78% in control to 17% in the highest exposure. No difference in germination rate occurred after 24 h of exposure, regardless of the size of the plastic used. Significant differences in root growth were observed after 24 h, but not after 48 or 72 h of exposure. Impacts on germination are likely due to physical blockage of the pores in the seed capsule by microplastics as shown by confocal microscopy of fluorescent microplastics. In later stages, the microplastics particularly accumulated on the root hairs. This is the first detailed study on the effect of nano- and microplastics on a vascular, terrestrial plant, and our results indicate short-term and transient adverse effects.