Water deficit modulates gene expression in growing zones of soybean seedlings. Analysis of differentially expressed cDNAs, a new beta-tubulin gene, and expression of genes encoding cell wall proteins

Seed priming with methyl jasmonate mitigates copper and cadmium toxicity by modifying biochemical attributes and antioxidants in Cajanus cajan

Contamination of agricultural soils with heavy metals (HMs) has posed major threat to the environment as well as human health. The aim of this study was to appraise the efficiency of key-antioxidant enzymes in enhancing plants' tolerance to HMs (heavy metals) like copper (Cu) and Cadmium (Cd), under the action of methyl jasmonate (Me-JA) in Cajanus cajan L. Seeds of C. cajan treated with Me-JA (0, 1 nM) were discretely subjected to noxious concentrations of Cu and Cd (0, 1, 5 mM) and raised for 12 days under controlled conditions in plant growth chamber for biochemical analysis. In contrast to Cd, Cu triggered oxidative stress more significantly (44.54% in 5 mM Cu increase in MDA as compared to control) and prominently thereby affecting plants' physiological and biochemical attributes. By activating the antioxidant machinery, Me-JA pre-treatment reduced HMs-induced oxidative stress, increased proline production, glutathione (41.95% under 5 mM Cu when treated with 1 nM Me-JA treatment) and ascorbic acid content by 160.4 % under aforemtioned treatments thus improving the redox status. Thus, in light of this our results put forward a firm basis of the positive role that Me-JA might play in the mitigation of oxidative stress caused due to HMs stress by stimulating antioxidant defense system leading to overall improvement of growth of C. cajan seedlings.

Jasmonic acid ameliorates alkaline stress by improving growth performance, ascorbate glutathione cycle and glyoxylase system in maize seedlings

Environmental pollution by alkaline salts, such as Na₂CO₃, is a permanent problem in agriculture. Here, we examined the putative role of jasmonic acid (JA) in improving Na₂CO₃-stress tolerance in maize seedlings. Pretreatment of maize seedlings with JA was found to significantly mitigate the toxic effects of excessive Na₂CO₃ on photosynthesis- and plant growth-related parameters. The JA-induced improved tolerance could be attributed to decreased Na uptake and Na₂CO₃-induced oxidative damage by lowering the accumulation of reactive oxygen species and malondialdehyde. JA counteracted the salt-induced increase in proline and glutathione content, and significantly improved ascorbic acid content and redox status. The major antioxidant enzyme activities were largely stimulated by JA pretreatment in maize plants exposed to excessive alkaline salts. Additionally, increased activities of glyoxalases I and II were correlated with reduced levels of methylglyoxal in JA-pretreated alkaline-stressed maize plants. These results indicated that modifying the endogenous Na⁺ and K⁺ contents by JA pretreatment improved alkaline tolerance in maize plants by inhibiting Na uptake and regulating the antioxidant and glyoxalase systems, thereby demonstrating the important role of JA in mitigating heavy metal toxicity. Our findings may be useful in the development of alkali stress tolerant crops by genetic engineering of JA biosynthesis.

Role of proline in cell wall synthesis and plant development and its implications in plant ontogeny

Proline is a proteogenic amino acid and accumulates both under stress and non-stress conditions as a beneficial solute in plants. Recent discoveries point out that proline plays an important role in plant growth and differentiation across life cycle. It is a key determinant of many cell wall proteins that plays important roles in plant development. The role of extensins, arabinogalactan proteins and hydroxyproline- and proline-rich proteins as important components of cell wall proteins that play pivotal roles in cell wall signal transduction cascades, plant development and stress tolerance is discussed in this review. Molecular insights are also provided here into the plausible roles of proline transporters modulating key events in plant development. In addition, the roles of proline during seed developmental transitions including storage protein synthesis are discussed.

Differential expression of the transcripts of Spartina alterniflora Loisel (smooth cordgrass) induced in response to petroleum hydrocarbon

Petroleum hydrocarbons (PHC) in soil are potentially toxic to plants and exert negative effect on the environment and human health. To understand the effect of PHC on the gene expression profile of a wetland plant Spartina alterniflora in the coastal Louisiana, plants were subject up to 40% PHC under greenhouse conditions. The plants exposed to PHC showed 21% reduction of leaf total chlorophyll after 2 weeks of stress. Using 20 annealing control primers, 28 differentially expressing genes (DEGs) were identified in leaf and root tissues of S. alterniflora in response to PHC stress. Eleven of these 28 DEGs had role in either molecular function (chlorophyll a-b binding protein, HSP70, NADH, RAN1-binding protein, and RNA-binding protein), biological processes (cell wall protein, nucelosome/chromatin assembly factor) or cellular function (30 S ribosomal protein). This indicated that genes in different regulatory pathways of S. alterniflora were involved in response to PHC. All DEGs showed reduced transcript accumulation in root under oil stress, whereas they showed up- or down-regulation in their transcript abundance in leaf depending on the concentration of the PHC. The genes identified through this study could be used in the genetic screen of S. alterniflora for resistance to PHC.

Differential proteomic responses to water stress induced by PEG in two creeping bentgrass cultivars differing in stress tolerance

Protein metabolism and expression play important role in plant adaptation to water stress. The objectives of this study were to examine proteomic responses to water stress induced by polyethylene glycol (PEG) in creeping bentgrass (Agrostis stolonifera L.) leaves and to identify proteins associated with stress tolerance. Plants of two cultivars ('Penncross' and 'Penn-A4') differing in water stress tolerance were grown in sand irrigated daily with water (control) or PEG solution (osmotic potential of -0.66MPa) to induce water stress, for 28d in growth chambers. Shoot extension rate, relative water content and cell membrane stability were measured to compare drought tolerance between the two cultivars. All parameters maintained at a significantly higher level in 'Penn-A4' than in 'Penncross' under PEG treatment. After 28d of water stress, proteins were extracted from leaves and separated by difference gel electrophoresis. Among 56 stress-responsive protein spots, 46 were identified using mass spectrometry. Some proteins involved in primary nitrogen and carbon metabolism were down-regulated by PEG-induced water stress in both cultivars. The abundance of antioxidant enzyme proteins (ascorbate peroxidase, catalase and glutathione-S-transferase) increased under water stress, particularly ascorbate peroxidase in 'Penn-A4'. The abundance levels of actins, UDP-sulfoquinovose synthase and glucan exohydrolase were greater in 'Penn-A4' than in 'Penncross' under PEG treatment. Our results suggest that proteins involved in membrane synthesis, cell wall loosening, cell turgor maintenance, and antioxidant defense may play roles in perennial grass adaptation to PEG-induced water stress.

Differential proteomic response to heat stress in thermal Agrostis scabra and heat-sensitive Agrostis stolonifera

Knowledge of heat-responsive proteins is critical for further understanding of the molecular mechanisms of heat tolerance. The objective of this study was to compare proteins differentially expressed in two C(3) grass species contrasting in heat tolerance, heat-tolerant thermal Agrostis scabra and heat-sensitive Agrostis stolonifera L., and to identify heat-responsive proteins for short- and long-term responses. Plants were exposed to 20/15 degrees C (day/night, control) or 40/35 degrees C (day/night, heat stress) in growth chambers. Leaves were harvested at 2 and 10 days after temperature treatment. Proteins were extracted and separated by fluorescence difference gel electrophoresis (DIGE). Thermal A. scabra had superior heat tolerance than A. stolonifera, as indicated by the maintenance of higher chlorophyll content and photochemical efficiency under heat stress. The two-dimensional difference electrophoresis detected 68 heat-responsive proteins in the two species. Thermal A. scabra had more protein spots either down- or up-regulated at 2 days of heat stress, but fewer protein spots were altered at 10 days of heat stress compared with A. stolonifera. Many protein spots exhibited transient down-regulation in thermal A. scabra (only at 2 days of heat treatment), whereas down-regulation of many proteins was also found at 10 days of heat treatment in A. stolonifera, which suggested that protein metabolism in thermal A. scabra might acclimate to heat stress more rapidly than those in A. stolonifera. The sequences of 56 differentially expressed protein spots were identified using mass spectrometry. The results suggest that the maintenance or less severe down-regulation of proteins during long-term (10 days) heat stress may contribute to the superior heat tolerance in thermal A. scabra, including those involved in photosynthesis [RuBisCo, RuBisCo activase, chloroplastic glyceraldehydes-3-phosphate dehydrogenase (GAPDH), chloroplastic aldolase, oxygen-evolving complex, photosystem I subunits], dark respiration (cytosolic GAPDH, cytoplasmic aldolase, malate dehydrogenase, hydroxypyruvate reductase, sedoheptulose-1,7-bisphosphatase), photorespiration [(hydroxypyruvate reductase, alanine aminotransferase (AlaAT), hydroxymethyltransferase (SHMT), glycine decarboxylase (GDC)], as well as heat and oxidative stress protection [heat shock cognate (HSC) 70 and FtsH-like protein].

Isolation and characterization of induced genes under drought stress at the flowering stage in maize (Zea mays)

Maize female organs are sensitive to drought stress, leading to reproductive failure and yield reduction. In the present study gene expression profiles of ears and silks of maize at the flowering stage under drought stress were investigated. From 1920 white positive clones of a forward suppression subtractive hybridization (SSH) library, 1439 available sequences of expression sequence tags (ESTs) were obtained, resulting in 361 unique ESTs after assembling. Data analysis showed that 218 of the unique ESTs had significant protein homology by BLASTX in UNIPROT database. Totally 99 uniESTs were found in TIGR maize gene indices and nr database by BLASTN, while 44 uniESTs were not found to have homologous nucleic acid sequences and putatively classified as "maize-specific" uniESTs. The 218 cDNAs with significant protein homology were sorted into 13 groups according to the functional categories of the Arabidopsis proteins. Among those genes, the genes associated with the metabolisms were the largest group (account for 27%), and the genes related to protein synthesis, protein fate, transcription, cell cycle and DNA processing accounted for 16, 10, 10 and 9%, respectively. After analysis of macroarray data and real-time quantitative polymerase chain reaction (PCR), it was found that 160 of the 218 homologous protein uniESTs were up-regulated genes in the ears, 129 in the silks, and 125 in both of the tissues. The present work provided a valuable starting point for further elucidation of the roles played by these genes/gene products in drought tolerance in maize.

Molecular cloning, expression profiling, and yeast complementation of 19 beta-tubulin cDNAs from developing cotton ovules

Microtubules are a major structural component of the cytoskeleton and participate in cell division, intracellular transport, and cell morphogenesis. In the present study, 795 cotton tubulin expressed sequence tags were analysed and 19 beta-tubulin genes (TUB) cloned from a cotton cDNA library. Among the group, 12 cotton TUBs (GhTUBs) are reported for the first time here. Transcription profiling revealed that nine GhTUBs were highly expressed in elongating fibre cells as compared with fuzzless-lintless mutant ovules. Treating cultured wild-type cotton ovules with exogenous phytohormones showed that individual genes can be induced by different agents. Gibberellin induced expression of GhTUB1 and GhTUB3, ethylene induced expression of GhTUB5, GhTUB9, and GhTUB12, brassinosteroids induced expression of GhTUB1, GhTUB3, GhTUB9, and GhTUB12, and lignoceric acid induced expression of GhTUB1, GhTUB3, and GhTUB12. When GhTUBs were transformed into the Saccharomyces cerevisiae inviable mutant, tub2, which is deficient in beta-tubulin, one ovule-specific and eight of nine fibre-preferential GhTUBs rescued this lethality. This study suggests that the proteins encoded by cotton GhTUBs are involved during cotton fibre development.

Proline-rich cell wall proteins accumulate in growing regions and phloem tissue in response to water deficit in common bean seedlings

Plant cell walls undergo dynamic changes in response to different environmental stress conditions. In response to water deficit, two related proline-rich glycoproteins, called p33 and p36, accumulate in the soluble fraction of the cell walls in Phaseolus vulgaris (Covarrubias et al. in Plant Physiol 107:1119-1128, 1995). In this work, we show that p33 and p36 are able to form a 240 kDa oligomer, which is found in the cell wall soluble fraction. We present evidence indicating that the highest accumulation of these proteins in response to water deficit occurs in the growing regions of common bean seedlings, particularly in the phloem tissues. These proteins were detected in P. vulgaris cell suspension cultures, where the p33/p36 ratio was higher under hyperosmotic conditions than in bean seedlings subjected to the same treatment. The results support a role for these proteins during the plant cell response to changes in its water status, and suggest that cell wall modifications are induced in active growing cells of common bean in response to water limitation.

A ginseng-specific abundant protein (GSAP) located on the cell wall is involved in abiotic stress tolerance

Ginseng ESTs allowed us to identify an unknown transcript which is highly abundant in rhizomes and seeds. We called the cDNA ginseng-specific abundant protein (GSAP), and identified three homologues, GSAP1, GSAP2, and GSAP3. GSAP cDNAs encode a small polypeptide consisting of 121 or 117 amino acids, and GSAP3 shows 87.6% amino acid sequence homology with GSAP1. GSAP transcripts were detected in most plant tissues, but GSAP3 is highly expressed in seeds, and is up-regulated under stressed conditions, water deficit. GSAP3-GFP fusion protein is located in the cell wall when expressed in onion epidermis cells. The transgenic Arabidopsis seedlings which over-expressed GSAP3 grew faster than those of the wild-type plant on the medium containing 300 mM mannitol and 100 mM NaCl. GSAP3 may play a role in altering the characteristics of the cell wall to allow for more tolerance of water deficit stress under abiotic stress conditions.

Expression of PsGRP1, a novel glycine rich protein gene of Pisum sativum, is induced in developing fruit and seed and by ABA in pistil and root

A novel glycine-rich protein gene, PsGRP1, has been identified in Pisum sativum L. Accumulation of PsGRP1 transcripts was observed in reproductive organs and vegetative tissues. They were localized in endocarp sclerenchyma during fruit development in cells that will lignify. PsGRP1 expression was also detected in senescent pistils and developing seeds and induced by ABA treatment in presenescent pistils. A raise in the expression was also observed in roots after treatment with ABA or mannitol but not under cold stress. A mannitol treatment induced a rise in ABA levels and fluridone treatment counteracted the mannitol induction of PsGRP1 expression. The results suggest a possible role for PsGRP1 in differentiation of the endocarp sclerenchyma and during seed development, pistil senescence and osmotic stress under ABA control.

Transcriptional profiling of sunflower plants growing under low temperatures reveals an extensive down-regulation of gene expression associated with chilling sensitivity

Being able to sow early to maximize the growing season and to escape drought stress has increased the importance of low-temperature tolerance in sunflower. Yet knowledge about the molecular basis of sunflower response to low temperature is still lacking. To address this issue, nylon microarrays containing >8000 putative unigenes were developed and used. Early- and late-flowering genotypes were sown at 15 degrees C and grown until the two-leaf stage when they were subjected to 7 degrees C until the four-leaf stage. The transcriptional profiles of low temperature-grown plants (15 degrees C and 7 degrees C) were compared with those grown under standard conditions (25 degrees C). Two-step ANOVA normalization and analysis models were used to identify the differentially expressed genes. A total of 108 cDNA clones having a P-value <10(-3) were found to be differentially expressed between the low temperature-grown plants (15 degrees C and 7 degrees C) and their corresponding two-leaf- and four-leaf-stage controls across the two genotypes. About 90% of these genes were down-regulated. This includes genes potentially involved in the metabolism of carbohydrate and energy, protein synthesis, signal transduction, and transport function. Comparing gene expression profiles at 15 degrees C and 7 degrees C revealed that only four genes can be considered as differentially expressed, in both genotypes, suggesting that similar genetic programmes underlie the response of sunflower plants to these temperature regimes. The analysis also revealed that early- and late-flowering genotypes respond similarly to low-temperature tolerance as justified by the low number of genes showing a significant genotype x treatment interaction effect. It seems likely that the down-regulation and/or non-induction of genes having a critical role in low-temperature tolerance may be responsible for the sensitivity of sunflower plants to low-temperature tolerance. The results reported provide an initial characterization of the transcriptome activity of sunflower, as a chilling-sensitive plant under suboptimal temperatures, and could be of importance to reveal the potential differences between chilling-sensitive and chilling-tolerant species.

Sorghum bicolor's transcriptome response to dehydration, high salinity and ABA

Genome wide changes in gene expression were monitored in the drought tolerant C4 cereal Sorghum bicolor, following exposure of seedlings to high salinity (150 mM NaCl), osmotic stress (20% polyethylene glycol) or abscisic acid (125 microM ABA). A sorghum cDNA microarray providing data on 12,982 unique gene clusters was used to examine gene expression in roots and shoots at 3- and 27-h post-treatment. Expression of approximately 2200 genes, including 174 genes with currently unknown functions, of which a subset appear unique to monocots and/or sorghum, was altered in response to dehydration, high salinity or ABA. The modulated sorghum genes had homology to proteins involved in regulation, growth, transport, membrane/protein turnover/repair, metabolism, dehydration protection, reactive oxygen scavenging, and plant defense. Real-time PCR was used to quantify changes in relative mRNA abundance for 333 genes that responded to ABA, NaCl or osmotic stress. Osmotic stress inducible sorghum genes identified for the first time included a beta-expansin expressed in shoots, actin depolymerization factor, inositol-3-phosphate synthase, a non-C4 NADP-malic enzyme, oleosin, and three genes homologous to 9-cis-epoxycarotenoid dioxygenase that may be involved in ABA biosynthesis. Analysis of response profiles demonstrated the existence of a complex gene regulatory network that differentially modulates gene expression in a tissue- and kinetic-specific manner in response to ABA, high salinity and water deficit. Modulation of genes involved in signal transduction, chromatin structure, transcription, translation and RNA metabolism contributes to sorghum's overlapping but nonetheless distinct responses to ABA, high salinity, and osmotic stress. Overall, this study provides a foundation of information on sorghum's osmotic stress responsive gene complement that will accelerate follow up biochemical, QTL and comparative studies.

Theoretical and experimental studies on freezing point depression and vapor pressure deficit as methods to measure osmotic pressure of aqueous polyethylene glycol and bovine serum albumin solutions

For survival in adverse environments where there is drought, high salt concentration or low temperature, some plants seem to be able to synthesize biochemical compounds, including proteins, in response to changes in water activity or osmotic pressure. Measurement of the water activity or osmotic pressure of simple aqueous solutions has been based on freezing point depression or vapor pressure deficit. Measurement of the osmotic pressure of plants under water stress has been mainly based on vapor pressure deficit. However, differences have been noted for osmotic pressure values of aqueous polyethylene glycol (PEG) solutions measured by freezing point depression and vapor pressure deficit. For this paper, the physicochemical basis of freezing point depression and vapor pressure deficit were first examined theoretically and then, the osmotic pressure of aqueous ethylene glycol and of PEG solutions were measured by both freezing point depression and vapor pressure deficit in comparison with other aqueous solutions such as NaCl, KCl, CaCl(2), glucose, sucrose, raffinose, and bovine serum albumin (BSA) solutions. The results showed that: (1) freezing point depression and vapor pressure deficit share theoretically the same physicochemical basis; (2) theoretically, they are proportional to the molal concentration of the aqueous solutions to be measured; (3) in practice, the osmotic pressure levels of aqueous NaCl, KCl, CaCl(2), glucose, sucrose, and raffinose solutions increase in proportion to their molal concentrations and there is little inconsistency between those measured by freezing point depression and vapor pressure deficit; (4) the osmotic pressure levels of aqueous ethylene glycol and PEG solutions measured by freezing point depression differed from the values measured by vapor pressure deficit; (5) the osmotic pressure of aqueous BSA solution measured by freezing point depression differed slightly from that measured by vapor pressure deficit.

Salinity- and ABA-induced up-regulation and light-mediated modulation of mRNA encoding glycine-rich RNA-binding protein from Sorghum bicolor

Glycine-rich RNA-binding proteins play an important role in post-transcriptional regulation of gene expression, including RNA processing, and are known to be up-regulated in response to a number of external stimuli. However, their regulation in response to salinity stress has not been reported. We have isolated a light- and salt-regulated, full-length cDNA clone encoding a putative glycine-rich protein containing conserved ribonucleoprotein motif from Sorghum bicolor designated as sbGR-RNP. Sequence analysis of the 701bp insert revealed that the open reading frame of 513bp encodes a 170 amino acid protein, with an apparent molecular mass of 16.68kDa and calculated pI of 6.59. The deduced amino acid sequence also revealed that protein is hydrophilic in nature and contains 38% glycine residues. Northern blot analysis revealed a transcript size of 630 nucleotides, which shows regulation by blue and red light. The transcript is initially up- and down-regulated rapidly within 5min of irradiation with blue and red light, respectively. This kind of rapid and opposite regulation by different light wavelengths could be a novel behavior of this photo-regulated gene. Furthermore, NaCl (500mM) and abscisic acid (10 microM) also stimulated the transcript levels of sbGR-RNP to fourfold and sevenfold, respectively. These novel regulations of sbGR-RNP in response to light and salinity are important phenomena, which will be helpful in understanding the molecular mechanisms of cross-talk between abiotic stress and light signaling in plants.

Differential mRNA degradation of two beta-tubulin isoforms correlates with cytosolic Ca2+ changes in glucan-elicited soybean cells

Transgenic soybean (Glycine max) culture cells expressing apoaequorin, a Ca2+ indicator, were exposed to glucan fragments derived from Phytophthora sojae or to chitin oligomers. The effects of these elicitors on cytosolic Ca2+ concentrations and on mRNA levels of two beta-tubulin isoforms, tubB1 and tubB2, were investigated. The glucan elicitors, to which the cells are known to react with a biphasic cytosolic Ca2+ increase, induced a down-regulation of the tubB1 mRNA levels while the tubB2 mRNA level remained constant. The decrease of tubB1 mRNA level was observed after 1 hour of glucan treatment. In contrast, chitin oligomers, known to provoke a monophasic Ca2+ increase of short duration, did not affect the tubB1 mRNA level. Pre-incubation with 10 mM 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid, an extracellular Ca2+ chelator, blocked the cytosolic Ca2+ increase as well as the decrease of tubB1 mRNA levels induced by glucan elicitors. Likewise, pre-incubation with 1 mM neomycin, which reduced only the second glucan-induced Ca2+ peak, blocked the decrease of tubB1 mRNA level. Experiments with cordycepin, a transcription inhibitor, indicated that glucan fragments induced the degradation of tubB1 mRNA. In conclusion, the glucan-induced cytosolic Ca2+ changes are correlated with a strong increase in tubB1 mRNA degradation.

Adaptation of roots to low water potentials by changes in cell wall extensibility and cell wall proteins

It is common for the root/shoot ratio of plants to increase when water availability is limiting. This ratio increases because roots are less sensitive than shoots to growth inhibition by low water potentials. The physiological and molecular mechanisms that assist root growth under drought conditions are reviewed, with a focus on changes in cell walls. Maize seedlings adapt to low water potential by making the walls in the apical part of the root more extensible. In part, this is accomplished by increases in expansin activity and in part by other, more complex changes in the wall. The role of xyloglucan endotransglycosylase, peroxidase and other wall enzymes in root adaptation to low water potential is evaluated and some of the complications in the field of study are listed.

Plant glycine-rich proteins: a family or just proteins with a common motif?

Twelve years ago a set of glycine-rich proteins (GRP) of plants were characterized and since then a wealth of new GRPs have been identified. The highly specific but diverse expression pattern of grp genes, taken together with the distinct sub-cellular localisation of some GRP groups, clearly indicate that these proteins are implicated in several independent physiological processes. Notwithstanding the absence of a clear definition of the role of GRPs in plant cells, studies conducted with these proteins have provided new and interesting insights on the molecular and cell biology of plants. Complex regulated promoters and distinct mechanisms of gene expression regulation have been demonstrated. New protein targeting pathways, as well as the exportation of GRPs from different cell types have been discovered. These data show that GRPs can be useful as markers and/or models to understand distinct aspects of plant biology. In this review, the structural and functional features of this family of plant proteins will be summarised. Special emphasis will be given to the gene expression regulation of GRPs isolated from different plant species, as it can help to unravel their possible biological functions.

StGCPRP, a potato gene strongly expressed in stomatal guard cells, defines a novel type of repetitive proline-rich proteins

Guard cells represent a highly differentiated cell type within the epidermis of plant leaves and stems. They respond to many endogenous and environmental signals and thereby modify the size of the stomatal pore they surround. We identified a novel gene that is highly expressed in guard cells of potato (Solanum tuberosum). It encodes a repetitive proline (Pro)-rich protein of 54 kD (491 amino acids) and was named StGCPRP (S. tuberosum guard cell Pro-rich protein). StGCPRP has a bipartite structure. The C-terminal part of StGCPRP contains a high percentage (46%) of Pro residues organized in distinct repetitive sequence motifs, whereas its extended N terminus is essentially free of Pros. StGCPRP represents the first member of a novel class of hybrid Pro-rich proteins that we designated NHyPRPs. In young but not in mature leaves, StGCPRP transcripts were also present at high levels in mesophyll cells (in addition to guard cells), indicating developmental regulation of StGCPRP gene expression. In addition, StGCPRP expression is regulated by environmental factors, as shown by a decrease in StGCPRP transcript levels under drought stress. Two proteins similar to StGCPRP were found to be encoded by the Arabidopsis genome, indicating that NHyPRPs are more widely distributed in higher plants.

Developmental expression and regulation by light of two closely related beta-tubulin genes in Lupinus albus

We present here the characterization of a Lupinus albus beta-tubulin gene, TubB2, which is closely related to TubB1. Both TubB1 and TubB2 transcripts are present in the embryonic axis of lupin dry seeds. The patterns of developmental expression of TubB1 and TubB2 beta-tubulin genes are strongly correlated. Both genes are expressed at higher levels in hypocotyls of 7-day-old etiolated plants compared to hypocotyls from plants grown under light/dark cycles. When etiolated plants are exposed to continuous white light, differential changes in the steady state levels of the TubB1 and TubB2 mRNAs from hypocotyls are observed. These changes are accompanied by an inhibition of hypocotyl extension.

Expression of the rice Osgrp1 promoter-Gus reporter gene is specifically associated with cell elongation/expansion and differentiation

To study the expression and regulation of a rice glycine-rich cell wall protein gene, Osgrp1, transgenic rice plants were regenerated that contain the Osgrp1 promoter or its 5' deletions fused with the bacterial beta-glucuronidase (GUS) reporter gene. We report here a detailed histochemical analysis of the Osgrp1-Gus expression patterns in transgenic rice plants. In roots of transgenic rice plants, GUS expression was specifically located in cell elongation and differentiation regions, and no GUS expression was detectable in the apical meristem and the mature region. In shoots, GUS activity was expressed only in young leaves or in the growing basal parts of developing leaves, and little GUS activity was expressed in mature leaves or mature parts of developing leaves. In shoot apices, GUS activity was detected only in those leaf cells which were starting to expand and differentiate, and GUS expression was not detected in the apical meristem and the young meristematic leaf primordia. GUS activity was highly expressed in the young stem tissue, particularly in the developing vascular bundles and epidermis. Thus, the expression of the Osgrp1 gene is closely associated with cell elongation/expansion during the post-mitotic cell differentiation process. The Osgrp1-Gus gene was also expressed in response to wounding and down-regulated by water-stress conditions in the elongation region of roots. Promoter deletion analysis indicates that both positive and negative mechanisms are involved in regulating the specific expression patterns. We propose a simple model for the developmental regulation of the Osgrp1 gene expression.

The Pisum sativum TubA1 gene, a member of a small family of alpha-tubulin sequences

alpha- and beta-tubulin proteins are subunits of microtubules, which as primary elements of the plant cytoskeleton play major roles in plant cell division and cell morphogenesis. Several higher-plant alpha- and beta-tubulin gene families have been reported to have at least six to nine members each. Using genomic Southern hybridizations and polymerase chain reaction (PCR) experiments, we have found that the Pisum sativum (garden pea) genome has only four copies of alpha-tubulin sequences and a similar number of beta-tubulin sequences. We have characterized the pea alpha-tubulin gene TubA1. Its nucleotide sequence predicts a 452 amino acid product which is 89-98% identical to those predicted for other plant alpha-tubulins. By S1 nuclease analysis we have located the transcript start site at 102 bases upstream of the ATG. We have also shown that the TubA1 gene is expressed by northern hybridization with a gene-specific probe.

Effect of drought stress on growth and essential oil metabolism in lemongrasses

Two lemongrasses. Cymbopogon nardus. (L.) Rendle var. confertiflorus (Steud.) Bor. and Cymbopogon pendulus (Steud.) Wats, were grown under mild and moderate water stress for 45 and 90 d. The impact of in situ drought stress on plants in terms of relative water content, $pS, concentration of proline, activities of PEP carboxylase and geraniol dehydrogenase, and geraniol and citral biogenesis, were investigated. The results revealed that the specific exhibited differential responses under mild and moderate stress treatments. In general, plant growth was reduced considerably whilst the level of essential oils was maintained or enhanced. Significant induction in catalytic activity of PKP carboxylase under water stress was one of the consistent metabolic responses of the aromatic grasses. The major oil constituents., geraniol and citral, increased substantially in both the species. Activity of geraniol dehydrogenase was also modulated under moisture stress. The responses varied depending Upon the level and duration of moisture stress. The observations have been analyzed in terms of possible relevance of some of these responses to their drought stress adaptability tolerance.

Differential accumulation of S-adenosylmethionine synthetase transcripts in response to salt stress

NaCl stress causes the accumulation of several mRNAs in tomato seedlings. An upregulated cDNA clone, SAM1, was found to encode a S-adenosyl-L-methionine synthetase enzyme (AdoMet synthetase). Expression of the cDNA SAM1 in a yeast mutant lacking functional SAM genes resulted in high AdoMet synthetase activity and AdoMet accumulation. We show that tomato plants contain at least four SAM isogenes. Clones corresponding to isogenes SAM2 and SAM3 have also been isolated and sequenced. They encode predicted polypeptides 95% and 92% identical, respectively, to the SAM1-encoded AdoMet Synthetase. RNA hybridization analysis showed a differential response of SAM genes to salt and other stress treatments. SAM1 and SAM3 mRNAs accumulated in the root in response to NaCl, mannitol or ABA treatments. SAM1 mRNA accumulated also in leaf tissue. These increases of mRNA level were apparent as soon as 8 h after the initiation of the salt treatment and were maintained for at least 3 days. A possible role for AdoMet synthetases in the adaptation to salt stress is discussed.

Structure and expression of genes coding for structural proteins of the plant cell wall

The best-known protein components of the plant cell wall have highly repetitive, proline-rich sequences. The use of recombinant DNA approaches has enabled complete sequences of these proteins to be determined and features of the expression of the corresponding genes to be examined. These results, coupled with the use of immunological techniques, have shown that proline-rich proteins are interesting probes to study developmental and defence processes in plants. In this review, the sequence and expression of different groups of proline-rich proteins in plants are presented. These groups include hydroxyproline-rich glycoproteins (HRGP) or extensins, proline-rich proteins (PRP) and glycine-rich proteins (GRP). The specific features of each group and the possible functions of these proteins are discussed, as well as the data available on the mechanisms controlling the expression of their corresponding genes. Contents Summary 259 I. Introduction 259 II. Hydroxypioline-rich glycoproteins (HRGPs) 261 III. Proline-rich proteins (PRPs) 270 IV. Glycine-rich proteins (GRPs) 274 V. Concluding remarks 277 References 279.

Developmental regulation and phytochrome-mediated induction of mRNAs encoding a proline-rich protein, glycine-rich proteins, and hydroxyproline-rich glycoproteins in Phaseolus vulgaris L

We have studied developmental and light regulation of mRNAs encoding a putative cell wall proline-rich protein (PvPRP1), cell wall glycine-rich proteins (GRPs), and cell wall hydroxyproline-rich glycoproteins (HRGPs) in bean (Phaseolus vulgaris). Light increases the levels of these mRNAs 2- to 150-fold in highly spatially regulated patterns during seedling development. These mRNA changes include differential regulation of transcripts derived from the GRP and HRGP multigene families. In 6-day-old light-grown seedlings, the PvPRP1 and GRP1.0 mRNAs were most abundant in the apical region of hypocotyls, epicotyls, and roots. In contrast, several HRGP transcripts were most abundant in the mature region of hypocotyls and roots in light-grown seedlings. When etiolated 6-day-old seedlings were illuminated with white light for 8 hr, maximal accumulation of PvPRP1 and GRP1.0 mRNAs occurred in the apical hook, whereas HRGP and GRP1.8 mRNAs accumulated in the mature region of hypocotyls. Etiolated seedlings subjected to a pulse of red light accumulated PvPRP1, GRP, and HRGP mRNAs in the hypocotyls. Far-red light inhibited red light induction of these mRNAs, indicating a phytochrome-mediated process. The possible roles of PRPs, GRPs, and HRGPs in cell differentiation and photomorphogenesis are discussed.

Jasmonic acid/methyl jasmonate accumulate in wounded soybean hypocotyls and modulate wound gene expression

Jasmonic acid (JA) and its methyl ester, methyl jasmonate (MeJA), are plant lipid derivatives that resemble mammalian eicosanoids in structure and biosynthesis. These compounds are proposed to play a role in plant wound and pathogen responses. Here we report the quantitative determination of JA/MeJA in planta by a procedure based on the use of [13C,2H3]MeJA as an internal standard. Wounded soybean (Glycine max [L] Merr. cv. Williams) stems rapidly accumulated MeJA and JA. Addition of MeJA to soybean suspension cultures also increased mRNA levels for three wound-responsive genes (chalcone synthase, vegetative storage protein, and proline-rich cell wall protein) suggesting a role for MeJA/JA in the mediation of several changes in gene expression associated with the plants' response to wounding.

Lipoxygenase gene expression is modulated in plants by water deficit, wounding, and methyl jasmonate

Two classes of lipoxygenase (LOX) cDNAs, designated loxA and loxB, were isolated from soybean. A third lipoxygenase cDNA, loxP1, was isolated from pea. The deduced amino acid sequences of loxA and loxB show 61-74% identity with those of soybean seed LOXs. loxA and loxB mRNAs are abundant in roots and non-growing regions of seedling hypocotyls. Lower levels of these mRNAs are found in hypocotyl growing regions. Exposure of soybean seedlings to water deficit causes a rapid increase in loxA and loxB mRNAs in the elongating hypocotyl region. Similarly, loxP1 mRNA levels increase rapidly when pea plants are wilted. loxA and loxB mRNA levels also increase in wounded soybean leaves, and these mRNAs accumulate in soybean suspension cultures treated with 20 microM methyl jasmonate. These results demonstrate that LOX gene expression is modulated in response to water deficit and wounding and suggest a role for lipoxygenase in plant responses to these stresses.