Flooding stress-induced glycine-rich RNA-binding protein from Nicotiana tabacum

BcGRP23: A novel gene involved in the chlorophyll metabolic pathway that is activated by BES1 in flowering Chinese cabbage

Glycine-rich proteins (GRPs) are a large family of proteins that play vital roles in cell wall remodeling, metabolism and development, and abiotic stress response. Although the functions of GRPs in cell wall remodeling have been extensively characterized, only a few studies have explored their effects on chlorophyll metabolism and hormone response. Accordingly, we aimed to determine the molecular mechanism of BcGRP23 and its role in chlorophyll metabolism and the BRI1-EMS-SUPPRESSOR 1 (BES1) signaling pathway in flowering Chinese cabbage. The expression levels of BcGRP23 in the leaves and stems gradually decreased with increasing growth and development of flowering Chinese cabbage, while BcGRP23 was barely expressed after flowering. As plant growth continued, the GUS (β-glucuronidase) stain gradually became lighter in hypocotyls and was largely free of growth points. The petioles and stems of BcGRP23-silenced plants lost their green color, and the contents of chlorophyll a (Chl a) and Chl b were significantly reduced. Further research revealed that the expression levels of chlorophyll degradation-related genes were significantly increased in silenced plants compared with the control; however, the opposite was noted for the BcGRP23-overexpressing lines. The BcGRP23 promoter sequence contains numerous hormone-responsive elements. In fact, the expression of BcGRP23 was upregulated in flowering Chinese cabbage following treatment with the hormones indole-3-acetic acid (IAA), gibberellin (GA), 6-benzylaminopurine (6-BA), methyl jasmonate (MeJA), and brassinosteroid (BR). Treatment with BR led to the most significant upregulation. BES1, in response to BRs, directly activated the BcGRP23 promoter. Overall, BcGRP23 regulated the expression of chlorophyll degradation-related genes, thereby affecting the chlorophyll content. Furthermore, the expression of BcGRP23 was significantly regulated by exogenous BR application and was directly activated by BES1. These findings preliminarily suggest the molecular mechanism and regulatory pathway of BcGRP23 in the growth and development of flowering Chinese cabbage plants and their response to environmental stress.

RNA-Binding Proteins: The Key Modulator in Stress Granule Formation and Abiotic Stress Response

To cope with abiotic environmental stress, plants rapidly change their gene expression transcriptionally and post-transcriptionally, the latter by translational suppression of selected proteins and the assembly of cytoplasmic stress granules (SGs) that sequester mRNA transcripts. RNA-binding proteins (RBPs) are the major players in these post-transcriptional processes, which control RNA processing in the nucleus, their export from the nucleus, and overall RNA metabolism in the cytoplasm. Because of their diverse modular domain structures, various RBP types dynamically co-assemble with their targeted RNAs and interacting proteins to form SGs, a process that finely regulates stress-responsive gene expression. This review summarizes recent findings on the involvement of RBPs in adapting plants to various abiotic stresses via modulation of specific gene expression events and SG formation. The relationship of these processes with the stress hormone abscisic acid (ABA) is discussed.

Physiological Responses of Two Contrasting Kiwifruit (Actinidia spp.) Rootstocks against Waterlogging Stress

Rootstocks from Actinidia valvata are much more tolerant to waterlogging stress than those from Actinidia deliciosa, which are commonly used in kiwifruit production. To date, the tolerance mechanism of A. valvata rootstocks' adaptation to waterlogging stress has not been well explored. In this study, the responses of KR5 (A. valvata) and 'Hayward' (A. deliciosa) to waterlogging stress were compared. Results showed that KR5 plants performed much better than 'Hayward' during waterlogging by exhibiting higher net photosynthetic rates in leaves, more rapid formation of adventitious roots at the base of stems, and less severe damage to the main root system. In addition to morphological adaptations, metabolic responses of roots including sufficient sucrose reserves, modulated adjustment of fermentative enzymes, avoidance of excess lactic acid and ethanol accumulation, and promoted accumulation of total amino acids all possibly rendered KR5 plants more tolerant to waterlogging stress compared to 'Hayward' plants. Lysine contents of roots under waterlogging stress were increased in 'Hayward' and decreased in KR5 compared with their corresponding controls. Overall, our results revealed the morphological and metabolic adaptations of two kiwifruit rootstocks to waterlogging stress, which may be responsible for their genotypic difference in waterlogging tolerance.

Molecular Characterization, Expression Pattern and Function Analysis of Glycine-Rich Protein Genes Under Stresses in Chinese Cabbage (Brassica rapa L. ssp. pekinensis)

Plant Glycine-rich proteins (GRP), a superfamily with a glycine-rich domain, play an important role in various stresses such as high or low temperature stress and drought stress. GRP genes have been studied in many plants, but seldom in Chinese cabbage (Brassica rapa L. ssp. pekinensis). In this study, a total of 64 GRP genes were identified in Chinese cabbage by homology comparative analysis. The physical and chemical characteristics predicted by ProtParam tool revealed that 62.5% of BrGRPs were alkaline, 53.1% were stable, and 79.7% were hydrophilic. Conserved domain analysis by MEME and TBtools showed that 64 BrGRPs contained 20 of the same conserved motifs, based on which BrGRPs were classified into five main classes and four subclasses in class IV to clarify their evolutionary relationship. Our results demonstrated that The BrGRP genes were located on ten chromosomes and in three different subgenomes of Chinese cabbage, and 43 pairs of orthologous GRP genes were found between Chinese cabbage and Arabidopsis. According to the transcriptome data, 64 BrGRP genes showed abnormal expression under high temperature stress, 52 under low temperature stress, 39 under drought stress, and 23 responses to soft rot. A large number of stress-related cis-acting elements, such as DRE, MYC, MYB, and ABRE were found in their promoter regions by PlantCare, which corresponded with differential expressions. Two BrGRP genes-w546 (Bra030284) and w1409 (Bra014000), both belonging to the subfamily Subclass IVa RBP-GRP (RNA binding protein-glycine rich protein), were up-regulated under 150 mmol⋅L-1 NaCl stress in Chinese cabbage. However, the overexpressed w546 gene could significantly inhibit seed germination, while w1409 significantly accelerated seed germination under 100 mmol⋅L-1 NaCl or 300 mmol⋅L-1 mannitol stresses. In short, most BrGRP genes showed abnormal expression under adversity stress, and some were involved in multiple stress responses, suggesting a potential capacity to resist multiple biotic and abiotic stresses, which is worthy of further study. Our study provides a systematic investigation of the molecular characteristics and expression patterns of BrGRP genes and promotes for further work on improving stress resistance of Chinese cabbage.

Identification and characterisation of a glycine-rich RNA-binding protein as an endogenous suppressor of RNA silencing from Nicotiana glutinosa

MAIN CONCLUSION

This study shows that NgRBP suppresses both local and systemic RNA silencing induced by sense- or double-stranded RNA, and the RNA binding activity is essential for its function. To counteract host defence, many plant viruses encode viral suppressors of RNA silencing targeting various stages of RNA silencing. There is increasing evidence that the plants also encode endogenous suppressors of RNA silencing (ESR) to regulate this pathway. In this study, using Agrobacterium infiltration assays, we characterized NgRBP, a glycine-rich RNA-binding protein from Nicotiana glutinosa, as an ESR. Our results indicated that NgRBP suppressed both local and systemic RNA silencing induced by sense- or double-stranded RNA. We also demonstrated that NgRBP could promote Potato Virus X (PVX) infection in N. benthamiana. NgRBP knockdown by virus-induced gene silencing enhanced PVX and Cucumber mosaic virus resistance in N. glutinosa. RNA immunoprecipitation and electrophoretic mobility shift assays showed that NgRBP bound to GFP mRNA, dsRNA rather than siRNA. These findings provide the evidence that NgRBP acts as an ESR and the RNA affinity of NgRBP plays the key role in its ESR activity. NgRBP responds to multiple signals such as ABA, MeJA, SA, and Tobacco mosaic virus infection. Therefore, it could participate in the regulation of gene expression under specific conditions.

Physiological, ultrastructural and proteomic responses of tobacco seedlings exposed to silver nanoparticles and silver nitrate

Since silver nanoparticles (AgNPs) are a dominant nanomaterial in consumer products, there is growing concern about their impact on the environment. Although numerous studies on the effects of AgNPs on living organisms have been conducted, the interaction of AgNPs with plants has not been fully clarified. To reveal the plant mechanisms activated after exposure to AgNPs and to differentiate between effects specific to nanoparticles and ionic silver, we investigated the physiological, ultrastructural and proteomic changes in seedlings of tobacco (Nicotiana tabacum) exposed to commercial AgNPs and ionic silver (AgNO3) from the seed stage. A higher Ag content was measured in seedlings exposed to AgNPs than in those exposed to the same concentration of AgNO3. However, the results on oxidative stress parameters obtained revealed that, in general, higher toxicity was recorded in AgNO3-treated seedlings than in those exposed to nanosilver. Ultrastructural analysis of root cells confirmed the presence of silver in the form of nanoparticles, which may explain the lower toxicity of AgNPs. However, the ultrastructural changes of chloroplasts as well as proteomic study showed that both AgNPs and AgNO3 can affect photosynthesis. Moreover, the majority of the proteins involved in the primary metabolism were up-regulated after both types of treatments, indicating that enhanced energy production, which can be used to reinforce defensive mechanisms, enables plants to cope with silver-induced toxicity.

An anther-specific gene PhGRP is regulated by PhMYC2 and causes male sterility when overexpressed in petunia anthers

An anther-specific GRP gene, regulated by PhMYC2 , causes a significant reduction of male fertility when overexpressed in petunia, and its promoter is efficient in genetic engineering of male-sterile lines. Glycine-rich proteins (GRPs) play important roles in plant anther development; however, the underlying mechanisms and related regulatory networks are poorly understood. In this study, a novel glycine-rich family gene designated as PhGRP was isolated from Petunia hybrida 'Fantasy Red'. The qRT-PCR analysis showed that it expressed specifically in anthers, and its expression peaked earlier than those well-known tapetum-specific genes, such as TA29, and several genes with the classic cis-regulatory element 'anther-box' in petunia during its anther development. The male fertility was significantly reduced in PhGRP overexpression lines, due to the abnormal formation of pollen wall. The PhGRP promoter (pPhGRP) could drive the GUS genes expressing specifically in the anthers of the transgenic Arabidopsis plants, indicating that the anther-specific characteristic of this promoter was conserved. In addition, when pPhGRP was used to drive the expression of BARNASE, complete male-sterile petunia lines were created without changes in vegetative organs and floral parts other than anthers. Finally, when pPhGRP was used as the bait to screen a yeast-one-hybrid (Y1H) library, a transcription factor (PhMYC2) belonging to the bHLH family was successfully selected, and the binding between pPhGRP and PhMYC2 was validated both by Y1H and dual-luciferase reporter assay. Overall, these results suggest that PhGRP, which is a male fertility-related gene that expresses specifically in anthers, is regulated by PhMYC2 and whose promoter can be used as an effective tool in the creation of male-sterile lines.

Protein expression changes during cotton fiber elongation in response to drought stress and recovery

An investigation to better understand the molecular mechanism of cotton (Gossypium hirsutum L.) fiber elongation in response to drought stress and recovery was conducted using a comparative proteomics analysis. Cotton plants (cv. NuCOTN 33B) were subjected to water deprivation for 10 days followed by a recovery period (with watering) of 5 days. The temporal changes in total proteins in cotton fibers were examined using 2DE. The results revealed that 163 proteins are significantly drought responsive. MS analysis led to the identification of 132 differentially expressed proteins that include some known as well as some novel drought-responsive proteins. These drought responsive fiber proteins in NuCOTN 33B are associated with a variety of cellular functions, i.e. signal transduction, protein processing, redox homeostasis, cell wall modification, metabolisms of carbon, energy, lipid, lignin, and flavonoid. The results suggest that the enhancement of the perception of drought stress, a new balance of the metabolism of the biosynthesis of cell wall components and cytoskeleton homeostasis plays an important role in the response of cotton fibers to drought stress. Overall, the current study provides an overview of the molecular mechanism of drought response in cotton fiber cells.

Structural basis of nucleic acid binding by Nicotiana tabacum glycine-rich RNA-binding protein: implications for its RNA chaperone function

Glycine-rich RNA-binding proteins (GR-RBPs) are involved in cold shock response of plants as RNA chaperones facilitating mRNA transport, splicing and translation. GR-RBPs are bipartite proteins containing a RNA recognition motif (RRM) followed by a glycine-rich region. Here, we studied the structural basis of nucleic acid binding of full-length Nicotiana tabacum GR-RBP1. NMR studies of NtGR-RBP1 show that the glycine-rich domain, while intrinsically disordered, is responsible for mediating self-association by transient interactions with its RRM domain (NtRRM). Both NtGR-RBP1 and NtRRM bind specifically and with low micromolar affinity to RNA and single-stranded DNA. The solution structure of NtRRM shows that it is a canonical RRM domain. A HADDOCK model of the NtRRM-RNA complex, based on NMR chemical shift and NOE data, shows that nucleic acid binding results from a combination of stacking and electrostatic interactions with conserved RRM residues. Finally, DNA melting experiments demonstrate that NtGR-RBP1 is more efficient in melting CTG containing nucleic acids than isolated NtRRM. Together, our study supports the model that self-association of GR-RBPs by the glycine-rich region results in cooperative unfolding of non-native substrate structures, thereby enhancing its chaperone function.

The rice OsDG2 encoding a glycine-rich protein is involved in the regulation of chloroplast development during early seedling stage

OsDG2 gene encoded a novel chloroplast-targeted GRP in rice. Disruption of the OsDG2 would lead to delayed greening phenotype and affected expression levels of genes associated with chloroplast development at early leaf stage of rice. Glycine-rich proteins (GRPs) participate in various biological processes in plants. However, the evidence of GRPs involved in chloroplast development in plants is quite limited. In this study, we identified a rice GRP gene mutant named osdg2 (O ryza s ativa d elayed g reening 2), which exhibits delayed greening phenotype characterized as bright yellow leaves before the three-leaf stage and thereafter turns to normal green. Further study showed that the mutant phenotype was consistent with changes in chlorophyll content and chloroplast development. The rice OsDG2 gene, encoding a novel GRP protein, was located on chromosome 2 through map-based cloning method and confirmed by molecular complementation tests. Subcellular localization results showed that OsDG2 was targeted in chloroplasts. In addition, the OsDG2 transcripts were highly expressed in leaves and undetectable in other tissues, showing the tissue-specific expression. In osdg2 mutant, the expression levels of most genes associated with chloroplast development were severely decreased in the 3rd leaves, but almost recovered to wild-type level in the 4th leaves. Our findings indicated that the nuclear-encoded OsDG2 plays important roles in chloroplast development at early leaf stage of rice.

Circadian oscillation and development-dependent expression of glycine-rich RNA binding proteins in tomato fruits

Glycine-rich RNA-binding proteins (GRPs) are involved in the modulation of the post-transcriptional processing of transcripts and participate as an output signal of the circadian clock. However, neither GRPs nor the circadian rhythmic have been studied in detail in fleshy fruits as yet. In the present work, the GRP1 gene family was analysed in Micro-Tom tomato (Solanum lycopersicum L.) fruit. Three highly homologous LeGRP1 genes (LeGRP1a-c) were identified. For each gene, three products were found, corresponding to the unspliced precursor mRNA (pre-mRNA), the mature mRNA and the alternatively spliced mRNA (preLeGRP1a-c, mLeGRP1a-c and asLeGRP1a-c, respectively). Tomato GRPs (LeGRPs) show the classic RNA recognition motif and glycine-rich region, and were found in the nucleus and in the cytosol of tomato fruit. By using different Escherichia coli mutants, it was found that LeGRP1s contained in vivo RNA-melting abilities and were able to complement the cold-sensitive phenotype of BX04 cells. Particular circadian profiles of expression, dependent on the fruits' developmental stage, were found for each LeGRP1 form. During ripening off the vine of fruits harvested at the mature green stage, the levels of all LeGRP1a-c forms drastically increased; however, incubation at 4°C prevented such increases. Analysis of the expression of all LeGRP1a-c forms suggests a positive regulation of expression in tomato fruit. Overall, the results obtained in this work reveal a complex pattern of expression of GRPs in tomato fruit, suggesting they might be involved in post-transcriptional modulation of circadian processes of this fleshy fruit.

Molecular cloning, characterization, and stress-responsive expression of genes encoding glycine-rich RNA-binding proteins in Camelina sativa L

Camelina sativa L. is an oil-seed crop that has potential for biofuel applications. Although the importance of C. sativa as a biofuel crop has increased in recent years, reports demonstrating the stress responsiveness of C. sativa and characterizing the genes involved in stress response of C. sativa have never been published. Here, we isolated and characterized three genes encoding glycine-rich RNA-binding proteins (GRPs) from camelina: CsGRP2a, CsGRP2b, and CsGRP2c. The three CsGRP2 proteins were very similar in amino acid sequence and contained a well-conserved RNA-recognition motif at the N-terminal region and glycine-rich domain at the C-terminal region. To understand the functional roles of CsGRP2s under stress conditions, we investigated the expression patterns of CsGRP2s under various environmental stress conditions. The expressions of the three CsGRP2s were highly up-regulated under cold stress. The expression of CsGRP2a was up-regulated under salt or dehydration stress, whereas the transcript levels of CsGRP2b and CsGRP2c were decreased under salt or dehydration stress conditions. The three CsGRP2s had the ability to complement cold-sensitive Escherichia coli mutants at low temperatures and harbored transcription anti-termination and nucleic acid-melting activities, indicating that the CsGRP2s possess RNA chaperone activity. The CsGRP2a protein was localized to both the nucleus and the cytoplasm. Expression of CsGRP2a in cold-sensitive Arabidopsis grp7 mutant plants resulted in decreased electrolyte leakage at freezing temperatures. Collectively, these results suggest that the stress-responsive CsGRP2s play a role as an RNA chaperone during the stress adaptation process in camelina.

Comparisons of protein profiles of beech bark disease resistant and susceptible American beech (Fagus grandifolia)

BACKGROUND

Beech bark disease is an insect-fungus complex that damages and often kills American beech trees and has major ecological and economic impacts on forests of the northeastern United States and southeastern Canadian forests. The disease begins when exotic beech scale insects feed on the bark of trees, and is followed by infection of damaged bark tissues by one of the Neonectria species of fungi. Proteomic analysis was conducted of beech bark proteins from diseased trees and healthy trees in areas heavily infested with beech bark disease. All of the diseased trees had signs of Neonectria infection such as cankers or fruiting bodies. In previous tests reported elsewhere, all of the diseased trees were demonstrated to be susceptible to the scale insect and all of the healthy trees were demonstrated to be resistant to the scale insect. Sixteen trees were sampled from eight geographically isolated stands, the sample consisting of 10 healthy (scale-resistant) and 6 diseased/infested (scale-susceptible) trees.

RESULTS

Proteins were extracted from each tree and analysed in triplicate by isoelectric focusing followed by denaturing gel electrophoresis. Gels were stained and protein spots identified and intensity quantified, then a statistical model was fit to identify significant differences between trees. A subset of BBD differential proteins were analysed by mass spectrometry and matched to known protein sequences for identification. Identified proteins had homology to stress, insect, and pathogen related proteins in other plant systems. Protein spots significantly different in diseased and healthy trees having no stand or disease-by-stand interaction effects were identified.

CONCLUSIONS

Further study of these proteins should help to understand processes critical to resistance to beech bark disease and to develop biomarkers for use in tree breeding programs and for the selection of resistant trees prior to or in early stages of BBD development in stands. Early identification of resistant trees (prior to the full disease development in an area) will allow forest management through the removal of susceptible trees and their root-sprouts prior to the onset of disease, allowing management and mitigation of costs, economic impact, and impacts on ecological systems and services.

Characterization of glycine-rich RNA-binding proteins in Brassica napus under stress conditions

Although the functional roles of glycine-rich RNA-binding proteins (GRPs) during stress adaptation have been extensively evaluated in Arabidopsis thaliana and rice (Oryza sativa), the stress-responsive roles of a majority of GRPs have not been characterized in other plant species including rapeseed (Brassica napus). Here, the characteristic features and stress-responsive expression patterns of GRPs in B. napus (BnGRPs) were investigated. The genome of B. napus contains seven closely related BnGRPs, where the amino acid sequences of a well-conserved RNA-recognition motif at the N-terminal region are highly similar to each other but the sequences of the C-terminal glycine-rich region vary greatly among different BnGRPs. The transcript levels of all BnGRPs were markedly upregulated by cold stress, while their expression was significantly downregulated by dehydration or high salinity stress. Among the seven BnGRPs evaluated, BnGRP1 was characterized in more detail for its cellular localization and functional role as an RNA chaperone under cold stress. Cold-induced BnGRP1 successfully complemented the cold-sensitive phenotype of Escherichia coli mutant BX04 cells under cold stress, and harbored DNA- and RNA-melting abilities. Ectopic expression of BnGRP1 in Arabidopsis resulted in accelerated seed germination and enhanced freezing tolerance of the plant under cold or freezing stress. Collectively, the results of this study support the emerging idea that GRPs are functionally conserved RNA chaperones during the cold adaptation process in diverse plant species.

EgRBP42 encoding an hnRNP-like RNA-binding protein from Elaeis guineensis Jacq. is responsive to abiotic stresses

RNA-binding proteins (RBPs) have been implicated as regulatory proteins involved in the post-transcriptional processes of gene expression in plants under various stress conditions. In this study, we report the cloning and characterization of a gene, designated as EgRBP42, encoding a member of the plant heterogeneous nuclear ribonucleoprotein (hnRNP)-like RBP family from oil palm (Elaeis guineensis Jacq.). EgRBP42 consists of two N-terminal RNA recognition motifs and a glycine-rich domain at the C-terminus. The upstream region of EgRBP42 has multiple light-responsive, stress-responsive regulatory elements and regulatory elements associated with flower development. Real-time RT-PCR analysis of EgRBP42 showed that EgRBP42 was expressed in oil palm tissues tested, including leaf, shoot apical meristem, root, female inflorescence, male inflorescence and mesocarp with the lowest transcript level in the roots. EgRBP42 protein interacted with transcripts associated with transcription, translation and stress responses using pull-down assay and electrophoretic mobility shift assay. The accumulation of EgRBP42 and its interacting transcripts were induced by abiotic stresses, including salinity, drought, submergence, cold and heat stresses in leaf discs. Collectively, the data suggested that EgRBP42 is a RBP, which responds to various abiotic stresses and could be advantageous for oil palm under stress conditions. Key message EgRBP42 may be involved in the post-transcriptional regulation of stress-related genes important for plant stress response and adaptation.

A glycine-rich RNA-binding protein can mediate physiological responses in transgenic plants under salt stress

Glycine-rich RNA-binding proteins (GRPs) are involved in post-transcriptional regulation of genes, which have been found to play a role in stress response. However, whether GRPs can mediate some physiological responses related to salt stress tolerance is still not known. In the present study, we investigated the role of GRPs in salt stress-induced physiological responses by generating transgenic tobacco lines overexpressing a GRP (LbGRP1) gene from Limonium bicolor (Bunge) Kuntze. Compared with wild type (WT) tobacco, the transgenic plants showed significantly improved superoxide dismutase and catalase activities under salt stress conditions. Levels of proline in the transgenic plants were significantly higher than those in the WT plants grown under NaCl stress conditions. Furthermore, Na(+) content and Na(+)/K(+) ratio in the transgenic plants were lower than those in the WT plants under both normal growth and stress conditions. These results suggested that overexpression of the LbGRP1 gene can affect some physiological processes associated with salt tolerance of plants. Therefore, we hypothesize that LbGST1 can enhance stress resistance by mediating some physiological pathways.

Beyond transcription: RNA-binding proteins as emerging regulators of plant response to environmental constraints

RNA-binding proteins (RBPs) govern many aspects of RNA metabolism, including pre-mRNA processing, transport, stability/decay and translation. Although relatively few plant RNA-binding proteins have been characterized genetically and biochemically, more than 200 RBP genes have been predicted in Arabidopsis and rice genomes, suggesting that they might serve specific plant functions. Besides their role in normal cellular functions, RBPs are emerging also as an interesting class of proteins involved in a wide range of post-transcriptional regulatory events that are important in providing plants with the ability to respond rapidly to changes in environmental conditions. Here, we review the most recent results and evidence on the functional role of RBPs in plant adaptation to various unfavourable environmental conditions and their contribution to enhance plant tolerance to abiotic stresses, with special emphasis on osmotic and temperature stress.

RNA regulation in plant abiotic stress responses

RNA regulatory processes such as transcription, degradation and stabilization control are the major mechanisms that determine the levels of mRNAs in plants. Transcriptional and post-transcriptional regulations of RNAs are drastically altered during plant stress responses. As a result of these molecular processes, plants are capable of adjusting to changing environmental conditions. Understanding the role of these mechanisms in plant stress responses is important and necessary for the engineering of stress-tolerant plants. Recent studies in the area of RNA regulation have increased our understanding of how plants respond to environmental stresses. This review highlights recent progress in RNA regulatory processes that are involved in plant stress responses, such as small RNAs, alternative splicing, RNA granules and RNA-binding proteins. This article is part of a Special Issue entitled: Plant gene regulation in response to abiotic stress.

Molecular characterization and expression analysis of a glycine-rich RNA-binding protein gene from Malus hupehensis Rehd

Members of the plant glycine-rich RNA-binding protein (GR-RBP) family play diverse roles in regulating RNA metabolism for various cellular processes. To understand better their function at the molecular level in stress responses, we cloned a GR-RBP gene, MhGR-RBP1, from Malus hupehensis. Its full-length cDNA is 558 bp long, with a 495-bp open reading frame, and it encodes 164 amino acids. The deduced amino acid sequence contains an RNA-recognition motif (RRM) at the amino terminal and a glycine-rich domain at the carboxyl terminal; these are highly homologous with those from other plant species. Multiple alignment and phylogenetic analyses show that the deduced protein is a novel member of the plant GR-RBP family. To characterize this gene, we also applied a model for predicting its homology of protein structure with other species. Both organ-specific and stress-related expression were detected by quantitative real-time PCR and semi-quantitative RT-PCR, indicating that MhGR-RBP1 is expressed abundantly in young leaves but weakly in roots and shoots. Transcript levels in the leaves were increased markedly by drought, hydrogen peroxide (H(2)O(2)), and mechanical wounding, slightly by salt stress. Furthermore, the transcript is initially up- and down-regulated rapidly within 24 h of abscisic acid (ABA) treatment. After 24 h of ABA and jasmonic acid (JA) treatments with different concentrations, the transcript levels of MhGR-RBP1 were significantly repressed. These results suggest that MhGR-RBP1 may be involved in the responses to abiotic stresses, H(2)O(2), ABA, or JA.

Proteomic profiling of proteins associated with the rejuvenation of Sequoia sempervirens (D. Don) Endl

Background

Restoration of rooting competence is important for rejuvenation in Sequoia sempervirens (D. Don) Endl and is achieved by repeatedly grafting Sequoia shoots after 16 and 30 years of cultivation in vitro.

Results

Mass spectrometry-based proteomic analysis revealed three proteins that differentially accumulated in different rejuvenation stages, including oxygen-evolving enhancer protein 2 (OEE2), glycine-rich RNA-binding protein (RNP), and a thaumatin-like protein. OEE2 was found to be phosphorylated and a phosphopeptide (YEDNFDGNSNVSVMVpTPpTDK) was identified. Specifically, the protein levels of OEE2 increased as a result of grafting and displayed a higher abundance in plants during the juvenile and rejuvenated stages. Additionally, SsOEE2 displayed the highest expression levels in Sequoia shoots during the juvenile stage and less expression during the adult stage. The expression levels also steadily increased during grafting.

Conclusion

Our results indicate a positive correlation between the gene and protein expression patterns of SsOEE2 and the rejuvenation process, suggesting that this gene is involved in the rejuvenation of Sequoia sempervirens.