Polyamines in the life of Arabidopsis: profiling the expression of S-adenosylmethionine decarboxylase (SAMDC) gene family during its life cycle

Epigenetic changes induced by chronic and acute chromium stress treatments in Arabidopsis thaliana identified by the MSAP-Seq

Chromium (Cr) is an highly toxic metal to plants and causes severe damage to their growth, development, and reproduction. Plant exposure to chronic and acute Cr stress treatments results in significant changes at short time in the gene expression profile and at long time in the genomic DNA methylation profile at a transgenerational level and, consequently, in gene expression. These epigenetic modifications and their implications imposed by the Cr stress are not yet completely known in plants. Herein, were identified the epigenetic changes induced by chronic and acute Cr stress treatments in Arabidopsis thaliana plants using Methylation Sensitive Amplification Polymorphism coupled with next-generation sequencing (MSAP-Seq). First-generation Arabidopsis plants (termed F0 plants) kept under hoagland solution were subjected to Cr stress treatments. For chronic Cr stress, plants were treated through hoagland solution with 2.5 μM Cr during the entire cultivation period until seed harvest. Meanwhile, for acute Cr stress, plants were treated with 5 μM Cr during the first three weeks and returned to unstressful control condition until seed harvest. Seeds from F0 plants were sown and F1 plants were re-submitted to the same Cr stress treatments. The seed germination rate was evaluated from F-2 seeds harvested of F1 plants kept under different Cr stress treatments (0, 10, 20, and 40 μM) compared to the unstressful control condition. These data showed significant changes in the germination rate of F-2 seeds originating from stressed F1 plants compared to F-2 seeds harvested from unstressful control plants. Given this data, F1 plants kept under these chronic and acute Cr stress treatments and unstressful control condition were evaluated for the transgenerational epigenetic modifications using MSAP-Seq. The MSAP-Seq data showed that several genes were modified in their methylation status as a consequence of chronic and acute Cr stress treatment to maintain plant defenses activated. In particular, RNA processing, protein translation, photorespiration, energy production, transmembrane transport, DNA transcription, plant development, and plant resilience were the major biological processes modulated by epigenetic mechanisms identified in F1 plants kept under chronic and acute Cr stress. Therefore, collective data suggested that Arabidopsis plants kept under Cr stress regulate their epigenetic status over generations based on DNA methylation to modulate defense and resilience mechanisms.

Genetic architecture of soybean tolerance to off-target dicamba

The adoption of dicamba-tolerant (DT) soybean in the United States resulted in extensive off-target dicamba damage to non-DT vegetation across soybean-producing states. Although soybeans are highly sensitive to dicamba, the intensity of observed symptoms and yield losses are affected by the genetic background of genotypes. Thus, the objective of this study was to detect novel marker-trait associations and expand on previously identified genomic regions related to soybean response to off-target dicamba. A total of 551 non-DT advanced breeding lines derived from 232 unique bi-parental populations were phenotyped for off-target dicamba across nine environments for three years. Breeding lines were genotyped using the Illumina Infinium BARCSoySNP6K BeadChip. Filtered SNPs were included as predictors in Random Forest (RF) and Support Vector Machine (SVM) models in a forward stepwise selection loop to identify the combination of SNPs yielding the highest classification accuracy. Both RF and SVM models yielded high classification accuracies (0.76 and 0.79, respectively) with minor extreme misclassifications (observed tolerant predicted as susceptible, and vice-versa). Eight genomic regions associated with off-target dicamba tolerance were identified on chromosomes 6 [Linkage Group (LG) C2], 8 (LG A2), 9 (LG K), 10 (LG O), and 19 (LG L). Although the genetic architecture of tolerance is complex, high classification accuracies were obtained when including the major effect SNP identified on chromosome 6 as the sole predictor. In addition, candidate genes with annotated functions associated with phases II (conjugation of hydroxylated herbicides to endogenous sugar molecules) and III (transportation of herbicide conjugates into the vacuole) of herbicide detoxification in plants were co-localized with significant markers within each genomic region. Genomic prediction models, as reported in this study, can greatly facilitate the identification of genotypes with superior tolerance to off-target dicamba.

Arabidopsis Nicotianamine Synthases (NAS) comprise a common core-NAS domain fused to a variable auto-inhibitory C-terminus

Nicotianamine Synthase (NAS) catalyzes the biosynthesis of the low-molecular-mass metal chelator nicotianamine (NA) from the 2-aminobutyrate moieties of three S-adenosylmethionine molecules. NA has central roles in metal nutrition and metal homeostasis of flowering plants. The enzymatic function of NAS remains poorly understood. Crystal structures are available of archaeal and bacterial NAS-like proteins that carry out simpler aminobutanoyl transferase reactions. Here we report amino acids essential for the activity of AtNAS1 based on structural modeling and site-directed mutagenesis. Using a newly developed enzyme-coupled continuous activity assay, we compare differing NAS proteins identified through multiple sequence alignments and phylogenetic analyses. In most NAS of dicotyledonous and monocotyledonous plants (class Ia and Ib), the core-NAS domain is fused to a variable C-terminal domain. Compared to fungal and moss NAS that comprise merely a core-NAS domain (class III), NA biosynthetic activities of the four paralogous Arabidopsis thaliana NAS proteins were far lower. C-terminally trimmed core-AtNAS variants exhibited strongly elevated activities. Of 320 amino acids of AtNAS1, twelve, 287-TRGCMFMPCNCS-298, accounted for the auto-inhibitory effect of the C-terminus, of which approximately one-third was attributed to N296 within a CNCS motif that is fully conserved in Arabidopsis. No detectable NA biosynthesis was mediated by two representative plant NAS proteins that naturally lack the C-terminal domain, class Ia Arabidopsis halleri NAS5, and Medicago truncatula NAS2 of class II which is found in dicots and diverged early during the evolution of flowering plants. Next we will address a possible post-translational release of auto-inhibition in class I NAS proteins.

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.

I Choose You: Selecting Accurate Reference Genes for qPCR Expression Analysis in Reproductive Tissues in Arabidopsis thaliana

Quantitative real-time polymerase chain reaction (qPCR) is a widely used method to analyse the gene expression pattern in the reproductive tissues along with detecting gene levels in mutant backgrounds. This technique requires stable reference genes to normalise the expression level of target genes. Nonetheless, a considerable number of publications continue to present qPCR results normalised to a single reference gene and, to our knowledge, no comparative evaluation of multiple reference genes has been carried out in specific reproductive tissues of Arabidopsis thaliana. Herein, we assessed the expression stability levels of ten candidate reference genes (UBC9, ACT7, GAPC-2, RCE1, PP2AA3, TUA2, SAC52, YLS8, SAMDC and HIS3.3) in two conditional sets: one across flower development and the other using inflorescences from different genotypes. The stability analysis was performed using the RefFinder tool, which combines four statistical algorithms (geNorm, NormFinder, BestKeeper and the comparative ΔCt method). Our results showed that RCE1, SAC52 and TUA2 had the most stable expression in different flower developmental stages while YLS8, HIS3.3 and ACT7 were the top-ranking reference genes for normalisation in mutant studies. Furthermore, we validated our results by analysing the expression pattern of genes involved in reproduction and examining the expression of these genes in published mutant backgrounds. Overall, we provided a pool of appropriate reference genes for expression studies in reproductive tissues of A. thaliana, which will facilitate further gene expression studies in this context. More importantly, we presented a framework that will promote a consistent and accurate analysis of gene expression in any scientific field. Simultaneously, we highlighted the relevance of clearly defining and describing the experimental conditions associated with qPCR to improve scientific reproducibility.

Tissue-specific mRNA profiling of the Brassica napus-Sclerotinia sclerotiorum interaction uncovers novel regulators of plant immunity

White mold is caused by the fungal pathogen Sclerotinia sclerotiorum and leads to rapid and significant loss in plant yield. Among its many brassicaceous hosts, including Brassica napus (canola) and Arabidopsis, the response of individual tissue layers directly at the site of infection has yet to be explored. Using laser microdissection coupled with RNA sequencing, we profiled the epidermis, mesophyll, and vascular leaf tissue layers of B. napus in response to S. sclerotiorum. High-throughput tissue-specific mRNA sequencing increased the total number of detected transcripts compared with whole-leaf assessments and provided novel insight into the conserved and specific roles of ontogenetically distinct leaf tissue layers in response to infection. When subjected to pathogen infection, the epidermis, mesophyll, and vasculature activate both specific and shared gene sets. Putative defense genes identified through transcription factor network analysis were then screened for susceptibility against necrotrophic, hemi-biotrophic, and biotrophic pathogens. Arabidopsis deficient in PR5-like RECEPTOR KINASE (PR5K) mRNA levels were universally susceptible to all pathogens tested and were further characterized to identify putative interacting partners involved in the PR5K signaling pathway. Together, these data provide insight into the complexity of the plant defense response directly at the site of infection.

Unraveling the genetics of polyamine metabolism in barley for senescence-related crop improvement

We explored the polyamine (PA) metabolic pathway genes in barley (Hv) to understand plant development and stress adaptation in Gramineae crops with emphasis on leaf senescence. Bioinformatics and functional genomics tools were utilized for genome-wide identification, comprehensive gene features, evolution, development and stress effects on the expression of the polyamine metabolic pathway gene families (PMGs). Three S-adenosylmethionine decarboxylases (HvSAMDCs), two ornithine decarboxylases (HvODCs), one arginine decarboxylase (HvADC), one spermidine synthase (HvSPDS), two spermine synthases (HvSPMSs), five copper amine oxidases (HvCuAOs) and seven polyamine oxidases (HvPAOs) members of PMGs were identified and characterized in barley. All the HvPMG genes were found to be distributed on all chromosomes of barley. The phylogenetic and comparative assessment revealed that PA metabolic pathway is highly conserved in plants and the prediction of nine H. vulgare miRNAs (hvu-miR) target sites, 18 protein-protein interactions and 961 putative CREs in the promoter region were discerned. Gene expression of HvSAMDC3, HvCuAO7, HvPAO4 and HvSPMS1 was apparent at every developmental stage. SPDS/SPMS gene family was found to be the most responsive to induced leaf senescence. This study provides a reference for the functional investigation of the molecular mechanism(s) that regulate polyamine metabolism in plants as a tool for future breeding decision management systems.

Polyamine: A Potent Ameliorator for Plant Growth Response and Adaption to Abiotic Stresses Particularly the Ammonium Stress Antagonized by Urea

Polyamine(s) (PA, PAs), a sort of N-containing and polycationic compound synthesized in almost all organisms, has been recently paid considerable attention due to its multifarious actions in the potent modulation of plant growth, development, and response to abiotic/biotic stresses. PAs in cells/tissues occur mainly in free or (non- or) conjugated forms by binding to various molecules including DNA/RNA, proteins, and (membrane-)phospholipids, thus regulating diverse molecular and cellular processes as shown mostly in animals. Although many studies have reported that an increase in internal PA may be beneficial to plant growth under abiotic conditions, leading to a suggestion of improving plant stress adaption by the elevation of endogenous PA via supply or molecular engineering of its biosynthesis, such achievements focus mainly on PA homeostasis/metabolism rather than PA-mediated molecular/cellular signaling cascades. In this study, to advance our understanding of PA biological actions important for plant stress acclimation, we gathered some significant research data to succinctly describe and discuss, in general, PA synthesis/catabolism, as well as PA as an internal ameliorator to regulate stress adaptions. Particularly, for the recently uncovered phenomenon of urea-antagonized NH₄ ⁺-stress, from a molecular and physiological perspective, we rationally proposed the possibility of the existence of PA-facilitated signal transduction pathways in plant tolerance to NH₄ ⁺-stress. This may be a more interesting issue for in-depth understanding of PA-involved growth acclimation to miscellaneous stresses in future studies.

TOR senses and regulates spermidine metabolism during seedling establishment and growth in maize and Arabidopsis

Spermidine (Spd) is a nitrogen sink and signaling molecule that plays pivotal roles in eukaryotic cell growth and must be finetuned to meet various energy demands. In eukaryotes, target of rapamycin (TOR) is a central nutrient sensor, especially N, and a master-regulator of growth and development. Here, we discovered that Spd stimulates the growth of maize and Arabidopsis seedlings through TOR signaling. Inhibition of Spd biosynthesis led to TOR inactivation and growth defects. Furthermore, disruption of a TOR complex partner RAPTOR1B abolished seedling growth stimulation by Spd. Strikingly, TOR activated by Spd promotes translation of key metabolic enzyme upstream open reading frame (uORF)-containing mRNAs, PAO and CuAO, by facilitating translation reinitiation and providing feedback to polyamine metabolism and TOR activation. The Spd-TOR relay protected young-age seedlings of maize from expeditious stress heat shock. Our results demonstrate Spd is an upstream effector of TOR kinase in planta and provide its potential application for crop protection.

•

Spermidine (Spd) stimulates growth of maize and Arabidopsis by activating TOR signaling

•

TOR stimulates translation efficiency of uORF-containing mRNAs involved in Spd catabolism

•

TOR provides feedback to polyamine homeostasis in response to excess of Spd

•

The Spd-TOR signaling axis protects maize seedlings from expeditious heat stress

Genomic analysis of the polyamine biosynthesis pathway in duckweed Spirodela polyrhiza L.: presence of the arginine decarboxylase pathway, absence of the ornithine decarboxylase pathway, and response to abiotic stresses

Identification of the polyamine biosynthetic pathway genes in duckweed S. polyrhiza reveals presence of prokaryotic as well as land plant-type ADC pathway but absence of ODC encoding genes. Their differential gene expression and transcript abundance is shown modulated by exogenous methyl jasmonate, salinity, and acidic pH. Genetic components encoding for polyamine (PA) biosynthetic pathway are known in several land plant species; however, little is known about them in aquatic plants. We utilized recently sequenced three duckweed (Spirodela polyrhiza) genome assemblies to map PA biosynthetic pathway genes in S. polyrhiza. PA biosynthesis in most higher plants except for Arabidopsis involves two pathways, via arginine decarboxylase (ADC) and ornithine decarboxylase (ODC). ADC-mediated PA biosynthetic pathway genes, namely, one arginase (SpARG1), two arginine decarboxylases (SpADC1, SpADC2), one agmatine iminohydrolase/deiminase (SpAIH), one N-carbamoyl putrescine amidase (SpCPA), three S-adenosylmethionine decarboxylases (SpSAMDc1, 2, 3), one spermidine synthase (SpSPDS1) and one spermine synthase (SpSPMS1) in S. polyrhiza genome were identified here. However, no locus was found for ODC pathway genes in this duckweed. Hidden Markov Model protein domain analysis established that SpADC1 is a prokaryotic/biodegradative type ADC and its molecular phylogenic classification fell in a separate prokaryotic origin ADC clade with SpADC2 as a biosynthetic type of arginine decarboxylase. However, thermospermine synthase (t-SPMS)/Aculis5 genes were not found present. Instead, one of the annotated SPDS may also function as SPMS, since it was found associated with the SPMS phylogenetic clade along with known SPMS genes. Moreover, we demonstrate that S. polyrhiza PA biosynthetic gene transcripts are differentially expressed in response to unfavorable conditions, such as exogenously added salt, methyl jasmonate, or acidic pH environment as well as in extreme temperature regimes. Thus, S. polyrhiza genome encodes for complete polyamine biosynthesis pathway and the genes are transcriptionally active in response to changing environmental conditions suggesting an important role of polyamines in this aquatic plant.

Interaction between polyamines and ethylene in the response to salicylic acid under normal photoperiod and prolonged darkness

The impact of salicylic acid (SA) on ethylene (ET) production and polyamine (PA) metabolism was investigated in wild type (WT) and ET receptor mutant Never ripe (Nr) tomato leaves under normal photoperiod and prolonged darkness. Nr displayed higher ET emanation compared to WT under control conditions and after SA treatments, but the ET signalling was blocked in these tissues. The accumulation of PAs was induced by 1 mM but not by 0.1 mM SA and was higher in WT than in Nr leaves. Upon 1 mM SA treatment, which caused hypersensitive response, illuminated leaves of WT showed high spermine (Spm) content in parallel with an increased expression of S-adenosylmethionine decarboxylase and Spm synthase (SlSPMS) suggesting that this process depended on the light. In Nr, however, Spm content and the expression of the SlSPMS gene were very low independently of the light conditions and SA treatments. This suggests that Spm synthesis needs functional ET perception. In WT leaves 1 mM SA enhanced putrescine (Put) synthesis by increasing the expression of Put biosynthesis genes, arginine and ornithine decarboxylases under darkness, while they were down-regulated in Nr. The activities of diamine (DAO) and polyamine oxidases (PAO), however, were generally higher in Nr compared to the WT after SA treatments. In Nr both SA applications increased the expression of SlPAO1 under normal photoperiod, while SlPAO2 was down-regulated in the dark suggesting a diverse role of PAOs in PA catabolism. These results indicated that ET could modulate the SA-induced PA metabolism in light-dependent manner.

Ornithine decarboxylase of the fungal pathogen Colletotrichum higginsianum plays an important role in regulating global metabolic pathways and virulence

Colletotrichum higginsianum is an important fungal pathogen causing anthracnose disease of cruciferous plants. In this study, we characterized a putative orthologue of yeast SPE1 in C. higginsianum, named ChODC. Deletion mutants of ChODC were defective in hyphal and conidial development. Importantly, deletion of ChODC significantly affected appressorium-mediated penetration in C. higginsianum. However, polyamines partially restore appressorium function and virulence indicating that loss of ChODC caused significantly decreased virulence by the crosstalk between polyamines and other metabolic pathways. Subsequently, transcriptomic and metabolomic analyses demonstrated that ChODC played an important role in metabolism of various carbon and nitrogen compounds including amino acids, carbohydrates and lipids. Along with these clues, we found deletion of ChODC affected glycogen and lipid metabolism, which were important for conidial storage utilization and functional appressorium formation. Loss of ChODC affected the mTOR signalling pathway via modulation of autophagy. Interestingly, cAMP treatment restored functional appressoria to the ΔChODC mutant, and rapamycin treatment also stimulated formation of functional appressoria in the ΔChODC mutant. Overall, ChODC was associated with the polyamine biosynthesis pathway, as a mediator of cAMP and mTOR signalling pathways to regulate appressorium function. Our study provides evidence of a link between ChODC and the cAMP signalling pathway and defines a novel mechanism by which ChODC regulates infection-associated autophagy and plant infection by fungi.

Overexpression of the white clover TrSAMDC1 gene enhanced salt and drought resistance in Arabidopsis thaliana

S-adenosylmethionine decarboxylase (SAMDC) mediates the biosynthesis of polyamines (PAs) and plays a positive role in plants' response to adversity stress tolerance. In this study, we isolated a SAMDC gene from white clover, which is located in mitochondria. It was strongly induced when white clover exposed to drought (15% PEG6000), salinity (200 mM NaCl), 20 μM spermidine, 100 μM abscisic acid, and 10 mM H₂O₂, especially in leaves. The INVSc1 yeast introduced with TrSAMDC1 had tolerance to drought, salt, and oxidative stress. Overexpression of TrSAMDC1 in Arabidopsis showed higher fresh weight and dry weight under drought and salt treatment and without growth inhibition under normal conditions. Leaf senescence induced by drought and saline was further delayed in transgenic plants, regardless of cultivation in 1/2 MS medium and soil. During drought and salt stress, transgenic plants exhibited a significant increase in relative water content, maximum photosynthesis efficiency (Fv/Fm), performance index on the absorption basis (PI_ABS), activities of antioxidant protective enzymes such as SOD, POD, CAT, and APX, and a significant decrease in accumulation of MDA and H₂O₂ as compared to the WT. The concentrations of total PAs, putrescine, spermidine, and spermidine in transgenic lines were higher in transgenic plants than in WT under normal and drought conditions. These results suggested that TrSAMDC1 could effectively mitigate abiotic stresses without the expense of production and be a potential candidate gene for improving the drought and salt resistance of crops.

Polyamine Metabolism Is Involved in the Direct Regeneration of Shoots from Arabidopsis Lateral Root Primordia

Plants can be regenerated from various explants/tissues via de novo shoot meristem formation. Most of these regeneration pathways are indirect and involve callus formation. Besides plant hormones, the role of polyamines (PAs) has been implicated in these processes. Interestingly, the lateral root primordia (LRPs) of Arabidopsis can be directly converted to shoot meristems by exogenous cytokinin application. In this system, no callus formation takes place. We report that the level of PAs, especially that of spermidine (Spd), increased during meristem conversion and the application of exogenous Spd improved its efficiency. The high endogenous Spd level could be due to enhanced synthesis as indicated by the augmented relative expression of PA synthesis genes (AtADC1,2, AtSAMDC2,4, AtSPDS1,2) during the process. However, the effect of PAs on shoot meristem formation might also be dependent on their catabolism. The expression of Arabidopsis POLYAMINE OXIDASE 5 (AtPAO5) was shown to be specifically high during the process and its ectopic overexpression increased the LRP-to-shoot conversion efficiency. This was correlated with Spd accumulation in the roots and ROS accumulation in the converting LRPs. The potential ways how PAO5 may influence direct shoot organogenesis from Arabidopsis LRPs are discussed.

Ectopic expression of GhSAMDC1 improved plant vegetative growth and early flowering through conversion of spermidine to spermine in tobacco

Polyamines play essential roles in plant development and various stress responses. In this study, one of the cotton S-adenosylmethionine decarboxylase (SAMDC) genes, GhSAMDC1, was constructed in the pGWB17 vector and overexpressed in tobacco. Leaf area and plant height increased 25.9-36.6% and 15.0-27.0%, respectively, compared to the wild type, and flowering time was advanced by 5 days in transgenic tobacco lines. Polyamine and gene expression analyses demonstrated that a decrease in spermidine and an increase in total polyamines and spermine might be regulated by NtSPDS4 and NtSPMS in transgenic plants. Furthermore, exogenous spermidine, spermine and spermidine synthesis inhibitor dicyclohexylamine were used for complementary tests, which resulted in small leaves and dwarf plants, big leaves and early flowering, and big leaves and dwarf plants, respectively. These results indicate that spermidine and spermine are mainly involved in the vegetative growth and early flowering stages, respectively. Expression analysis of flowering-related genes suggested that NtSOC1, NtAP1, NtNFL1 and NtFT4 were upregulated in transgenic plants. In conclusion, ectopic GhSAMDC1 is involved in the conversion of spermidine to spermine, resulting in rapid vegetative growth and early flowering in tobacco, which could be applied to genetically improve plants.

Comparative co-expression network analysis extracts the SlHSP70 gene affecting to shoot elongation of tomato

Tomato is one of vegetables crops that has the highest value in the world. Thus, researchers are continually improving the agronomical traits of tomato fruits. Auxins and gibberellins regulate plant growth and development. Aux/indole-3-acetic acid 9 (SlIAA9) and the gene encoding the DELLA protein (SlDELLA) are well-known genes that regulate plant growth and development, including fruit set and enlargement by cell division and cell expansion. The absence of tomato SlIAA9 and SlDELLA results in abnormal shoot growth and leaf shape and giving rise to parthenocarpy. To investigate the key regulators that exist up- or downstream of SlIAA9 and SlDELLA signaling pathways for tomato growth and development, we performed gene co-expression network analysis by using publicly available microarray data to extract genes that are directly connected to the SlIAA9 and SlDELLA nodes, respectively. Consequently, we chose a gene in the group of heat-shock protein (HSP)70s that was connected with the SlIAA9 node and SlDELLA node in each co-expression network. To validate the extent of effect of SlHSP70-1 on tomato growth and development, overexpressing lines of the target gene were generated. We found that overexpression of the targeted SlHSP70-1 resulted in internode elongation, but the overexpressing lines did not show abnormal leaf shape, fruit set, or fruit size when compared with that of the wild type. Our study suggests that the targeted SlHSP70-1 is likely to function in shoot growth, like SlIAA9 and SlDELLA, but it does not contribute to parthenocarpy as well as fruit set. Our study also shows that only a single SlHSP70 out of 25 homologous genes could change the shoot length.

Transcriptome and digital gene expression analysis unravels the novel mechanism of early flowering in Angelica sinensis

Angelica sinensis (Oliv.) Diels is a widely used medicinal plant mainly originated in Gansu, China. Angelica sinensis is greatly demanded in the clinical practice of Chinese medicine due to its broad pharmacological activities of hematopoietic and anti-inflammatory properties. But, the percentage of early flowering in Angelica sinensis arrives to 20%~30%, which severely affects its quality and quantity. Here, transcriptome profiling and digital gene expression analysis were applied to study the mechanism of early flowering in Angelica sinensis. A total of 49,183,534 clean reads were obtained and assembled into 68,262 unigenes, and 49,477 unigenes (72.5%) could be annotated to a minimum of one database in the Nr, Nt, Swiss-Pro, GO, COG and KEGG. Taking the above transcriptome data as a reference, digital gene expression result showed that 5,094 genes expression level were significant changed during early flowering. These annotated genes offered much information promoting that the biosynthesis of secondary metabolites pathway, the hormone signal transduction pathway, and the transcription regulation system may be closely related to the early flowering phenomenon of Angelica sinensis. Further expression patterns of key genes contribute to early flowering were analyzed using quantitative real-time PCR. The transcriptome result offered important gene expression information about early flowering in Angelica sinensis.

Transcriptional Modulation of Polyamine Metabolism in Fruit Species Under Abiotic and Biotic Stress

Polyamines are growth regulators that have been widely implicated in abiotic and biotic stresses. They are also associated with fruit set, ripening, and regulation of fruit quality-related traits. Modulation of their content confers fruit resilience, with polyamine application generally inhibiting postharvest decay. Changes in the content of free and conjugated polyamines in response to stress are highly dependent on the type of abiotic stress applied or the lifestyle of the pathogen. Recent studies suggest that exogenous application of polyamines or modulation of polyamine content by gene editing can confer tolerance to multiple abiotic and biotic stresses simultaneously. In this review, we explore data on polyamine synthesis and catabolism in fruit related to pre- and postharvest stresses. Studies of mutant plants, priming of stress responses, and treatments with polyamines and polyamine inhibitors indicate that these growth regulators can be manipulated to increase fruit productivity with reduced use of pesticides and therefore, under more sustainable conditions.

Contribution of Maize Polyamine and Amino Acid Metabolism Toward Resistance Against Aspergillus flavus Infection and Aflatoxin Production

Polyamines (PAs) are ubiquitous polycations found in plants and other organisms that are essential for growth, development, and resistance against abiotic and biotic stresses. The role of PAs in plant disease resistance depends on the relative abundance of higher PAs [spermidine (Spd), spermine (Spm)] vs. the diamine putrescine (Put) and PA catabolism. With respect to the pathogen, PAs are required to achieve successful pathogenesis of the host. Maize is an important food and feed crop, which is highly susceptible to Aspergillus flavus infection. Upon infection, the fungus produces carcinogenic aflatoxins and numerous other toxic secondary metabolites that adversely affect human health and crop value worldwide. To evaluate the role of PAs in aflatoxin resistance in maize, in vitro kernel infection assays were performed using maize lines that are susceptible (SC212) or resistant (TZAR102, MI82) to aflatoxin production. Results indicated significant induction of both PA biosynthetic and catabolic genes upon A. flavus infection. As compared to the susceptible line, the resistant maize lines showed higher basal expression of PA metabolism genes in mock-inoculated kernels that increased upon fungal infection. In general, increased biosynthesis and conversion of Put to Spd and Spm along with their increased catabolism was evident in the resistant lines vs. the susceptible line SC212. There were higher concentrations of amino acids such as glutamate (Glu), glutamine (Gln) and γ-aminobutyric acid (GABA) in SC212. The resistant lines were significantly lower in fungal load and aflatoxin production as compared to the susceptible line. The data presented here demonstrate an important role of PA metabolism in the resistance of maize to A. flavus colonization and aflatoxin contamination. These results provide future direction for the manipulation of PA metabolism in susceptible maize genotypes to improve aflatoxin resistance and overall stress tolerance.