Arabidopsis cold shock domain protein 2 influences ABA accumulation in seed and negatively regulates germination

Unveiling the regulatory role of GRP7 in ABA signal-mediated mRNA translation efficiency regulation

Abscisic acid (ABA) is a crucial phytohormone involved in plant growth and stress responses. While the transcriptional regulation triggered by ABA is well-documented, its effects on translational regulation have been less studied. Through Ribo-seq and RNA-seq analyses, we find that ABA treatment not only influences gene expression at the mRNA level but also significantly impacts mRNA translation efficiency (TE) in Arabidopsis thaliana. ABA inhibits global mRNA translation via its core signaling pathway, which includes ABA receptors, protein phosphatase 2Cs (PP2Cs), and SNF1-related protein kinase 2 s (SnRK2s). Upon ABA treatment, Glycine-rich RNA-binding proteins 7 and 8 (GRP7&8) protein levels decrease due to both reduced mRNA level and decreased TE, which diminishes their association with polysomes and leads to a global decline in mRNA TE. The absence of GRP7&8 results in a global impairment of ABA-regulated translational changes, linking ABA signaling to GRP7-dependent modulation of mRNA translation. The regulation of GRP7 on TE relies significantly on its direct binding to target mRNAs. Moreover, mRNA translation efficiency under drought stress is partially dependent on the ABA-GRP7&8 pathways. Collectively, our study reveals GRP7's role downstream of SnRK2s in mediating translation regulation in ABA signaling, offering a model for ABA-triggered multi-route regulation of environmental adaptation.

Physiology and transcriptome of Eucommia ulmoides seeds at different germination stages

E. ulmoides (Eucommia ulmoides) has significant industrial and medicinal value and high market demand. E. ulmoides grows seedlings through sowing. According to previous studies, plant hormones have been shown to regulate seed germination. To understand the relationship between hormones and E. ulmoides seed germination, we focused on examining the changes in various indicators during the germination stage of E. ulmoides seeds. We measured the levels of physiological and hormone indicators in E. ulmoides seeds at different germination stages and found that the levels of abscisic acid (ABA), gibberellin (GA), and indole acetic acid (IAA) significantly varied as the seeds germinated. Furthermore, we confirmed that ABA, GA, and IAA are essential hormones in the germination of E. ulmoides seeds using Gene Ontology and Kyoto Encyclopedia of Genes and Genomics enrichment analyses of the transcriptome. The discovery of hormone-related synthesis pathways in the control group of Eucommia seeds at different germination stages further confirmed this conclusion. This study provides a basis for further research into the regulatory mechanisms of E. ulmoides seeds at different germination stages and the relationship between other seed germination and plant hormones.

Structural basis of nucleic acid recognition by the N-terminal cold shock domain of the plant glycine-rich protein AtGRP2

AtGRP2 is a glycine-rich, RNA-binding protein that plays pivotal roles in abiotic stress response and flowering time regulation in Arabidopsis thaliana. AtGRP2 consists of an N-terminal cold shock domain (CSD) and two C-terminal CCHC-type zinc knuckles interspersed with glycine-rich regions. Here, we investigated the structure, dynamics, and nucleic acid-binding properties of AtGRP2-CSD. The 2D [1H,15N] heteronuclear single quantum coherence spectrum of AtGRP2-CSD1-79 revealed the presence of a partially folded intermediate in equilibrium with the folded state. The addition of 11 residues at the C terminus stabilized the folded conformation. The three-dimensional structure of AtGRP2-CSD1-90 unveiled a β-barrel composed of five antiparallel β-strands and a 310 helical turn, along with an ordered C-terminal extension, a conserved feature in eukaryotic CSDs. Direct contacts between the C-terminal extension and the β3-β4 loop further stabilized the CSD fold. AtGRP2-CSD1-90 exhibited nucleic acid binding via solvent-exposed residues on strands β2 and β3, as well as the β3-β4 loop, with higher affinity for DNA over RNA, particularly favoring pyrimidine-rich sequences. Furthermore, DNA binding induced rigidity in the β3-β4 loop, evidenced by 15N-{1H} NOE values. Mutation of residues W17, F26, and F37, in the central β-sheet, completely abolished DNA binding, highlighting the significance of π-stacking interactions in the binding mechanism. These results shed light on the mechanism of nucleic acid recognition employed by AtGRP2, creating a framework for the development of biotechnological strategies aimed at enhancing plant resistance to abiotic stresses.

Genome-wide identification of cold shock proteins (CSPs) in sweet cherry (Prunus avium L.) and exploring the differential responses of PavCSP1 and PavCSP3 to low temperature and salt stress

BACKGROUND

Cold shock proteins (CSPs) are ubiquitous nucleic acid-binding proteins involved in growth, development, and stress response across various organisms. While extensively studied in many species, their regulatory roles in sweet cherry (Prunus avium L.) remain unclear.

OBJECTIVE

To identify and analyze CSP genes (PavCSPs) in sweet cherry genome, and explore the differential responses of PavCSP1 and PavCSP3 to low temperature and salt stress.

METHODS

Three methods were employed to identify and characterize CSP in sweet cherry genomes. To explore the potential functions and evolutionary relationships of sweet cherry CSP proteins, sequence alignment and phylogenetic tree incorporating genes from five species were conducted and constructed, respectively. To investigate the responses to abiotic stresses, cis-acting elements analysis and gene expression patterns to low-temperature and salt stress were examined. Moreover, transgenic yeasts overexpressing PavCSP1 or PavCSP3 were generated and their growth under stress conditions were observed.

RESULTS

In this study, three CSP genes (PavCSPs) were identified and comprehensively analyzed. The quantitative real-time PCR revealed diverse expression patterns, with PavCSP1-3 demonstrating a particular activity in the upper stem and all members were responsive to low-temperature and salt stress. Further investigation demonstrated that transgenic yeasts overexpressing PavCSP1 or PavCSP3 exhibited improved growth states following high-salt and low-temperature stress.

CONCLUSION

These findings elucidated the responses of PavCSP1 and PavCSP3 to salt and low-temperature stresses, laying the groundwork for further functional studies of PavCSPs in response to abiotic stresses.

Genome-Wide Analyses of CCHC Family Genes and Their Expression Profiles under Drought Stress in Rose (Rosa chinensis)

CCHC-type zinc finger proteins (CCHC-ZFPs), ubiquitous across plant species, are integral to their growth, development, hormonal regulation, and stress adaptation. Roses (Rosa sp.), as one of the most significant and extensively cultivated ornamentals, account for more than 30% of the global cut-flower market. Despite its significance, the CCHC gene family in roses (Rosa sp.) remains unexplored. This investigation identified and categorized 41 CCHC gene members located on seven chromosomes of rose into 14 subfamilies through motif distribution and phylogenetic analyses involving ten additional plant species, including Ginkgo biloba, Ostreococcus lucimarinus, Arabidopsis thaliana, and others. This study revealed that dispersed duplication likely plays a crucial role in the diversification of the CCHC genes, with the Ka/Ks ratio suggesting a history of strong purifying selection. Promoter analysis highlighted a rich presence of cis-acting regulatory elements linked to both abiotic and biotic stress responses. Differential expression analysis under drought conditions grouped the 41 CCHC gene members into five distinct clusters, with those in group 4 exhibiting pronounced regulation in roots and leaves under severe drought. Furthermore, virus-induced gene silencing (VIGS) of the RcCCHC25 member from group 4 compromised drought resilience in rose foliage. This comprehensive analysis lays the groundwork for further investigations into the functional dynamics of the CCHC gene family in rose physiology and stress responses.

A rice seed-specific glycine-rich protein OsDOR1 interacts with GID1 to repress GA signaling and regulates seed dormancy

Seed dormancy is an important agronomic trait under the control of complex genetic and environmental interactions, which have not been yet comprehensively understood. From the field screening of rice mutant library generated by a Ds transposable element, we identified a pre-harvest sprouting (PHS) mutant dor1. This mutant has a single insertion of Ds element at the second exon of OsDOR1 (LOC_Os03g20770), which encodes a novel seed-specific glycine-rich protein. This gene successfully complemented the PHS phenotype of dor1 mutant and its ectopic expression enhanced seed dormancy. Here, we demonstrated that OsDOR1 protein binds to the GA receptor protein, OsGID1 in rice protoplasts, and interrupts with the formation OsGID1-OsSLR1 complex in yeast cells. Co-expression of OsDOR1 with OsGID1 in rice protoplasts attenuated the GA-dependent degradation of OsSLR1, the key repressor of GA signaling. We showed the endogenous OsSLR1 protein level in the dor1 mutant seeds is significantly lower than that of wild type. The dor1 mutant featured a hypersensitive GA-response of α-amylase gene expression during seed germination. Based on these findings, we suggest that OsDOR1 is a novel negative player of GA signaling operated in the maintenance of seed dormancy. Our findings provide a novel source of PHS resistance.

Developing Genetic Engineering Techniques for Control of Seed Size and Yield

Many signaling pathways regulate seed size through the development of endosperm and maternal tissues, which ultimately results in a range of variations in seed size or weight. Seed size can be determined through the development of zygotic tissues (endosperm and embryo) and maternal ovules. In addition, in some species such as rice, seed size is largely determined by husk growth. Transcription regulator factors are responsible for enhancing cell growth in the maternal ovule, resulting in seed growth. Phytohormones induce significant effects on entire features of growth and development of plants and also regulate seed size. Moreover, the vegetative parts are the major source of nutrients, including the majority of carbon and nitrogen-containing molecules for the reproductive part to control seed size. There is a need to increase the size of seeds without affecting the number of seeds in plants through conventional breeding programs to improve grain yield. In the past decades, many important genetic factors affecting seed size and yield have been identified and studied. These important factors constitute dynamic regulatory networks governing the seed size in response to environmental stimuli. In this review, we summarized recent advances regarding the molecular factors regulating seed size in Arabidopsis and other crops, followed by discussions on strategies to comprehend crops' genetic and molecular aspects in balancing seed size and yield.

Proteomic analysis response of rice (Oryza sativa) leaves to ultraviolet-B radiation stress

Rice (Oryza sativa) is a human staple food and serves as a model organism for genetic and molecular studies. Few studies have been conducted to determine the effects of ultraviolet-B (UV-B) stress on rice. UV-B stress triggers morphological and physiological changes in plants. However, the underlying mechanisms governing these integrated responses are unknown. In this study, we conducted a proteomic response of rice leaves to UV-B stress using two-dimensional gel electrophoresis and identified the selected proteins by mass spectrometry analysis. Four levels of daily biologically effective UV-B radiation intensities were imposed to determine changes in protein accumulation in response to UV-B stress: 0 (control), 5, 10, and 15 kJ m^-2 d^-1in two cultivars, i.e., IR6 and REX. To mimic the natural environment, we conducted this experiment in Sunlit Soil-Plant-Atmosphere-Research (SPAR) chambers. Among the identified proteins, 11% of differentially expressed proteins were found in both cultivars. In the Rex cultivar, only 45% of proteins are differentially expressed, while only 27.5% were expressed in IR6. The results indicate that REX is more affected by UV-B stress than IR6 cultivars. The identified protein TSJT1 (spot 16) in both cultivars plays a crucial role in plant growth and development during stress treatment. Additionally, we found that UV-B stress altered many antioxidant enzymes associated with redox homeostasis and cell defense response. Another enzyme, the glyceraldehyde-3-phosphate dehydrogenase (GAPDH), has been identified as spot 15, which plays an essential role in glycolysis and cellular energy production. Another vital protein identified is glycosyl hydrolase (GH) as spot 9, which catalyzes the hydrolysis of glycosidic bonds in cell wall polymers and significantly affects cell wall architecture. Some identified proteins are related to photosynthesis, protein biosynthesis, signal transduction, and stress response. The findings of our study provide new insights into understanding how rice plants are tailored to UV-B stress via modulating the expression of UV-B responsive proteins, which will help develop superior rice breeds in the future to combat UV-B stress. Data are available via ProteomeXchange with identifier PXD032163.

Comprehensive Genome-Wide Identification, Characterization, and Expression Analysis of CCHC-Type Zinc Finger Gene Family in Wheat (Triticum aestivum L.)

The CCHC-type zinc finger proteins (CCHC-ZFPs) play versatile roles in plant growth, development and adaptation to the environment. However, little is known about functions of CCHC-ZFP gene family memebers in Triticum aestivum. In the present study, we identified a total of 50 TaCCHC-ZFP genes from the 21 wheat chromosomes, which were phylogenetically classified into eight groups based on their specific motifs and gene structures. The 43 segmentally duplicated TaCCHC-ZFP genes were retrieved, which formed 36 segmental duplication gene pairs. The collinearity analyses among wheat and other eight mono/dicots revealed that no gene pairs were found between wheat and the three dicots. The promoter analyses of the TaCCHC-ZFP genes showed that 636 environmental stress-responsive and phytohormone-responsive cis-elements. The gene ontology enrichment analysis indicated that all the TaCCHC-ZFP genes were annotated under nucleic acid binding and metal ion binding. A total of 91 MicroRNA (miRNA) binding sites were identified in 34 TaCCHC-ZFP genes according to the miRNA target analysis. Based on the public transcriptome data, the 38 TaCCHC-ZFP genes were identified as differentially expressed gene. The expression profiles of 15 TaCCHC-ZFP genes were verified by the quantitative real-time PCR assays, and the results showed that these genes were responsive to drought or heat treatments. Our work systematically investigated the gene structures, evolutionary features, and potential functions of TaCCHC-ZFP genes. It lays a foundation for further research and application of TaCCHC-ZFP genes in genetic improvement of T. aestivum.

Natural variation in glycine-rich region of Brassica oleracea cold shock domain protein 5 (BoCSDP5) is associated with low temperature tolerance

BACKGROUND

Low temperature (LT) or cold stress is a major environmental stress that seriously affects plant growth and development, limiting crop productivity. Cold shock domain proteins (CSDPs), which are present in most living organism, are involved in RNA metabolisms influencing abiotic stress tolerance.

OBJECTIVE

The aims of this study are to identify target gene for LT-tolerance, like CSDPs, characterize genetics, and develop molecular marker distinguishing LT-tolerance in cabbage (Brassica oleracea var. capitata).

METHODS

Semi-quantitative RT-PCR or qRT-PCR was used in gene expression study. LT-tolerance was determined by electrolyte leakage and PCR with allelic specific primers.

RESULTS

Allelic variation was found in BoCSDP5 coding sequence (CDs) between LT-tolerant (BN106 and BN553) and -susceptible inbred lines (BN107 and BN554). LT-tolerant inbred lines contained variant type of BoCSDP5 (named as BoCSDP5v) which encodes extra CCHC zinc finger domain at C-terminus. Association of LT-tolerance with BoCSDP5v was confirmed by electrolyte leakage and segregation using genetic population derived from BN553 and BN554 cross. Allelic variation in BoCSDP5 gene does not influence the rate of gene expression, but produces different proteins with different number of CCHC zinc finger domains. LT-tolerance marker designed on the basis of polymorphism between BoCSDP5 and BoCSDP5v was confirmed with samples used in previous B. oleracea CIRCADIAN CLOCK ASSOCIATED 1 (BoCCA1) marker validation.

CONCLUSIONS

LT-tolerant allele (BoCSDP5v) is dominant and independent of CBF pathway, and sufficient to generate molecular markers to identify LT-tolerant cabbage when it is used in combination with another marker, like BoCCA1-derived one. Production and analysis of overexpressing plants of BoCSDP1, BoCSDP3, BoCSDP5 and BoCSDP5v will be required for elucidating the function of CCHC zinc finger domains in LT-tolerance.

In silico identification and evaluation of Bacillus subtilis cold shock protein B (cspB)-like plant RNA chaperones

Cold shock domain (CSD) proteins with nucleic acid binding properties are well conserved from bacteria to higher organisms. In bacteria, the cold shock proteins (CSPs) are single domain RNA chaperones, whereas in animals and plants, CSDs are accompanied by additional domains with roles in transcription regulation. Bacterial CSPs (Escherischia coli-cspA and Bacilus subtilis-cspB) have successfully imparted drought tolerance in transgenic plants; however, these cannot be deployed in food crops due to their low public acceptance of transgenics with bacterial genes. Therefore, this study aimed to identify CSPB-like proteins from plants that can be used for developing drought tolerant transgenic crops. Twelve single domain plant CSPs presenting >40% sequence identity with CSPB were identified. All 12 plant CSPs were modeled by homology modeling and refined by molecular dynamics simulation for 10 ns. Selected plant CSPs and CSPB exhibited high structural similarity (Tm-score: 0.63-0.86). Structure based phylogenetic analysis revealed that Triticum aestivum-csp1 and Aegilops tauschii-cspE are structurally closer to CSPB compared to their orthologs and paralogs. Molecular docking with three RNA molecules (5U, UC3U, and C2UC) indicates that Ricinus communis-csd1 and T. aestivum-csp1 have a binding pattern and docking scores similar to those of CSPB. Furthermore, MD simulations for 20 ns and analysis of RMSD, RMSF, Rg as well as the number of hydrogen bonds in all the three complexes revealed that plant CSP-RNA complexes behave in a similar manner to that of the CSPB-RNA complex, making them highly potential candidate genes for developing drought tolerance in transgenic plants. Communicated by Ramaswamy H. Sarma.

Cloning and Partial Characterization of a Cold Shock Domain-Containing Protein Gene from the Dinoflagellate Scrippsiella trochoidea

CSPs, cold shock domain (CSD) containing proteins, are demonstrated to be involved in low temperature responses and various cellular processes under normal growth conditions. Here, we used the cosmopolitan, toxic, and resting cyst-producing dinoflagellate Scrippsiella trochoidea as a representative harmful algal bloom-forming dinoflagellate to investigate the expression patterns of CSP in vegetative cells in response to temperature shocks and in resting cysts, with an objective to probe the possible function of CSP in dinoflagellates. The full-length cDNA of a CSP gene from S. trochoidea (StCSP) was obtained which has a solely N-terminal CSD with conserved nucleic acids binding motifs. The qPCR results together indicated StCSP expression was not modulated by temperature at the transcriptional level and implied this gene may not be associated with temperature stress responses in S. trochoidea as the gene's name implies. However, we observed significantly higher StCSP transcripts in resting cysts (newly formed and maintained in dormancy for different periods of time) than that observed in vegetative cells (at exponential and stationary stages), indicating StCSP is actively expressed during dormancy of S. trochoidea. Taking together our recent transcriptomic work on S. trochoidea into consideration, we postulate that StCSP may play roles during encystment and cyst dormancy of the species.

Gene Regulation and Signal Transduction in the ICE-CBF-COR Signaling Pathway during Cold Stress in Plants

Low temperature is an abiotic stress that adversely affects the growth and production of plants. Resistance and adaptation of plants to cold stress is dependent upon the activation of molecular networks and pathways involved in signal transduction and the regulation of cold-stress related genes. Because it has numerous and complex genes, regulation factors, and pathways, research on the ICE-CBF-COR signaling pathway is the most studied and detailed, which is thought to be rather important for cold resistance of plants. In this review, we focus on the function of each member, interrelation among members, and the influence of manipulators and repressors in the ICE-CBF-COR pathway. In addition, regulation and signal transduction concerning plant hormones, circadian clock, and light are discussed. The studies presented provide a detailed picture of the ICE-CBF-COR pathway.

The pivotal role of abscisic acid signaling during transition from seed maturation to germination

Seed maturation and germination are two continuous developmental processes that link two distinct generations in spermatophytes; the precise genetic control of these two processes is, therefore, crucially important for the survival of the next generation. Pieces of experimental evidence accumulated so far indicate that a concerted action of endogenous signals and environmental cues is required to govern these processes. Plant hormone abscisic acid (ABA) has been suggested to play a predominant role in directing seed maturation and maintaining seed dormancy under unfavorable environmental conditions until antagonized by gibberellins (GA) and certain environmental cues to allow the commencement of seed germination when environmental conditions are favorable; therefore, the balance of ABA and GA is a major determinant of the timing of seed germination. Due to the advent of new technologies and system biology approaches, molecular studies are beginning to draw a picture of the sophisticated genetic network that drives seed maturation during the past decade, though the picture is still incomplete and many details are missing. In this review, we summarize recent advances in ABA signaling pathway in the regulation of seed maturation as well as the transition from seed maturation to germination, and highlight the importance of system biology approaches in the study of seed maturation.

Evidence for ACD5 ceramide kinase activity involvement in Arabidopsis response to cold stress

Although sphingolipids emerged as important signals for plant response to low temperature, investigations have been limited so far to the function of long-chain base intermediates. The formation and function of ceramide phosphates (Cer-Ps) in chilled Arabidopsis were explored. Cer-Ps were analysed by thin layer chromatography (TLC) following in vivo metabolic radiolabelling. Ceramide kinase activity, gene expression and growth phenotype were determined in unstressed and cold-stressed wild type (WT) and Arabidopsis ceramide kinase mutant acd5. A rapid and transient formation of Cer-P occurs in cold-stressed WT Arabidopsis plantlets and cultured cells, which is strongly impaired in acd5 mutant. Although concomitant, Cer-P formation is independent of long-chain base phosphate (LCB-P) formation. No variation of ceramide kinase activity was measured in vitro in WT plantlets upon cold stress but the activity in acd5 mutant was further reduced by cold stress. At the seedling stage, acd5 response to cold was similar to that of WT. Nevertheless, acd5 seed germination was hypersensitive to cold and abscisic acid (ABA), and ABA-dependent gene expression was modified in acd5 seeds when germinated at low temperature. Our data involve for the first time Cer-P and ACD5 in low temperature response and further underline the complexity of sphingolipid signalling operating during cold stress.

Stress-responsive expression patterns and functional characterization of cold shock domain proteins in cabbage (Brassica rapa) under abiotic stress conditions

Although the functional roles of cold shock domain proteins (CSDPs) have been demonstrated during the growth, development, and stress adaptation of Arabidopsis (Arabidopsis thaliana), rice (Oryza sativa), and wheat (Triticum aestivum), the functions of CSDPs in other plants species, including cabbage (Brassica rapa), are largely unknown. To gain insight into the roles of CSDPs in cabbage under stress conditions, the genes encoding CSDPs in cabbage were isolated, and the functional roles of CSDPs in response to environmental stresses were analyzed. Real-time RT-PCR analysis revealed that the levels of BrCSDP transcripts increased during cold, salt, or drought stress, as well as upon ABA treatment. Among the five BrCSDP genes found in the cabbage genome, one CSDP (BRU12051), named BrCSDP3, was unique in that it is localized to the chloroplast as well as to the nucleus. Ectopic expression of BrCSDP3 in Arabidopsis resulted in accelerated seed germination and better seedling growth compared to the wild-type plants under high salt or dehydration stress conditions, and in response to ABA treatment. BrCSDP3 did not affect the splicing of intron-containing genes and processing of rRNAs in the chloroplast. BrCSDP3 had the ability to complement RNA chaperone-deficient Escherichia coli mutant cells under low temperatures as well as DNA- and RNA-melting abilities, suggesting that it possesses RNA chaperone activity. Taken together, these results suggest that BrCSDP3, harboring RNA chaperone activity, plays a role as a positive regulator in seed germination and seedling growth under stress conditions.

An RNA chaperone, AtCSP2, negatively regulates salt stress tolerance

Cold shock domain (CSD) proteins are RNA chaperones that destabilize RNA secondary structures. Arabidopsis Cold Shock Domain Protein 2 (AtCSP2), one of the 4 CSD proteins (AtCSP1-AtCSP4) in Arabidopsis, is induced during cold acclimation but negatively regulates freezing tolerance. Here, we analyzed the function of AtCSP2 in salt stress tolerance. A double mutant, with reduced AtCSP2 and no AtCSP4 expression (atcsp2-3 atcsp4-1), displayed higher survival rates after salt stress. In addition, overexpression of AtCSP2 resulted in reduced salt stress tolerance. These data demonstrate that AtCSP2 acts as a negative regulator of salt stress tolerance in Arabidopsis.