Overexpression of SAMDC1 gene in Arabidopsis thaliana increases expression of defense-related genes as well as resistance to Pseudomonas syringae and Hyaloperonospora arabidopsidis

Spermine deficiency shifts the balance between jasmonic acid and salicylic acid-mediated defence responses in Arabidopsis

Polyamines are small aliphatic polycations present in all living organisms. In plants, the most abundant polyamines are putrescine (Put), spermidine (Spd) and spermine (Spm). Polyamine levels change in response to different pathogens, including Pseudomonas syringae pv. tomato DC3000 (Pst DC3000). However, the regulation of polyamine metabolism and their specific contributions to defence are not fully understood. Here we report that stimulation of Put biosynthesis by Pst DC3000 is dependent on coronatine (COR) perception and jasmonic acid (JA) signalling, independently of salicylic acid (SA). Conversely, lack of Spm in spermine synthase (spms) mutant stimulated galactolipids and JA biosynthesis, and JA signalling under basal conditions and during Pst DC3000 infection, whereas compromised SA-pathway activation and defence outputs through SA-JA antagonism. The dampening of SA responses correlated with COR and Pst DC3000-inducible deregulation of ANAC019 expression and its key SA-metabolism gene targets. Spm deficiency also led to enhanced disease resistance to the necrotrophic fungal pathogen Botrytis cinerea and stimulated endoplasmic reticulum (ER) stress signalling in response to Pst DC3000. Overall, our findings provide evidence for the integration of polyamine metabolism in JA- and SA-mediated defence responses, as well as the participation of Spm in buffering ER stress during defence.

Influence of a phyA Mutation on Polyamine Metabolism in Arabidopsis Depends on Light Spectral Conditions

The aim of the study was to reveal the influence of phyA mutations on polyamine metabolism in Arabidopsis under different spectral compositions. Polyamine metabolism was also provoked with exogenous spermine. The polyamine metabolism-related gene expression of the wild type and phyA plants responded similarly under white and far-red light conditions but not at blue light. Blue light influences rather the synthesis side, while far red had more pronounced effects on the catabolism and back-conversion of the polyamines. The observed changes under elevated far-red light were less dependent on PhyA than the blue light responses. The polyamine contents were similar under all light conditions in the two genotypes without spermine application, suggesting that a stable polyamine pool is important for normal plant growth conditions even under different spectral conditions. However, after spermine treatment, the blue regime had more similar effects on synthesis/catabolism and back-conversion to the white light than the far-red light conditions. The additive effects of differences observed on the synthesis, back-conversion and catabolism side of metabolism may be responsible for the similar putrescine content pattern under all light conditions, even in the presence of an excess of spermine. Our results demonstrated that both light spectrum and phyA mutation influence polyamine metabolism.

Spermine inhibits PAMP-induced ROS and Ca2+ burst and reshapes the transcriptional landscape of PAMP-triggered immunity in Arabidopsis

Polyamines are small polycationic amines whose levels increase during defense. Previous studies support the contribution of the polyamine spermine to defense responses. However, the potential contribution of spermine to pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI) has not been completely established. Here, we compared the contribution of spermine and putrescine to early and late PTI responses in Arabidopsis. We found that putrescine and spermine have opposite effects on PAMP-elicited reactive oxygen species (ROS) production, with putrescine increasing and spermine lowering the flg22-stimulated ROS burst. Through genetic and pharmacological approaches, we found that the inhibitory effect of spermine on flg22-elicited ROS production is independent of polyamine oxidation, nitric oxide, and salicylic acid signaling but resembles chemical inhibition of RBOHD (RESPIRATORY BURST OXIDASE HOMOLOG D). Spermine can also suppress ROS elicited by FLS2-independent but RBOHD-dependent pathways, thus pointing to compromised RBOHD activity. Consistent with this, we found that spermine but not putrescine dampens flg22-stimulated cytosolic Ca2+ influx. Finally, we found that both polyamines differentially reshape transcriptional responses during PTI and disease resistance to Pseudomonas syringae. Overall, we provide evidence for the differential contributions of putrescine and spermine to PTI, with an impact on plant defense.

Improvement of cold tolerance in maize (Zea mays L.) using Agrobacterium-mediated transformation of ZmSAMDC gene

Maize (Zea mays L.) is a food crop sensitive to low temperatures. As one of the abiotic stress hazards, low temperatures seriously affect the yield of maize. However, the genetic basis of low-temperature adaptation in maize is still poorly understood. In this study, maize S-adenosylmethionine decarboxylase (SAMDC) was localized to the nucleus. We used Agrobacterium-mediated transformation technology to introduce the SAMDC gene into an excellent maize inbred line variety GSH9901 and produced a cold-tolerant transgenic maize line. After three years of single-field experiments, the contents of polyamines (PAs), proline (Pro), malondialdehyde (MDA), antioxidant enzymes and ascorbate peroxidases (APXs) in the leaves of the transgenic maize plants overexpressing the SAMDC gene significantly increased, and the expression of elevated CBF and cold-responsive genes effectively increased. The agronomic traits of the maize overexpressing the SAMDC gene changed, and the yield traits significantly improved. However, no significant changes were found in plant height, ear length, and shaft thickness. Therefore, SAMDC enzymes can effectively improve the cold tolerance of maize.

Response of Tomato-Pseudomonas Pathosystem to Mild Heat Stress

Higher plants suffer from mild heat stress when temperatures increase by 5 °C above optimum growth temperatures. This produces changes at the cellular and metabolic levels, allowing plants to adapt to heat conditions. This study investigated an increase of 5 °C above the optimum growth temperature (26 °C) of tomato plants in the tomato–Pseudomonas syringae pv. tomato pathosystem. A temperature increase above 26 °C affects plant development, the defensive pathways activated against Pseudomonas syringae pv. tomato strain DC3000 (PstDC3000), and the bacterial growth and virulence machinery. The results demonstrated that tomato plants were able to acclimate to mild heat stress, showing no symptoms of damage. Moreover, plants subjected to a 5 °C increase (T31 °C plants) showed higher basal levels of metabolites such as proline and putrescine, which probably act as compatible osmolytes. This demonstrates their importance as key components of thermotolerance. When grown under mild heat stress, plants were less susceptible to PstDC3000 and showed increased accumulation of abscisic acid, jasmonic acid-isoleucine, and spermine. In addition, the temperature increase negatively affected the infectivity of PstDC3000. Inhibition of the genes responsible for quorum sensing establishment and synthesis of flagellin and coronatine was observed in bacteria extracted from T31 °C plants. Analysis of the genes involved in the synthesis of the type III secretion system indicates the important role of this system in bacterial growth under these conditions. As the known resistance mechanisms involved in the defense against PstDC3000 were not activated, the changes in its virulence mechanisms under high temperatures may explain the lower infection observed in the T31 °C plants.

Mitogen-Activated Protein Kinase 4-Regulated Metabolic Networks

Mitogen-activated protein kinase 4 (MPK4) was first identified as a negative regulator of systemic acquired resistance. It is also an important kinase involved in many other biological processes in plants, including cytokinesis, reproduction, and photosynthesis. Arabidopsis thaliana mpk4 mutant is dwarf and sterile. Previous omics studies including genomics, transcriptomics, and proteomics have revealed new functions of MPK4 in different biological processes. However, due to challenges in metabolomics, no study has touched upon the metabolomic profiles of the mpk4 mutant. What metabolites and metabolic pathways are potentially regulated by MPK4 are not known. Metabolites are crucial components of plants, and they play important roles in plant growth and development, signaling, and defense. Here we used targeted and untargeted metabolomics to profile metabolites in the wild type and the mpk4 mutant. We found that in addition to the jasmonic acid and salicylic acid pathways, MPK4 is involved in polyamine synthesis and photosynthesis. In addition, we also conducted label-free proteomics of the two genotypes. The integration of metabolomics and proteomics data allows for an insight into the metabolomic networks that are potentially regulated by MPK4.

Hydroxycinnamate Amides: Intriguing Conjugates of Plant Protective Metabolites

The syntheses of aromatic monoamines and aliphatic polyamines (PAs) are responsive to environmental stresses, with some modulating aspects of plant defense. Conjugation of amines to hydroxycinnamic acids (HCAs) generates HCA amides (HCAAs), with the conjugates possessing properties from both compounds. Conjugation may reduce the polarity of the resulting metabolite and assist in translocation, stability, and compartmentalization. Recent metabolomic insights identified HCAAs as biomarkers during plant-pathogen interactions, supporting a functional role in defense. The conjugates may contribute to regulation of the dynamic metabolic pool of hydroxycinnamates. This review highlights the occurrence of aromatic amines (AAs) and PAs in stress metabolism, conjugation to HCAs, and the roles of HCAAs during host defense, adding emphasis on their involvement in hydrogen peroxide (H₂O₂) production and cell-wall strengthening.

Putrescine elicits ROS-dependent activation of the salicylic acid pathway in Arabidopsis thaliana

Polyamines are small amines that accumulate during stress and contribute to disease resistance through as yet unknown signaling pathways. Using a comprehensive RNA-sequencing analysis, we show that early transcriptional responses triggered by each of the most abundant polyamines (putrescine, spermidine, spermine, thermospermine and cadaverine) exhibit specific quantitative differences, suggesting that polyamines (rather than downstream metabolites) elicit defense responses. Signaling by putrescine, which accumulates in response to bacteria that trigger effector triggered immunity (ETI) and systemic acquired resistance (SAR), is largely dependent on the accumulation of hydrogen peroxide, and is partly dependent on salicylic acid (SA), the expression of ENHANCED DISEASE SUSCEPTIBILITY (EDS1) and NONEXPRESSOR of PR GENES1 (NPR1). Putrescine elicits local SA accumulation as well as local and systemic transcriptional reprogramming that overlaps with SAR. Loss-of-function mutations in arginine decarboxylase 2 (ADC2), which is required for putrescine synthesis and copper amine oxidase (CuAO), which is involved in putrescine oxidation, compromise basal defenses, as well as putrescine and pathogen-triggered systemic resistance. These findings confirm that putrescine elicits ROS-dependent SA pathways in the activation of plant defenses.

Empowering crop resilience to environmental multiple stress through the modulation of key response components

Crop plants have developed a multitude of defense and adaptation responses to protect themselves against invading pathogens and challenging environmental stresses, mostly operating jointly. The plant perception of overall stress induces a coordinated response mediated by complex signaling networks. Experimental evidences proved that plant response to combined biotic and abiotic stresses substantially diverge from the responses to individual stresses. Moreover, the cross-talk of signaling pathways involved in responding to biotic and abiotic stresses is pivoted on several converging elements able to simultaneously modulate the timing and amplitude of the overall plant response. Comprehensively, the interaction between biotic and abiotic stresses can dramatically changes the plant response to the individual stress and the phenotypical outcome of each stress factor. System biology and data mining can synergistically help biologists in finding out regulative mechanisms and key genes controlling the response to biotic and abiotic stresses. Deploying new genetic engineering solutions can rely on the modification of genes involved in resistance/tolerance processes and/or in the modulation of regulatory elements. Finally, a model of the engineered crop for enhanced tolerance to pressures resulting from invasive pathogens and abiotic constraints in semiarid and warm environment is discussed.

Spermine Is a Potent Plant Defense Activator Against Gray Mold Disease on Solanum lycopersicum, Phaseolus vulgaris, and Arabidopsis thaliana

Polyamines (PAs) are ubiquitous aliphatic amines that play important roles in growth, development, and environmental stress responses in plants. In this study, we report that exogenous application of spermine (Spm) is effective in the induction of resistance to gray mold disease, which is caused by the necrotrophic fungal pathogen Botrytis cinerea, on tomato (Solanum lycopersicum), bean (Phaseolus vulgaris), and Arabidopsis thaliana. High throughput transcriptome analysis revealed a priming role for the Spm molecule in the genus Arabidopsis, resulting in strong upregulation of several important defense-associated genes, particularly those involved in systemic-acquired resistance. Microscopic analysis confirmed that Spm application potentiates endogenous defense responses in tomato leaves through the generation of reactive oxygen species and the hypersensitive response, which effectively contained B. cinerea growth within the inoculated area. Moreover, co-application of Spm and salicylic acid resulted in a synergistic effect against the pathogen, leading to higher levels of resistance than those induced by separate applications of the two compounds. The Spm plus salicylic acid treatment also reduced infection in systemic nontreated leaves of tomato plants. Our findings suggest that Spm, particularly when applied in combination with salicylic acid, functions as a potent plant defense activator that leads to effective local and systemic resistance against B. cinerea.

Overexpression of a S-Adenosylmethionine Decarboxylase from Sugar Beet M14 Increased Araidopsis Salt Tolerance

Polyamines play an important role in plant growth and development, and response to abiotic stresses. Previously, differentially expressed proteins in sugar beet M14 (BvM14) under salt stress were identified by iTRAQ-based quantitative proteomics. One of the proteins was an S-adenosylmethionine decarboxylase (SAMDC), a key rate-limiting enzyme involved in the biosynthesis of polyamines. In this study, the BvM14-SAMDC gene was cloned from the sugar beet M14. The full-length BvM14-SAMDC was 1960 bp, and its ORF contained 1119 bp encoding the SAMDC of 372 amino acids. In addition, we expressed the coding sequence of BvM14-SAMDC in Escherichia coli and purified the ~40 kD BvM14-SAMDC with high enzymatic activity. Quantitative real-time PCR analysis revealed that the BvM14-SAMDC was up-regulated in the BvM14 roots and leaves under salt stress. To investigate the functions of the BvM14-SAMDC, it was constitutively expressed in Arabidopsis thaliana. The transgenic plants exhibited greater salt stress tolerance, as evidenced by longer root length and higher fresh weight and chlorophyll content than wild type (WT) under salt treatment. The levels of spermidine (Spd) and spermin (Spm) concentrations were increased in the transgenic plants as compared with the WT. Furthermore, the overexpression plants showed higher activities of antioxidant enzymes and decreased cell membrane damage. Compared with WT, they also had low expression levels of RbohD and RbohF, which are involved in reactive oxygen species (ROS) production. Together, these results suggest that the BvM14-SAMDC mediated biosynthesis of Spm and Spd contributes to plant salt stress tolerance through enhancing antioxidant enzymes and decreasing ROS generation.

Overexpression of a S-Adenosylmethionine Decarboxylase from Sugar Beet M14 Increased Araidopsis Salt Tolerance

Polyamines play an important role in plant growth and development, and response to abiotic stresses. Previously, differentially expressed proteins in sugar beet M14 (BvM14) under salt stress were identified by iTRAQ-based quantitative proteomics. One of the proteins was an S-adenosylmethionine decarboxylase (SAMDC), a key rate-limiting enzyme involved in the biosynthesis of polyamines. In this study, the BvM14-SAMDC gene was cloned from the sugar beet M14. The full-length BvM14-SAMDC was 1960 bp, and its ORF contained 1119 bp encoding the SAMDC of 372 amino acids. In addition, we expressed the coding sequence of BvM14-SAMDC in Escherichia coli and purified the ~40 kD BvM14-SAMDC with high enzymatic activity. Quantitative real-time PCR analysis revealed that the BvM14-SAMDC was up-regulated in the BvM14 roots and leaves under salt stress. To investigate the functions of the BvM14-SAMDC, it was constitutively expressed in Arabidopsis thaliana. The transgenic plants exhibited greater salt stress tolerance, as evidenced by longer root length and higher fresh weight and chlorophyll content than wild type (WT) under salt treatment. The levels of spermidine (Spd) and spermin (Spm) concentrations were increased in the transgenic plants as compared with the WT. Furthermore, the overexpression plants showed higher activities of antioxidant enzymes and decreased cell membrane damage. Compared with WT, they also had low expression levels of RbohD and RbohF, which are involved in reactive oxygen species (ROS) production. Together, these results suggest that the BvM14-SAMDC mediated biosynthesis of Spm and Spd contributes to plant salt stress tolerance through enhancing antioxidant enzymes and decreasing ROS generation.

Insect egg deposition renders plant defence against hatching larvae more effective in a salicylic acid-dependent manner

Plants can improve their antiherbivore defence by taking insect egg deposition as cue of impending feeding damage. Previous studies showed that Pieris brassicae larvae feeding upon egg-deposited Brassicaceae perform worse and gain less weight than larvae on egg-free plants. We investigated how P. brassicae oviposition on Arabidopsis thaliana affects the plant's molecular and chemical responses to larvae. A transcriptome comparison of feeding-damaged leaves without and with prior oviposition revealed about 200 differently expressed genes, including enhanced expression of PR5, which is involved in salicylic acid (SA)-signalling. SA levels were induced by larval feeding to a slightly greater extent in egg-deposited than egg-free plants. The adverse effect of egg-deposited wild-type (WT) plants on larval weight was absent in an egg-deposited PR5-deficient mutant or other mutants impaired in SA-mediated signalling, that is, sid2/ics1, ald1, and pad4. In contrast, the adverse effect of egg-deposited WT plants on larvae was retained in egg-deposited npr1 and wrky70 mutants impaired further downstream in SA-signalling. Oviposition induced accumulation of flavonols in WT plants with and without feeding damage, but not in the PR5-deficient mutant. We demonstrated that egg-mediated improvement of A. thaliana's antiherbivore defence involves SA-signalling in an NPR1-independent manner and is associated with accumulation of flavonols.

Spermine Differentially Refines Plant Defense Responses Against Biotic and Abiotic Stresses

Roles of the major polyamines (mPA), putrescine, spermidine, and spermine (Spm), in various developmental and physiological processes in plants have been well documented. Recently, there has been increasing focus on the link between mPA metabolism and defense response during plant-stress interactions. Empirical evidence is available for a unique role of Spm, distinct from the other mPA, in eliciting an effective defense response to (a)biotic stresses. Our understanding of the precise molecular mechanism(s) by which Spm modulates these defense mechanisms is limited. Further analysis of recent studies indicates that plant Spm functions differently during biotic and abiotic interactions in the regulation of oxidative homeostasis and phytohormone signaling. Here, we summarize and integrate current knowledge about Spm-mediated modulation of plant defense responses to (a)biotic stresses, highlighting the importance of Spm as a potent plant defense activator with broad-spectrum protective effects. A model is proposed to explain how Spm refines defense mechanisms to tailor an optimal resistance response.

The Polyamine Putrescine Contributes to H2O2 and RbohD/F-Dependent Positive Feedback Loop in Arabidopsis PAMP-Triggered Immunity

Polyamines are involved in defense against pathogenic microorganisms in plants. However, the role of the polyamine putrescine (Put) during plant defense has remained elusive. In this work, we studied the implication of polyamines during pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI) in the model species Arabidopsis thaliana. Our data indicate that polyamines, particularly Put, accumulate in response to non-pathogenic Pseudomonas syringae pv. tomato DC3000 hrcC and in response to the purified PAMP flagellin22. Exogenously supplied Put to Arabidopsis seedlings induces defense responses compatible with PTI activation, such as callose deposition and transcriptional up-regulation of several PTI marker genes. Consistent with this, we show that Put primes for resistance against pathogenic bacteria. Through chemical and genetic approaches, we find that PTI-related transcriptional responses induced by Put are hydrogen peroxide and NADPH oxidase (RBOHD and RBOHF) dependent, thus suggesting that apoplastic ROS mediates Put signaling. Overall, our data indicate that Put amplifies PTI responses through ROS production, leading to enhanced disease resistance against bacterial pathogens.

Polyamine Metabolism Responses to Biotic and Abiotic Stress

Plants have developed different strategies to cope with the environmental stresses they face during their life cycle. The responses triggered under these conditions are usually characterized by significant modifications in the metabolism of polyamines such as putrescine, spermidine, and spermine. Several works have demonstrated that a fine-tuned regulation of the enzymes involved in the biosynthesis and catabolism of polyamines leads to the increment in the concentration of these compounds. Polyamines exert different effects that could help plants to deal with stressful conditions. For instance, they interact with negatively charged macromolecules and regulate their functions, they may act as compatible osmolytes, or present antimicrobial activity against plant pathogens. In addition, they have also been proven to act as regulators of gene expression during the elicitation of stress responses. In this chapter, we reviewed the information available till date in relation to the roles played by polyamines in the responses of plants during biotic and abiotic stress.

Partial alleviation of oxidative stress induced by gamma irradiation in Vigna radiata by polyamine treatment

PURPOSE

Environmental changes generate free radicals and reactive oxygen species (ROS) resulting in abiotic stress in plants. This causes alterations in germination, morphology, growth and development ultimately leading to yield loss. Gamma irradiation was used to experimentally induce oxidative damage in an important pulse crop Vigna radiata (L.) Wilczek or mung bean. Our research was aimed towards augmentation of oxidative stress tolerance through treatment with a group of aliphatic amines known as polyamines.

MATERIALS AND METHODS

We used sub-lethal doses of gamma irradiation to generate oxidative damage which was evaluated using Nitro blue tetrazolium (NBT) staining, total antioxidant activity, 1, 1-Diphenyl-2-picryl hydrazyl (DPPH) radical scavenging assay, proline content and lipid peroxidation. Changes in internal free polyamines and messenger ribonucleic acid (mRNA) expression of key rate-limiting S-adenosylmethionine decarboxylase (SAMDC) enzyme in polyamine biosynthetic pathway was studied using real-time polymerase chain reaction (PCR).

RESULTS

We observed increased oxidative damage with higher irradiation dose which was partially alleviated by putrescine treatment. Internal levels of putrescine and spermidine increased with 1 mM (50 and 100 Gy) and 2 mM putrescine treatment. Expression of SAMDC also increased with putrescine treatment.

CONCLUSION

This study shows that treatment with putrescine can partially alleviate oxidative damage caused by gamma rays.

Molecular cloning and characterization of S-adenosylmethionine decarboxylase gene in rubber tree (Hevea brasiliensis)

S-Adenosylmethionine decarboxylase (SAMDC) is a key rate-limiting enzyme involved in polyamines biosynthesis, and it plays important roles in plant growth, development and stresses response. However, no SAMDC gene was reported in rubber tree. Here we report characteristics of an SAMDC gene (HbSAMDC1) in rubber tree. HbSAMDC1 contains a 1080 bp open reading frame (ORF) encoding 359 amino acids. Quantitative real-time PCR analyses revealed that HbSAMDC1 exhibited distinct expression patterns in different tissues and was regulated by various stresses, including drought, cold, salt, wounding, and H₂O₂ treatments. HbSAMDC1 5' untranslated region (UTR) contains a highly conserved overlapping tiny and small upstream ORFs (uORFs), encoding 2 and 52 amino acid residues, respectively. No introns were located in the main ORF of HbSAMDC1, whereas two introns were found in the 5' UTR. In transgenic tobaccos, the highly conserved small uORF of HbSAMDC1 is found to be responsible for translational repression of downstream β-glucuronidase reporter. To our knowledge, this is the first report on molecular cloning, expression profiles, and 5' UTR characteristics of HbSAMDC1. These results lay solid foundation for further elucidating HbSAMDC1 function in rubber tree.

QTL mapping and candidate genes for resistance to Fusarium ear rot and fumonisin contamination in maize

BACKGROUND

Fusarium verticillioides is a common maize pathogen causing ear rot (FER) and contamination of the grains with the fumonisin B1 (FB1) mycotoxin. Resistance to FER and FB1 contamination are quantitative traits, affected by environmental conditions, and completely resistant maize genotypes to the pathogen are so far unknown. In order to uncover genomic regions associated to reduced FER and FB1 contamination and identify molecular markers for assisted selection, an F2:3 population of 188 progenies was developed crossing CO441 (resistant) and CO354 (susceptible) genotypes. FER severity and FB1 contamination content were evaluated over 2 years and sowing dates (early and late) in ears artificially inoculated with F. verticillioides by the use of either side-needle or toothpick inoculation techniques.

RESULTS

Weather conditions significantly changed in the two phenotyping seasons and FER and FB1 content distribution significantly differed in the F3 progenies according to the year and the sowing time. Significant positive correlations (P < 0.01) were detected between FER and FB1 contamination, ranging from 0.72 to 0.81. A low positive correlation was determined between FB1 contamination and silking time (DTS). A genetic map was generated for the cross, based on 41 microsatellite markers and 342 single nucleotide polymorphisms (SNPs) derived from Genotyping-by-Sequencing (GBS). QTL analyses revealed 15 QTLs for FER, 17 QTLs for FB1 contamination and nine QTLs for DTS. Eight QTLs located on linkage group (LG) 1, 2, 3, 6, 7 and 9 were in common between FER and FB1, making possible the selection of genotypes with both low disease severity and low fumonisin contamination. Moreover, five QTLs on LGs 1, 2, 4, 5 and 9 located close to previously reported QTLs for resistance to other mycotoxigenic fungi. Finally, 24 candidate genes for resistance to F. verticillioides are proposed combining previous transcriptomic data with QTL mapping.

CONCLUSIONS

This study identified a set of QTLs and candidate genes that could accelerate breeding for resistance of maize lines showing reduced disease severity and low mycotoxin contamination determined by F. verticillioides.

Identification of MsHsp20 Gene Family in Malus sieversii and Functional Characterization of MsHsp16.9 in Heat Tolerance

Heat shock proteins (Hsps) are common molecular chaperones present in all plants that accumulate in response to abiotic stress. Small heat shock proteins (sHsps) play important roles in alleviating diverse abiotic stresses, especially heat stress. However, very little is known about the MsHsp20 gene family in the wild apple Malus sieversii, a precious germplasm resource with excellent resistance characteristics. In this study, 12 putative M. sieversii Hsp20 genes were identified from RNA-Seq data and analyzed in terms of gene structure and phylogenetic relationships. A new Hsp20 gene, MsHsp16.9, was cloned and its function studied in response to stress. MsHsp16.9 expression was strongly induced by heat, and transgenic Arabidopsis plants overexpressing MsHsp16.9 displayed improved heat resistance, enhanced antioxidant enzyme activity, and decreased peroxide content. Overexpression of MsHsp16.9 did not alter the growth or development under normal conditions, or the hypersensitivity to exogenous ABA. Gene expression analysis indicated that MsHsp16.9 mainly modulates the expression of proteins involved in antioxidant enzyme synthesis, as well as ABA-independent stress signaling in 35S:MsHsp16.9-L11. However, MsHsp16.9 could activate ABA-dependent signaling pathways in all transgenic plants. Additionally, MsHsp16.9 may function alongside AtHsp70 to maintain protein homeostasis and protect against cell damage. Our results suggest that MsHsp16.9 is a protein chaperone that positively regulates antioxidant enzyme activity and ABA-dependent and independent signaling pathway to attenuate plant responses to severe stress. Transgenic plants exhibited luxuriant growth in high temperature environments.

Arabidopsis NATA1 Acetylates Putrescine and Decreases Defense-Related Hydrogen Peroxide Accumulation

Biosynthesis of the polyamines putrescine, spermidine, and spermine is induced in response to pathogen infection of plants. Putrescine, which is produced from Arg, serves as a metabolic precursor for longer polyamines, including spermidine and spermine. Polyamine acetylation, which has important regulatory functions in mammalian cells, has been observed in several plant species. Here we show that Arabidopsis (Arabidopsis thaliana) N-ACETYLTRANSFERASE ACTIVITY1 (NATA1) catalyzes acetylation of putrescine to N-acetylputrescine and thereby competes with spermidine synthase for a common substrate. NATA1 expression is strongly induced by the plant defense signaling molecule jasmonic acid and coronatine, an effector molecule produced by DC3000, a Pseudomonas syringae strain that initiates a virulent infection in Arabidopsis ecotype Columbia-0. DC3000 growth is reduced in nata1 mutant Arabidopsis, suggesting a role for NATA1-mediated putrescine acetylation in suppressing antimicrobial defenses. During infection by P. syringae and other plant pathogens, polyamine oxidases use spermidine and spermine as substrates for the production of defense-related H2O2 Compared to wild-type Columbia-0 Arabidopsis, the response of nata1mutants to P. syringae infection includes reduced accumulation of acetylputrescine, greater abundance of nonacetylated polyamines, elevated H2O2 production by polyamine oxidases, and higher expression of genes related to pathogen defense. Together, these results are consistent with a model whereby P. syringae growth is improved in a targeted manner through coronatine-induced putrescine acetylation by NATA1.

Cotton S-adenosylmethionine decarboxylase-mediated spermine biosynthesis is required for salicylic acid- and leucine-correlated signaling in the defense response to Verticillium dahliae

Cotton S-adenosylmethionine decarboxylase-, rather than spermine synthase-, mediated spermine biosynthesis is required for salicylic acid- and leucine-correlated signaling in the defense response to Verticillium dahliae. Spermine (Spm) signaling is correlated with plant resistance to the fungal pathogen Verticillium dahliae. We identified genes for key rate-limiting enzymes in the biosynthesis of Spm, namely S-adenosylmethionine decarboxylase (GhSAMDC) and Spm synthase (GhSPMS). These were found by screening suppression subtractive hybridization and cDNA libraries of cotton (Gossypium) species tolerant to Verticillium wilt. Both were induced early and strongly by inoculation with V. dahliae and application of plant hormones. Silencing of GhSPMS or GhSAMDC in cotton leaves led to a significant accumulation of upstream substrates and, ultimately, enhanced plant susceptibility to Verticillium infection. Exogenous supplementation of Spm to the silenced cotton plants improved resistance. When compared with the wild type (WT), constitutive expression of GhSAMDC in Arabidopsis thaliana was associated with greater Verticillium wilt resistance and higher accumulations of Spm, salicylic acid, and leucine during the infection period. By contrast, transgenic Arabidopsis plants that over-expressed GhSPMS were unexpectedly more susceptible than the WT to V. dahliae and they also had impaired levels of putrescine (Put) and salicylic acid (SA). The susceptibility exhibited in GhSPMS-overexpressing Arabidopsis plants was partially reversed by the exogenous supply of Put or SA. In addition, the responsiveness of those two transgenic Arabidopsis lines to V. dahliae was associated with an alteration in transcripts of genes involved in plant resistance to epidermal penetrations and amino acid signaling. Together, these results suggest that GhSAMDC-, rather than GhSPMS-, mediated spermine biosynthesis contributes to plant resistance against V. dahliae through SA- and leucine-correlated signaling.

Molecular Cloning and Characterization of Spermine Synthesis Gene Associated with Cold Tolerance in Tea Plant (Camellia sinensis)

Spermine synthase (SPMS, EC 2.5.1.22), enzyme of spermine (Spm) biosynthesis, has been shown to be related to stress response. In this study, attempts were made to clone and characterize a gene encoding SPMS from tea plant (Camellia sinensis). The effect of exogenous application of Spm in C. sinensis subjected to low-temperature stress was also investigated. A full-length SPMS complementary DNA (cDNA) (CsSPMS) with an open reading frame of 1113 bp was cloned using reverse transcription-PCR and rapid amplification of cDNA ends (RACE) techniques from cultivar "Yingshuang". The CsSPMS gene, which encoded a 371 amino acid polypeptide, in four cultivars is highly homologous. Quantitative real-time PCR indicated that the CsSPMS gene shows tissue-specific expression, mainly in the leaf and root of tea plant. The expression analysis demonstrated that the CsSPMS gene is quickly induced by cold stress and had similar trends in four cultivars. Spm-supplemented "Baicha" cultivar contains higher endogenous polyamines compared to the control, coupling with higher expression levels of ADC and SPMS. In addition, activities of peroxidase (POD), superoxide dismutase (SOD), catalase (CAT), as well as free proline content in the Spm-supplemented samples were higher than the control during the experiment course or at a given time point, indicating that Spm exerted a positive effect on antioxidant systems. Moreover, Agrobacterium-mediated expression of CsSPMS in tobacco leaves showed relatively higher cold tolerance. Taken together, these findings will enhance the understanding of the relationships among CsSPMS gene regulatory, polyamines accumulation, and cold tolerance in tea plant.

Polyamine metabolism in flax in response to treatment with pathogenic and non-pathogenic Fusarium strains

Flax crop yield is limited by various environmental stress factors, but the largest crop losses worldwide are caused by Fusarium infection. Polyamines are one of the many plant metabolites possibly involved in the plant response to infection. However, in flax plants the polyamine composition, genes involved in polyamine synthesis, and in particular their regulation, were previously unknown. The aim of this study was to investigate the polyamine synthesis pathway in flax and its involvement in response to pathogen infection. It is well established that polyamines are essential for the growth and development of both plants and fungi, but their role in pathogen infection still remains unknown. In our study we correlated the expression of genes involved in polyamine metabolism with the polyamine levels in plant tissues and compared the results for flax seedlings treated with two pathogenic and one non-pathogenic strains of Fusarium. We observed an increase in the expression of genes participating in polyamine synthesis after fungal infection, and it was reflected in an increase of polyamine content in the plant tissues. The highest level of mRNA was characteristic for ornithine decarboxylase during infection with all tested, pathogenic and non-pathogenic, Fusarium strains and the arginine decarboxylase gene during infection with the pathogenic strain of Fusarium culmorum. The main polyamine identified in the flax seedlings was putrescine, and its level changed the most during infection. Moreover, the considerable increase in the contents of cell wall-bound polyamines compared to the levels of free and conjugated polyamines may indicate that their main role during pathogen infection lies in strengthening of the cell wall. In vitro experiments showed that the polyamines inhibit Fusarium growth, which suggests that they play an important role in plant defense mechanisms. Furthermore, changes in metabolism and content of polyamines indicate different defense mechanisms activated in flax in response to infection by pathogenic and non-pathogenic Fusarium strains.