Tobacco ZFT1, a transcriptional repressor with a Cys2/His2 type zinc finger motif that functions in spermine-signaling pathway

Genome-wide identification of the Q-type C2H2 zinc finger protein gene family and expression analysis under abiotic stress in lotus (Nelumbo nucifera G.)

BACKGROUND

Lotus (Nelumbo nucifera G.) is an important aquatic plant with high ornamental, economic, cultural and ecological values, but abiotic stresses seriously affect its growth and distribution. Q-type C2H2 zinc finger proteins (ZFPs) play an important role in plant growth development and environmental stress responses. Although the Q-type C2H2 gene family has been identified in some plants, limited reports has been carried out it in lotus.

RESULTS

In this study, we identified 45 Q-type NnZFP members in lotus. Based on the phylogenetic tree, these Q-type NnZFP gene family members were divided into 4 groups, including C1-1i, C1-2i, C1-3i and C1-4i. Promoter cis-acting elements analysis indicated that most Q-type NnZFP gene family members in lotus were associated with response to abiotic stresses. Through collinearity analyses, no tandem duplication gene pairs and 14 segmental duplication gene pairs were identified, which showed that duplication events might play a key role in the expansion of the Q-type NnZFP gene family. The synteny results suggested that 54 and 28 Q-type NnZFP genes were orthologous to Arabidopsis and rice, respectively. The expression patterns of these Q-type NnZFP genes revealed that 30 Q-type NnZFP genes were expressed in at least one lotus tissue. Nn5g30550 showed relatively higher expression levels in all tested tissues. 12 genes were randomly selected with at least one gene from each phylogenetic clade, and the expression of these selected genes were confirmed by qRT-PCR (quantitative real-time polymerase chain reaction). The results indicated that Q-type NnZFP genes were extensively involved in cadmium, drought, salt and cold stresses responses. Among them, 11 genes responded to at least three different stress treatments, especially Nn2g12894, which induced by all four treatments.

CONCLUSIONS

These results could increase our understanding of the characterization of the Q-type NnZFP gene family and provide relevant information for further functional analysis of Q-type NnZFP genes in plant development, and abiotic stress tolerance in lotus.

A diverse panel of 755 bread wheat accessions harbors untapped genetic diversity in landraces and reveals novel genetic regions conferring powdery mildew resistance

KEY MESSAGE

A bread wheat panel reveals rich genetic diversity in Turkish, Pakistani and Iranian landraces and novel resistance loci to diverse powdery mildew isolates via subsetting approaches in association studies. Wheat breeding for disease resistance relies on the availability and use of diverse genetic resources. More than 800,000 wheat accessions are globally conserved in gene banks, but they are mostly uncharacterized for the presence of resistance genes and their potential for agriculture. Based on the selective reduction of previously assembled collections for allele mining for disease resistance, we assembled a trait-customized panel of 755 geographically diverse bread wheat accessions with a focus on landraces, called the LandracePLUS panel. Population structure analysis of this panel based on the TaBW35K SNP array revealed an increased genetic diversity compared to 632 landraces genotyped in an earlier study and 17 high-quality sequenced wheat accessions. The additional genetic diversity found here mostly originated from Turkish, Iranian and Pakistani landraces. We characterized the LandracePLUS panel for resistance to ten diverse isolates of the fungal pathogen powdery mildew. Performing genome-wide association studies and dividing the panel further by a targeted subsetting approach for accessions of distinct geographical origin, we detected several known and already cloned genes, including the Pm2a gene. In addition, we identified 22 putatively novel powdery mildew resistance loci that represent useful sources for resistance breeding and for research on the mildew-wheat pathosystem. Our study shows the value of assembling trait-customized collections and utilizing a diverse range of pathogen races to detect novel loci. It further highlights the importance of integrating landraces of different geographical origins into future diversity studies.

Comparative RNA-seq analysis of resistant and susceptible banana genotypes reveals molecular mechanisms in response to banana bunchy top virus (BBTV) infection

Bananas hold significant economic importance as an agricultural commodity, serving as a primary livelihood source, a favorite fruit, and a staple crop in various regions across the world. However, Banana bunchy top disease (BBTD), which is caused by banana bunchy top virus (BBTV), poses a considerable threat to banana cultivation. To understand the resistance mechanism and the interplay of host suitability factors in the presence of BBTV, we conducted RNA-seq-based comparative transcriptomics analysis on mock-inoculated and BBTV-inoculated samples from resistant (wild Musa balbisiana) and susceptible (Musa acuminata 'Lakatan') genotypes. We observed common patterns of expression for 62 differentially expressed genes (DEGs) in both genotypes, which represent the typical defense response of bananas to BBTV. Furthermore, we identified 99 DEGs exclusive to the 'Lakatan' banana cultivar, offering insights into the host factors and susceptibility mechanisms that facilitate successful BBTV infection. In parallel, we identified 151 DEGs unique to the wild M. balbisiana, shedding light on the multifaceted mechanisms of BBTV resistance, involving processes such as secondary metabolite biosynthesis, cell wall modification, and pathogen perception. Notably, our validation efforts via RT-qPCR confirmed the up-regulation of the glucuronoxylan 4-O-methyltransferase gene (14.28 fold-change increase), implicated in xylan modification and degradation. Furthermore, our experiments highlighted the potential recruitment of host's substrate adaptor ADO (30.31 fold-change increase) by BBTV, which may play a role in enhancing banana susceptibility to the viral pathogen. The DEGs identified in this work can be used as basis in designing associated gene markers for the precise integration of resistance genes in marker-assisted breeding programs. Furthermore, the findings can be applied to develop genome-edited banana cultivars targeting the resistance and susceptibility genes, thus developing novel cultivars that are resilient to important diseases.

Genome-Wide Identification and Analysis of the Genes Encoding Q-Type C2H2 Zinc Finger Proteins in Grapevine

Q-type C2H2 zinc finger proteins (ZFPs), the largest family of transcription factors, have been extensively studied in plant genomes. However, the genes encoding this transcription factor family have not been explored in grapevine genomes. Therefore, in this study, we conducted a genome-wide identification of ZFP genes in three species of grapevine, namely Vitis vinifera, Vitis riparia, and Vitis amurensis, based on the sequence databases and phylogenetic and their conserved domains. We identified 52, 54, and 55 members of Q-type C2H2 ZFPs in V. vinifera, V. riparia, and V. amurensis, respectively. The physical and chemical properties of VvZFPs, VrZFPs, and VaZFPs were examined. The results showed that these proteins exhibited differences in the physical and chemical properties and that they all were hydrophobic proteins; the instability index showed that the four proteins were stable. The subcellular location of the ZFPs in the grapevine was predicted mainly in the nucleus. The phylogenetic tree analysis of the amino acid sequences of VvZFP, VaZFP, VrZFP, and AtZFP proteins showed that they were closely related and were divided into six subgroups. Chromosome mapping analysis showed that VvZFPs, VrZFPs, and VaZFPs were unevenly distributed on different chromosomes. The clustered gene analysis showed that the motif distribution was similar and the sequence of genes was highly conserved. Exon and intron structure analysis showed that 118 genes of ZFPs were intron deletion types, and the remaining genes had variable numbers of introns, ranging from 2 to 15. Cis-element analysis showed that the promoter of VvZFPs contained multiple cis-elements related to plant hormone response, stress resistance, and growth, among which the stress resistance elements were the predominant elements. Finally, the expression of VvZFP genes was determined using real-time quantitative PCR, which confirmed that the identified genes were involved in response to methyl jasmonate (MeJA), abscisic acid (ABA), salicylic acid (SA), and low-temperature (4 °C) stress. VvZFP10-GFP and VvZFP46-GFP fusion proteins were localized in the nucleus of tobacco cells, and VvZFP10 is the most responsive gene among all VvZFPs with the highest relative expression level to MeJA, ABA, SA and low-temperature (4 °C) stress. The present study provides a theoretical basis for exploring the mechanism of response to exogenous hormones and low-temperature tolerance in grapes and its molecular breeding in the future.

Genome-Wide Identification of the Q-type C2H2 Transcription Factor Family in Alfalfa (Medicago sativa) and Expression Analysis under Different Abiotic Stresses

Q-type C2H2 zinc-finger protein (C2H2-ZFP) transcription factors are associated with many plant growth development and environmental stress responses. To date, there have been few analyses of the Q-type C2H2-ZFP gene family in alfalfa (Medicago sativa subsp. sativa). In this study, we identified 58 Q-type C2H2-ZFPs across the entire alfalfa genome, and the gene structure, motif composition, chromosomal mapping, and cis-regulatory elements were explored, as well as the expression profiles of specific tissues and the response under different abiotic stresses. According to their phylogenetic features, these 58 MsZFPs were divided into 12 subgroups. Synteny analysis showed that duplication events play a vital role in the expansion of the MsZFP gene family. The collinearity results showed that a total of 26 and 42 of the 58 MsZFP genes were homologous with Arabidopsis and M. truncatula, respectively. The expression profiles showed that C2H2-ZFP genes played various roles in different tissues and abiotic stresses. The results of subsequent quantitative real-time polymerase chain reaction (qRT-PCR) showed that the nine selected MsZFP genes were rapidly induced under different abiotic stresses, indicating that C2H2-ZFP genes are closely related to abiotic stress. This study provides results on MsZFP genes, their response to various abiotic stresses, and new information on the C2H2 family in alfalfa.

A single amino acid mutant in the EAR motif of IbMYB44.2 reduced the inhibition of anthocyanin accumulation in the purple-fleshed sweetpotato

Purple-fleshed sweetpotato (Ipomoea batatas（L.）Lam.) is rich in anthocyanins. R2R3-type MYB transcription factors（TFs）with EAR motifs inhibiting anthocyanin biosynthesis have been reported, and there is still a lack of information on how mutations in the EAR motifs of MYBs affect anthocyanin accumulation. In this study, we obtained three IbMYB44 TFs by bioinformatics. Among these TFs, IbMYB44.1, IbMYB44.3 with a complete EAR motif and IbMYB44.2 with a single amino acid mutant in the EAR motif caused an amino acid substitution from leucine to valine. RT-qPCR analysis showed that IbMYB44s was expressed at lower levels in the purple-fleshed sweetpotato than in nonpurple-fleshed sweetpotato (P < 0.01). Transient expression assays showed that the inhibitory effect of IbMYB44.1/3 was stronger than IbMYB44.2 in tobacco leaves and red-skinned pears. RT-qPCR analysis further proved that IbMYB44.1/3 significantly inhibited the expression of anthocyanin biosynthesis-related genes compared with IbMYB44.2 in tobacco leaves and red-skinned pears. A dual luciferase reporter assay showed that IbMYB44s cannot directly activate the IbANS promoter, and the result was also verified by yeast one-hybrid (Y1H) experiments. Moreover, we identified the interaction of IbMYB340 with IbMYB44.1, IbMYB44.2 and IbMYB44.3 via yeast two-hybrid (Y2H) assays. Thus, IbMYB44.1/3 could interact with IbMYB340 to negatively regulate anthocyanin biosynthesis. This study enriched the regulatory network of anthocyanins and also provided a theoretical basis for a single amino acid mutant from leucine to valine in the EAR motif of IbMYB44.2 affecting anthocyanin biosynthesis in the purple-fleshed sweetpotato.

Genome-Wide Analyses of the Genetic Screening of C2H2-Type Zinc Finger Transcription Factors and Abiotic and Biotic Stress Responses in Tomato (Solanum lycopersicum) Based on RNA-Seq Data

C₂H₂-type zinc finger proteins are classic and extensively studied members of the zinc finger family. C₂H₂-type zinc finger proteins participate in plant growth, development and stress responses. In this study, 99 C₂H₂-type zinc finger protein genes were identified and classified into four groups, and many functionally related cis-elements were identified. Differential C₂H₂-ZFP gene expression and specific responses were analyzed under drought, cold, salt, and pathogen stresses based on RNA-Seq data. Thirty-two C₂H₂ genes were identified in response to multiple stresses. Seven, 3, 5, and 8 genes were specifically expressed under drought, cold, salt, and pathogenic stresses, respectively. Five glycometabolism and sphingolipid-related pathways and the endocytosis pathway were enriched by KEGG analysis. The results of this study represent a foundation for further study of the function of C₂H₂-type zinc finger proteins and will provide us with genetic resources for stress tolerance breeding.

Genome-wide identification and analysis of the Q-type C2H2 gene family in potato (Solanum tuberosum L.)

Plant Q-type C2H2 zinc finger proteins play an important role in plant tolerance to abiotic stresses. Although the Q-type C2H2 gene family has been identified in many plants, little is known about it in potato (Solanum tuberosum). In the present study, a total of 79 Q-type C2H2 proteins in potato (StZFPs) were identified and their distribution on chromosomes, gene structure, and conserved motifs was assessed. According to their protein structural and phylogenetic features, these 79 StZFPs were classified into 12 distinct subclasses. Collinearity analysis showed that tandem and segmental duplication events played a crucial role in expansion of the StZFP gene family. Synteny analysis indicated that 11 and 21 StZFP genes were orthologous to Arabidopsis and wheat (Triticum aestivum), respectively. RNA-seq data were used to analyze the tissue-specific expression and abiotic stress responses of the StZFP genes. Furthermore, we analyzed the expression of StZFP genes in drought-sensitive and drought-tolerant potato cultivars under drought stress. Subsequently, we used qPCR (Quantitative real-time-PCR) to calculate the relative expression of candidate genes in potato plantlets treated with NaCl (100 mM) and PEG 6000 (10% w/v) for 24 h. Such candidate genes could provide valuable information for abiotic stress resistance research in potato.

Molecular cloning and characterization of PtrZPT2-1, a ZPT2 family gene encoding a Cys2/His2-type zinc finger protein from trifoliate orange (Poncirus trifoliata (L.) Raf.) that enhances plant tolerance to multiple abiotic stresses

In plants, most Cys2/His2 (C2H2) zinc finger proteins with two zinc finger domains (ZPT2) are involved in abiotic stress responses. In this study, a ZPT2 family gene PtrZPT2-1 was cloned from trifoliate orange (Poncirus trifoliata (L.) Raf.). PtrZPT2-1 is composed of 245 amino acids, has a putative molecular weight of 25.99kDa and an isoelectric point of 8.41. PtrZPT2-1 contained two C2H2 zinc finger domains, one nuclear localization signal (B-box), one transcription repression domain (DLN-box), and one protein-protein interaction domain (L-box). PtrZPT2-1 was localized to the nucleus. The PtrZPT2-1 expression was strongly induced by cold, drought, salt and ABA stresses. Overexpression of PtrZPT2-1 increased the survival rates, and the ABA, soluble sugar and proline levels but decreased the ion leakage, the malondialdehyde (MDA) content and reduced the H2O2 accumulation in the transgenic tobacco after cold, drought or salt treatments. Furthermore, the expression levels of 15 abiotic stress-related genes were significantly increased in the transgenic tobacco overexpressing PtrZPT2-1 after cold, drought or salt stress treatments. Our results indicated that overexpression of PtrZPT2-1 in the transgenic tobacco could improve the cold, drought and salt resistance of the plants by increasing the levels of osmotic regulatory solutes and decreasing the accumulation of H2O2.

Molecular and physiological stages of priming: how plants prepare for environmental challenges

Being sessile organisms, plants must respond to various challenges in the environment. The priming process consists of three clear stages. The first stage includes all the cellular changes in the absence of the challenge so-called pre-challenge priming stage. These changes are expected to be rather subtle, affecting the preparation of the plant to properly manage subsequent responses to pathogens with no major fitness costs. Most of the research that has been conducted at this stage has been dedicated to the study of changes in gene expression and protein phosphorylation. However, the metabolic changes that occur during the pre-challenge priming stage are poorly understood. The second stage affects the early to late stages of the defence response, which occurs after the interaction with a pathogen has been established. Most studies involving priming are dedicated to the molecular events that take place during this stage. Most studies have shown that defence priming is strongly hormonally regulated; however, there is also evidence of the involvement of phenolic derivative compounds and many other secondary metabolites, leading to stronger and faster plant responses. The third priming phase ranges from long lasting defence priming to trans-generational acquired resistance. Long-term metabolic transitions, that occur in the offspring of primed plants, remain to be elucidated. Here we review existing information in the literature that relates to the metabolic changes that occur during all three defence priming stages and highlight the metabolic transitions that are associated with the stimulation of priming and the characteristics of the pathogens whenever possible.

Overexpression of a novel chrysanthemum SUPERMAN-like gene in tobacco affects lateral bud outgrowth and flower organ development

Previous studies have shown that the SUP genes play important roles in flower development and plant growth and morphogenesis. In this study, we isolated and characterized a SUPERMAN-like gene DgSZFP from chrysanthemum. DgSZFP contains one conserved Cys2/His2-type zinc finger motifs in the N-terminal region and an EAR-box in C-terminus. Its expression was significantly higher in nodes, flower buds, disc stamens, and petals than in the other tissues. Overexpression of DgSZFP in tobacco resulted in enhanced branching, reduced plant height, increased the width of petal tubes, produced the staminoid petals and petaloid stamens in flowers, and enhanced the seed weight and size. In addition, DgSZFP-overexpression tobacco plants accumulated high concentrations of cytokinin and chlorophyll. These results suggest that DgSZFP may be the candidate gene for regulating branching and floral organ development in chrysanthemum.

Thermospermine catabolism increases Arabidopsis thaliana resistance to Pseudomonas viridiflava

This work investigated the roles of the tetraamine thermospermine (TSpm) by analysing its contribution to Arabidopsis basal defence against the biotrophic bacterium Pseudomonas viridiflava. The participation of polyamine oxidases (PAOs) in TSpm homeostasis and TSpm-mediated defence was also investigated. Exogenous supply of TSpm, as well as ectopic expression of the TSpm biosynthetic gene ACL5, increased Arabidopsis Col-0 resistance to P. viridiflava, while null acl5 mutants were less resistant than Col-0 plants. The above-mentioned increase in resistance was blocked by the PAO inhibitor SL-11061, thus demonstrating the participation of TSpm oxidation. Analysis of PAO genes expression in transgenic 35S::ACL5 and Col-0 plants supplied with TSpm suggests that PAO 1, 3, and 5 are the main PAOs involved in TSpm catabolism. In summary, TSpm exhibited the potential to perform defensive functions previously reported for its structural isomer Spm, and the relevance of these findings is discussed in the context of ACL5 expression and TSpm concentration in planta. Moreover, this work demonstrates that manipulation of TSpm metabolism modifies plant resistance to pathogens.

DNA binding specificity of ATAF2, a NAC domain transcription factor targeted for degradation by Tobacco mosaic virus

BACKGROUND

Control of the host transcriptome represents a key battleground in the interaction of plants and pathogens. Specifically, plants have evolved complex defense systems that induce profound transcriptional changes in response to pathogen attack while pathogens have evolved mechanisms to subvert or disable these defenses. Several NAC transcription factors such as ATAF2 have been linked to plant defense responses, including those targeting viruses. The replication protein of Tobacco mosaic virus (TMV) has been shown to interact with and target the degradation of ATAF2. These findings suggest that the transcriptional targets of ATAF2 are involved in defense against TMV.

RESULTS

To detect potential ATAF2 transcriptional targets, a genomic pull-down assay was utilized to identify ATAF2 promoter binding sequences. Subsequent mobility shift and DNA footprinting assays identified a 30-bp ATAF2 binding sequence. An in vivo GUS reporter system confirmed the function of the identified 30-bp binding sequence as an ATAF2 specific transcriptional activator in planta. Gel filtration studies of purified ATAF2 protein and mutagenesis studies of the 30-bp binding sequence indicate ATAF2 functions as a dimer. Computational analysis of interacting promoter sequences identified a corresponding 25-bp A/T-rich consensus sequence with repeating [GC]AAA motifs. Upon ATAF2 induction real-time qRT-PCR studies confirmed the accumulation of select gene transcripts whose promoters contain this consensus sequence.

CONCLUSION

We report the identification of a cis-regulatory binding sequence for ATAF2. Different from other known NAC protein binding sequences, the A/T-rich ATAF2 binding motif represents a novel binding sequence for NAC family proteins. Combined this information represents a unique tool for the identification of ATAF2 target genes.

Exogenous thermospermine has an activity to induce a subset of the defense genes and restrict cucumber mosaic virus multiplication in Arabidopsis thaliana

We previously proposed the defensive role of a signal pathway triggered by the polyamine spermine (Spm) in the reaction against avirulent viral pathogens in Nicotiana tabacum and Arabidopsis thaliana. In this study, we showed that thermospermine (T-Spm), an isomer of Spm, is also active in inducing the expression of the genes involved in the Spm-signal pathway at a similar dose as Spm. Furthermore, we found that T-Spm enhances the expression of a subset of pathogenesis-related genes whose expression is induced during cucumber mosaic virus (CMV)-triggered hypersensitive response. In consistent with the above observation, we further showed that exogenous T-Spm can repress CMV multiplication with same efficiency as Spm.

KEY MESSAGE

Polyamine thermospermine, an isomer of spermine, is able to induce a subset of hypersensitive response-related defense genes and can suppress cucumber mosaic virus multiplication in Arabidopsis thaliana.

Involvement of plant C(2)H(2)-type zinc finger transcription factors in stress responses

Abiotic and biotic stresses frequently impose constraints on plant distribution and affect agricultural productivity. Various aspects of the multiplicity and the complexity of stress responsive gene networks have been previously studied. Many of individual transcription factors in plants and their family classes that regulate the expression of several genes in responses to environmental stresses have been identified. One such class of transcription regulators is the C(2)H(2) class of zinc finger proteins. Numerous members of the C(2)H(2)-type zinc finger family have been shown to play diverse roles in the plant stress response and the hormone signal transduction. Transcription profiling analyses have demonstrated that the transcript level of many C(2)H(2)-type zinc finger proteins is elevated under different abiotic stress conditions such as low temperature, salt, drought, osmotic stress and oxidative stress. Some C(2)H(2)-type proteins are additionally involved in the biotic stress signaling pathway. Moreover, it has been reported that overexpression of some C(2)H(2)-type zinc finger protein genes resulted in both the activation of some stress-related genes and enhanced tolerance to various stresses. Current genetic studies have focused on possible interactions between different zinc finger transcription factors during stresses to regulate transcription. This review highlights the role of the C(2)H(2) class of the zinc finger proteins in regulating abiotic and biotic stress tolerance in the plants.

Polyamines attenuate ethylene-mediated defense responses to abrogate resistance to Botrytis cinerea in tomato

Transgenic tomato (Solanum lycopersicum) lines overexpressing yeast spermidine synthase (ySpdSyn), an enzyme involved in polyamine (PA) biosynthesis, were developed. These transgenic lines accumulate higher levels of spermidine (Spd) than the wild-type plants and were examined for responses to the fungal necrotrophs Botrytis cinerea and Alternaria solani, bacterial pathogen Pseudomonas syringae pv tomato DC3000, and larvae of the chewing insect tobacco hornworm (Manduca sexta). The Spd-accumulating transgenic tomato lines were more susceptible to B. cinerea than the wild-type plants; however, responses to A. solani, P. syringae, or M. sexta were similar to the wild-type plants. Exogenous application of ethylene precursors, S-adenosyl-Met and 1-aminocyclopropane-1-carboxylic acid, or PA biosynthesis inhibitors reversed the response of the transgenic plants to B. cinerea. The increased susceptibility of the ySpdSyn transgenic tomato to B. cinerea was associated with down-regulation of gene transcripts involved in ethylene biosynthesis and signaling. These data suggest that PA-mediated susceptibility to B. cinerea is linked to interference with the functions of ethylene in plant defense.

Polyamines, polyamine oxidases and nitric oxide in development, abiotic and biotic stresses

Nitric oxide (NO), polyamines (PAs), diamine oxidases (DAO) and polyamine oxidases (PAO) play important roles in wide spectrum of physiological processes such as germination, root development, flowering and senescence and in defence responses against abiotic and biotic stress conditions. This functional overlapping suggests interaction of NO and PA in signalling cascades. Exogenous application of PAs putrescine, spermidine and spermine to Arabidopsis seedlings induced NO production as observed by fluorimetry and fluorescence microscopy using the NO-binding fluorophores DAF-2 and DAR-4M. The observed NO release induced by 1 mM spermine treatment in the Arabidopsis seedlings was very rapid without apparent lag phase. These observations pave a new insight into PA-mediated signalling and NO as a potential mediator of PA actions. When comparing the functions of NO and PA in plant development and abiotic and biotic stresses common to both signalling components it can be speculated that NO may be a link between PA-mediated stress responses filing a gap between many known physiological effects of PAs and amelioration of stresses. NO production indicated by PAs could be mediated either by H(2)O(2), one reaction product of oxidation of PAs by DAO and PAO, or by unknown mechanisms involving PAs, DAO and PAO.

Polyamines in aging and disease

Polyamines are polycations that interact with negatively charged molecules such as DNA, RNA and proteins. They play multiple roles in cell growth, survival and proliferation. Changes in polyamine levels have been associated with aging and diseases. Their levels decline continuously with age and polyamine (spermidine or high-polyamine diet) supplementation increases life span in model organisms. Polyamines have also been involved in stress resistance. On the other hand, polyamines are increased in cancer cells and are a target for potential chemotherapeutic agents. In this review, we bring together these various results and draw a picture of the state of our knowledge on the roles of polyamines in aging, stress and diseases.

Polyamines: natural and engineered abiotic and biotic stress tolerance in plants

Polyamines (PAs) are ubiquitous biogenic amines that have been implicated in diverse cellular functions in widely distributed organisms. In plants, mutant and transgenic plants with altered activity pointed to their involvement with different abiotic and biotic stresses. Furthermore, microarray, transcriptomic and proteomic approaches have elucidated key functions of different PAs in signaling networks in plants subjected to abiotic and biotic stresses, however the exact molecular mechanism remains enigmatic. Here, we argue that PAs should not be taken only as a protective molecule but rather like a double-faced molecule that likely serves as a major area for further research efforts. This review summarizes recent advances in plant polyamine research ranging from transgenic and mutant characterization to potential mechanisms of action during environmental stresses and diseases.

Ustilago maydis induced accumulation of putrescine in maize leaves

Polyamines are implicated in the regulation of many processes in the plant cell, including functioning of ion channels, DNA replication, gene transcription, mRNA translation, cell proliferation and programmed cell death. Plant polyamines occur either in free form, covalently bound to proteins, or conjugated to hydroxycinnamic acids forming phenol amides. Ustilago maydis is a dimorphic and biotrophic pathogenic fungus responsible for common smut or “huitlacoche” in maize; and it is considered an excellent model for the study of plant-pathogen interactions. Recently, we reported alterations in polyamine metabolism of maize tumors induced on leaf blades by Ustilago maydis infection. Our data revealed a striking increase in maize polyamine biosynthesis, mainly free and conjugated putrescine in the tumors and in the green plant tissue surrounding the tumor. In this addendum, we describe that changes in polyamine metabolism take place even in earlier stages of maize plant infection with Ustilago maydis .

Cyclic nucleotide gated channels and related signaling components in plant innate immunity

Although plants lack the mobile sentry cells present in animal innate immune systems, plants have developed complex innate immune reactions triggering basal resistance and the hypersensitive response (HR). Cytosolic Ca(2+) elevation is considered to be an important early event in this pathogen response signal transduction cascade. Plasma membrane (PM)-localized cyclic nucleotide gated channels (CNGCs) contribute to the cytosolic Ca(2+) rise upon pathogen perception. Recent work suggests that some PM-localized leucine-rich-repeat receptor-like kinases (LRR-RLKs) may be involved in the perception of pathogen associated molecular pattern molecules and triggering some pathogen responses in plants, some of these LRR-RLKs might have cyclic nucleotide cyclase activity. The recognition of pathogens may be connected to cyclic nucleotide generation and the activation of CNGCs, followed by cytosolic Ca(2+) increase and downstream signaling events (possibly involving nitric oxide, reactive oxygen species (ROS), calmodulin (CaM), CaM-like protein (CML) and protein kinases). Notably, CaM or CML could be the crucial sensor downstream from the early Ca(2+) signal leading to nitric oxide (NO) production during plant innate immune responses.

Spermine signaling plays a significant role in the defense response of Arabidopsis thaliana to cucumber mosaic virus

We have proposed that the polyamine spermine (Spm) functions as a signaling molecule to evoke defense reactions/cell death in avirulent pathogen-attacked tobacco plants. To understand its molecular basis in depth, Spm-responsive genes in Arabidopsis thaliana were identified by SuperSAGE analysis. Close to 90% of the Spm-responsive genes also responded during cucumber mosaic virus (CMV)-elicited hypersensitive response. Spm modulated the expression of genes of redox components, and genes involved in protein folding and secretion, protein degradation and defense. Two other prominent changes, the coordinately enhanced expression of members of the photorespiration pathway and a diversion in electron flow from the primary electron transfer chain of respiration to an alternative oxidase pathway, occurred in response to Spm. Spm activated the expression of 6 transcription factor genes including ZAT7, ZAT12, AtWRKY40 and AtbZIP60, of which the former three genes' products are currently assigned as components of H(2)O(2) signaling pathway, suggesting the involvement of H(2)O(2) in Spm-triggered responses. Since AtbZIP60 plays a proven master role in the unfolded protein response in Arabidopsis thaliana, it may function to control the expression of genes participating in protein folding and secretion, which were mentioned above. Spm induction and CMV-triggered up-regulation of the genes described mainly coincided and their induction was suppressed by inhibitors of Spm oxidation. Furthermore, treatment with those inhibitors prior to CMV inoculation allowed higher viral multiplication in Arabidopsis thaliana plants. These results support the existence of a Spm-signaling pathway in Arabidopsis thaliana and its significant role in defense against CMV.

Plant polyamine catabolism: The state of the art

Polyamines have long been implicated in plant growth and development, as well as adaptation to abiotic and biotic stress. As a general rule of thumb the higher the polyamine titers the better. However, their molecular roles in plant stress responses still remain obscure. It has been postulated that they could act through their catabolism, which generates molecules which may act as secondary messengers signalling networks of numerous developmental and stress adaptation processes. Recently it was shown that plant and mammalian polyamine catabolism share critical features, giving new insight in plant polyamine catabolism. In this review, the advances in genes and proteins of polyamine catabolism in plants is presented and compared to other models.

NtbZIP60, an endoplasmic reticulum-localized transcription factor, plays a role in the defense response against bacterial pathogens in Nicotiana tabacum

A spermine-based signal transduction pathway plays a defensive role against incompatible pathogens. We identified a novel spermine-responsive cDNA from Nicotiana tabacum that encodes a basic region/leucine zipper protein with a putative transmembrane domain. Identity to Arabidopsis thaliana AtbZIP60 was sufficiently high to name the novel cDNA NtbZIP60. Expression analysis revealed that NtbZIP60 is a component of the spermine-signal pathway, and is also involved in the unfolded protein response (UPR), as demonstrated for AtbZIP60. The gene product, NtbZIP60, localizes to the endoplasmic reticulum (ER) in plant cells; once the putative transmembrane domain is eliminated from the intact protein, it targets the nucleus. The putative processed form of NtbZIP60 transactivates target genes through binding to plant-specific UPR cis-elements. Expression of NbbZIP60, an NtbZIP60 ortholog in Nicotiana benthamiana, was significantly up-regulated at 6 h and later time points upon infection with the non-host pathogen Pseudomonas cichorii, while it was unaffected by infection with the compatible pathogen Pseudomonas syringae pv. tabaci. Furthermore, NbbZIP60-silenced N. benthamiana plants allowed higher multiplication of P. cichorii compared to the control plants. Taken together, the results suggest that this ER-localized transcription factor is involved in the spermine-signal transduction pathway and plays an important role in plant innate immunity.

Polyamine metabolism in maize tumors induced by Ustilago maydis

Alterations occurring in polyamine metabolism of maize in tumors formed during the interaction with the biotrophic pathogenic fungus Ustilago maydis were analyzed. During the process, a striking increase in maize polyamine biosynthesis, mainly free and conjugated putrescine occurred in the tumors induced by the fungus, and in the neighbor plant tissues. This increase correlated with an activation mainly of Adc, Samdc1, Zmsamdc2 and Zmsamdc3, but not of Zmodc, Zmspds1 and Zmspds2 genes, and an elevation in arginine decarboxylase activity, confirming a predominant role of this enzyme in the process. Evidences for a possible contribution of spermidine and spermine degradation by polyamine oxidase activity, probably related to cell wall stiffening or lignification during tumor growth, were also obtained. It is suggested that polyamines, mainly putrescine, might play an active role in the pathosystem maize-U. maydis.

Polyamines: essential factors for growth and survival

Polyamines are low molecular weight, aliphatic polycations found in the cells of all living organisms. Due to their positive charges, polyamines bind to macromolecules such as DNA, RNA, and proteins. They are involved in diverse processes, including regulation of gene expression, translation, cell proliferation, modulation of cell signalling, and membrane stabilization. They also modulate the activities of certain sets of ion channels. Because of these multifaceted functions, the homeostasis of polyamines is crucial and is ensured through regulation of biosynthesis, catabolism, and transport. Through isolation of the genes involved in plant polyamine biosynthesis and loss-of-function experiments on the corresponding genes, their essentiality for growth is reconfirmed. Polyamines are also involved in stress responses and diseases in plants, indicating their importance for plant survival. This review summarizes the recent advances in polyamine research in the field of plant science compared with the knowledge obtained in microorganisms and animal systems.

The Q-type C2H2 zinc finger subfamily of transcription factors in Triticum aestivum is predominantly expressed in roots and enriched with members containing an EAR repressor motif and responsive to drought stress

Q-type C2H2 zinc finger proteins (ZFPs) form a subfamily of transcription factors that contain a plant-specific QALGGH amino acid motif. A total of 47 expressed Q-type C2H2 zinc finger genes in bread wheat (Triticum aestivum) (designated TaZFP) were identified from the current databases. Protein sequence analysis for the presence of ERF-associated amphiphilic repressor (EAR) motif sequences from known transcriptional repressors revealed that 26% of the TaZFP subfamily members contain an EAR motif. Quantitative RT-PCR analysis of the mRNA distribution of 44 TaZFP genes in various organs revealed that 30 genes were predominantly expressed in the roots. The majority of the TaZFP genes showed significant changes in their mRNA levels during leaf development and aging. Expression of 37 TaZFP genes in the leaves and roots responded to drought stress at least in one organ with 74% of the drought-responsive TaZFP genes being down-regulated in the drought-stressed roots. In contrast, only 6 out of the 44 TaZFP genes showed expression changes in the leaves with sucrose treatment. Expression of 50% of the drought-responsive TaZFP genes in the leaves (16 genes analysed) did not respond to ABA treatment, indicating that some TaZFP genes are involved in ABA-independent signalling pathways. These results indicate that the Q-type TaZFP subfamily is likely to have an important role in wheat roots and is enriched with members that are potentially involved in regulating cellular activities during changes of the physiological status of plant cells, as it occurs during drought stress or leaf development/aging.

A novel CaAbsi1 gene induced by early-abiotic stresses in pepper

The full-length cDNA of CaAbsi1 encodes a presumptive protein of 134 amino acid residues that has homology to a putative zinc finger protein in its C-terminus. The deduced amino acid sequence has 50% homology to Oryza sativa NP001049-274, the function of which is unknown. Expression of CaAbsi1 was reduced in response to inoculation of non-host pathogens. On the other hand it was induced one hour after exposure to high concentrations of NaCl or mannitol, and six hours after transfer to low temperature. Induction also occurred in response to oxidative stress, methyl viologen, hydrogen peroxide and abscisic acid. Our results suggest that CaAbsi1 plays a role in multiple responses to wounding and abiotic stresses.

Modulation of spermidine and spermine levels in maize seedlings subjected to long-term salt stress

Salinity is one of the major abiotic stresses affecting plant agriculture worldwide. Polyamines, a group of aliphatic amines, are known to accumulate under salt stress conditions in different plant systems, resulting in presumed protective effects, acting as free radical scavengers, stabilizing cellular membranes and maintaining cellular ionic balance under these conditions. In the present study, we measured the polyamine content in maize leaves of semi-hydroponically grown seedlings subjected to 1 and 7 days of salt stress. We observed that the maize plants tend to maintain or accumulate the levels of spermidine and spermine, while putrescine levels fluctuate depending on the NaCl concentration. The effect of salt stress on the expression of the main genes involved in polyamine biosynthesis was also assessed. Our data show a time and NaCl dependent regulation of the Zmspds2 and Zmspds1 genes, suggesting that the former might be hyperosmotic responsive while the later NaCl responsive. Interestingly, the maize adc, Zmspds1 and Zmspds2 genes are regulated at the transcriptional level by the plant growth regulator abscisic acid. A connection between polyamine metabolism, abiotic stress and abscisic acid is discussed.

Identification of a novel Cys2/His2-type zinc-finger protein as a component of a spermine-signaling pathway in tobacco

In a previous work, we identified a Cys(2)/His(2)-type zinc-finger transcription repressor, (ZFT1), that functions in a spermine-mediated signal transduction pathway in tobacco plants. Database search disclosed the presence of another Cys(2)/His(2)-type zinc-finger protein ZFP1 (accession number AAC06243) in tobacco plants. In this work, we characterized ZFP1 and investigated whether this protein is also involved in a Spm-signaling pathway. This factor showed the highest identity to petunia ZPT2-2 and higher similarity to petunia ZPT2-3, Arabidopsis STZ/ZAT10, soybean SCOF-1, red pepper CAZFP1/CaPIF1 as well as to tobacco ZFT1. ZFP1 localized to the nucleus and had a specific DNA-binding activity, supportive to be a transcription factor. Furthermore, the protein had a mild repression activity on transcription in plant cells. The expression of ZFP1, encoding ZFP1, was upregulated during tobacco mosaic virus-induced hypersensitive response. ZFP1 expression was also induced by exogenously applied spermine and its induction was repressed by inhibitors of amine oxidase/polyamine oxidase. Collectively, our data indicate that ZFP1 is a new transcription factor which functions in a spermine-signaling pathway in tobacco.

Advances in polyamine research in 2007

Polyamines are small aliphatic amines found in all living organisms except some Archaea. In plants, putrescine, spermidine, and spermine are major components which are not only involved in fundamental cellular processes, for example cell proliferation, differentiation, and programmed cell death, but also in adaptive responses to environmental stress. In this article we review plant polyamine research focusing on recent studies.

Polyamines and abiotic stress: recent advances

In this review we will concentrate in the results published the last years regarding the involvement of polyamines in the plant responses to abiotic stresses, most remarkably on salt and drought stress. We will also turn to other types of abiotic stresses, less studied in relation to polyamine metabolism, such as mineral deficiencies, chilling, wounding, heavy metals, UV, ozone and paraquat, where polyamine metabolism is also modified. There is a great amount of data demonstrating that under many types of abiotic stresses, an accumulation of the three main polyamines putrescine, spermidine and spermine does occur. However, there are still many doubts concerning the role that polyamines play in stress tolerance. Several environmental challenges (osmotic stress, salinity, ozone, UV) are shown to induce ADC activity more than ODC. The rise in Put is mainly attributed to the increase in ADC activity as a consequence of the activation of ADC genes and their mRNA levels. On the other hand, free radicals are now accepted as important mediators of tissue injury and cell death. The polycationic nature of polyamines, positively charged at physiological pH, has attracted the attention of researchers and has led to the hypothesis that polyamines could affect physiological systems by binding to anionic sites, such as those associated with nucleic acids and membrane phospholipids. These amines, involved with the control of numerous cellular functions, including free radical scavenger and antioxidant activity, have been found to confer protection from abiotic stresses but their mode of action is not fully understood yet. In this review, we will also summarize information about the involvement of polyamines as antioxidants against the potential abiotic stress-derived oxidative damage.

Plant signal transduction and defense against viral pathogens

Viral infection of plants is a complex process whereby the virus parasitizes the host and utilizes its cellular machinery to multiply and spread. In turn, plants have evolved signaling mechanisms that ultimately limit the ingress and spread of viral pathogens, resulting in resistance. By dissecting the interaction between host and virus, knowledge of signaling pathways that are deployed for resistance against these pathogens has been gained. Advances in this area have shown that resistance signaling against viruses does not follow a prototypic pathway but rather different host factors may play a role in resistance to different viral pathogens. Some components of viral resistance signaling pathways also appear to be conserved with those functioning in signaling pathways operational against other nonviral pathogens, however, these pathways may or may not overlap. This review aims to document the advances that have improved our understanding of plant resistance to viruses.

Negative regulation of defence and stress genes by EAR-motif-containing repressors

Although positive control or activation mechanism(s) involved in plant defence- and stress-related gene expression is relatively well studied, little is known about what keeps defensive armoury under control when not needed. Recent reports suggest that transcriptional repression of gene expression by EAR-motif-containing repressor proteins plays a key role in modulating plant defence and stress responses.