A wheat (Triticum aestivum) protein phosphatase 2A catalytic subunit gene provides enhanced drought tolerance in tobacco

Adaptation of protein phosphatases in Oryza sativa and Cucumis sativus to microcystins

Microcystins (MCs) in irrigation water could inhibit crop growth and yield. Protein phosphatases (PPs) play an important role in regulating physiological mechanisms in plants to adapt abiotic stresses. To clarify the adaptation mechanism in plants to MCs stress, we compared PPs in rice and cucumber leaves by analyzing PPs total activity, protein phosphatase-2A (PP2A) activity and expression, as well as related growth and gas exchange parameters. After 7-day exposure of MCs (5 ~ 100 µg/L) and 7-day recovery without MCs, rice showed higher tolerance to MCs by analyzing dry weight and gas exchange parameters. Both crops may regulate PPs activity to adapt MCs stress by increasing the expression of genes encoding PPs. Among them, PP2A activity in two crops showed more sensitivity to MCs than total PPs activity. In addition, the higher expressions of PP2A catalytic and regulatory subunits and lower decrease PP2A activity were observed in rice leaves compared to cucumber. All results suggest that the expression levels of PP2A subunits could play a role in maintaining the activity of PP2A to regulating plant tolerance to MCs stress.

The protein phosphatase 2A catalytic subunit StPP2Ac2b enhances susceptibility to Phytophthora infestans and senescence in potato

The serine/threonine protein phosphatases type 2A (PP2A) are involved in several physiological responses in plants, playing important roles in developmental programs, stress responses and hormone signaling. Six PP2A catalytic subunits (StPP2Ac) were identified in cultivated potato. Transgenic potato plants constitutively overexpressing the catalytic subunit StPP2Ac2b (StPP2Ac2b-OE) were developed to determine its physiological roles. The response of StPP2Ac2b-OE plants to the oomycete Phytophthora infestans, the causal agent of late blight, was evaluated. We found that overexpression of StPP2Ac2b enhances susceptibility to the pathogen. Further bioinformatics, biochemical, and molecular analyses revealed that StPP2Ac2b positively regulates developmental and pathogen-induced senescence, and that P. infestans infection promotes senescence, most likely through induction of StPP2Ac2b expression.

TaNBR1, a Novel Wheat NBR1-like Domain Gene Negatively Regulates Drought Stress Tolerance in Transgenic Arabidopsis

Drought stress is an important factor that severely affects crop yield and quality. Autophagy has a crucial role in the responses to abiotic stresses. In this study, we explore TaNBR1 in response to drought stress. Expression of the TaNBR1 gene was strongly induced by NaCl, PEG, and abscisic acid treatments. The TaNBR1 protein is localized in the Golgi apparatus and autophagosome. Transgenic Arabidopsis plants overexpressing TaNBR1 exhibited reduced drought tolerance. When subjected to drought stress, compared to the wild-type (WT) lines, the transgenic overexpressing TaNBR1 plants had a lower seed germination rate, relative water content, proline content, and reduced accumulation of antioxidant enzymes, i.e., superoxide dismutase, peroxidase, and catalase, as well as higher chlorophyll losses, malondialdehyde contents, and water loss. The transgenic plants overexpressing TaNBR1 produced much shorter roots in response to mannitol stress, in comparison to the WT plants, and they exhibited greater sensitivity to abscisic acid treatment. The expression levels of the genes related to stress in the transgenic plants were affected in response to drought stress. Our results indicate that TaNBR1 negatively regulates drought stress responses by affecting the expression of stress-related genes in Arabidopsis.

Physiological and transcriptome analyses for assessing the effects of exogenous uniconazole on drought tolerance in hemp (Cannabis sativa L.)

Uniconazole (S-(+)-uniconazole), a plant growth retardant, exerts key roles in modulating growth and development and increasing abiotic stress tolerance in plants. However, the underlying mechanisms by which uniconazole regulates drought response remain largely unknown. Here, the effects of exogenous uniconazole on drought tolerance in hemp were studied via physiological and transcriptome analyses of the drought-sensitive industrial hemp cultivar Hanma No. 2 grown under drought stress. Exogenous uniconazole treatment increased hemp tolerance to drought-induced damage by enhancing chlorophyll content and photosynthesis capacity, regulating activities of enzymes involved in carbon and nitrogen metabolism, and altering endogenous hormone levels. Expression of genes associated with porphyrin and chlorophyll metabolism, photosynthesis-antenna proteins, photosynthesis, starch and sucrose metabolism, nitrogen metabolism, and plant hormone signal transduction were significantly regulated by uniconazole compared with that by control (distilled water) under drought stress. Numerous genes were differentially expressed to increase chlorophyll content, enhance photosynthesis, regulate carbon-nitrogen metabolism-related enzyme activities, and alter endogenous hormone levels. Thus, uniconazole regulated physiological and molecular characteristics of photosynthesis, carbon-nitrogen metabolism, and plant hormone signal transduction to enhance drought resistance in industrial hemp.

Conserved and Unique Roles of Chaperone-Dependent E3 Ubiquitin Ligase CHIP in Plants

Protein quality control (PQC) is essential for maintaining cellular homeostasis by reducing protein misfolding and aggregation. Major PQC mechanisms include protein refolding assisted by molecular chaperones and the degradation of misfolded and aggregated proteins using the proteasome and autophagy. A C-terminus of heat shock protein (Hsp) 70-interacting protein [carboxy-terminal Hsp70-interacting protein (CHIP)] is a chaperone-dependent and U-box-containing E3 ligase. CHIP is a key molecule in PQC by recognizing misfolded proteins through its interacting chaperones and targeting their degradation. CHIP also ubiquitinates native proteins and plays a regulatory role in other cellular processes, including signaling, development, DNA repair, immunity, and aging in metazoans. As a highly conserved ubiquitin ligase, plant CHIP plays an important role in response to a broad spectrum of biotic and abiotic stresses. CHIP protects chloroplasts by coordinating chloroplast PQC both outside and inside the important photosynthetic organelle of plant cells. CHIP also modulates the activity of protein phosphatase 2A (PP2A), a crucial component in a network of plant signaling, including abscisic acid (ABA) signaling. In this review, we discuss the structure, cofactors, activities, and biological function of CHIP with an emphasis on both its conserved and unique roles in PQC, stress responses, and signaling in plants.

Genome-wide characterization and expression analysis of TOPP-type protein phosphatases in soybean (Glycine max L.) reveal the role of GmTOPP13 in drought tolerance

BACKGROUND

In response to various abiotic stressors such as drought, many plants engage different protein phosphatases linked to several physiological and developmental processes. However, comprehensive analysis of this gene family is lacking for soybean.

OBJECTIVE

This study was performed to identify the TOPP-type protein phosphatase family in soybean and investigate the gene's role under drought stress.

METHODS

Soybean genome sequences and transcriptome data were downloaded from the Phytozome v.12, and the microarray data were downloaded from NCBI GEO datasets GSE49537. Expression profiles of GmTOPP13 were obtained based on qRT-PCR results. GmTOPP13 gene was transformed into tobacco plants via Agrobacterium mediated method, and the drought tolerance was analyzed by water deficit assay.

RESULTS

15 GmTOPP genes were identified in the soybean genome database (GmTOPP1-15). GmTOPP genes were distributed on 9 of 20 chromosomes, with similar exon-intron structure and motifs arrangement. All GmTOPPs contained Metallophos and STPPase_N domains as well as the core catalytic sites. Cis-regulatory element analysis predicted that GmTOPPs were widely involved in plant development, stress and hormone response in soybean. Expression profiles showed that GmTOPPs expressed in different tissues and exhibited divergent expression patterns in leaf and root in response to drought stimulus. Moreover, GmTOPP13 gene was isolated and expression pattern analysis indicated that this gene was highly expressed in seed, root, leaf and other tissues detected, and intensively induced upon PEG6000 treatment. In addition, overexpression of GmTOPP13 gene enhanced the drought tolerance in tobacco plants. The transgenic tobacco plants showed regulation of stress-responsive genes including CAT, SOD, ERD10B and TIP during drought stress.

CONCLUSIONS

This study provides valuable information for the study of GmTOPP gene family in soybean, and lays a foundation for further functional studies of GmTOPP13 gene under drought and other abiotic stresses.

Crosstalk between phytohormones and secondary metabolites in the drought stress tolerance of crop plants: A review

Drought stress negatively affects crop performance and weakens global food security. It triggers the activation of downstream pathways, mainly through phytohormones homeostasis and their signaling networks, which further initiate the biosynthesis of secondary metabolites (SMs). Roots sense drought stress, the signal travels to the above-ground tissues to induce systemic phytohormones signaling. The systemic signals further trigger the biosynthesis of SMs and stomatal closure to prevent water loss. SMs primarily scavenge reactive oxygen species (ROS) to protect plants from lipid peroxidation and also perform additional defense-related functions. Moreover, drought-induced volatile SMs can alert the plant tissues to perform drought stress mitigating functions in plants. Other phytohormone-induced stress responses include cell wall and cuticle thickening, root and leaf morphology alteration, and anatomical changes of roots, stems, and leaves, which in turn minimize the oxidative stress, water loss, and other adverse effects of drought. Exogenous applications of phytohormones and genetic engineering of phytohormones signaling and biosynthesis pathways mitigate the drought stress effects. Direct modulation of the SMs biosynthetic pathway genes or indirect via phytohormones' regulation provides drought tolerance. Thus, phytohormones and SMs play key roles in plant development under the drought stress environment in crop plants.

Salt tolerance involved candidate genes in rice: an integrative meta-analysis approach

BACKGROUND

Salinity, as one of the main abiotic stresses, critically threatens growth and fertility of main food crops including rice in the world. To get insight into the molecular mechanisms by which tolerant genotypes responds to the salinity stress, we propose an integrative meta-analysis approach to find the key genes involved in salinity tolerance. Herein, a genome-wide meta-analysis, using microarray and RNA-seq data was conducted which resulted in the identification of differentially expressed genes (DEGs) under salinity stress at tolerant rice genotypes. DEGs were then confirmed by meta-QTL analysis and literature review.

RESULTS

A total of 3449 DEGs were detected in 46 meta-QTL positions, among which 1286, 86, 1729 and 348 DEGs were observed in root, shoot, seedling, and leaves tissues, respectively. Moreover, functional annotation of DEGs located in the meta-QTLs suggested some involved biological processes (e.g., ion transport, regulation of transcription, cell wall organization and modification as well as response to stress) and molecular function terms (e.g., transporter activity, transcription factor activity and oxidoreductase activity). Remarkably, 23 potential candidate genes were detected in Saltol and hotspot-regions overlying original QTLs for both yield components and ion homeostasis traits; among which, there were many unreported salinity-responsive genes. Some promising candidate genes were detected such as pectinesterase, peroxidase, transcription regulator, high-affinity potassium transporter, cell wall organization, protein serine/threonine phosphatase, and CBS domain cotaining protein.

CONCLUSIONS

The obtained results indicated that, the salt tolerant genotypes use qualified mechanisms particularly in sensing and signalling of the salt stress, regulation of transcription, ionic homeostasis, and Reactive Oxygen Species (ROS) scavenging in response to the salt stress.

Genome-wide association mapping for adult resistance to powdery mildew in common wheat

Blumeria graminis f. sp. tritici, the causal agent of wheat powdery mildew disease, can occur at all stages of the crop and constantly threatens wheat production. To identify candidate resistance genes for powdery mildew, we performed GWAS (genome-wide association studies) on a total set of 329 wheat varieties obtained from different origins. These wheat materials were genotyped using wheat 90K SNP array and evaluated for their resistance in either field or glasshouse condition from 2016 to 2018. Using a mixed linear model, 33 SNP markers of which 14 QTL (quantitative trait loci) were later defined were observed to associate with powdery mildew resistance. Among these, QTL on chromosome 3A, 3B, 6D and 7D were concluded as potentially new QTL. Exploration of candidate genes for new QTL suggested roles of these genes involved in encoding disease resistance and defence-related proteins, and regulating early immune response to the pathogen. Overall, the results reveal that GWAS can be an effective means of identifying marker-trait associations, though further functional validation and fine-mapping of gene candidates are required before creating opportunities for developing new resistant genotypes.

PP2A Phosphatases Take a Giant Leap in the Post-Genomics Era

BACKGROUND

Protein phosphorylation is an important reversible post-translational modifica-tion, which regulates a number of critical cellular processes. Phosphatases and kinases work in a con-certed manner to act as a "molecular switch" that turns-on or - off the regulatory processes driving the growth and development under normal circumstances, as well as responses to multiple stresses in plant system. The era of functional genomics has ushered huge amounts of information to the framework of plant systems. The comprehension of who's who in the signaling pathways is becoming clearer and the investigations challenging the conventional functions of signaling components are on a rise. Protein phosphatases have emerged as key regulators in the signaling cascades. PP2A phosphatases due to their diverse holoenzyme compositions are difficult to comprehend.

CONCLUSION

In this review, we highlight the functional versatility of PP2A members, deciphered through the advances in the post-genomic era.

Co-overexpression of AVP1 and PP2A-C5 in Arabidopsis makes plants tolerant to multiple abiotic stresses

Abiotic stresses are major threats to agricultural production. Drought and salinity as two of the major abiotic stresses cause billions of losses in agricultural productivity worldwide each year. Thus, it is imperative to make crops more tolerant. Overexpression of AVP1 or PP2A-C5 was previously shown to increase drought and salt stress tolerance, respectively, in transgenic plants. In this study, the hypothesis that co-overexpression of AVP1 and PP2A-C5 would combine their respective benefits and further improve salt tolerance was tested. The two genes were inserted into the same T-DNA region of the binary vector and then introduced into the Arabidopsis genome through Agrobacterium-mediated transformation. Transgenic Arabidopsis plants expressing both AVP1 and PP2A-C5 at relatively high levels were identified and analyzed. These plants displayed enhanced tolerance to NaCl compared to either AVP1 or PP2A-C5 overexpressing plants. They also showed tolerance to other stresses such as KNO₃ and LiCl at harmful concentrations, drought, and phosphorus deficiency at comparable levels with either AVP1 or PP2A-C5 overexpressing plants. This study demonstrates that introducing multiple genes in single T-DNA region is an effective approach to create transgenic plants with enhanced tolerance to multiple stresses.

Characterization of PP2A-A3 mRNA expression and growth patterns in Arabidopsis thaliana under drought stress and abscisic acid

Phosphoprotein phosphatase 2A (PP2A) plays a crucial role in cellular processes via reversible dephosphorylation of proteins. The activity of this enzyme depends on its subunits. There is little information about mRNA expression of each subunit and the relationship between these gene expressions and the growth patterns under stress conditions and hormones. Here, mRNA expression of subunit A3 of PP2A and its relationship with growth patterns under different levels of drought stress and abscisic acid (ABA) concentration were analyzed in Arabidopsis thaliana. The mRNA expression profiles showed different levels of the up- and down-regulation of PP2AA3 in roots and shoots of A. thaliana under drought conditions and ABA treatments. The results demonstrated that the regulation of PP2AA3 expression under the mentioned conditions could indirectly modulate growth patterns such that seedlings grown under severe drought stress and those grown under 4 µM ABA had the maximum number of lateral roots and the shortest primary roots. In contrast, the minimum number of lateral roots and the longest primary roots were observed under mild drought stress and 0.5 µM ABA. Differences in PP2AA3 mRNA expression showed that mechanisms involved in the regulation of this gene under drought conditions would probably be different from those that regulate the PP2AA3 expression under ABA. Co-expression of PP2AA3 with each of PIN1-4,7 (PP2A activity targets) depends on the organ type and different levels of drought stress and ABA concentration. Furthermore, fluctuations in the PP2AA3 expression proved that this gene cannot be suitable as a reference gene although PP2AA3 is widely used as a reference gene.

Overexpression of the protein phosphatase 2A regulatory subunit a gene ZmPP2AA1 improves low phosphate tolerance by remodeling the root system architecture of maize

Phosphate (Pi) limitation is a constraint for plant growth and development in many natural and agricultural ecosystems. In this study, a gene encoding Zea mays L. protein phosphatase 2A regulatory subunit A, designated ZmPP2AA1, was induced in roots by low Pi availability. The function of the ZmPP2AA1 gene in maize was analyzed using overexpression and RNA interference. ZmPP2AA1 modulated root gravitropism, negatively regulated primary root (PR) growth, and stimulated the development of lateral roots (LRs). A detailed characterization of the root system architecture (RSA) in response to different Pi concentrations with or without indole-3-acetic acid and 1-N-naphthylphthalamic acid revealed that auxin was involved in the RSA response to low Pi availability. Overexpression of ZmPP2AA1 enhanced tolerance to Pi starvation in transgenic maize in hydroponic and soil pot experiments. An increased dry weight (DW), root-to-shoot ratio, and total P content and concentration, along with a delayed and reduced accumulation of anthocyanin in overexpressing transgenic maize plants coincided with their highly branched root system and increased Pi uptake capability under low Pi conditions. Inflorescence development of the ZmPP2AA1 overexpressing line was less affected by low Pi stress, resulting in higher grain yield per plant under Pi deprivation. These data reveal the biological function of ZmPP2AA1, provide insights into a linkage between auxin and low Pi responses, and drive new strategies for the efficient utilization of Pi by maize.

The protein phosphatase 2A catalytic subunit StPP2Ac2b acts as a positive regulator of tuberization induction in Solanum tuberosum L

This study provides the first genetic evidence for the role of PP2A in tuberization, demonstrating that the catalytic subunit StPP2Ac2b positively modulates tuber induction, and that its function is related to the regulation of gibberellic acid metabolism. The results contribute to a better understanding of the molecular mechanism controlling tuberization induction, which remains largely unknown. The serine/threonine protein phosphatases type 2A (PP2A) are implicated in several physiological processes in plants, playing important roles in hormone responses. In cultivated potato (Solanum tuberosum), six PP2A catalytic subunits (StPP2Ac) were identified. The PP2Ac of the subfamily I (StPP2Ac1, 2a and 2b) were suggested to be involved in the tuberization signaling in leaves, where the environmental and hormonal signals are perceived and integrated. The aim of this study was to investigate the role of PP2A in the tuberization induction in stolons. We selected one of the catalytic subunits of the subfamily I, StPP2Ac2b, to develop transgenic plants overexpressing this gene (StPP2Ac2b-OE). Stolons from StPP2Ac2b-OE plants show higher tuber induction rates in vitro, as compared to wild type stolons, with no differences in the number of tubers obtained at the end of the process. This effect is accompanied by higher expression levels of the gibberellic acid (GA) catabolic enzyme StGA2ox1. GA up-regulates StPP2Ac2b expression in stolons, possibly as part of the feedback system by which the hormone regulates its own level. Sucrose, a tuber-promoting factor in vitro, increases StPP2Ac2b expression. We conclude that StPP2Ac2b acts in stolons as a positive regulator tuber induction, integrating different tuberization-related signals mainly though the modulation of GA metabolism.

Phosphatase ABI1 and okadaic acid-sensitive phosphoprotein phosphatases inhibit salt stress-activated SnRK2.4 kinase

BACKGROUND

SNF1-related protein kinases 2 (SnRK2s) are key regulators of the plant response to osmotic stress. They are transiently activated in response to drought and salinity. Based on a phylogenetic analysis SnRK2s are divided into three groups. The classification correlates with their response to abscisic acid (ABA); group 1 consists SnRK2s non-activated in response to ABA, group 2, kinases non-activated or weakly activated (depending on the plant species) by ABA treatment, and group 3, ABA-activated kinases. The activity of all SnRK2s is regulated by phosphorylation. It is well established that clade A phosphoprotein phosphatases 2C (PP2Cs) are negative regulators of ABA-activated SnRK2s, whereas regulators of SnRK2s from group 1 remain unidentified.

RESULTS

Here, we show that ABI1, a PP2C clade A phosphatase, interacts with SnRK2.4, member of group 1 of the SnRK2 family, dephosphorylates Ser158, whose phosphorylation is needed for the kinase activity, and inhibits the kinase, both in vitro and in vivo. Our data indicate that ABI1 and the kinase regulate primary root growth in response to salinity; the phenotype of ABI1 knockout mutant (abi1td) exposed to salt stress is opposite to that of the snrk2.4 mutant. Moreover, we show that the activity of SnRK2s from group 1 is additionally regulated by okadaic acid-sensitive phosphatase(s) from the phosphoprotein phosphatase (PPP) family.

CONCLUSIONS

Phosphatase ABI1 and okadaic acid-sensitive phosphatases of the PPP family are negative regulators of salt stress-activated SnRK2.4. The results show that ABI1 inhibits not only the ABA-activated SnRK2s but also at least one ABA-non-activated SnRK2, suggesting that the phosphatase is involved in the cross talk between ABA-dependent and ABA-independent stress signaling pathways in plants.

PP2A Phosphatase as a Regulator of ROS Signaling in Plants

Reactive oxygen species (ROS) carry out vital functions in determining appropriate stress reactions in plants, but the molecular mechanisms underlying the sensing, signaling and response to ROS as signaling molecules are not yet fully understood. Recent studies have underscored the role of Protein Phosphatase 2A (PP2A) in ROS-dependent responses involved in light acclimation and pathogenesis responses in Arabidopsis thaliana. Genetic, proteomic and metabolomic studies have demonstrated that trimeric PP2A phosphatases control metabolic changes and cell death elicited by intracellular and extracellular ROS signals. Associated with this, PP2A subunits contribute to transcriptional and post-translational regulation of pro-oxidant and antioxidant enzymes. This review highlights the emerging role of PP2A phosphatases in the regulatory ROS signaling networks in plants.

Physiological performance, secondary metabolite and expression profiling of genes associated with drought tolerance in Withania somnifera

Physiological, biochemical, and gene expression responses under drought stress were studied in Withania somnifera. Photosynthesis rate, stomatal conductance, transpiration rate, relative water content, chlorophyll content, and quantum yield of photosystems I and II (PSI and PSII) decreased in response to drought stress. Comparative expression of genes involved in osmoregulation, detoxification, signal transduction, metabolism, and transcription factor was analyzed through quantitative RT-PCR. The genes encoding 1-pyrroline-5-carboxylate synthetase (P5CS), glutathione S-transferase (GST), superoxide dismutase (SOD), serine threonine-protein kinase (STK), serine threonine protein phosphatase (PSP), aldehyde dehydrogenase (AD), leucoanthocyanidin dioxygenase/anthocyanin synthase (LD/AS), HSP, MYB, and WRKY have shown upregulation in response to drought stress condition in leaf tissues. Enhanced detoxification and osmoregulation along with increased withanolides production were also observed under drought stress. The results of this study will be helpful in developing stress-tolerant and high secondary metabolite yielding genotypes.

Identification of genes involved in the drought adaptation and recovery in Portulaca oleracea by differential display

Portulaca oleracea is one of the richest plant sources of ω-3 and ω-6 fatty acids and other compounds potentially valuable for nutrition. It is broadly established in arid, semiarid and well-watered fields, thus making it a promising candidate for research on abiotic stress resistance mechanisms. It is capable of withstanding severe drought and then of recovering upon rehydration. Here, the adaptation to drought and the posterior recovery was evaluated at transcriptomic level by differential display validated by qRT-PCR. Of the 2279 transcript-derived fragments amplified, 202 presented differential expression. Ninety of them were successfully isolated and sequenced. Selected genes were tested against different abiotic stresses in P. oleracea and the behavior of their orthologous genes in Arabidopsis thaliana was also explored to seek for conserved response mechanisms. In drought adapted and in recovered plants changes in expression of many protein metabolism-, lipid metabolism- and stress-related genes were observed. Many genes with unknown function were detected, which also respond to other abiotic stresses. Some of them are also involved in the seed desiccation/imbibition process and thus would be of great interest for further research. The potential use of candidate genes to engineer drought tolerance improvement and recovery is discussed.

Comparative study of the protein profiles of Sunki mandarin and Rangpur lime plants in response to water deficit

BACKGROUND

Rootstocks play a major role in the tolerance of citrus plants to water deficit by controlling and adjusting the water supply to meet the transpiration demand of the shoots. Alterations in protein abundance in citrus roots are crucial for plant adaptation to water deficit. We performed two-dimensional electrophoresis (2-DE) separation followed by LC/MS/MS to assess the proteome responses of the roots of two citrus rootstocks, Rangpur lime (Citrus limonia Osbeck) and 'Sunki Maravilha' (Citrus sunki) mandarin, which show contrasting tolerances to water deficits at the physiological and molecular levels.

RESULTS

Changes in the abundance of 36 and 38 proteins in Rangpur lime and 'Sunki Maravilha' mandarin, respectively, were observed via LC/MS/MS in response to water deficit. Multivariate principal component analysis (PCA) of the data revealed major changes in the protein profile of 'Sunki Maravilha' in response to water deficit. Additionally, proteomics and systems biology analyses allowed for the general elucidation of the major mechanisms associated with the differential responses to water deficit of both varieties. The defense mechanisms of Rangpur lime included changes in the metabolism of carbohydrates and amino acids as well as in the activation of reactive oxygen species (ROS) detoxification and in the levels of proteins involved in water stress defense. In contrast, the adaptation of 'Sunki Maravilha' to stress was aided by the activation of DNA repair and processing proteins.

CONCLUSIONS

Our study reveals that the levels of a number of proteins involved in various cellular pathways are affected during water deficit in the roots of citrus plants. The results show that acclimatization to water deficit involves specific responses in Rangpur lime and 'Sunki Maravilha' mandarin. This study provides insights into the effects of drought on the abundance of proteins in the roots of two varieties of citrus rootstocks. In addition, this work allows for a better understanding of the molecular basis of the response to water deficit in citrus. Further analysis is needed to elucidate the behaviors of the key target proteins involved in this response.

Genetic control of functional traits related to photosynthesis and water use efficiency in Pinus pinaster Ait. drought response: integration of genome annotation, allele association and QTL detection for candidate gene identification

BACKGROUND

Understanding molecular mechanisms that control photosynthesis and water use efficiency in response to drought is crucial for plant species from dry areas. This study aimed to identify QTL for these traits in a Mediterranean conifer and tested their stability under drought.

RESULTS

High density linkage maps for Pinus pinaster were used in the detection of QTL for photosynthesis and water use efficiency at three water irrigation regimes. A total of 28 significant and 27 suggestive QTL were found. QTL detected for photochemical traits accounted for the higher percentage of phenotypic variance. Functional annotation of genes within the QTL suggested 58 candidate genes for the analyzed traits. Allele association analysis in selected candidate genes showed three SNPs located in a MYB transcription factor that were significantly associated with efficiency of energy capture by open PSII reaction centers and specific leaf area.

CONCLUSIONS

The integration of QTL mapping of functional traits, genome annotation and allele association yielded several candidate genes involved with molecular control of photosynthesis and water use efficiency in response to drought in a conifer species. The results obtained highlight the importance of maintaining the integrity of the photochemical machinery in P. pinaster drought response.

Cloning and characterization of TaPP2AbB"-α, a member of the PP2A regulatory subunit in wheat

Protein phosphatase 2A (PP2A), a major Serine/Threonine protein phosphatase, consists of three subunits; a highly conserved structural subunit A, a catalytic subunit C, and a highly variable regulatory subunit B which determines the substrate specificity. Although the functional mechanism of PP2A in signaling transduction in Arabidopsis is known, their physiological roles in wheat remain to be characterized. In this study, we identified a novel regulatory subunit B, TaPP2AbB"-α, in wheat (Triticum aestivum L.). Subcellular localization indicated that TaPP2AbB"-α is located in the cell membrane, cytoplasm and nucleus. It interacts with both TaPP2Aa and TaPP2Ac. Expression pattern analyses revealed that TaPP2AbB"-α is strongly expressed in roots, and responds to NaCl, polyethylene glycol (PEG), cold and abscisic acid (ABA) stresses at the transcription level. Transgenic Arabidopsis plants overexpressing TaPP2AbB"-α developed more lateral roots, especially when treated with mannitol or NaCl. These results suggest that TaPP2AbB"-α, in conjunction with the other two PP2A subunits, is involved in multi-stress response, and positively regulates lateral root development under osmotic stress.

Comparative quantitative proteomics analysis of the ABA response of roots of drought-sensitive and drought-tolerant wheat varieties identifies proteomic signatures of drought adaptability

Wheat is one of the most highly cultivated cereals in the world. Like other cultivated crops, wheat production is significantly affected by abiotic stresses such as drought. Multiple wheat varieties suitable for different geographical regions of the world have been developed that are adapted to different environmental conditions; however, the molecular basis of such adaptations remains unknown in most cases. We have compared the quantitative proteomics profile of the roots of two different wheat varieties, Nesser (drought-tolerant) and Opata (drought-sensitive), in the absence and presence of abscisic acid (ABA, as a proxy for drought). A labeling LC-based quantitative proteomics approach using iTRAQ was applied to elucidate the changes in protein abundance levels. Quantitative differences in protein levels were analyzed for the evaluation of inherent differences between the two varieties as well as the overall and variety-specific effect of ABA on the root proteome. This study reveals the most elaborate ABA-responsive root proteome identified to date in wheat. A large number of proteins exhibited inherently different expression levels between Nesser and Opata. Additionally, significantly higher numbers of proteins were ABA-responsive in Nesser roots compared with Opata roots. Furthermore, several proteins showed variety-specific regulation by ABA, suggesting their role in drought adaptation.

Cloning and characterization of TaSnRK2.3, a novel SnRK2 gene in common wheat

Environmental stresses such as drought, salinity, and cold are major adverse factors that significantly affect agricultural productivity. Protein phosphorylation/dephosphorylation is a major signalling event induced by osmotic stress in higher plants. Sucrose non-fermenting 1-related protein kinase 2 (SnRK2) family members play essential roles in the response to hyperosmotic stresses in plants. In this study, the TaSnRK2.3 gene, a novel SnRK2 member was cloned, and three copies located on chromosomes 1A, 1B, and 1D were identified in common wheat. TaSnRK2.3 was strongly expressed in leaves, and responded to polyethylene glycol, NaCl, abscisic acid, and cold stresses. To characterize its function, transgenic Arabidopsis overexpressing TaSnRK2.3-GFP controlled by the cauliflower mosaic virus 35S promoter was generated and subjected to severe abiotic stresses. Overexpression of TaSnRK2.3 resulted in an improved root system and significantly enhanced tolerance to drought, salt, and freezing stresses, simultaneously demonstrated by enhanced expression of abiotic stress-responsive genes and ameliorative physiological indices, including a decreased rate of water loss, enhanced cell membrane stability, improved photosynthetic potential, and significantly increased osmotic potential and free proline content under normal and/or stressed conditions. These results demonstrate that TaSnRK2.3 is a multifunctional regulator, with potential for utilization in transgenic breeding for improved abiotic stress tolerance in crop plants.

Identification of microRNAs from Eugenia uniflora by high-throughput sequencing and bioinformatics analysis

Background

microRNAs or miRNAs are small non-coding regulatory RNAs that play important functions in the regulation of gene expression at the post-transcriptional level by targeting mRNAs for degradation or inhibiting protein translation. Eugenia uniflora is a plant native to tropical America with pharmacological and ecological importance, and there have been no previous studies concerning its gene expression and regulation. To date, no miRNAs have been reported in Myrtaceae species.

Results

Small RNA and RNA-seq libraries were constructed to identify miRNAs and pre-miRNAs in Eugenia uniflora. Solexa technology was used to perform high throughput sequencing of the library, and the data obtained were analyzed using bioinformatics tools. From 14,489,131 small RNA clean reads, we obtained 1,852,722 mature miRNA sequences representing 45 conserved families that have been identified in other plant species. Further analysis using contigs assembled from RNA-seq allowed the prediction of secondary structures of 25 known and 17 novel pre-miRNAs. The expression of twenty-seven identified miRNAs was also validated using RT-PCR assays. Potential targets were predicted for the most abundant mature miRNAs in the identified pre-miRNAs based on sequence homology.

Conclusions

This study is the first large scale identification of miRNAs and their potential targets from a species of the Myrtaceae family without genomic sequence resources. Our study provides more information about the evolutionary conservation of the regulatory network of miRNAs in plants and highlights species-specific miRNAs.

Modulation of plant HMG-CoA reductase by protein phosphatase 2A: positive and negative control at a key node of metabolism

The enzyme HMG-CoA reductase (HMGR) has a key regulatory role in the mevalonate pathway for isoprenoid biosynthesis, critical not only for normal plant development, but also for the adaptation to demanding environmental conditions. Consistent with this notion, plant HMGR is modulated by many diverse endogenous signals and external stimuli. Protein phosphatase 2A (PP2A) is involved in auxin, abscisic acid, ethylene and brassinosteroid signaling and now emerges as a positive and negative multilevel regulator of plant HMGR, both during normal growth and in response to a variety of stress conditions. The interaction with HMGR is mediated by B" regulatory subunits of PP2A, which are also calcium binding proteins. The new discoveries uncover the potential of PP2A to integrate developmental and calcium-mediated environmental signals in the control of plant HMGR.

Identification and validation of genomic regions that affect shoot fly resistance in sorghum [Sorghum bicolor (L.) Moench]

Shoot fly is one of the most important pests affecting the sorghum production. The identification of quantitative trait loci (QTL) affecting shoot fly resistance enables to understand the underlying genetic mechanisms and genetic basis of complex interactions among the component traits. The aim of the present study was to detect QTL for shoot fly resistance and the associated traits using a population of 210 RILs of the cross 27B (susceptible) × IS2122 (resistant). RIL population was phenotyped in eight environments for shoot fly resistance (deadheart percentage), and in three environments for the component traits, such as glossiness, seedling vigor and trichome density. Linkage map was constructed with 149 marker loci comprising 127 genomic-microsatellite, 21 genic-microsatellite and one morphological marker. QTL analysis was performed by using MQM approach. 25 QTL (five each for leaf glossiness and seedling vigor, 10 for deadhearts, two for adaxial trichome density and three for abaxial trichome density) were detected in individual and across environments. The LOD and R (2) (%) values of QTL ranged from 2.44 to 24.1 and 4.3 to 44.1%, respectively. For most of the QTLs, the resistant parent, IS2122 contributed alleles for resistance; while at two QTL regions, the susceptible parent 27B also contributed for resistance traits. Three genomic regions affected multiple traits, suggesting the phenomenon of pleiotrophy or tight linkage. Stable QTL were identified for the traits across different environments, and genetic backgrounds by comparing the QTL in the study with previously reported QTL in sorghum. For majority of the QTLs, possible candidate genes were identified. The QTLs identified will enable marker assisted breeding for shoot fly resistance in sorghum.

Water stress induces up-regulation of DOF1 and MIF1 transcription factors and down-regulation of proteins involved in secondary metabolism in amaranth roots (Amaranthus hypochondriacus L.)

Roots are the primary sites of water stress perception in plants. The aim of this work was to study differential expression of proteins and transcripts in amaranth roots (Amaranthus hypochondriacus L.) when the plants were grown under drought stress. Changes in protein abundance within the roots were examined using two-dimensional electrophoresis and LC/ESI-MS/MS, and the differential expression of transcripts was evaluated with suppression subtractive hybridisation (SSH). Induction of drought stress decreased relative water content in leaves and increased solutes such as proline and total soluble sugars in roots. Differentially expressed proteins such as SOD(Cu-Zn) , heat shock proteins, signalling-related and glycine-rich proteins were identified. Up-regulated transcripts were those related to defence, stress, signalling (Ser, Tyr-kinases and phosphatases) and water transport (aquaporins and nodulins). More noteworthy was identification of the transcription factors DOF1, which has been related to several plant-specific biological processes, and MIF1, whose constitutive expression has been related to root growth reduction and dwarfism. The down-regulated genes/proteins identified were related to cell differentiation (WOX5A) and secondary metabolism (caffeic acid O-methyltransferase, isoflavone reductase-like protein and two different S-adenosylmethionine synthetases). Amaranth root response to drought stress appears to involve a coordinated response of osmolyte accumulation, up-regulation of proteins that control damage from reactive oxygen species, up-regulation of a family of heat shock proteins that stabilise other proteins and up-regulation of transcription factors related to plant growth control.

Isolation and characterization of a gene encoding a polyethylene glycol-induced cysteine protease in common wheat

Plant cysteine protease (CP) genes are induced by abiotic stresses such as drought, yet their functions remain largely unknown. We isolated the full-length cDNA encoding a Triticum aestivum CP gene, designated TaCP, from wheat by the rapid amplification of cDNA ends (RACE) method. Sequence analysis revealed that TaCP contains an open reading frame encoding a protein of 362 amino acids, which is 96% identical to barley cysteine protease HvSF42. The TaCP transcript level in wheat seedlings was upregulated during polyethylene glycol (PEG) stress, with a peak appearing around 12 h after treatment. TaCP expression level increased rapidly with NaCl treatment at 48 h. TaCP responded strongly to low temperature (4 degree C) treatment from 1 h post-treatment and reached a peak of about 40-fold at 72 h. However, it showed only a very slight response to abscisic acid (ABA). More than one copy of TaCP was present in each of the three genomes of hexaploid wheat and its diploid donors. TaCP fused with green fluorescent protein (GFP) was located in the plasma membrane of onion epidermis cells. Transgenic Arabidopsis plants overexpressing TaCP showed stronger drought tolerance and higher CP activity under water-stressed conditions than wild-type Arabidopsis plants. The results suggest that TaCP plays a role in tolerance to water deficit.

Sugar signaling of fructan metabolism: New insights on protein phosphatases in sucrose-fed wheat leaves

Protein phosphatase type 2A (PP2A) activity is required for the sucrose induction of fructan metabolism in wheat leaves, as shown in experiments with the addition of the specific inhibitor okadaic acid (OA) together with sucrose. However, a decrease in total PP2A activity has been found along sucrose treatment. Here we analyze the effect of sucrose feeding to wheat leaves on PP2A activity profiles after Deae-Sephacel and Superose separation, in comparison with those of control leaves. The results show no evidence of changes in PP2A activity profiles as a consequence of sucrose feeding. In all, our data suggest that constitutive levels of PP2A activity may be sufficient for the sucrose-mediated induction of fructan metabolism and that general decrease of PP2A activity produced by long-term treatment with sucrose may be due to a negative feedback regulation.

Sugar signaling of fructan metabolism: New insights on protein phosphatases in sucrose-fed wheat leaves

Protein phosphatase type 2A (PP2A) activity is required for the sucrose induction of fructan metabolism in wheat leaves, as shown in experiments with the addition of the specific inhibitor okadaic acid (OA) together with sucrose. However, a decrease in total PP2A activity has been found along sucrose treatment. Here we analyze the effect of sucrose feeding to wheat leaves on PP2A activity profiles after Deae-Sephacel and Superose separation, in comparison with those of control leaves. The results show no evidence of changes in PP2A activity profiles as a consequence of sucrose feeding. In all, our data suggest that constitutive levels of PP2A activity may be sufficient for the sucrose-mediated induction of fructan metabolism and that general decrease of PP2A activity produced by long-term treatment with sucrose may be due to a negative feedback regulation.

Functional analysis of TaDi19A, a salt-responsive gene in wheat

A salinity stress upregulated expressed sequence tag (EST) was selected from a suppression subtractive hybridization cDNA library, constructed from the salinity-tolerant wheat cultivar Shanrong No. 3. Sequence analysis showed that the corresponding gene (named TaDi19A) belonged to the Di19 family. TaDi19A was constitutively expressed in both the root and leaf of wheat seedlings grown under non-stressed conditions, but was substantially up-regulated by the imposition of stress (salinity, osmotic stress and cold), or the supply of stress-related hormones [abscisic acid (ABA) and ethylene]. The heterologous over-expression of TaDi19A in Arabidopsis thaliana increased the plants' sensitivity to salinity stress, ABA and mannitol during the germination stage. Root elongation in these transgenic lines showed a reduced tolerance to salinity stress and a reduced sensitivity to ethophon. The expression of the ABA signal pathway genes ABI1, RAB18, ERD15 and ABF3, and SOS2 (SOS pathway) was altered in the transgenic lines. TaDi19A plays a role in the plant's response to abiotic stress, and some possible mechanisms of its action are proposed.

Serine/threonine protein phosphatases type 2A and their roles in stress signaling

Serine/threonine protein phosphatases are ubiquitous enzymes in all eukaryotes but many of their physiological roles in plants remain unknown. The available results have demonstrated critical functions for these enzymes in the regulation of adaptive stress responses, and recent studies have directed attention to the functional roles of Ser/Thr phosphatases type 2A (PP2A) as components of stress signaling pathways. This review is focused primarily on plant PP2As and their participation in the control of biotic and abiotic stress responses.

Diversity in subcellular targeting of the PP2A B'eta subfamily members

Protein phosphatase 2A (PP2A) is a serine/threonine-specific phosphatase comprising a catalytic subunit (C), a scaffolding subunit (A), and a regulatory subunit (B). The B subunits are believed to be responsible for substrate specificity and localization of the PP2A complex. In plants, three families of B subunits exist, i.e. B (B55), B', and B''. Here, we report differential subcellular targeting within the Arabidopsis B'eta subfamily, which consists of the close homologs B'eta, B'theta, B'gamma and B'zeta. Phenotypes of corresponding knockouts were observed, and particularly revealed delayed flowering for the B'eta knockout. The B' subunits were linked to fluorescent tags and transiently expressed in various tissues of onion, tobacco and Arabidopsis. B'eta and B'gamma targeted the cytosol and nucleus. B'zeta localized to the cytoplasm and partly co-localized with mitochondrial markers when the N-terminus was free. Provided its C-terminus was free, the B'theta subunit targeted peroxisomes. The importance of the C-terminal end for peroxisomal targeting was further confirmed by truncation of the C-terminus. The results revealed that the closely related B' subunits are targeting different organelles in plants, and exemplify the usage of the peptide serine-serine-leucine as a PTS1 peroxisomal signaling peptide.

Characterization of potato (Solanum tuberosum) and tomato (Solanum lycopersicum) protein phosphatases type 2A catalytic subunits and their involvement in stress responses

Protein phosphorylation/dephosphorylation plays critical roles in stress responses in plants. This report presents a comparative characterization of the serine/threonine PP2A catalytic subunit family in Solanum tuberosum (potato) and S. lycopersicum (tomato), two important food crops of the Solanaceae family, based on the sequence analysis and expression profiles in response to environmental stress. Sequence homology analysis revealed six isoforms in potato and five in tomato clustered into two subfamilies (I and II). The data presented in this work show that the expression of different PP2Ac genes is regulated in response to environmental stresses in potato and tomato plants and suggest that, in general, mainly members of the subfamily I are involved in stress responses in both species. However, the differences found in the expression profiles between potato and tomato suggest divergent roles of PP2A in the plant defense mechanisms against stress in these closely related species.

Cloning the PvP5CS gene from common bean (Phaseolus vulgaris) and its expression patterns under abiotic stresses

A full-length cDNA denominated PvP5CS for Delta(1)-pyrroline-5-carboxylate synthetase (P5CS), an enzyme involved in the biosynthesis of proline, was cloned from common bean using a candidate gene approach. PvP5CS contains an open reading frame encoding a 716 amino acid polypeptide. Sequence analysis showed that PvP5CS shares 95.1% homology in nucleotide sequence and 93.2% identity in amino acid sequence with the mothbean (Vigna aconitifolia) P5CS. The expression patterns of PvP5CS in common bean treated with drought, cold (4 degrees C), and salt (200 mM NaCl) stresses were examined using real-time quantitative PCR. These abiotic stresses caused significant up-regulation of the expression of PvP5CS in leaves. The PvP5CS mRNA transcript increased to 2.5 times the control level after 4d drought stress. A rapid up-regulation of PvP5CS, to about 16.3 times the control at 2h post-treatment was observed under salt stress. A significant increase in PvP5CS expression (11.7-fold) was detected after 2h of cold stress. The peaks of proline accumulation appeared at 8d for drought, 24h for cold and 9h for salt stress, somewhat later than the peaks of PvP5CS expression. These results suggest that PvP5CS was a stress-inducible gene regulating the accumulation of proline in plants subjected to stress. Finally, subcellular localization assays showed that the PvP5CS protein was present in the nucleus and at the plasmalemma.

The effect of drought and heat stress on reproductive processes in cereals

As the result of intensive research and breeding efforts over the last 20 years, the yield potential and yield quality of cereals have been greatly improved. Nowadays, yield safety has gained more importance because of the forecasted climatic changes. Drought and high temperature are especially considered as key stress factors with high potential impact on crop yield. Yield safety can only be improved if future breeding attempts will be based on the valuable new knowledge acquired on the processes determining plant development and its responses to stress. Plant stress responses are very complex. Interactions between plant structure, function and the environment need to be investigated at various phases of plant development at the organismal, cellular as well as molecular levels in order to obtain a full picture. The results achieved so far in this field indicate that various plant organs, in a definite hierarchy and in interaction with each other, are involved in determining crop yield under stress. Here we attempt to summarize the currently available information on cereal reproduction under drought and heat stress and to give an outlook towards potential strategies to improve yield safety in cereals.