Molecular cloning and expression analysis of an arginine decarboxylase gene from peach (Prunus persica)

The Peach (Prunus persica) CBL and CIPK Family Genes: Protein Interaction Profiling and Expression Analysis in Response to Various Abiotic Stresses

The plant calcineurin B-like protein-CBL interacting protein kinase (CBL-CIPK) signaling pathway is a Ca2+-related signaling pathway that responds strongly to both biological and abiotic environmental stimuli. This study identified eight CBL and eighteen CIPK genes from peach for the first time. Their basic properties and gene structure were analyzed, and the CBL and CIPK members from Arabidopsis and apple were combined to study their evolutionary relationships. Using RT-qPCR and RNA-seq data, we detected the expression patterns of PprCBLs and PprCIPKs in different tissues and fruit development stages of peach. Among them, the expression levels of PprCBL1 and PprCIPK18 were stable in various tissues and stages. The expression patterns of other members showed specificity between cultivars and developmental stages. By treating shoots with drought and salt stress simulated using PEG6000 and NaCl, it was found that PprCIPK3, PprCIPK6, PprCIPK15 and PprCIPK16 were strongly responsive to salt stress, and PprCIPK3, PprCIPK4, PprCIPK10, PprCIPK14, PprCIPK15, PprCIPK16 and PprCIPK18 were sensitive to drought stress. Three genes, PprCIPK3, PprCIPK15 and PprCIPK16, were sensitive to both salt and drought stress. We cloned four PprCBL and several PprCIPK genes and detected their interaction by yeast two-hybrid assay (Y2H). The results of Y2H show not only the evolutionary conservation of the interaction network of CBL-CIPK but also the specificity among different species. In conclusion, CBL and CIPK genes are important in peach and play an important role in the response to various abiotic stresses.

Grafting Watermelon Onto Pumpkin Increases Chilling Tolerance by Up Regulating Arginine Decarboxylase to Increase Putrescine Biosynthesis

Low temperature is a major environmental factor that severely impairs plant growth and productivity. Watermelon (Citrullus lanatus) is a chilling-sensitive crop. Grafting of watermelon onto pumpkin rootstock is an effective technique to increase the chilling tolerance of watermelon when exposure to short-time chilling stress. However, the mechanism by which pumpkin rootstock increases chilling tolerance remains poorly understood. Under 10°C/5°C (day/night) chilling stress treatment, pumpkin-grafted watermelon seedlings showed higher chilling tolerance than self-grafted watermelon plants with significantly reduced lipid peroxidation and chilling injury (CI) index. Physiological analysis revealed that pumpkin rootstock grafting led to the notable accumulation of putrescine in watermelon seedlings under chilling conditions. Pre-treat foliar with 1 mM D-arginine (inhibitor of arginine decarboxylase, ADC) increased the electrolyte leakage (EL) of pumpkin-grafted watermelon leaves under chilling stress. This result can be ascribed to the decrease in transcript levels of ADC, ornithine decarboxylase, spermidine synthase, and polyamine oxidase genes involved in the synthesis and metabolism of polyamines. Transcriptome analysis showed that pumpkin rootstock improved chilling tolerance in watermelon seedlings by regulating differential gene expression under chilling stress. Pumpkin-grafted seedling reduced the number and expression level of differential genes in watermelon scion under chilling stress. It specifically increased the up-regulated expression of ADC (Cla97C11G210580), a key gene in the polyamine metabolism pathway, and ultimately promoted the accumulation of putrescine. In conclusion, pumpkin rootstock grafting increased the chilling tolerance of watermelon through transcription adjustments, up regulating the expression level of ADC, and promoting the synthesis of putrescine, which ultimately improved the chilling tolerance of pumpkin-grafted watermelon plants.

Litoribacter populi sp. nov., isolated from the soil of a Populus euphratica forest

A Gram-stain-negative, rod-shaped, and orange-pigmented bacterium, designated XAAS-A1^T, was isolated from the soil of a Populus euphratica forest. The main respiratory quinone of XAAS-A1^T is MK-7, and the principal cellular fatty acids are iso-C_15:0, C_17:1 ω6c, Iso-C_17:0 3OH, and summed feature 3 (C_16:1ω6c and/or C_16:1ω7c). The major polar lipids are phosphatidylethanolamine, phosphatidylcholine, and two unidentified lipids. The 16S rRNA gene sequence analysis indicated that XAAS-A1^T belongs to the genus Litoribacter within the family Cyclobacteriaceae, having the highest sequence similarities to Litoribacter ruber KCTC 22899^T (97.1%) and L. alkaliphilus KCTC 32217^T (96.9%). XAAS-A1^T has a DNA G + C content of 42.1 mol%. The orthoANI and the digital DNA-DNA hybridization values were markedly lower than the recommended threshold values of 96% and 70%. Phenotypic and genotypic data suggest that XAAS-A1^T represents a novel species of the genus Litoribacter, for which we propose the name Litoribacter populi sp. nov. and XAAS-A1^T (= CCTCC AB 2017159^T = KCTC 62045^T) as the type strain.

Role of genes and metabolites involved in polyamines synthesis pathways and nitric oxide synthase in stomatal closure on Rosa damascena Mill. under drought stress

In order to evaluate the genes involved in polyamines synthesis pathway and the role of nitric oxide synthase (NOS) and H₂O₂ in stomatal closure under drought stress, a research conducted with three irrigation levels (100, 50 and 25% field capacity) at 1, 3, 6 and 12 days on Rosa damascena Mill. HPLC and qPCR results showed that putrescine (Put) accumulation occurred at first day in both 50 and 25% of field capacity and then decreased the other days. Furthermore, Put accumulation in the indirect pathway (ADC, AIH and CPA) was more effective related to the direct pathway (ODC) under severe stress. Increased expression of genes involved in production of spermidine (Spd) and spermine (Spm) i.e., SAMDC, SPDS and SPMS correlated with the highest accumulation of Spd and Spm under 50% FC at 6 d and 25% FC at 12 d, respectively. Moreover, results showed that Put reduction simultaneously accumulated H₂O₂, which subsequently increased NOS expression suggesting a key signal for stomatal closure.

The Interplay among Polyamines and Nitrogen in Plant Stress Responses

The interplay between polyamines (PAs) and nitrogen (N) is emerging as a key factor in plant response to abiotic and biotic stresses. The PA/N interplay in plants connects N metabolism, carbon (C) fixation, and secondary metabolism pathways. Glutamate, a pivotal N-containing molecule, is responsible for the biosynthesis of proline (Pro), arginine (Arg) and ornithine (Orn) and constitutes a main common pathway for PAs and C/N assimilation/incorporation implicated in various stresses. PAs and their derivatives are important signaling molecules, as they act largely by protecting and preserving the function/structure of cells in response to stresses. Use of different research approaches, such as generation of transgenic plants with modified intracellular N and PA homeostasis, has helped to elucidate a plethora of PA roles, underpinning their function as a major player in plant stress responses. In this context, a range of transgenic plants over-or under-expressing N/PA metabolic genes has been developed in an effort to decipher their implication in stress signaling. The current review describes how N and PAs regulate plant growth and facilitate crop acclimatization to adverse environments in an attempt to further elucidate the N-PAs interplay against abiotic and biotic stresses, as well as the mechanisms controlling N-PA genes/enzymes and metabolites.

Polyamine Action under Metal/Metalloid Stress: Regulation of Biosynthesis, Metabolism, and Molecular Interactions

Polyamines (PAs) are found in all living organisms and serve many vital physiological processes. In plants, PAs are ubiquitous in plant growth, physiology, reproduction, and yield. In the last decades, PAs have been studied widely for exploring their function in conferring abiotic stresses (salt, drought, and metal/metalloid toxicity) tolerance. The role of PAs in enhancing antioxidant defense mechanism and subsequent oxidative stress tolerance in plants is well-evident. However, the enzymatic regulation in PAs biosynthesis and metabolism is still under research and widely variable under various stresses and plant types. Recently, exogenous use of PAs, such as putrescine, spermidine, and spermine, was found to play a vital role in enhancing stress tolerance traits in plants. Polyamines also interact with other molecules like phytohormones, nitric oxides, trace elements, and other signaling molecules to providing coordinating actions towards stress tolerance. Due to the rapid industrialization metal/metalloid(s) contamination in the soil and subsequent uptake and toxicity in plants causes the most significant yield loss in cultivated plants, which also hamper food security. Finding the ways in enhancing tolerance and remediation mechanism is one of the critical tasks for plant biologists. In this review, we will focus the recent update on the roles of PAs in conferring metal/metalloid(s) tolerance in plants.

Interactive effects of abscisic acid and nitric oxide on chilling resistance and active oxygen metabolism in peach fruit during cold storage

BACKGROUND

Cold conditions can accelerate the production of reactive oxygen species (ROS), and excessive ROS may attack biological macromolecules, disrupt related signal pathways, induce oxidative stress and influence plant metabolism. The cross-talk between nitric oxide (NO) and abscisic acid (ABA) and the inhibitions by NO or ABA on oxidative damage have been reported in fruits. However, there are few reports about the roles of NO-ABA interactions in chilling stress and antioxidant defense in fruits during cold storage. This study was conducted to investigate the roles of NO, ABA and interactions between NO and ABA in response to chilling stress on peach fruit (Prunus persica (L.) Batsch, cv. 'Xintaihong').

RESULTS

Treatments with 15 µmol L^-1 NO, 100 µmol L^-1 ABA and 15 µmol L^-1 NO + 5 mmol L^-1 sodium tungstate solution could reduce ROS content, alleviate lipid peroxidation and enhance antioxidant enzyme activities and antioxidant capacities. However, treatments with 5 µmol L^-1 potassium 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (c-PTIO), 5 mmol L^-1 sodium tungstate and 100 µmol L^-1 ABA + 5 µmol L^-1 c-PTIO differentially blocked these protective effects and significantly increased ROS content and lipid peroxidation of peaches under low-temperature conditions.

CONCLUSIONS

Application of exogenous ABA could increase the resistance to cold-induced oxidative stress by enhancing the efficiency of enzymatic and non-enzymatic systems, which were partially mediated by NO. © 2018 Society of Chemical Industry.

PbrMYB21, a novel MYB protein of Pyrus betulaefolia, functions in drought tolerance and modulates polyamine levels by regulating arginine decarboxylase gene

MYB comprises a large family of transcription factors that play significant roles in plant development and stress response in plants. However, knowledge concerning the functions of MYBs and the target genes remains poorly understood. Here, we report the identification and functional characterization of a novel stress-responsive MYB gene from Pyrus betulaefolia. The MYB gene, designated as PbrMYB21, belongs to the R2R3-type and shares high degree of sequence similarity to MdMYB21. The transcript levels of PbrMYB21 were up-regulated under various abiotic stresses, particularly dehydration. PbrMYB21 was localized in the nucleus with transactivation activity. Overexpression of PbrMYB21 in tobacco conferred enhanced tolerance to dehydration and drought stresses, whereas down-regulation of PbrMYB21 in Pyrus betulaefolia by virus-induced gene silencing (VIGS) resulted in elevated drought sensitivity. Transgenic tobacco exhibited higher expression levels of ADC (arginine decarboxylase) and accumulated larger amount of polyamine in comparison with wild type (WT). VIGS of PbrMYB21 in Pyrus betulaefolia down-regulated ADC abundance and decreased polyamine level, accompanied by compromised drought tolerance. The promoter region of PbrADC contains one MYB-recognizing cis-element, which was shown to be interacted with PbrMYB21, indicating the ADC may be a target gene of PbrMYB21. Take together, these results demonstrated that PbrMYB21 plays a positive role in drought tolerance, which may be, at least in part, due to the modulation of polyamine synthesis by regulating the ADC expression.

Draft Genome Sequence of the Plant Growth-Promoting Pseudomonas punonensis Strain D1-6 Isolated from the Desert Plant Erodium hirtum in Jordan

Pseudomonas punonensis strain D1-6 was isolated from roots of the desert plant Erodium hirtum, near the Dead Sea in Jordan. The genome of strain D1-6 reveals several key plant growth-promoting and herbicide-resistance genes, indicating a possible specialized role for this endophyte.

Overexpression of Prunus mume Dehydrin Genes in Tobacco Enhances Tolerance to Cold and Drought

Dehydrins, known as group 2 or D-11 family late-embryogenesis-abundant (LEA) proteins, play important roles in plant growth and stress tolerance. Six dehydrin genes were previously identified from the genome of Prunus mume. In this study, five of them (PmLEA8, PmLEA10, PmLEA19, PmLEA20, and PmLEA29) were cloned from cold-resistant P. mume 'Beijingyudie'. Real-time RT-PCR analysis indicated that all these genes could be up-regulated by one or several treatments (ABA, SA, low temperature, high temperature, PEG, and NaCl treatments). The results of spot assay demonstrated that the expression of all these dehydrins, except PmLEA8, conferred improved osmotic and freezing-resistance to the recombinant Escherichia coli. So four dehydrin genes, PmLEA10, PmLEA19, PmLEA20 and PmLEA29 were chosen for individual over-expression in tobacco plants. The transgenic tobacco plants showed lower relative content of malondialdehyde, relative electrolyte leakage and higher relative content of water than control plants when exposed to cold and drought stress. These results demonstrated that PmLEAs were involved in plant responses to cold and drought.

Characterization of the expression of the stress-responsive PpERS1 gene from peach and analysis of its promoter using transgenic tomato

The PpERS1 gene, which encodes an ethylene receptor and responds to abiotic and biotic stresses, was cloned from peach (Prunus persica L. Batsch cv Okubao). The genomic DNA sequence of PpERS1 comprises seven exons which are separated by six introns, interestingly alternative splicing of the first intron produced three different PpERS1 transcripts. In addition, a 2.8-kb sequence including the promoter of PpERS1 was isolated and analyzed by placing expressing of the GUS reporter gene under its control. Several putative cis-elements were identified in the promoter of PpERS1, including two ethylene-responsive elements (EREs), five W boxes, and four putative binding sites for MYB-type transcription factors. Deletion analysis indicated the presence of an enhancer element in the PpERS1 promoter. Temporal and spatial expression analysis of the PpERS1 promoter using histochemical GUS staining showed GUS activity in all tissues examined throughout the development of transgenic tomato plants. Exposure to various stresses caused similar changes in expression patterns in peach and transgenic tomato plants. Overall, our results suggested that PpERS1 gene might play important roles in response to multiple stresses via signal transduction mediated by ethylene receptors. The characterization of the PpERS1 promoter contributes to our understanding of the transcriptional regulation of this ethylene receptor in peach.

A NAC Transcription Factor Represses Putrescine Biosynthesis and Affects Drought Tolerance

Arginine decarboxylase (ADC)-mediated putrescine biosynthesis plays an important role in plant stress responses, but the transcriptional regulation of ADC in response to abiotic stress is not well understood. We isolated a NAM, ATAF1/2, and CUC (NAC) domain-containing transcription factor, PtrNAC72, from trifoliate orange (Poncirus trifoliata) by yeast one-hybrid screening. PtrNAC72, localized to the nucleus, binds specifically to the promoter of PtADC and acts as a transcriptional repressor. PtrNAC72 expression was induced by cold, drought, and abscisic acid. ADC messenger RNA abundance and putrescine levels were decreased in transgenic tobacco (Nicotiana nudicaulis) plants overexpressing PtrNAC72 but increased, compared with the wild type, in an Arabidopsis (Arabidopsis thaliana) transfer DNA insertion mutant, nac72 While transgenic tobacco lines overexpressing PtrNAC72 were more sensitive to drought, plants of the Arabidopsis nac72 mutant exhibited enhanced drought tolerance, consistent with the accumulation of reactive oxygen species in the tested genotypes. In addition, exogenous application of putrescine to the overexpression lines restored drought tolerance, while treatment with d-arginine, an ADC inhibitor, compromised the drought tolerance of nac72 Taken together, these results demonstrate that PtrNAC72 is a repressor of putrescine biosynthesis and may negatively regulate the drought stress response, at least in part, via the modulation of putrescine-associated reactive oxygen species homeostasis.

FcWRKY70, a WRKY protein of Fortunella crassifolia, functions in drought tolerance and modulates putrescine synthesis by regulating arginine decarboxylase gene

WRKY comprises a large family of transcription factors in plants, but most WRKY members are still poorly understood. In this study, we report functional characterization of a Group III WRKY gene (FcWRKY70) from Fortunella crassifolia. FcWRKY70 was greatly induced by drought and abscisic acid, but slightly or negligibly by salt and cold. Overexpression of FcWRKY70 in tobacco (Nicotiana nudicaulis) and lemon (Citrus lemon) conferred enhanced tolerance to dehydration and drought stresses. Transgenic tobacco and lemon exhibited higher expression levels of ADC (arginine decarboxylase), and accumulated larger amount of putrescine in comparison with wild type (WT). Treatment with D-arginine, an inhibitor of ADC, caused transgenic tobacco plants more sensitive to dehydration. Knock-down of FcWRKY70 in kumquat down-regulated ADC abundance and decreased putrescine level, accompanied by compromised dehydration tolerance. The promoter region of FcADC contained two W-box elements, which were shown to be interacted with FcWRKY70. Taken together, our data demonstrated that FcWRKY70 functions in drought tolerance by, at least partly, promoting production of putrescine via regulating ADC expression.

Molecular cloning and characterization of the light-harvesting chlorophyll a/b gene from the pigeon pea (Cajanus cajan)

Light-harvesting chlorophyll a/b-binding proteins (LHCB) have been implicated in the stress response. In this study, a gene encoding LHCB in the pigeon pea was cloned and characterized. Based on the sequence of a previously obtained 327 bp Est, a full-length 793 bp cDNA was cloned using the rapid amplification of cDNA ends (RACE) method. It was designated CcLHCB1 and encoded a 262 amino acid protein. The calculated molecular weight of the CcLHCB1 protein was 27.89 kDa, and the theoretical isoelectric point was 5.29. Homology search and sequence multi-alignment demonstrated that the CcLHCB1 protein sequence shared a high identity with LHCB from other plants. Bioinformatics analysis revealed that CcLHCB1 was a hydrophobic protein with three transmembrane domains. By fluorescent quantitative real-time polymerase chain reaction (PCR), CcLHCB1 mRNA transcripts were detectable in different tissues (leaf, stem, and root), with the highest level found in the leaf. The expression of CcLHCB1 mRNA in the leaves was up-regulated by drought stimulation and AM inoculation. Our results provide the basis for a better understanding of the molecular organization of LCHB and might be useful for understanding the interaction between plants and microbes in the future.

ICE1 of Poncirus trifoliata functions in cold tolerance by modulating polyamine levels through interacting with arginine decarboxylase

ICE1 (Inducer of CBF Expression 1) encodes a MYC-like basic helix-loop-helix transcription factor that acts as a central regulator of cold response. In this study, we elucidated the function and underlying mechanisms of PtrICE1 from trifoliate orange [Poncirus trifoliata (L.) Raf.]. PtrICE1 was upregulated by cold, dehydration, and salt, with the greatest induction under cold conditions. PtrICE1 was localized in the nucleus and could bind to a MYC-recognizing sequence. Ectopic expression of PtrICE1 in tobacco and lemon conferred enhanced tolerance to cold stresses at either chilling or freezing temperatures. Yeast two-hybrid screening revealed that 21 proteins belonged to the PtrICE1 interactome, in which PtADC (arginine decarboxylase) was confirmed as a bona fide protein interacting with PtrICE1. Transcript levels of ADC genes in the transgenic lines were slightly elevated under normal growth condition but substantially increased under cold conditions, consistent with changes in free polyamine levels. By contrast, accumulation of the reactive oxygen species, H2O2 and O2 (-), was appreciably alleviated in the transgenic lines under cold stress. Higher activities of antioxidant enzymes, such as superoxide dismutase and catalase, were detected in the transgenic lines under cold conditions. Taken together, these results demonstrated that PtrICE1 plays a positive role in cold tolerance, which may be due to modulation of polyamine levels through interacting with the ADC gene.

Polyamines function in stress tolerance: from synthesis to regulation

Plants are challenged by a variety of biotic or abiotic stresses, which can affect their growth and development, productivity, and geographic distribution. In order to survive adverse environmental conditions, plants have evolved various adaptive strategies, among which is the accumulation of metabolites that play protective roles. A well-established example of the metabolites that are involved in stress responses, or stress tolerance, is the low-molecular-weight aliphatic polyamines, including putrescine, spermidine, and spermine. The critical role of polyamines in stress tolerance is suggested by several lines of evidence: firstly, the transcript levels of polyamine biosynthetic genes, as well as the activities of the corresponding enzymes, are induced by stresses; secondly, elevation of endogenous polyamine levels by exogenous supply of polyamines, or overexpression of polyamine biosynthetic genes, results in enhanced stress tolerance; and thirdly, a reduction of endogenous polyamines is accompanied by compromised stress tolerance. A number of studies have demonstrated that polyamines function in stress tolerance largely by modulating the homeostasis of reactive oxygen species (ROS) due to their direct, or indirect, roles in regulating antioxidant systems or suppressing ROS production. The transcriptional regulation of polyamine synthesis by transcription factors is also reviewed here. Meanwhile, future perspectives on polyamine research are also suggested.

Improvement of plant abiotic stress tolerance through modulation of the polyamine pathway

Polyamines (mainly putrescine (Put), spermidine (Spd), and spermine (Spm)) have been widely found in a range of physiological processes and in almost all diverse environmental stresses. In various plant species, abiotic stresses modulated the accumulation of polyamines and related gene expression. Studies using loss-of-function mutants and transgenic overexpression plants modulating polyamine metabolic pathways confirmed protective roles of polyamines during plant abiotic stress responses, and indicated the possibility to improve plant tolerance through genetic manipulation of the polyamine pathway. Additionally, putative mechanisms of polyamines involved in plant abiotic stress tolerance were thoroughly discussed and crosstalks among polyamine, abscisic acid, and nitric oxide in plant responses to abiotic stress were emphasized. Special attention was paid to the interaction between polyamine and reactive oxygen species, ion channels, amino acid and carbon metabolism, and other adaptive responses. Further studies are needed to elucidate the polyamine signaling pathway, especially polyamine-regulated downstream targets and the connections between polyamines and other stress responsive molecules.

Molecular cloning and characterization of CrNCED1, a gene encoding 9-cis-epoxycarotenoid dioxygenase in Citrus reshni, with functions in tolerance to multiple abiotic stresses

Abscisic acid (ABA) is an important stress phytohormone that plays an essential role in mediating the signaling networks associated with plant responses to various abiotic stresses. In the present study, we isolated a gene CrNCED1 encoding the rate-limiting enzyme of ABA synthesis, 9-cis-epoxycarotenoid dioxygenase (NCED), from Citrus reshni. Expression patterns of CrNCED1 varied among different tissues, in which higher levels were measured in the leaves than in the roots. The steady-state mRNA levels of CrNCED1 were progressively elevated by dehydration and ABA, only transiently induced by cold, but not affected by salt. To examine its function in stress tolerance, transgenic tobacco (Nicotiana nudicaulis) plants constitutively overexpressing CrNCED1 were generated, which contained higher ABA levels than the wild type (WT) under both normal growth conditions and drought stress. The transgenic lines displayed enhanced tolerance to dehydration, drought, salt and oxidative stresses when compared with the WT. Lower levels of reactive oxygen species (H₂O₂ and O₂⁻) were detected in the transgenic plants than in the WT under dehydration and salt stress. On the contrary, transcript levels of several genes associated with ROS scavenging, osmoticum adjustment, and water maintenance, and activities of two antioxidant enzymes were higher in the transgenic plants relative to the WT under the dehydration stress. Taken together, CrNCED1 overexpression confers enhanced tolerance to multiple abiotic stresses, which may be, at least in part, ascribed to the positive activation of the stress-responsive genes.

Genome-wide identification and analysis of late embryogenesis abundant (LEA) genes in Prunus mume

Late embryogenesis abundant (LEA) proteins play important roles in plant desiccation tolerance. In this study, 30 LEA genes were identified from Chinese plum (Prunus mume) through genome-wide analysis. The PmLEA genes are distributed on all Chinese plum chromosomes except chromosome 3. Twelve (40 %) and five PmLEA genes are arranged in tandem and segmental duplications, respectively. The PmLEA genes could be divided into eight groups (LEA_1, LEA_2, LEA_3, LEA_4, LEA_5, PvLEA18, dehydrin and seed maturation protein). Ten gene conversion events were observed and most of them (70 %) were identified in dehydrin group. Most PmLEA genes were highly expressed in flower (22/30) and up-regulated by ABA treatment (19/30).

Genome-wide identification and analysis of late embryogenesis abundant (LEA) genes in Prunus mume

Late embryogenesis abundant (LEA) proteins play important roles in plant desiccation tolerance. In this study, 30 LEA genes were identified from Chinese plum (Prunus mume) through genome-wide analysis. The PmLEA genes are distributed on all Chinese plum chromosomes except chromosome 3. Twelve (40 %) and five PmLEA genes are arranged in tandem and segmental duplications, respectively. The PmLEA genes could be divided into eight groups (LEA_1, LEA_2, LEA_3, LEA_4, LEA_5, PvLEA18, dehydrin and seed maturation protein). Ten gene conversion events were observed and most of them (70 %) were identified in dehydrin group. Most PmLEA genes were highly expressed in flower (22/30) and up-regulated by ABA treatment (19/30).

Overexpression of PtADC confers enhanced dehydration and drought tolerance in transgenic tobacco and tomato: effect on ROS elimination

Drought is a major environmental factor that limits plant growth and productivity. Polyamines have been shown to act as stress molecules that accumulate in plant adaptation to abiotic stresses. In this study, an arginine decarboxylase gene isolated from Poncirus trifoliata, PtADC, was introduced into tobacco and tomato to investigate its function in drought tolerance. We demonstrate that the transgenic plants showed an improvement in dehydration and drought tolerance. Under dehydration stress conditions, the accumulation of reactive oxygen species (ROS) was remarkably decreased in the transgenic lines as compared with the wild type. Moreover, the transcript levels of three stress-responsive genes were increased in the transgenic tobacco lines. Taken together, our results suggest that PtADC plays a key role in drought tolerance, which is, at least partially, attributed to its role in ROS detoxification.

An arginine decarboxylase gene PtADC from Poncirus trifoliata confers abiotic stress tolerance and promotes primary root growth in Arabidopsis

Arginine decarboxylase (ADC) is an important enzyme responsible for polyamine synthesis under stress conditions. In this study, the gene encoding ADC in Poncirus trifoliata (PtADC) was isolated and it existed as a single-copy member. Transcript levels of PtADC were up-regulated by low temperature and dehydration. Overexpression of PtADC in an Arabidopsis thaliana ADC mutant adc1-1 promoted putrescine synthesis in the transgenic line and the stomatal density was reverted to that in the wild type. The transgenic line showed enhanced resistance to high osmoticum, dehydration, long-term drought, and cold stress compared with the wild type and the mutant. The accumulation of reactive oxygen species (ROS) in the transgenic line was appreciably decreased under the stresses, but ROS scavenging capacity was compromised when the transgenic plants were treated with the ADC inhibitor D-arginine prior to stress treatment. In addition, the transgenic line had longer roots than the wild type and the mutant under both normal and stressful conditions, consistent with larger cell number and length of the root meristematic zone. Taken together, these results demonstrated that PtADC is involved in tolerance to multiple stresses, and its function may be due, at least partly, to efficient ROS elimination and to its influence on root growth conducive to drought tolerance.

Spermine pretreatment confers dehydration tolerance of citrus in vitro plants via modulation of antioxidative capacity and stomatal response

Polyamines, small aliphatic polycations, have been suggested to play key roles in a number of biological processes. In this paper, attempts were made to investigate the possibility of improving dehydration tolerance of citrus in vitro plants by exogenous application of spermine (Spm). 'Red Tangerine' (Citrus reticulata Blanco) in vitro plants pretreated with 1 mM Spm exhibited less wilted phenotype and lower water loss and electrolyte leakage than the control under dehydration. Spm-pretreated plants contained higher endogenous polyamine content during the course of the experiment relative to the control, particularly at the end of dehydration, coupled with higher expression levels of ADC and SPMS. Histochemical staining showed that the Spm-pretreated leaves were stained to a lower extent than those without Spm pretreatment, implying generation of less reactive oxygen species (ROS). On the contrary, activities of peroxidase (POD) and superoxide dismutase (SOD) in the Spm-pretreated samples were higher than the control at a given time point or during the whole experiment, suggesting that Spm exerted a positive effect on antioxidant systems. In addition, significantly smaller stomatal aperture size was observed in Spm-pretreated epidermal peels, which showed that stomatal closure was promoted by polyamines. All of these data suggest that Spm pretreatment causes accumulation of higher endogenous polyamines and accordingly leads to more effective ROS scavenging (less tissue damage) and stimulated stomatal closure (lower water loss) upon dehydration, which may function collectively to enhance dehydration tolerance.

Molecular characterization of the Arginine decarboxylase gene family in rice

Arginine decarboxylase (ADC) is a key enzyme in plants that converts arginine into putrescine, an important mediator of abiotic stress tolerance. Adc genes have been isolated from a number of dicotyledonous plants but the oat and rice Adc genes are the only representatives of monocotyledonous species described thus far. Rice has a small family of Adc genes, and OsAdc1 expression has been shown to fluctuate under drought and chilling stress. We identified and characterized a second rice Adc gene (OsAdc2) which encodes a 629-amino-acid protein with a predicted molecular mass of 67 kDa. An unusual feature of the OsAdc2 gene is the presence of an intron and a short upstream open reading frame in the 5'-UTR. Sequence comparisons showed that OsAdc2 is more closely related to the oat Adc gene than to OsAdc1 or to its dicot homologs, and mRNA analysis showed that the two rice genes are also differently regulated. Whereas OsAdc1 is expressed in leaf, root and stem, OsAdc2 expression is restricted to stem tissue. Protein expression was investigated with specific antibodies against ADC1 and ADC2, corroborating the mRNA data. We discuss the expression profiles of OsAdc1 and OsAdc2 and potential functions for the two corresponding proteins.