Spatial and temporal analysis of the local response to wounding in Arabidopsis leaves

Exposure to Light of the Abaxial versus Adaxial Side of Detached Kalanchoë blossfeldiana Leaves Affects Anthocyanin Content and Composition Differently

The accumulation and composition of anthocyanins in leaves of Kalanchoë blossfeldiana, detached and kept for five days under natural light conditions, were investigated. The presence of fifteen derivatives of cyanidin, petunidin, and delphinidin was found. Changes in the content of each anthocyanin in the leaves before and after exposure to light on the abaxial (naturally upper) and adaxial (naturally lower) sides of the leaves were compared. When the adaxial side was exposed to light, the anthocyanin contents of the leaves did not change. In contrast, when the abaxial side of detached leaves was exposed to light, there was enhanced accumulation of delphinidin-rhamnoside-glucoside, cyanidin-rhamnoside-glucoside, cyanidin-glucoside-glucoside, and two unknown derivatives of petunidin and delphinidin. Application of methyl jasmonate (JA-Me) on the abaxial side exposed to light inhibited the accumulation of these anthocyanins. This effect could probably be due to the presence of these anthocyanins in the epidermal cells of K. blossfeldiana leaves and was visible in the microscopic view of its cross-section. These anthocyanins were directly exposed to JA-Me, leading to inhibition of their formation and/or accumulation. The lack of significant effects of JA-Me on anthocyanin mono- and tri-glycosides may indicate that they are mainly present in the mesophyll tissue of the leaf.

Multi-omic characterization of bifunctional peroxidase 4-coumarate 3-hydroxylase knockdown in Brachypodium distachyon provides insights into lignin modification-associated pleiotropic effects

A bifunctional peroxidase enzyme, 4-coumarate 3-hydroxylase (C3H/APX), provides a parallel route to the shikimate shunt pathway for the conversion of 4-coumarate to caffeate in the early steps of lignin biosynthesis. Knockdown of C3H/APX (C3H/APX-KD) expression has been shown to reduce the lignin content in Brachypodium distachyon. However, like many other lignin-modified plants, C3H/APX-KDs show unpredictable pleiotropic phenotypes, including stunted growth, delayed senescence, and reduced seed yield. A system-wide level understanding of altered biological processes in lignin-modified plants can help pinpoint the lignin-modification associated growth defects to benefit future studies aiming to negate the yield penalty. Here, a multi-omic approach was used to characterize molecular changes resulting from C3H/APX-KD associated lignin modification and negative growth phenotype in Brachypodium distachyon. Our findings demonstrate that C3H/APX knockdown in Brachypodium stems substantially alters the abundance of enzymes implicated in the phenylpropanoid biosynthetic pathway and disrupt cellular redox homeostasis. Moreover, it elicits plant defense responses associated with intracellular kinases and phytohormone-based signaling to facilitate growth-defense trade-offs. A deeper understanding along with potential targets to mitigate the pleiotropic phenotypes identified in this study could aid to increase the economic feasibility of lignocellulosic biofuel production.

Modeling temporal and hormonal regulation of plant transcriptional response to wounding

Plants respond to wounding stress by changing gene expression patterns and inducing the production of hormones including jasmonic acid. This wounding transcriptional response activates specialized metabolism pathways such as the glucosinolate pathways in Arabidopsis thaliana. While the regulatory factors and sequences controlling a subset of wound-response genes are known, it remains unclear how wound response is regulated globally. Here, we how these responses are regulated by incorporating putative cis-regulatory elements, known transcription factor binding sites, in vitro DNA affinity purification sequencing, and DNase I hypersensitive sites to predict genes with different wound-response patterns using machine learning. We observed that regulatory sites and regions of open chromatin differed between genes upregulated at early and late wounding time-points as well as between genes induced by jasmonic acid and those not induced. Expanding on what we currently know, we identified cis-elements that improved model predictions of expression clusters over known binding sites. Using a combination of genome editing, in vitro DNA-binding assays, and transient expression assays using native and mutated cis-regulatory elements, we experimentally validated four of the predicted elements, three of which were not previously known to function in wound-response regulation. Our study provides a global model predictive of wound response and identifies new regulatory sequences important for wounding without requiring prior knowledge of the transcriptional regulators.

WIND transcription factors orchestrate wound-induced callus formation, vascular reconnection and defense response in Arabidopsis

Wounding triggers de novo organogenesis, vascular reconnection and defense response but how wound stress evoke such a diverse array of physiological responses remains unknown. We previously identified AP2/ERF transcription factors, WOUND INDUCED DEDIFFERENTIATION1 (WIND1) and its homologs, WIND2, WIND3 and WIND4, as key regulators of wound-induced cellular reprogramming in Arabidopsis. To understand how WIND transcription factors promote downstream events, we performed time-course transcriptome analyses after WIND1 induction. We observed a significant overlap between WIND1-induced genes and genes implicated in cellular reprogramming, vascular formation and pathogen response. We demonstrated that WIND transcription factors induce several reprogramming genes to promote callus formation at wound sites. We, in addition, showed that WIND transcription factors promote tracheary element formation, vascular reconnection and resistance to Pseudomonas syringae pv. tomato DC3000. These results indicate that WIND transcription factors function as key regulators of wound-induced responses by promoting dynamic transcriptional alterations. This study provides deeper mechanistic insights into how plants control multiple physiological responses after wounding.

A New Approach for Wounding Research: MYC2 Gene Expression and Protein Stability in Wounded Arabidopsis Protoplasts

Wounding is a constant threat to plant survival throughout their lifespan; therefore, understanding the biological responses to wounds at the cellular level is important. The protoplast system is versatile for molecular biology, however, no wounding studies on this system have been reported. We established a new approach for wounding research using mechanically damaged Arabidopsis mesophyll protoplasts. Wounded protoplasts showed typical wounding responses, such as increased MPK6 kinase activity and upregulated JAZ1 expression. We also assessed expression profiles and protein stability of the basic helix-loop-helix transcription factor MYC2 in wounded protoplasts. Promoter activity, gene expression, and protein stability of MYC2 were compromised, but recovered in the early stage of wounding. In the late stage, the promoter activity and expression of MYC2 were increased, but the protein stability was not changed. According to the results of the present study, this new cell-based approach will be of use in various molecular studies on plant wounding.

Application of naturally occurring mechanical forces in in vitro plant tissue culture and biotechnology

Cues and signals of the environment in nature can be either beneficial or detrimental from the growth and developmental perspectives. Plants, despite their limited spatial mobility, have developed advanced strategies to overcome the various and changing environmental impacts including stresses. In vitro plantlets, tissues and cells are constantly exposed to the influence of their environment that is well controlled. Light has a widely known morphogenetic effect on plants; however, other physical cues and signals are at least as important but were often neglected. In this review, I summarize our knowledge about the role of the mechanical stimuli, like sound, ultrasound, touch, or wounding in in vitro plant cultures. I summarize the molecular, biochemical, physiological, growth, and developmental changes they cause and how these processes are controlled; moreover, how their regulating or stimulating roles are applied in various plant biotechnological applications. Recent studies revealed that mechanical forces can be used for affecting the plant development and growth in plant tissue culture efficiently, and for increasing the efficacy of other plant biotechnological methods, like genetic transformation and secondary metabolite production.

Breaking Bad News: Dynamic Molecular Mechanisms of Wound Response in Plants

Recognition and repair of damaged tissue are an integral part of life. The failure of cells and tissues to appropriately respond to damage can lead to severe dysfunction and disease. Therefore, it is essential that we understand the molecular pathways of wound recognition and response. In this review, we aim to provide a broad overview of the molecular mechanisms underlying the fate of damaged cells and damage recognition in plants. Damaged cells release the so-called damage associated molecular patterns to warn the surrounding tissue. Local signaling through calcium (Ca2+), reactive oxygen species (ROS), and hormones, such as jasmonic acid, activates defense gene expression and local reinforcement of cell walls to seal off the wound and prevent evaporation and pathogen colonization. Depending on the severity of damage, Ca2+, ROS, and electrical signals can also spread throughout the plant to elicit a systemic defense response. Special emphasis is placed on the spatiotemporal dimension in order to obtain a mechanistic understanding of wound signaling in plants.

Study on the Accumulation Mechanism of Amino Acids during Bruising and Withering Treatment of Oolong Tea

Amino acids are very important for oolong tea brisk-smooth mouthfeel which is mainly associated with bruising and withering treatment (BWT). In this study, metabolome and transcriptome analyses were performed to comprehensively investigate the changes in abundance of amino acids and the expression pattern of relevant genes during BWT of oolong tea manufacturing. Levels of most amino acids increased during BWT in the leaves harvested from 4 cultivars, while expression of the relevant function genes responsible for synthesis and transformation of amino acids up-regulated accordingly. Upstream hub genes including receptor-like protein kinase IKU2, serine/threonine-protein kinase PBL11, MYB transcription factor MYB2, ethylene-responsive transcription factor ERF114, WRKY transcription factor WRKY71, aspartate aminotransferase AATC, UDP-glycosyltransferase U91D1, and 4-hydroxy-4-methyl-2-oxoglutarate aldolase 2 RRAA2, were predicted to be involved in regulation of the function genes expression and the amino acids metabolism through weighted gene coexpression network analysis. A modulation mechanism for accumulation of amino acids during BWT was also proposed. These findings give a deep insight into the metabolic reprogramming mechanism of amino acids during BWT of oolong tea.

Organic Farming Sharpens Plant Defenses in the Field

Plants deploy a variety of chemical and physical defenses to protect themselves against herbivores and pathogens. Organic farming seeks to enhance these responses by improving soil quality, ultimately altering bottom up regulation of plant defenses. While laboratory studies suggest this approach is effective, it remains unclear whether organic agriculture encourages more-active plant defenses under real-world conditions. Working on the farms of cooperating growers, we examined gene expression in the leaves of two potato (Solanum tuberosum) varieties, grown on organic vs. conventional farms. For one variety, Norkotah, we found significantly heightened initiation of genes associated with plant-defense pathways in plants grown in organic vs. conventional fields. Organic Norkotah fields exhibited lower levels of nitrate in soil and of nitrogen in plant foliage, alongside differences in communities of soil bacteria, suggesting possible links between soil management and observed differences in plant defenses. Additionally, numbers of predatory and phloem-feeding insects were higher in organic than conventional fields. A second potato variety, Alturas, which is generally grown using fewer inputs and in poorer-quality soils, exhibited lower overall herbivore and predator numbers, few differences in soil ecology, and no differences in gene-activity in organic and conventional farming systems. Altogether, our results suggest that organic farming has the potential to increase plants' resistance to herbivores, possibly facilitating reduced need for insecticide applications. These benefits appear to be mediated by plant variety and/or farming context.

Transcriptomic analyses reveal a systemic defense role of the uninfested adjacent leaf in tea plant (Camellia sinensis) attacked by tea geometrids (Ectropis obliqua)

To get a more detailed understanding of the interaction between tea plant (Camellia sinensis) and tea geometrids (Ectropis obliqua), transcriptomic profile in undamaged adjacent leaf (TGL) of tea geometrids fed local leaves (LL) was investigated for the first time. Here, approximately 245 million clean reads contained 39.39 Gb of sequence data were obtained from TGL. Further analysis revealed that systemic response was induced in TGL after tea geometrids feeding on LL, although the defense response was weaker than that in LL. The differentially expressed genes (DEGs) identification analysis showed little overlap of DEGs between TGL and LL. Comparative transcriptome analysis suggested that JA signal regulated resistant pathway was induced in LL; whereas primary metabolism pathway was activated in TGL in response to tea geometrids feeding. This study reveals a novel resistance mechanism of TGL to tea geometrids feeding.

Secoiridoids Metabolism Response to Wounding in Common Centaury (Centaurium erythraea Rafn) Leaves

Centaurium erythraea Rafn produces and accumulates various biologically active specialized metabolites, including secoiridoid glucosides (SGs), which help plants to cope with unfavorable environmental conditions. Specialized metabolism is commonly modulated in a way to increase the level of protective metabolites, such as SGs. Here, we report the molecular background of the wounding-induced changes in SGs metabolism for the first time. The mechanical wounding of leaves leads to a coordinated up-regulation of SGs biosynthetic genes and corresponding JA-related transcription factors (TFs) after 24 h, which results in the increase of metabolic flux through the biosynthetic pathway and, finally, leads to the elevated accumulation of SGs 96 h upon injury. The most pronounced increase in relative expression was detected for secologanin synthase (CeSLS), highlighting this enzyme as an important point for the regulation of biosynthetic flux through the SG pathway. A similar expression pattern was observed for CeBIS1, imposing itself as the TF that is prominently involved in wound-induced regulation of SGs biosynthesis genes. The high degree of positive correlations between and among the biosynthetic genes and targeted TFs expressions indicate the transcriptional regulation of SGs biosynthesis in response to wounding with a significant role of CeBIS1, which is a known component of the jasmonic acid (JA) signaling pathway.

Occurrence and tolerance mechanisms of seed cracking under low temperatures in soybean (Glycine max)

MAIN CONCLUSION

In soybean, occurrence of, or tolerance to, seed cracking under low temperatures may be related to the presence or absence, respectively, of proanthocyanidin accumulation in the seed coat dorsal region. Soybean seeds sometimes undergo cracking during low temperatures in summer. In this study, we focused on the occurrence and tolerance mechanisms of low-temperature-induced seed cracking in the sensitive yellow soybean cultivar Yukihomare and the tolerant yellow soybean breeding line Toiku 248. Yukihomare exhibited seed cracking when subjected to a 21-day low-temperature treatment from 10 days after flowering. In yellow soybeans, seed coat pigmentation is inhibited, leading to low proanthocyanidin levels in the seed coat. Proanthocyanidins accumulated on the dorsal side of the seed coat in Yukihomare under the 21-day low-temperature treatment. In addition, a straight seed coat split occurred on the dorsal side at the full-sized seed stage, resulting in seed cracking in this cultivar. Conversely, proanthocyanidin accumulation was suppressed throughout the seed coat in low-temperature-treated Toiku 248. We propose the following mechanism of seed cracking: proanthocyanidin accumulation and subsequent lignin deposition under low temperatures affects the physical properties of the seed coat, making it more prone to splitting. Further analyses uncovered differences in the physical properties of the seed coat between Yukihomare and Toiku 248. In particular, seed coat hardness decreased in Yukihomare, but not in Toiku 248, under the low-temperature treatment. Seed coat flexibility was higher in Toiku 248 than in Yukihomare under the low-temperature treatment, suggesting that the seed coat of low-temperature-treated Toiku 248 is more flexible than that of low-temperature-treated Yukihomare. These physical properties of the Toiku 248 seed coat observed under low-temperature conditions may contribute to its seed-cracking tolerance.

An OPR3-independent pathway uses 4,5-didehydrojasmonate for jasmonate synthesis

Biosynthesis of the phytohormone jasmonoyl-isoleucine (JA-Ile) requires reduction of the JA precursor 12-oxo-phytodienoic acid (OPDA) by OPDA reductase 3 (OPR3). Previous analyses of the opr3-1 Arabidopsis mutant suggested an OPDA signaling role independent of JA-Ile and its receptor COI1; however, this hypothesis has been challenged because opr3-1 is a conditional allele not completely impaired in JA-Ile biosynthesis. To clarify the role of OPR3 and OPDA in JA-independent defenses, we isolated and characterized a loss-of-function opr3-3 allele. Strikingly, opr3-3 plants remained resistant to necrotrophic pathogens and insect feeding, and activated COI1-dependent JA-mediated gene expression. Analysis of OPDA derivatives identified 4,5-didehydro-JA in wounded wild-type and opr3-3 plants. OPR2 was found to reduce 4,5-didehydro-JA to JA, explaining the accumulation of JA-Ile and activation of JA-Ile-responses in opr3-3 mutants. Our results demonstrate that in the absence of OPR3, OPDA enters the β-oxidation pathway to produce 4,5-ddh-JA as a direct precursor of JA and JA-Ile, thus identifying an OPR3-independent pathway for JA biosynthesis.

Spatial regulation of monolignol biosynthesis and laccase genes control developmental and stress-related lignin in flax

BACKGROUND

Bast fibres are characterized by very thick secondary cell walls containing high amounts of cellulose and low lignin contents in contrast to the heavily lignified cell walls typically found in the xylem tissues. To improve the quality of the fiber-based products in the future, a thorough understanding of the main cell wall polymer biosynthetic pathways is required. In this study we have carried out a characterization of the genes involved in lignin biosynthesis in flax along with some of their regulation mechanisms.

RESULTS

We have first identified the members of the phenylpropanoid gene families through a combination of in silico approaches. The more specific lignin genes were further characterized by high throughput transcriptomic approaches in different organs and physiological conditions and their cell/tissue expression was localized in the stems, roots and leaves. Laccases play an important role in the polymerization of monolignols. This multigenic family was determined and a miRNA was identified to play a role in the posttranscriptional regulation by cleaving the transcripts of some specific genes shown to be expressed in lignified tissues. In situ hybridization also showed that the miRNA precursor was expressed in the young xylem cells located near the vascular cambium. The results obtained in this work also allowed us to determine that most of the genes involved in lignin biosynthesis are included in a unique co-expression cluster and that MYB transcription factors are potentially good candidates for regulating these genes.

CONCLUSIONS

Target engineering of cell walls to improve plant product quality requires good knowledge of the genes responsible for the production of the main polymers. For bast fiber plants such as flax, it is important to target the correct genes from the beginning since the difficulty to produce transgenic material does not make possible to test a large number of genes. Our work determined which of these genes could be potentially modified and showed that it was possible to target different regulatory pathways to modify lignification.

Mechanical wounding promotes local and long distance response in the halophyte Cakile maritima through the involvement of the ROS and RNS metabolism

Mechanical wounding in plants, which are capable of generating defense responses possibly associated with nitro-oxidative stress, can be caused by (a)biotic factors such as rain, wind, herbivores and insects. Sea rocket (Cakile maritima L.), a halophyte plant belonging to the mustard family Brassicaceae, is commonly found on sandy coasts throughout Europe. Using 7-day-old Cakile maritima L. seedlings, mechanical wounding was induced in hypocotyls by pinching with a striped-tip forceps; after 3 h, several biochemical parameters were analyzed in both the damaged and unwounded organs (green cotyledons and roots). We thus determined NO production, H₂O₂ content, lipid oxidation as well as protein nitration patterns; we also identified several antioxidant enzymes including catalase, superoxide dismutase (SOD) isozymes, peroxidases, ascorbate-glutathione cycle enzymes and NADP-dehydrogenases. All these parameters were differentially modulated in the damaged (hypocotyls) and unwounded organs, which clearly indicated an induction of CuZnSOD V in the three organs, an increase in protein nitration in green cotyledons and an induction of NADP-isocitrate dehydrogenase activity in roots. On the whole, our results indicate that the wounding of hypocotyls, which showed an active ROS metabolism and oxidative stress, causes long-distance signals that also trigger responses in unwounded tissues with a more active RNS metabolism. These data therefore confirm the existence of local and long-distance responses which counteract negative effects and provide appropriate responses, enabling the wounded seedlings to survive.

Transcripts of pectin-degrading enzymes and isolation of complete cDNA sequence of a pectate lyase gene induced by coffee white stem borer (Xylotrechus quadripes) in the bark tissue of Coffea canephora (robusta coffee)

Of the two commercially cultivated coffee (Coffea) species, C. arabica (arabica) is highly susceptible and C. canephora (robusta) is highly resistant to the insect pest Xylotrechus quadripes (Coleoptera: Cerambycidae), commonly known as coffee white stem borer (CWSB). We constructed a forward-subtracted cDNA library by Suppression Subtractive Hybridization (SSH) from robusta bark tissue for profiling genes induced by CWSB infestation. Among the 265 unigenes of the SSH EST library, 7 unigenes (5 contigs and 2 singletons) matching different pectin-degrading enzymes were discovered. These ESTs matched one pectate lyase, three polygalacturonases, and one pectin acetylesterase gene. Quantitative real-time PCR (qRT-PCR) revealed that CWSB infestation strongly induces the pectate lyase gene at 72 h. Complete cDNA sequence of the pectate lyase gene was obtained through 3' and 5' RACE reactions. It was a 1595 bp long sequence that included full CDS and both UTRs. Against C. canephora genome sequences in Coffee Genome Hub database ( http://coffee-genome.org/ ), it had 22 matches to different pectate lyase genes mapped on 9 of the 11 pseudochromosomes, the top match being Cc07_g00190 Pectate lyase. In NCBI database, it matched pectate lyase sequences of several plants. Apart from C. canephora, the closest pectate lyase matches were from Sesamum indicum and Nicotiana tabacum. The pectinolytic enzymes discovered here are thought to play a role in the production of oligogalacturonides (OGs) which act as Damage-Associated Molecular Pattern (DAMP) signals eliciting innate immunity in plants. The pectate lyase gene, induced by CWSB infestation, along with other endogenous pectinolytic enzymes and CWSB-specific elicitors, may be involved in triggering basal defense responses to protect the CWSB-damaged tissue against pathogens, as well as to contain CWSB in robusta.

Wound signaling: The missing link in plant regeneration

Wounding is the first event that occurs in plant regeneration. However, wound signaling in plant regeneration is barely understood. Using a simple system of de novo root organogenesis from Arabidopsis thaliana leaf explants, we analyzed the genes downstream of wound signaling. Leaf explants may produce at least two kinds of wound signals to trigger short-term and long-term wound signaling. Short-term wound signaling is primarily involved in controlling auxin behavior and the fate transition of regeneration-competent cells, while long-term wound signaling mainly modulates the cellular environment at the wound site and maintains the auxin level in regeneration-competent cells. YUCCA (YUC) genes, which are involved in auxin biogenesis, are targets of short-term wound signaling in mesophyll cells and of long-term wound signaling in regeneration-competent cells. The expression patterns of YUCs provide important information about the molecular basis of wound signaling in plant regeneration.

Comprehensive analysis and discovery of drought-related NAC transcription factors in common bean

BACKGROUND

Common bean (Phaseolus vulgaris L.) is an important warm-season food legume. Drought is the most important environmental stress factor affecting large areas of common bean via plant death or reduced global production. The NAM, ATAF1/2 and CUC2 (NAC) domain protein family are classic transcription factors (TFs) involved in a variety of abiotic stresses, particularly drought stress. However, the NAC TFs in common bean have not been characterized.

RESULTS

In the present study, 86 putative NAC TF proteins were identified from the common bean genome database and located on 11 common bean chromosomes. The proteins were phylogenetically clustered into 8 distinct subfamilies. The gene structure and motif composition of common bean NACs were similar in each subfamily. These results suggest that NACs in the same subfamily may possess conserved functions. The expression patterns of common bean NAC genes were also characterized. The majority of NACs exhibited specific temporal and spatial expression patterns. We identified 22 drought-related NAC TFs based on transcriptome data for drought-tolerant and drought-sensitive genotypes. Quantitative real-time PCR (qRT-PCR) was performed to confirm the expression patterns of the 20 drought-related NAC genes.

CONCLUSIONS

Based on the common bean genome sequence, we analyzed the structural characteristics, genome distribution, and expression profiles of NAC gene family members and analyzed drought-responsive NAC genes. Our results provide useful information for the functional characterization of common bean NAC genes and rich resources and opportunities for understanding common bean drought stress tolerance mechanisms.

Wound signaling of regenerative cell reprogramming

Plants are sessile organisms that must deal with various threats resulting in tissue damage, such as herbivore feeding, and physical wounding by wind, snow or crushing by animals. During wound healing, phytohormone crosstalk orchestrates cellular regeneration through the establishment of tissue-specific asymmetries. In turn, hormone-regulated transcription factors and their downstream targets coordinate cellular responses, including dedifferentiation, cell cycle reactivation and vascular regeneration. By comparing different examples of wound-induced tissue regeneration in the model plant Arabidopsis thaliana, a number of key regulators of developmental plasticity of plant cells have been identified. We present the relevance of these findings and of the dynamic establishment of differential auxin gradients for cell reprogramming after wounding.

Signal transduction and regulation of IbpreproHypSys in sweet potato

Hydroxyproline-rich glycopeptides (HypSys) are small signalling peptides containing 18-20 amino acids. The expression of IbpreproHypSys, encoding the precursor of IbHypSys, was induced in sweet potato (Ipomoea batatas cv. Tainung 57) through wounding and IbHypSys treatments by using jasmonate and H2 O2 . Transgenic sweet potatoes overexpressing (OE) and silencing [RNA interference (RNAi)] IbpreproHypSys were created. The expression of the wound-inducible gene for ipomoelin (IPO) in the local and systemic leaves of OE plants was stronger than the expression in wild-type (WT) and RNAi plants after wounding. Furthermore, grafting experiments indicated that IPO expression was considerably higher in WT stocks receiving wounding signals from OE than from RNAi scions. However, wounding WT scions highly induced IPO expression in OE stocks. These results indicated that IbpreproHypSys expression contributed towards sending and receiving the systemic signals that induced IPO expression. Analysing the genes involved in the phenylpropanoid pathway demonstrated that lignin biosynthesis was activated after synthetic IbHypSys treatment. IbpreproHypSys expression in sweet potato suppressed Spodoptera litura growth. In conclusion, wounding induced the expression of IbpreproHypSys, whose protein product was processed into IbHypSys. IbHypSys stimulated IbpreproHypSys and IPO expression and enhanced lignin biosynthesis, thus protecting plants from insects.

GRP-3 and KAPP, encoding interactors of WAK1, negatively affect defense responses induced by oligogalacturonides and local response to wounding

Conserved microbe-associated molecular patterns (MAMPs) and damage-associated molecular patterns (DAMPs) act as danger signals to activate the plant immune response. These molecules are recognized by surface receptors that are referred to as pattern recognition receptors. Oligogalacturonides (OGs), DAMPs released from the plant cell wall homogalacturonan, have also been proposed to act as local signals in the response to wounding. The Arabidopsis Wall-Associated Kinase 1 (WAK1), a receptor of OGs, has been described to form a complex with a cytoplasmic plasma membrane-localized kinase-associated protein phosphatase (KAPP) and a glycine-rich protein (GRP-3) that we find localized mainly in the cell wall and, in a small part, on the plasma membrane. By using Arabidopsis plants overexpressing WAK1, and both grp-3 and kapp null insertional mutant and overexpressing plants, we demonstrate a positive function of WAK1 and a negative function of GRP-3 and KAPP in the OG-triggered expression of defence genes and the production of an oxidative burst. The three proteins also affect the local response to wounding and the basal resistance against the necrotrophic pathogen Botrytis cinerea. GRP-3 and KAPP are likely to function in the phasing out of the plant immune response.

The Alcohol Dehydrogenase Gene Family in Melon (Cucumis melo L.): Bioinformatic Analysis and Expression Patterns

Alcohol dehydrogenases (ADH), encoded by multigene family in plants, play a critical role in plant growth, development, adaptation, fruit ripening and aroma production. Thirteen ADH genes were identified in melon genome, including 12 ADHs and one formaldehyde dehydrogenease (FDH), designated CmADH1-12 and CmFDH1, in which CmADH1 and CmADH2 have been isolated in Cantaloupe. ADH genes shared a lower identity with each other at the protein level and had different intron-exon structure at nucleotide level. No typical signal peptides were found in all CmADHs, and CmADH proteins might locate in the cytoplasm. The phylogenetic tree revealed that 13 ADH genes were divided into three groups respectively, namely long-, medium-, and short-chain ADH subfamily, and CmADH1,3-11, which belongs to the medium-chain ADH subfamily, fell into six medium-chain ADH subgroups. CmADH12 may belong to the long-chain ADH subfamily, while CmFDH1 may be a Class III ADH and serve as an ancestral ADH in melon. Expression profiling revealed that CmADH1, CmADH2, CmADH10 and CmFDH1 were moderately or strongly expressed in different vegetative tissues and fruit at medium and late developmental stages, while CmADH8 and CmADH12 were highly expressed in fruit after 20 days. CmADH3 showed preferential expression in young tissues. CmADH4 only had slight expression in root. Promoter analysis revealed several motifs of CmADH genes involved in the gene expression modulated by various hormones, and the response pattern of CmADH genes to ABA, IAA and ethylene were different. These CmADHs were divided into ethylene-sensitive and -insensitive groups, and the functions of CmADHs were discussed.

A novel PR10 promoter from Erianthus arundinaceus directs high constitutive transgene expression and is enhanced upon wounding in heterologous plant systems

In genetic engineering, inducible promoters play an important role as the expression of genes driven by them can be turned on or off under situations like biotic or abiotic factors. There are few reports on inducible promoters that can be employed in the development of transgenic plants, particularly in sugarcane. In the present study, four wound inducible genes (Chitinase, PR1A, PR10 and HRGP) were selected and were amplified from Erianthus arundinaceus, a distant relative of sugarcane. In order to determine the gene that is highly induced upon wounding, RT-qPCR was performed, which showed that PR10 gene expression was instantaneous and higher upon wounding when compared to the other three genes. Using the random amplification of genomic ends technique, a 592 bp promoter sequence was obtained and in silico analysis of the upstream regulatory region revealed a 469 bp promoter and 123 bp of 5' untranslated region (UTR). Functional analyses of the promoter sequence (with and without 5' UTR) in tobacco, rice and sugarcane using β-glucuronidase (GUS) as the reporter gene revealed the constitutive and inducible nature of the PR10 promoter. Our studies have demonstrated that the PR10 promoter, though highly constitutive, was quickly induced upon wounding as well as on treatment with abscisic acid and methyl jasmonate hormones. This is the first report on the isolation and characterization of a PR10 promoter from a wild grass and is expected to have application for development of transgenic plants.

The cell biology of lignification in higher plants

BACKGROUND

Lignin is a polyphenolic polymer that strengthens and waterproofs the cell wall of specialized plant cell types. Lignification is part of the normal differentiation programme and functioning of specific cell types, but can also be triggered as a response to various biotic and abiotic stresses in cells that would not otherwise be lignifying.

SCOPE

Cell wall lignification exhibits specific characteristics depending on the cell type being considered. These characteristics include the timing of lignification during cell differentiation, the palette of associated enzymes and substrates, the sub-cellular deposition sites, the monomeric composition and the cellular autonomy for lignin monomer production. This review provides an overview of the current understanding of lignin biosynthesis and polymerization at the cell biology level.

CONCLUSIONS

The lignification process ranges from full autonomy to complete co-operation depending on the cell type. The different roles of lignin for the function of each specific plant cell type are clearly illustrated by the multiple phenotypic defects exhibited by knock-out mutants in lignin synthesis, which may explain why no general mechanism for lignification has yet been defined. The range of phenotypic effects observed include altered xylem sap transport, loss of mechanical support, reduced seed protection and dispersion, and/or increased pest and disease susceptibility.

Transcriptome and hormone profiling reveals Eucalyptus grandis defence responses against Chrysoporthe austroafricana

BACKGROUND

Eucalyptus species and interspecific hybrids exhibit valuable growth and wood properties that make them a highly desirable commodity. However, these trees are challenged by a wide array of biotic stresses during their lifetimes. The Eucalyptus grandis reference genome sequence provides a resource to study pest and pathogen defence mechanisms in long-lived woody plants. E. grandis trees are generally susceptible to Chrysoporthe austroafricana, a causal agent of stem cankers on eucalypts. The aim of this study was to characterize the defence response of E. grandis against C. austroafricana.

RESULTS

Hormone profiling of susceptible and moderately resistant clonal E. grandis genotypes indicated a reduction in salicylic acid and gibberellic acid levels at 3 days post inoculation. We hypothesized that these signaling pathways may facilitate resistance. To further investigate other defence mechanisms at this time point, transcriptome profiling was performed. This revealed that cell wall modifications and response to oxidative stress form part of the defence responses common to both genotypes, whilst changes in the hormone signaling pathways may contribute to resistance. Additionally the expression of selected candidate defence response genes was induced earlier in moderately resistant trees than in susceptible trees, supporting the hypothesis that a delayed defence response may occur in the susceptible interaction.

CONCLUSION

The ability of a host to fine-tune its defence responses is crucial and the responses identified in this study extends our understanding of plant defence, gained from model systems, to woody perennials.

Wounding induces local resistance but systemic susceptibility to Botrytis cinerea in pepper plants

Cotyledon wounding in pepper caused the early generation of hydrogen peroxide both locally (cotyledons) and systemically (upper true leaves). However, 72 h later there is a different wound response between local and systemic organs, as shown by resistance to the pathogenic fungus Botrytis cinerea, that increased locally and decreased systemically. Signaling by ethylene and jasmonic acid was assessed by using two inhibitors: 1-methylcyclopropene (MCP, inhibitor of ethylene receptors) and ibuprofen (inhibitor of jasmonate biosynthesis). MCP did not affect the modulation of resistance levels to Botrytis by wounding, ruling out the involvement of ethylene signaling. Ibuprofen did not inhibit wound-induced resistance at the local level, but inhibited wound-induced systemic susceptibility. Moreover, changes of biochemical and structural defenses in response to wounding were studied. Peroxidase activity and the expression of a peroxidase gene (CAPO1) increased locally as a response to wounding, but no changes were observed systemically. Lignin deposition was induced in wounded cotyledons, but was repressed in systemic leaves of wounded plants, whereas soluble phenolics did not change locally and decreased systemically. The expression of two other genes involved in plant defense (CABPR1 and CASC1) was also differentially regulated locally and systemically, pointing to a generalized increase in plant defenses at the local level and a systemic decrease as a response to wounding. Wound-induced defenses at the local level coincided with resistance to the necrotroph fungus B. cinerea, whereas depleted defenses in systemic leaves of wounded plants correlated to induced susceptibility against this pathogen. It may be that the local response acts as a sink of energy resources to mount a defense against pathogens, whereas in systemic organs the resources for defense are lower.

Roles for jasmonate- and ethylene-induced transcription factors in the ability of Arabidopsis to respond differentially to damage caused by two insect herbivores

Plant responses to insects and wounding involve substantial transcriptional reprogramming that integrates hormonal, metabolic, and physiological events. The ability to respond differentially to various stresses, including wounding, generally involves hormone signaling and trans-acting regulatory factors. Evidence of the importance of transcription factors (TFs) in responses to insects is also accumulating. However, the relationships among hormone signaling, TF activity, and ability to respond specifically to different insects are uncertain. We examined transcriptional and hormonal changes in Arabidopsis thaliana after herbivory by larvae of two lepidopteran species, Spodoptera exigua (Hübner) and Pieris rapae L. over a 24-h time course. Transcriptional responses to the two insects differed and were frequently weaker or absent in response to the specialist P. rapae. Using microarray analysis and qRT-PCR, we found 141 TFs, including many AP2/ERFs (Ethylene Response Factors) and selected defense-related genes, to be differentially regulated in response to the two insect species or wounding. Jasmonic Acid (JA), JA-isoleucine (JA-IL), and ethylene production by Arabidopsis plants increased after attack by both insect species. However, the amounts and timing of ethylene production differed between the two herbivory treatments. Our results support the hypothesis that the different responses to these two insects involve modifications of JA-signaling events and activation of different subsets of ERF TFs, resulting in different degrees of divergence from responses to wounding alone.

Wound-induced expression of DEFECTIVE IN ANTHER DEHISCENCE1 and DAD1-like lipase genes is mediated by both CORONATINE INSENSITIVE1-dependent and independent pathways in Arabidopsis thaliana

Endogenous JA production is not necessary for wound-induced expression of JA-biosynthetic lipase genes such as DAD1 in Arabidopsis. However, the JA-Ile receptor COI1 is often required for their JA-independent induction. Wounding is a serious event in plants that may result from insect feeding and increase the risk of pathogen infection. Wounded plants produce high amounts of jasmonic acid (JA), which triggers the expression of insect and pathogen resistance genes. We focused on the transcriptional regulation of DEFECTIVE IN ANTHER DEHISCENCE1 and six of its homologs including DONGLE (DGL) in Arabidopsis, which encode lipases involved in JA biosynthesis. Plants constitutively expressing DAD1 accumulated a higher amount of JA than control plants after wounding, indicating that the expression of these lipase genes contributes to determining JA levels. We found that the expression of DAD1, DGL, and other DAD1-LIKE LIPASE (DALL) genes is induced upon wounding. Some DALLs were also expressed in unwounded leaves. Further experiments using JA-biosynthetic and JA-response mutants revealed that the wound induction of these genes is regulated by several distinct pathways. DAD1 and most of its homologs other than DALL4 were fully induced without relying on endogenous JA-Ile production and were only partly affected by JA deficiency, indicating that positive feedback by JA is not necessary for induction of these genes. However, DAD1 and DGL required CORONATINE INSENSITIVE1 (COI1) for their expression, suggesting that a molecule other than JA might act as a regulator of COI1. Wound induction of DALL1, DALL2, and DALL3 did not require COI1. This differential regulation of DAD1 and its homologs might explain their functions at different time points after wounding.

Sequence and functional analyses of the aldehyde dehydrogenase 7B4 gene promoter in Arabidopsis thaliana and selected Brassicaceae: regulation patterns in response to wounding and osmotic stress

Aldehyde dehydrogenases metabolise a wide range of aliphatic and aromatic aldehydes, which become cytotoxic at high levels. Family 7 aldehyde dehydrogenase genes, often described as antiquitins or turgor-responsive genes in plants, are broadly conserved across all domains. Despite the high conservation of the plant ALDH7 proteins and their importance in stress responses, their regulation has not been investigated. Here, we compared ALDH7 genes of different Brassicaceae and found that, in contrast to the gene organisation and protein coding sequences, similarities in the promoter sequences were limited to the first few hundred nucleotides upstream of the translation start codon. The function of this region was studied by isolating the core promoter of the Arabidopsis thaliana ALDH7B4 gene, taken as model. The promoter was found to be responsive to wounding in addition to salt and dehydration stress. Cis-acting elements involved in stress responsiveness were analysed and two conserved ACGT-containing motifs proximal to the translation start codon were found to be essential for the responsiveness to osmotic stress in leaves and in seeds. The integrity of an upstream ACGT motif and a dehydration-responsive element/C-repeat-low temperature-responsive element was found to be necessary for ALDH7B4 expression in seeds and induction by salt, dehydration and ABA in leaves. The comparison of the gene expression in selected Arabidopsis mutants demonstrated that osmotic stress-induced ALDH7B4 expression in leaves and seeds involves both ABA- and lipid-signalling components.

Differential activation of sporamin expression in response to abiotic mechanical wounding and biotic herbivore attack in the sweet potato

BACKGROUND

Plants respond differently to mechanical wounding and herbivore attack, using distinct pathways for defense. The versatile sweet potato sporamin possesses multiple biological functions in response to stress. However, the regulation of sporamin gene expression that is activated upon mechanical damage or herbivore attack has not been well studied.

RESULTS

Biochemical analysis revealed that different patterns of Reactive oxygen species (ROS) and antioxidant mechanism exist between mechanical wounding (MW) and herbivore attack (HA) in the sweet potato leaf. Using LC-ESI-MS (Liquid chromatography electrospray ionization mass spectrometry analysis), only the endogenous JA (jasmonic acid) level was found to increase dramatically after MW in a time-dependent manner, whereas both endogenous JA and SA (salicylic acid) increase in parallel after HA. Through yeast one-hybrid screening, two transcription factors IbNAC1 (no apical meristem (NAM), Arabidopsis transcription activation factor (ATAF), and cup-shaped cotyledon (CUC)) and IbWRKY1 were isolated, which interact with the sporamin promoter fragment of SWRE (sporamin wounding-responsive element) regulatory sequences. Exogenous application of MeJA (methyl jasmonate), SA and DIECA (diethyldithiocarbamic acid, JAs biosynthesis inhibitor) on sweet potato leaves was employed, and the results revealed that IbNAC1 mediated the expression of sporamin through a JA-dependent signaling pathway upon MW, whereas both IbNAC1 and IbWRKY1 coordinately regulated sporamin expression through JA- and SA-dependent pathways upon HA. Transcriptome analysis identified MYC2/4 and JAZ2/TIFY10A (jasmonate ZIM/tify-domain), the repressor and activator of JA and SA signaling among others, as the genes that play an intermediate role in the JA and SA pathways, and these results were further validated by qRT-PCR (quantitative real-time polymerase chain reaction).

CONCLUSION

This work has improved our understanding of the differential regulatory mechanism of sporamin expression. Our study illustrates that sweet potato sporamin expression is differentially induced upon abiotic MW and biotic HA that involves IbNAC1 and IbWRKY1 and is dependent on the JA and SA signaling pathways. Thus, we established a model to address the plant-wounding response upon physical and biotic damage.

Early steps of adventitious rooting: morphology, hormonal profiling and carbohydrate turnover in carnation stem cuttings

The rooting of stem cuttings is a common vegetative propagation practice in many ornamental species. A detailed analysis of the morphological changes occurring in the basal region of cultivated carnation cuttings during the early stages of adventitious rooting was carried out and the physiological modifications induced by exogenous auxin application were studied. To this end, the endogenous concentrations of five major classes of plant hormones [auxin, cytokinin (CK), abscisic acid, salicylic acid (SA) and jasmonic acid] and the ethylene precursor 1-aminocyclopropane-1-carboxylic acid were analyzed at the base of stem cuttings and at different stages of adventitious root formation. We found that the stimulus triggering the initiation of adventitious root formation occurred during the first hours after their excision from the donor plant, due to the breakdown of the vascular continuum that induces auxin accumulation near the wounding. Although this stimulus was independent of exogenously applied auxin, it was observed that the auxin treatment accelerated cell division in the cambium and increased the sucrolytic activities at the base of the stem, both of which contributed to the establishment of the new root primordia at the stem base. Further, several genes involved in auxin transport were upregulated in the stem base either with or without auxin application, while endogenous CK and SA concentrations were specially affected by exogenous auxin application. Taken together our results indicate significant crosstalk between auxin levels, stress hormone homeostasis and sugar availability in the base of the stem cuttings in carnation during the initial steps of adventitious rooting.

Stress inducible proteomic changes in Capsicum annuum leaves

Herbivore attack induces defense responses in plants, activating several signaling cascades. As a result, molecules deterrent to the herbivores are produced and accumulated in plants. Expression of defense mechanism/traits requires reorganization of the plant metabolism, redirecting the resources otherwise meant for growth. In the present work, protein profile of Capsicum annuum leaves was examined after herbivore attack/induction. Majority of proteins identified as differentially accumulated, were having roles in redox metabolism and photosynthesis. For example, superoxide dismutase and NADP oxidoreductase were upregulated by 10- and 6-fold while carbonic anhydrase and fructose-1,6-bisphosphatase were downregulated by 9- and 4-fold, respectively. Also, superoxide dismutase, NADPH quinone oxidoreductase and NADP dependent isocitrate dehydrogenase transcripts showed a higher accumulation in induced leaf tissues at early time points. In general, proteins having role in defense and damage repair were upregulated while those involved in photosynthesis appeared downregulated. Thus metabolic reconfiguration to balance defense and tolerance was evident in the stress-induced leaves.

Wounding in the plant tissue: the defense of a dangerous passage

Plants are continuously exposed to agents such as herbivores and environmental mechanical stresses that cause wounding and open the way to the invasion by microbial pathogens. Wounding provides nutrients to pathogens and facilitates their entry into the tissue and subsequent infection. Plants have evolved constitutive and induced defense mechanisms to properly respond to wounding and prevent infection. The constitutive defenses are represented by physical barriers, i.e., the presence of cuticle or lignin, or by metabolites that act as toxins or deterrents for herbivores. Plants are also able to sense the injured tissue as an altered self and induce responses similar to those activated by pathogen infection. Endogenous molecules released from wounded tissue may act as Damage-Associated Molecular Patterns (DAMPs) that activate the plant innate immunity. Wound-induced responses are both rapid, such as the oxidative burst and the expression of defense-related genes, and late, such as the callose deposition, the accumulation of proteinase inhibitors and of hydrolytic enzymes (i.e., chitinases and gluganases). Typical examples of DAMPs involved in the response to wounding are the peptide systemin, and the oligogalacturonides, which are oligosaccharides released from the pectic component of the cell wall. Responses to wounding take place both at the site of damage (local response) and systemically (systemic response) and are mediated by hormones such as jasmonic acid, ethylene, salicylic acid, and abscisic acid.

Arabidopsis WIND1 induces callus formation in rapeseed, tomato, and tobacco

The capacity to promote cell dedifferentiation is widespread among plant species. We have recently reported that an AP2/ERF transcription factor WOUND INDUCED DEDIFFERENTIATION 1 (WIND1) and its paralogues, WIND2-4, promote cell dedifferentiation in Arabidopsis (Arabidopsis thaliana). Phylogenetic analyses suggest that AtWIND1 orthologs are found in land plants and that the shared peptide motifs between Arabidopsis paralogues are conserved in putative orthologs in dicotyledonous and monocotyledonous plants. In this study we show that AtWIND1 chemically induced rapeseed and tomato, as well as AtWIND1 constitutively expressed tobacco, promote callus formation on phytohormone-free medium. Our results suggest that the WIND1-mediated signaling cascade to promote cell dedifferentiation might be conserved in at least several species of Brassicaceae and Solanaceae.

Molecular characterization of ferulate 5-hydroxylase gene from kenaf (Hibiscus cannabinus L.)

The purpose of this study is to clone and characterize the expression pattern of a F5H gene encoding ferulate 5-hydroxylase in the phenylpropanoid pathway from kenaf (Hibiscus cannabinus L.). Kenaf is a fast-growing dicotyledonous plant valued for its biomass. F5H, a cytochrome P450-dependent monooxygenase (CYP84), is a key enzyme for syringyl lignin biosynthesis. The full length of the F5H ortholog was cloned and characterized. The full-length F5H ortholog consists of a 1,557-bp open reading frame (ORF) encoding 518 amino acids (GenBank Accession number JX524278). The deduced amino acid sequence showed that kenaf F5H had the highest similarity (78%) with that of Populus trichocarpa. Transcriptional analysis of F5H ortholog was conducted using quantitative real-time PCR during the developmental stages of various tissues and in response to various abiotic stresses. The highest transcript level of the F5H ortholog was observed in immature flower tissues and in early stage (6 week-old) of stem tissues, with a certain level of expression in all tissues tested. The highest transcript level of F5H ortholog was observed at the late time points after treatments with NaCl (48 h), wounding (24 h), cold (24 h), abscisic acid (24 h), and methyl jasmonate (24 h).

Interaction of small RNA-8105 and the intron of IbMYB1 RNA regulates IbMYB1 family genes through secondary siRNAs and DNA methylation after wounding

Small RNAs (sRNAs) play important roles in plants under stress conditions. However, limited research has been performed on the sRNAs involved in plant wound responses. In the present study, a novel wounding-induced sRNA, sRNA8105, was identified in sweet potato (Ipomoea batatas cv. Tainung 57) using microarray analysis. It was found that expression of sRNA8105 increased after mechanical wounding. Furthermore, Dicer-like 1 (DCL1) is required for the sRNA8105 precursor (pre-sRNA8105) to generate 22 and 24 nt mature sRNA8105. sRNA8105 targeted the first intron of IbMYB1 (MYB domain protein 1) before RNA splicing, and mediated RNA cleavage and DNA methylation of IbMYB1. The interaction between sRNA8105 and IbMYB1 was confirmed by cleavage site mapping, agro-infiltration analyses, and use of a transgenic sweet potato over-expressing pre-sRNA8105 gene. Induction of IbMYB1-siRNA was observed in the wild-type upon wounding and in transgenic sweet potato over-expressing pre-sRNA8105 gene without wounding, resulting in decreased expression of the whole IbMYB1 gene family, i.e. IbMYB1 and the IbMYB2 genes, and thus directing metabolic flux toward biosynthesis of lignin in the phenylpropanoid pathway. In conclusion, sRNA8105 induced by wounding binds to the first intron of IbMYB1 RNA to methylate IbMYB1, cleave IbMYB1 RNA, and trigger production of secondary siRNAs, further repressing the expression of the IbMYB1 family genes and regulating the phenylpropanoid pathway.

Plant core environmental stress response genes are systemically coordinated during abiotic stresses

Studying plant stress responses is an important issue in a world threatened by global warming. Unfortunately, comparative analyses are hampered by varying experimental setups. In contrast, the AtGenExpress abiotic stress experiment displays intercomparability. Importantly, six of the nine stresses (wounding, genotoxic, oxidative, UV-B light, osmotic and salt) can be examined for their capacity to generate systemic signals between the shoot and root, which might be essential to regain homeostasis in Arabidopsis thaliana. We classified the systemic responses into two groups: genes that are regulated in the non-treated tissue only are defined as type I responsive and, accordingly, genes that react in both tissues are termed type II responsive. Analysis of type I and II systemic responses suggest distinct functionalities, but also significant overlap between different stresses. Comparison with salicylic acid (SA) and methyl-jasmonate (MeJA) responsive genes implies that MeJA is involved in the systemic stress response. Certain genes are predominantly responding in only one of the categories, e.g., WRKY genes respond mainly non-systemically. Instead, genes of the plant core environmental stress response (PCESR), e.g., ZAT10, ZAT12, ERD9 or MES9, are part of different response types. Moreover, several PCESR genes switch between the categories in a stress-specific manner.

Real time measurement of cytoplasmic ions with ion-selective microelectrodes

Ion-selective microelectrodes can be used to report intracellular ion concentrations. The ion-selective barrels of microelectrodes are filled with a sensor cocktail containing several different components including an ion-selective molecule, sensor or exchanger, a solvent or plasticizer, lipophilic cation/anion additives, and a matrix to solidify the membrane. For many ions, the readymade membrane cocktail can be purchased, but the individual chemical components can be bought from suppliers and mixing the cocktail saves money. For commercially available liquid membrane cocktails the membrane matrix is often not included. For plants a matrix is essential for intracellular impalements because without it cell turgor will displace the liquid membrane from the electrode tip, giving decreased or even lost sensitivity. The matrix frequently used is a high molecular weight poly(vinyl chloride). This addition increases the electrical resistance of the electrode, slowing the response time of the electrode. The use of multi-barreled electrodes enables the identification of the cellular compartment. For example, the inclusion of a pH-selective electrode enables the cytoplasm and vacuole to be distinguished.

A pleiotropic drug resistance transporter in Nicotiana tabacum is involved in defense against the herbivore Manduca sexta

Pleiotropic drug resistance (PDR) transporters are a group of membrane proteins belonging to the ABCG sub-family of ATP binding cassette (ABC) transporters. There is clear evidence for the involvement of plant ABC transporters in resistance to fungal and bacterial pathogens, but not in the biotic stress response to insect or herbivore attack. Here, we describe a PDR transporter, ABCG5/PDR5, from Nicotiana tabacum. GFP fusion and subcellular fractionation studies revealed that ABCG5/PDR5 is localized to the plasma membrane. Staining of transgenic plants expressing the GUS reporter gene under the control of the ABCG5/PDR5 transcription promoter and immunoblotting of wild-type plants showed that, under standard growth conditions, ABCG5/PDR5 is highly expressed in roots, stems and flowers, but is only expressed at marginal levels in leaves. Interestingly, ABCG5/PDR5 expression is induced in leaves by methyl jasmonate, wounding, pathogen infiltration, or herbivory by Manduca sexta. To address the physiological role of ABCG5/PDR5, N. tabacum plants silenced for the expression of ABCG5/PDR5 were obtained. No phenotypic modification was observed under standard conditions. However, a small increase in susceptibility to the fungus Fusarium oxysporum was observed. A stronger effect was observed in relation to herbivory: silenced plants allowed better growth and faster development of M. sexta larvae than wild-type plants, indicating an involvement of this PDR transporter in resistance to M. sexta herbivory.

MicroR828 regulates lignin and H2O2 accumulation in sweet potato on wounding

MicroRNAs (miRNAs) are small noncoding RNAs which post-transcriptionally regulate gene expression by directing mRNA cleavage or translational inhibition. miRNAs play multiple roles in the growth, development and stress responses in plants. However, little is known of the wounding-responsive miRNAs and their regulation. Here, we investigated the expression patterns of microR828 (miR828) on wounding in sweet potato (Ipomoea batatas cv Tainung 57). The expression of miR828 was only detected in leaves, and was induced by wounding rather than by ethylene, hydrogen peroxide (H2O2), methyl jasmonate or nitric oxide (NO). Moreover, cyclic guanosine monophosphate (cGMP) was necessary for miR828 accumulation in leaves on wounding. Two miR828 target candidates, named IbMYB and IbTLD, were obtained by cDNA cloning, and their mRNA cleavage caused by miR828 was confirmed by cleavage site mapping, agro-infiltration and transgenics studies. The reduction in IbMYB and IbTLD expression coincided with the induction of miR828, demonstrating that IbMYB and IbTLD might be miR828 targets. Furthermore, transgenic sweet potato overexpressing miR828 precursor affected lignin and H2O2 contents. These results showed that cGMP could regulate wounding-responsive miR828, which repressed the expression of IbMYB and IbTLD. Subsequently, lignin and H2O2 were accumulated to participate in defense mechanisms.

Computational modeling of the regulatory network organizing the wound response in Arabidopsis thaliana

Plants are frequently wounded by mechanical impact or by insects, and their ability to adequately respond to wounding is essential for their survival and reproductive success. The wound response is mediated by a signal transduction and regulatory network. Molecular studies in Arabidopsis have identified the COI1 gene as a central component of this network. Current models of these networks qualitatively describe the wound response, but they are not directly assessed using quantitative gene expression data. We built a model comprising the key components of the Arabidopsis wound response using the transsys framework. For comparison, we constructed a null model that is devoid of any regulatory interactions, and various alternative models by rewiring the wound response model. All models were parametrized by computational optimization to generate synthetic gene expression profiles that approximate the empirical data set. We scored the fit of the synthetic to the empirical data with various distance measures, and used the median distance after optimization to directly and quantitatively assess the wound response model and its alternatives. Discrimination of candidate models depends substantially on the measure of gene expression profile distance. Using the null model to assess quality of the distance measures for discrimination, we identify correlation of log-ratio profiles as the most suitable distance. Our wound response model fits the empirical data significantly better than the alternative models. Gradual perturbation of the wound response model results in a corresponding gradual decline in fit. The optimization approach provides insights into biologically relevant features, such as robustness. It is a step toward enabling integrative studies of multiple cross-talking pathways, and thus may help to develop our understanding how the genome informs the mapping of environmental signals to phenotypic traits.

Genetic evidence of a redox-dependent systemic wound response via Hayan protease-phenoloxidase system in Drosophila

Systemic wound response (SWR) through intertissue communication in response to local wounds is an essential biological phenomenon that occurs in all multicellular organisms from plants to animals. However, our understanding of SWR has been greatly hampered by the complexity of wound signalling communication operating within the context of an entire organism. Here, we show genetic evidence of a redox-dependent SWR from the wound site to remote tissues by identifying critical genetic determinants of SWR. Local wounds in the integument rapidly induce activation of a novel circulating haemolymph serine protease, Hayan, which in turn converts pro-phenoloxidase (PPO) to phenoloxidase (PO), an active form of melanin-forming enzyme. The Haemolymph Hayan-PO cascade is required for redox-dependent activation of the c-Jun N-terminal kinase (JNK)-dependent cytoprotective program in neuronal tissues, thereby achieving organism level of homeostasis to resist local physical trauma. These results imply that the PO-activating enzyme cascade, which is a prominent defense system in humoral innate immunity, also mediates redox-dependent SWR, providing a novel link between wound response and the nervous system.

WIND1: a key molecular switch for plant cell dedifferentiation

Cellular dedifferentiation is often observed in both plants and animals at an early step of wound-induced regeneration. Some plant species develop callus, a mass of unorganised cells, after wounding and this response is thought to involve cell dedifferentiation since callus cells are usually ready to exert totipotency, an ability to regenerate any new organ including somatic embryos. It is well established that a balance of the two plant hormones, auxin and cytokinin, is central in controlling plant cell dedifferentiation and subsequent redifferentiation but molecular mechanisms underlying these processes are still unclear. In a recent study we reported that an AP2/ERF transcription factor WOUND INDUCED DEDIFFERENTIATION 1 (WIND1) and its close homologs, WIND2–4, are induced by wounding and that they promote cell dedifferentiation in Arabidopsis. Our data show that WIND proteins are required to activate the local cytokinin response at the wound site.

Light exerts multiple levels of influence on the Arabidopsis wound response

Light plays important roles in modulating plant responses to attack by pests and pathogens. Here, we test the hypothesis that darkness modifies the response to wounding, and examine possible mechanisms for such an effect. We investigated changes in the Arabidopsis transcriptome following a light-dark transition and the response to wounding either in the light or in the dark. The transcriptional response to the light-dark transition strongly resembles responses associated with carbon depletion. The dark shift and wound responses acted largely independently, but more complex interactions were identified at a number of levels. Darkness attenuates the overall transcriptional response to wounding, and we identified genes and physiological processes, such as anthocyanin accumulation, that exhibit light-dependent wound responses. Transcriptional activation of light-dependent wound-induced genes requires a chloroplast-derived signal originating from photosynthetic electron transport. We also present evidence of a role for the circadian clock in modifying wound responses. Our results show that darkness impacts on the wound response at a number of levels, which may imply differences in induced herbivore defences during the day and night.

Gene expression analysis of wounding-induced root-to-shoot communication in Arabidopsis thaliana

Root-to-shoot communication plays an important role in the adaptation to environmental stress. In this study, we established a model system for root-to-shoot signalling to observe global gene expression in Arabidopsis thaliana. The roots of Arabidopsis seedlings were wounded and the expression in the shoots of 68 and 5 genes was up-regulated threefold at 30 min and 6 h post-injury, respectively. These genes were designated early and late Root-to-Shoot responsive (RtS) genes, respectively. Many of the early RtS genes were found to encode transcription factors such as AtERFs, whereas others were associated with jasmonic acid (JA) and ethylene (ET). Some of the late RtS genes were shown to be regulated by 12-oxo-phytodienoic acid (OPDA). In fact, elevated levels of JA and OPDA were detected in the shoots of seedlings 30 min and 6 h, respectively, after wounding of the roots. A mutant analysis revealed that JA and ET are involved in the expression of the early RtS genes. Thus, root-to-shoot communication for many RtS genes is associated with the systemic production of JA, OPDA and possibly ET.

The octadecanoid signaling pathway participates in the chilling-induced transcription of ω-3 fatty acid desaturases in Arabidopsis

The jasmonate signaling pathway is known to be involved in various stress responses in plants, but little is known specifically on the role of the octadecanoid pathway in the regulation of ω-3 fatty acid desaturase (FAD) genes in response to low temperature. To uncover this problem, the expression level of three ω-3 FAD genes (AtFAD3, AtFAD7, and AtFAD8) and the content of linolenic acid (C18:3) in both wild type (WT) and mutant (or WT suppressed) plants disrupted in the octadecanoid pathway were analyzed under normal conditions and the chilling treatment (4 °C), respectively. As compared with WT plants, chilling-induced organ-specific expressions of ω-3 FAD genes significantly changed when the octadecanoid pathway was blocked or suppressed, and presented either the "suppressed increase" or the "enhanced decrease" tendency. Meanwhile, chilling-induced increases in the content of C18:3 found in WT plants, obviously reduced in both leaves and roots, and even turned to a decrease in stems when the octadecanoid pathway was disrupted. Overall, the transcription of ω-3 FAD genes and the proportion of C18:3 in the whole plant both of aos mutants and salicylic acid (SA)-treated plants under chilling stress were evidently lower than those of WT plants, except the expression of AtFAD3 gene in leaves. All these findings indicate that the octadecanoid pathway does participate in the chilling-induced transcription of ω-3 FAD genes in Arabidopsis.

Abiotic and biotic stresses and changes in the lignin content and composition in plants

Lignin is a polymer of phenylpropanoid compounds formed through a complex biosynthesis route, represented by a metabolic grid for which most of the genes involved have been sequenced in several plants, mainly in the model-plants Arabidopsis thaliana and Populus. Plants are exposed to different stresses, which may change lignin content and composition. In many cases, particularly for plant-microbe interactions, this has been suggested as defence responses of plants to the stress. Thus, understanding how a stressor modulates expression of the genes related with lignin biosynthesis may allow us to develop study-models to increase our knowledge on the metabolic control of lignin deposition in the cell wall. This review focuses on recent literature reporting on the main types of abiotic and biotic stresses that alter the biosynthesis of lignin in plants.

Molecular analysis and expression of a floral organ-specific polygalacturonase gene isolated from rapeseed (Brassica napus L.)

High throughput screening of stage-specific differentially expressed genes in a Brassica napus two-line Rs1046A/B subtractive library was used to identify the BnQRT3 gene associated with cell wall metabolism. Phylogenetic analysis indicates the protein product of BnQRT3 is polygalacturonase. According to cytological comparisons of Rs1046 sterile and fertile anthers, RT-PCR studies and in situ hybridizations, BnQRT3 is expressed most strongly in floral organs and may play an essential role in pollen maturation. Analysis of the histological staining pattern of BnQRT3 promoter-GUS constructs in transgenic Arabidopsis and Brassica napus revealed that proximal part of 5'-flanking region directed expression in the vascular tissue of filaments, veins in sepal and petals, stigma, branch connective and the floral organ abscission zone during the open flower stage. In the meanwhile, Activity of BnQRT3 was detected in the anthers, which commences at the microsporocyte stage and persists as anther approaches dehiscence. Strong GUS expression also can be observed in the vascular tissue of leaves and stem by compression with forceps or excision, suggesting that the BnQRT3 promoter is responsive to wounding.