Exogenous auxin regulates multi-metabolic network and embryo development, controlling seed secondary dormancy and germination in Nicotiana tabacum L

The elongation factor 1-alpha as storage reserve and environmental sensor in Nicotiana tabacum L. seeds

Given their critical role in plant reproduction and survival, seeds demand meticulous regulatory mechanisms to effectively store and mobilize reserves. Within seeds, the condition of storage reserves heavily depends on environmental stimuli and hormonal activation. Unlike non-protein reserves that commonly employ dedicated regulatory proteins for signaling, proteinaceous reserves may show a unique form of 'self-regulation', amplifying efficiency and precision in this process. Proteins rely on stability to carry out their functions. However, in specific physiological contexts, particularly in seed germination, protein instability becomes essential, fulfilling roles from signaling to regulation. In this study, the elongation factor 1-alpha has been identified as a main proteinaceous reserve in Nicotiana tabacum L. seeds and showed peculiar changes in stability based on tested chemical and physical conditions. A detailed biochemical analysis followed these steps to enhance our understanding of these protein attributes. The protein varied its behavior under different conditions of pH, temperature, and salt concentration, exhibiting shifts within physiological ranges. Notably, distinct solubility transitions were observed, with the elongation factor 1-alpha becoming insoluble upon reaching specific thresholds determined by the tested chemical and physical conditions. The findings are discussed within the context of seed signaling in response to environmental conditions during the key transitions of dormancy and germination.

Unraveling the role of PlARF2 in regulating deed formancy in Paeonia lactiflora

MAIN CONCLUSION

PlARF2 can positively regulate the seed dormancy in Paeonia lactiflora Pall. and bind the RY cis-element. Auxin, a significant phytohormone influencing seed dormancy, has been demonstrated to be regulated by auxin response factors (ARFs), key transcriptional modulators in the auxin signaling pathway. However, the role of this class of transcription factors (TFs) in perennials with complex seed dormancy mechanisms remains largely unexplored. Here, we cloned and characterized an ARF gene from Paeonia lactiflora, named PlARF2, which exhibited differential expression levels in the seeds during the process of seed dormancy release. The deduced amino acid sequence of PlARF2 had high homology with those of other plants and contained typical conserved Auxin_resp domain of the ARF family. Phylogenetic analysis revealed that PlARF2 was closely related to VvARF3 in Vitis vinifera. The subcellular localization and transcriptional activation assay showed that PlARF2 is a nuclear protein possessing transcriptional activation activity. The expression levels of dormancy-related genes in transgenic callus indicated that PlARF2 was positively correlated with the contents of PlABI3 and PlDOG1. The germination assay showed that PlARF2 promoted seed dormancy. Moreover, TF Centered Yeast one-hybrid assay (TF-Centered Y1H), electrophoretic mobility shift assay (EMSA) and dual-luciferase reporter assay analysis (Dual-Luciferase) provided evidence that PlARF2 can bind to the 'CATGCATG' motif. Collectively, our findings suggest that PlARF2, as TF, could be involved in the regulation of seed dormancy and may act as a repressor of germination.

BSISTER transcription factors directly binds to the promoter of IAA19 and IAA29 genes to up-regulate gene expression and promote the root development

Roots play an important role in the growth and development of plants and auxin participates in regulating plant root development. Some studies have shown that BS (BSISTER) gene (the closest gene of class B gene) is involved in plant root development, but whether BS regulates root development via auxin signaling still not clear. To explore VviBS1 and VviBS2 roles in root development, VviBS1 and VviBS2 were overexpressedin Arabidopsis tt16 mutant and we found that they could restore the phenotype of shorter PR (primary roots) and high density of LR (lateral root) of tt16 compared with the wild type Ws Arabidopsis seedlings. However, the addition of exogenous NAA (naphthalene acetic acid) could not significantly promote the PR length of tt16 Arabidopsis, and the auxin signal transduction of tt16 may be blocked. The expression levels of auxin signal transduction pathway genes in Ws, tt16, p35s:VviBS1 in tt16 and p35s:VviBS2 in tt16 seedlings were detected. It was found that the expression of AtARF2, AtARF12, AtARF14, AtARF15, AtARF20, AtGH3, AtGH3-2 and AtSAUR51 genes in tt16 seedlings was higher than that in Ws, while the expression of AtIAA19 and AtIAA29 in Ws seedlings was higher than that of tt16. More importantly, BS may up regulate AtIAA19 and AtIAA29 expression directly by binding to their promoter. In addition, VviBS1 and VviBS2 also affect seed germination and may regulate leaf yellowing by regulating ethylene synthase. Therefore, our findings reveal a molecular mechanism that BS may modulate root system development via Aux/IAA-based auxin signaling, and provide insight into the BS function in regulation of leaf yellowing.

OsHIPL1, a hedgehog-interacting protein-like 1 protein, increases seed vigour in rice

The cultivation of rice varieties with high seed vigour is vital for the direct seeding of rice, and the molecular basis of regulation of seed vigour remains elusive. Here, we cloned a new gene OsHIPL1, which encodes hedgehog-interacting protein-like 1 protein as a causal gene of the major QTL qSV3 for rice seed vigour. OsHIPL1 was mainly localized in the plasma membrane and nucleus. RNA sequencing (RNA-seq) revealed that the ABA-related genes were involved in the OsHIPL1 regulation of seed vigour in rice. The higher levels of endogenous ABA were measured in germinating seeds of OsHIPL1 mutants and NIL-qsv3 line compared to IR26 plants, with two up-regulated ABA biosynthesis genes (OsZEP and OsNCED4) and one down-regulated ABA catabolism gene OsABA8ox3. The expression of abscisic acid-insensitive 3 (OsABI3), OsABI4 and OsABI5 was significantly up-regulated in germinating seeds of OsHIPL1 mutants and NIL-qsv3 line compared to IR26 plants. These results indicate that the regulation of seed vigour of OsHIPL1 may be through modulating endogenous ABA levels and altering OsABIs expression during seed germination in rice. Meanwhile, we found that OsHIPL1 interacted with the aquaporin OsPIP1;1, then affected water uptake to promote rice seed germination. Based on analysis of single-nucleotide polymorphism data of rice accessions, we identified a Hap1 haplotype of OsHIPL1 that was positively correlated with seed germination. Our findings showed novel insights into the molecular mechanism of OsHIPL1 on seed vigour.

Salicylic Acid in Root Growth and Development

In plants, salicylic acid (SA) is a hormone that mediates a plant’s defense against pathogens. SA also takes an active role in a plant’s response to various abiotic stresses, including chilling, drought, salinity, and heavy metals. In addition, in recent years, numerous studies have confirmed the important role of SA in plant morphogenesis. In this review, we summarize data on changes in root morphology following SA treatments under both normal and stress conditions. Finally, we provide evidence for the role of SA in maintaining the balance between stress responses and morphogenesis in plant development, and also for the presence of SA crosstalk with other plant hormones during this process.

Regulation of the Bud Dormancy Development and Release in Micropropagated Rhubarb 'Malinowy'

Culinary rhubarb is a vegetable crop, valued for its stalks, very rich in different natural bioactive ingredients. In commercial rhubarb stalk production, the bud dormancy development and release are crucial processes that determine the yields and quality of stalks. To date, reports on rhubarb bud dormancy regulation, however, are lacking. It is known that dormancy status depends on cultivars. The study aimed to determine the dormancy regulation in a valuable selection of rhubarb ‘Malinowy’. Changes in carbohydrate, total phenolic, endogenous hormone levels, and gene expression levels during dormancy development and release were studied in micropropagated rhubarb plantlets. Dormancy developed at high temperature (25.5 °C), and long day. Leaf senescence and dying were consistent with a significant increase in starch, total phenolics, ABA, IAA and SA levels. Five weeks of cooling at 4 °C were sufficient to break dormancy, but rhizomes stored for a longer duration showed faster and more uniformity leaf growing, and higher stalk length. No growth response was observed for non-cooled rhizomes. The low temperature activated carbohydrate and hormone metabolism and signalling in the buds. The increased expression of AMY3, BMY3, SUS3, BGLU17, GAMYB genes were consistent with a decrease in starch and increase in soluble sugars levels during dormancy release. Moreover, some genes (ZEP, ABF2, GASA4, GA2OX8) related to ABA and GA metabolism and signal transduction were activated. The relationship between auxin (IAA, IBA, 5-Cl-IAA), and phenolic, including SA levels and dormancy status was also observed.

Increased Longevity and Dormancy of Soil-Buried Seeds from Advanced Crop–Wild Rice Hybrids Overexpressing the EPSPS Transgene

Simple Summary

Estimating the survival and reproductive ability caused by a transgene moved from a genetically engineered (GE) crop to its wild relative populations through gene flow plays an important role in assessing the potential environmental risks of the GE crop. Such estimation has essentially focused on the survival and reproduction-related characteristics above the ground, but with little attention to the GE seeds shattered in the soil seed banks. We demonstrated that the herbicide-resistant transgene overexpressing the rice endogenous EPSP enzyme increased the survival and longevity of the GE crop–wild (Oryza rufipogon) hybrid seeds in soil seed banks. In addition, enhanced survival and longevity of the GE hybrid seeds are likely associated with increases in seed dormancy and a growth hormone (auxin) via overexpressing the EPSPS transgene. Therefore, the EPSPS transgene can persist in the soil seed banks and spread in the environment, causing unwanted environmental impacts.

Abstract

Estimating the fitness effect conferred by a transgene introgressed into populations of wild relative species from a genetically engineered (GE) crop plays an important role in assessing the potential environmental risks caused by transgene flow. Such estimation has essentially focused on the survival and fecundity-related characteristics measured above the ground, but with little attention to the fate of GE seeds shattered in the soil seed banks after maturation. To explore the survival and longevity of GE seeds in soil, we examined the germination behaviors of crop–wild hybrid seeds (F₄–F₆) from the lineages of a GE herbicide-tolerant rice (Oryzasativa) line that contains an endogenous EPSPS transgene hybridized with two wild O. rufipogon populations after the seeds were buried in soil. The results showed significantly increased germination of the GE crop–wild hybrid seeds after soil burial, compared with that of the non-GE hybrid seeds. Additionally, the proportion of dormant seeds and the content of the growth hormone auxin (indole-3-acetic acid, IAA) in the GE crop–wild hybrid seeds significantly increased. Evidently, the EPSPS transgene enhances the survival and longevity of GE crop–wild rice seeds in the soil seed banks. The enhanced survival and longevity of the GE hybrid seeds is likely associated with the increases in seed dormancy and auxin (IAA) by overexpressing the rice endogenous EPSPS transgene. Thus, the fate of GE seeds in the soil seed banks should be earnestly considered when assessing the environmental risks caused by transgene flow.

Melatonin inhibits seed germination by crosstalk with abscisic acid, gibberellin, and auxin in Arabidopsis

Seed germination, an important developmental stage in the life cycle of seed plants, is regulated by complex signals. Melatonin is a signaling molecule associated with seed germination under stressful conditions, although the underlying regulatory mechanisms are largely unknown. In this study, we showed that a low concentration (10 µM or 100 µM) of melatonin had no effect on seed germination, but when the concentration of melatonin increased to 500 µM or 1000 µM, seed germination was significantly inhibited in Arabidopsis. RNA sequencing analysis showed that melatonin regulated seed germination correlated to phytohormones abscisic acid (ABA), gibberellin (GA), and auxin. Further investigation revealed that ABA and melatonin synergistically inhibited seed germination, while GA and auxin antagonized the inhibitory effect of seed germination by melatonin. Disruption of the melatonin biosynthesis enzyme gene serotonin N-acetyltransferase (SNAT) or N-acetylserotonin methyltransferase (ASMT) promoted seed germination, while overexpression of ASMT inhibited seed germination. Taken together, our study sheds new light on the function and mechanism of melatonin in modulating seed germination in Arabidopsis.

Temperature Regulation of Primary and Secondary Seed Dormancy in Rosa canina L.: Findings from Proteomic Analysis

Temperature is a key environmental factor restricting seed germination. Rose (Rosa canina L.) seeds are characterized by physical/physiological dormancy, which is broken during warm, followed by cold stratification. Exposing pretreated seeds to 20 °C resulted in the induction of secondary dormancy. The aim of this study was to identify and functionally characterize the proteins associated with dormancy control of rose seeds. Proteins from primary dormant, after warm and cold stratification (nondormant), and secondary dormant seeds were analyzed using 2-D electrophoresis. Proteins that varied in abundance were identified by mass spectrometry. Results showed that cold stratifications affected the variability of the highest number of spots, and there were more common spots with secondary dormancy than with warm stratification. The increase of mitochondrial proteins and actin during dormancy breaking suggests changes in cell functioning and seed preparation to germination. Secondary dormant seeds were characterized by low levels of legumin, metabolic enzymes, and actin, suggesting the consumption of storage materials, a decrease in metabolic activity, and cell elongation. Breaking the dormancy of rose seeds increased the abundance of cellular and metabolic proteins that promote germination. Induction of secondary dormancy caused a decrease in these proteins and germination arrest.

Plant hormonal changes and differential expression profiling reveal seed dormancy removal process in double dormant plant-herbaceous peony

Herbaceous peony (Paeonia lactiflora Pall.) is a popular ornamental and medicinal plant. Taking approximately six to seven months, the seeds germination under natural conditions experiences dual dormancies, which seriously affects horticultural cultivation. Few studies have been conducted on exploring both biological and molecular mechanism that regulates dormancy removal process in hypocotyls double dormant plants. Here, we first measured ABA and GA₃ content changes at four key dormancy break stages, and then performed transcriptomic analyses to identify the differentially expressed genes (DEGs) using RNA-seq. We subsequently carried out Quantitative real-time PCR (qRT-PCR) to validate RNA-seq data. ABA content decreased during the whole dormancy removal process and GA₃ content exhibited decreasing slightly and then increasing trend. RNA sequencing de novo assembly generated a total of 99,577 unigenes. 20,344 unigenes were differentially expressed in the whole dormancy release process. The qPCR results of 54 selected unigenes were consistent with the FPKM values obtained from RNA-seq. Our results summarize a valuable collection of gene expression profiles characterizing the dormancy release process. The DEGs are candidates for functional analyses of genes affecting the dormancy release, which is a precious resource for the on-going physiological and molecular investigation of seeds dormancy removal in other perennial plants.

Revisiting the attempts to fortify methionine content in plant seeds

The sulfur-containing amino acid methionine belongs to the group of essential amino acids, meaning that humans and animals must consume it in their diets. However, plant seeds have low levels of methionine, limiting their nutritional potential. For this reason, efforts have been made over the years to increase methionine levels in seeds. Here, we summarize these efforts and focus particularly on those utilizing diverse genetic and molecular tools. Four main approaches are described: (i) expression of methionine-rich storage proteins in a seed-specific manner to incorporate more soluble methionine into the protein fraction; (ii) reduction of methionine-poor storage proteins inside the seeds to reinforce the accumulation of methionine-rich proteins; (iii) silencing methionine catabolic enzymes; and (iv) up-regulation of key biosynthetic enzymes participating in methionine synthesis. We focus on the biosynthetic genes that operate de novo in seeds and that belong to the sulfur assimilation and aspartate family pathways, as well as genes from the methionine-specific pathway. We also include those enzymes that operate in non-seed tissues that contribute to the accumulation of methionine in seeds, such as S-methylmethionine enzymes. Finally, we discuss the biotechnological potential of these manipulations to increase methionine content in plant seeds and their effect on seed germination.

Hydrogen peroxide burst triggers accumulation of jasmonates and salicylic acid inducing sesquiterpene biosynthesis in wounded Aquilaria sinesis

Agarwood, a non-timber fragrant wood, is produced in wounded Aquilaria trees and widely used in perfume, incense, and medicine. Sesquiterpene is one of its main active compounds. It has been demonstrated that hydrogen peroxide (H₂O₂) plays a role in promoting agarwood sesquiterpene biosynthesis, but little is known about its signaling pathway. In this study, the pruning of actively growing saplings of A. sinensis resulted in an H₂O₂ burst and the accumulation of jasmonic acid (JA), salicylic acid (SA), and ethylene (ET), which was followed by the up-regulation of sesquiterpene synthase and the production of sesquiterpene in the pruned stems. This process could be enhanced by absorbed H₂O₂ and inhibited by an H₂O₂ scavenger (ascorbate, AsA) in pruned stems, although the concentration of ET and transcription of ET-related synthase genes remained unaffected. These results confirmed that the H₂O₂ burst in wounded stems triggered JA and SA accumulation to promote agarwood sesquiterpene biosynthesis. ET was also activated by injury that was independent with H₂O₂. All results excavated a full-scale signaling transduction nets among multiple stress signals during wound-induced agarwood production in A. sinensis and provide a new insight into improving the artificial technology of agarwood production.

Exogenous auxin represses soybean seed germination through decreasing the gibberellin/abscisic acid (GA/ABA) ratio

Auxin is an important phytohormone which mediates diverse development processes in plants. Published research has demonstrated that auxin induces seed dormancy. However, the precise mechanisms underlying the effect of auxin on seed germination need further investigation, especially the relationship between auxins and both abscisic acid (ABA) and gibberellins (GAs), the latter two phytohormones being the key regulators of seed germination. Here we report that exogenous auxin treatment represses soybean seed germination by enhancing ABA biosynthesis, while impairing GA biogenesis, and finally decreasing GA1/ABA and GA4/ABA ratios. Microscope observation showed that auxin treatment delayed rupture of the soybean seed coat and radicle protrusion. qPCR assay revealed that transcription of the genes involved in ABA biosynthetic pathway was up-regulated by application of auxin, while expression of genes involved in GA biosynthetic pathway was down-regulated. Accordingly, further phytohormone quantification shows that auxin significantly increased ABA content, whereas the active GA1 and GA4 levels were decreased, resulting insignificant decreases in the ratiosGA1/ABA and GA4/ABA.Consistent with this, ABA biosynthesis inhibitor fluridone reversed the delayed-germination phenotype associated with auxin treatment, while paclobutrazol, a GA biosynthesis inhibitor, inhibited soybean seed germination. Altogether, exogenous auxin represses soybean seed germination by mediating ABA and GA biosynthesis.