Col-0 Plants Research Articles

Expression of the Tobacco Non-symbiotic Class 1 Hemoglobin Gene Hb1 Reduces Cadmium Levels by Modulating Cd Transporter Expression Through Decreasing Nitric Oxide and ROS Level in Arabidopsis.

Hemoglobin (Hb) proteins are ubiquitous in plants, and non-symbiotic class 1 hemoglobin (Hb1) is involved in various biotic and abiotic stress responses. Here, the expression of the tobacco (Nicotiana tabacum) hemoglobin gene NtHb1 in Arabidopsis (Arabidopsis thaliana) showed higher cadmium (Cd) tolerance and lower accumulations of Cd, nitric oxide (NO), and reactive oxygen species (ROS) like hydrogen peroxide (H2O2). NtHb1-expressing Arabidopsis exhibited a reduced induction of NO levels in response to Cd, suggesting scavenging of NO by Hb1. In addition, transgenic plants had reduced accumulation of ROS and increased activities of antioxidative enzymes (catalase, superoxide dismutase, and glutathione reductase) in response to Cd. While the expression of the Cd exporters ABC transporter (PDR8) and Ca2+/H+ exchangers (CAXs) was increased, that of the Cd importers iron responsive transporter 1 (IRT1) and P-type 2B Ca2+ ATPase (ACA10) was reduced in response to Cd. When Col-0 plants were treated with the NO donor sodium nitroprusside (SNP) and H2O2, the expression pattern of Cd transporters (PDR8, CAX3, IRT1, and ACA10) was reversed, suggesting that NtHb1 expression decreased the Cd level by regulating the expression of Cd transporters via decreased NO and ROS. Correspondingly, NtHb1-expressing Arabidopsis showed increased Cd export. In summary, the expression of NtHb1 reduces Cd levels by regulating Cd transporter expression via decreased NO and ROS levels in Arabidopsis.

Impact of UV-B radiation on the photosystem II activity, pro-/antioxidant balance and expression of light-activated genes in Arabidopsis thaliana hy4 mutants grown under light of different spectral composition

The effect of UV-B irradiation on the photosystem II (PSII) activity, the content of photosynthetic and UV-absorbing pigments (UAPs), activity of antioxidant enzymes such as catalase (CAT) and peroxidase (POD), as well as H2O2 content in 25-day-old wild type (WT) and the cryptochrome 1 (Cry1) mutant hy4 of Arabidopsis thaliana Col-0 plants was studied. In addition, expression of photoreceptor genes Cry1, Cry2 and UVR8, photomorphogenetic gene COP1 and transcription factors genes HY5, HYH, the gene of chlorophyll-binding protein of the PSII CAB1 as well as the flavonoid biosynthesis genes CHS, PAL and thylakoid ascorbate peroxidase gene tAPX was examined. It has been shown that UV-B leads to a decrease in the photochemical activity of PSII (FV/FM) and the PSII performance index (PIABS) of WT plants grown on white (WL) and red (RL) light and also hy4 mutants grown on WL, RL and blue light (BL). In plants grown on BL and WL, the decrease in the PSII photochemical activity was significantly greater in hy4 compared to WT. The PSII of WT plants grown in BL was resistant to UV-B. The UAPs content of hy4 grown on BL and WL was lower than that in WT. The POD and CAT activities of WT grown in BL were significantly higher than in the mutant. In WT and hy4 plants grown in RL, a noticeable difference in these enzymes activity was not found. In both types of plants grown in BL and RL, the expression of photomorphogenetic genes HYH, HY5 markedly increased after UV-B treatment but the expression of the UV-B photoreceptor gene UVR8 was reduced in hy4 grown in BL and RL. It is assumed that reduced resistance of PSII in hy4 plants grown in BL and WL can be associated with low UAPs content as well as lowered POD and CAT activities. In addition, we suggest the lowered expression of UVR8 and COP1 genes caused by Cry1 deficiency leads to a shift of balance of oxidants and antioxidants towards oxidants.

CKB1 regulates expression of ribosomal protein L10 family gene and plays a role in UV-B response.

Plastid casein kinase 2 (CK2), which is a major Ser/Thr-specific enzyme in higher organisms, plays an essential role in plant development and diverse abiotic stresses. CKB1 is a regulatory subunit beta of CK2. To expand our understand of functions of the CKB1 gene in Arabidopsis thaliana, protein changes among wild-type (WT) and CKB1 gain- and loss-of-function mutants were compared. Proteins extracted from the CKB1 knockout mutant and overexpressing mutant were compared with Col-0 plants using 2D-PAGE. Proteins regulated by CKB1 were identified with matrix-assisted laser desorption ionisation time-of-flight/time-of-flight mass spectrometry (MALDI-TOF/TOF), and its transcript was verified by qRT-PCR. Bioinformatics analysis, including gene ontology and protein-protein interaction analysis, were employed. The results of mass spectra and bioinformatics analysis suggest that CKB1 may have functions in regulation of the ribosomal protein L10 (RPL10) family and is involved in ultraviolet-B (UV-B) response. Furthermore, qRT-PCR verification showed CKB1 expression was up-regulated by UV-B stress. The expression levels of five genes in the RPL10 family were reduced in the ckb1 T-DNA insertion mutants, whereas they increased in the CKB1 overexpressing mutants under both normal conditions and UV-B treatment. In conclusion, CKB1 has important functions in UV-B radiation stress. Our study implies that CKB1 positively regulates UV-B radiation stress signalling, possibly through modulating expression of the RPL10 family.

Effects of short-term arsenic exposure in Arabidopsis thaliana: tolerance versus toxicity responses

The metalloid arsenic (As) is highly phytotoxic, in part due to the similarity of the arsenates to phosphates, but also due to its ability to induce reactive oxygen species (ROS) formation, and in the form of arsenite directly interact with certain enzymes. Here we aimed to determine the effects of a short period of As exposure on Arabidopsis thaliana. Particular focus was given to shoot responses, which have received less attention in previous studies. A. thaliana (ecotype Col-0) plants (28-d-old) were cultivated hydroponically in the presence of 0, 27, 108, and 216 µM arsenic in the form of sodium arsenate for five days. Translocation of As from root to shoot increased with increasing As concentration in the medium and caused a reduction in growth. Photosynthesis was severely affected due to stomatal closure, increased ROS accumulation, and alterations in expression of genes involved in oxidative stress responses and As detoxification. Primary metabolism was also perturbed, suggesting both the direct inhibition of certain enzymes as well as active defensive responses. Overall the effects of As toxicity depended greatly on the degree of translocation from root to shoot and involved both direct effects on biological processes and secondary effects caused by the accumulation of ROS.

Cloning and function analysis of a novel flowering time regulatory gene BraELF6 in Brassica rapa

Histone methyltransferases and demethylases are two major enzymes that regulate histone methylation, which in turn influences hundreds of genes in plants. Early Flowering 6 (AtELF6), which contains a Jumonji C (JmjC) domain, is a demethylase that plays a vital role in regulating flowering time in Arabidopsis thaliana. In the present study, the BraELF6 gene of Brassica rapa cultivar ‘1510746’ was cloned to elucidate its role on flowering time. Homologous genes of BraELF6 were identified in Brassica AA/CC genomes, but not in the BB genome. Analysis of the BraELF6 gene structure identified three domains, namely, JmjN, JmjC, and ZnF C2H2. The relative expression of BraELF6 increased with plant growth and was the highest in the flowers compared to that in the roots, stems, and leaves. The BraELF6 gene was transfected into the Arabidopsis elf6-4 mutants, and Northern blot analysis confirmed its expression in the transgenic plants. The T1 plants showed the later flowering than the elf6-4 mutants, which recovered to the level of Col plants. In addition, the expression of the BraELF6 and AtFLC genes was relatively higher in the transgenic plants. In the T2 plants, the flowering phenotype segregated to some extent, which may be associated with the number of transgenic genes integrated into the genome. This present study lays the foundation for elucidating the mechanism underlying the regulation of flowering time in B. rapa by the BraELF6 gene, as well as excavating more earlier or later flowering germplasm materials in the future.

Proteomic Analysis Provides Insights into Arabidopsis thaliana Response Under Narrow-Wavelength LED of 595 nm light

A growing body of evidence has highlighted that a wide range of plant processes including growth, photosynthesis, and stress response are regulated by 595 nm light. However, the molecular mechanisms underlying 595 nm-induced signals are not known. The aim of this work was to study the comparative proteomic changes in leaves of Arabidopsis thaliana Col-0 plants treated with narrow-wavelength 595 nm light or fluorescent light for 5 days. Harvested plant samples were analyzed using inline RP-SCX-RP liquid chromatography coupled with LTQ mass spectrometer, resulting in the identification of 1538 proteins. Linear regression modeling of proteins’ relative abundance revealed a total of 23 differentially abundant proteins (DAPs). Functional analysis of these DAPs demonstrated the role of several biological mechanisms in A. thaliana’s response to 595 nm light including stress response and metabolic processes. A network analysis of these DAPs revealed the importance of energy and redox regulation mechanisms. Further analyses determined potentially important roles for proteins associated with glycolysis, ATP synthase complex, cell wall modification, and thylakoid membrane that may modulate the plant’s adaptive response to 595 nm light. A significant enrichment of DAPs for PSII tolerance capacity, as well as associated Ca2+ and ROS signaling pathways were also identified. Collectively, this study provides an important insight into potential molecular pathways that sustain a plant’s response to 595 nm light.

Proteome-Wide Analysis of Cysteine Reactivity during Effector-Triggered Immunity.

A surge in the accumulation of oxidants generates shifts in the cellular redox potential during early stages of plant infection with pathogens and activation of effector-triggered immunity (ETI). The redoxome, defined as the proteome-wide oxidative modifications of proteins caused by oxidants, has a well-known impact on stress responses in metazoans. However, the identity of proteins and the residues sensitive to oxidation during the plant immune response remain largely unknown. Previous studies of the thimet oligopeptidases TOP1 and TOP2 placed them in the salicylic acid dependent branch of ETI, with a current model wherein TOPs sustain interconnected organellar and cytosolic pathways that modulate the oxidative burst and development of cell death. Herein, we characterized the ETI redoxomes in Arabidopsis (Arabidopsis thaliana) wild-type Col-0 and top1top2 mutant plants using a differential alkylation-based enrichment technique coupled with label-free mass spectrometry-based quantification. We identified cysteines sensitive to oxidation in a wide range of protein families at multiple time points after pathogen infection. Differences were detected between Col-0 and top1top2 redoxomes regarding the identity and number of oxidized cysteines, and the amplitude of time-dependent fluctuations in protein oxidation. Our results support a determining role for TOPs in maintaining the proper level and dynamics of proteome oxidation during ETI. This study significantly expands the repertoire of oxidation-sensitive plant proteins and can guide future mechanistic studies.

Mediation of Impacts of Elevated CO2 and Light Environment on Arabidopsis thaliana (L.) Chemical Defense against Insect Herbivory Via Photosynthesis.

Elevated CO2 alters C3 plant tolerance to insect herbivory, as well as the induction kinetics of defense hormones salicylic acid (SA) and jasmonic acid (JA), but the underlying physiological mechanism causing this response is not well understood. In principle, SA could be induced under elevated CO2 by reactive oxygen signals generated in photosynthesis, ultimately influencing chemical defense. To test whether the effects of elevated CO2 on C3 plant chemical defense against herbivorous insects are modulated by photosynthesis, Arabidopsis thaliana var. Col-0 plants were grown in two 2 × 2 × 2 nested factorial combinations of ambient (400ppm) and elevated (800ppm) CO2, and two dimensions of light regimes comprising intensity ('mild' 150μmol E m-2s-1 vs. 'low' light, 75μmol E m-2s-1) and periodicity ('continuous', 150μmol E m-2s-1 vs. 'dynamic', in which lights were turned off, then on, for 15min every 2h). Plants were challenged with herbivore damage from third instar Trichoplusia ni (cabbage looper). Consistent with experimental predictions, elevated CO2 interacted with light as well as herbivory to induce foliar concentration of SA, while JA was suppressed. Under dynamic light, foliar content of total glucosinolates was reduced. Under combination of elevated CO2 and dynamic light, T. ni removed significantly more leaf tissue relative to control plants. The observations that CO2 and light interactively modulate defense against T. ni in A. thaliana provide an empirical argument for a role of photosynthesis in C3 plant chemical defense.

NRT1.1-Related NH4 + Toxicity Is Associated with a Disturbed Balance between NH4 + Uptake and Assimilation.

A high concentration of ammonium (NH4 +) as the sole source of nitrogen in the growth medium often is toxic to plants. The nitrate transporter NRT1.1 is involved in mediating the effects of NH4 + toxicity; however, the mechanism remains undefined. In this study, wild-type Arabidopsis (Arabidopsis thaliana Columbia-0 [Col-0]) and NRT1.1 mutants (chl1-1 and chl1-5) were grown hydroponically in NH4NO3 and (NH4)2SO4 media to assess the function of NRT1.1 in NH4 + stress responses. All the plants grew normally in medium containing mixed nitrogen sources, but Col-0 displayed more chlorosis and lower biomass and photosynthesis than the NRT1.1 mutants in (NH4)2SO4 medium. Grafting experiments between Col-0 and chl1-5 further confirmed that NH4 + toxicity is influenced by NRT1.1. In (NH4)2SO4 medium, NRT1.1 induced the expression of NH4 + transporters, increasing NH4 + uptake. Additionally, the activities of glutamine synthetase and glutamate synthetase in roots of Col-0 plants decreased and soluble sugar accumulated significantly, whereas pyruvate kinase-mediated glycolysis was not affected, all of which contributed to NH4 + accumulation. By contrast, the NRT1.1 mutants showed reduced NH4 + accumulation and enhanced NH4 + assimilation through glutamine synthetase, glutamate synthetase, and glutamate dehydrogenase. Moreover, the up-regulation of genes involved in ethylene synthesis and senescence in Col-0 plants treated with (NH4)2SO4 suggests that ethylene is involved in NH4 + toxicity responses. This study showed that NH4 + toxicity is related to a nitrate-independent signaling function of NRT1.1 in Arabidopsis, characterized by enhanced NH4 + accumulation and altered NH4 + metabolism, which stimulates ethylene synthesis, leading to plant senescence.

A kinase-dead version of FERONIA receptor-like kinase has dose-dependent impacts on rosette morphology and RALF1-mediated stomatal movements.

The receptor-like kinase FERONIA (FER) pleiotropically affects plant reproduction, development, and stress tolerance. We recently showed that the FER ligand RALF1 promotes stomatal closure and inhibits stomatal opening in a G-protein-dependent manner. FER responses have been designated as kinase-dependent or kinase-independent, based largely on fer complementation assays employing a kinase-dead FERK565R. Our quantification of FERK565R-GFP transcript and FERK565R-GFP protein in fer complementation lines reveal that, even within individual complementation lines, different levels of FERK565R expression prevail. FERK565R-GFP expression comparable to that of FER in Col-0 plants fail to elicit complementation of either fer rosette phenotypes or RALF1-elicited stomatal movements, whereas overexpression levels of FERK565R-GFP result in complementation. These results suggest possible alternative interpretations of previous conclusions regarding kinase-independent FER signaling.

A tomato ERF transcription factor, SlERF84, confers enhanced tolerance to drought and salt stress but negatively regulates immunity against Pseudomonas syringae pv. tomato DC3000

ERF proteins are plant-specific transcription factors that play significant roles in plant defense against various stresses. However, only little information regarding stress-related ERF genes is available in tomato (Solanum lycopersicum, Sl). In this study, a tomato ERF gene, SlERF84, was cloned and functionally characterized. The nucleus localization of SlERF84-sGFP was confirmed through a transient expression assay. Transactivation assays in yeast demonstrated that SlERF84 functions as a transcriptional activator. Real-time PCR analysis revealed that SlERF84 could be markedly induced by drought, salt and by several phytohormones (ABA, MeJA and ACC). Overexpression of SlERF84 in Arabidopsis endows transgenic plants with ABA hypersensitivity and enhanced tolerance to drought and salt stress. Histochemical staining assay showed that SlERF84 renders transgenic plants better ROS-scavenging capability. Pathogen inoculation assay revealed that SlERF84 might negatively modulate plant defense response to Pseudomonas syringae pv. tomato DC3000. Moreover, the transcript levels of pathogenesis-related genes AtPR1 and AtPR3 were compromised in transgenic Arabidopsis, as compared to that in Col-0 plants when inoculated with Pseudomonas syringae pv. tomato DC3000. These results suggest that SlERF84 functions as a stress-responsive transcription factor in differentially modulation of abiotic and biotic stress tolerance, and may have applications in the engineering of economically important crops.

Expression of a maize NBS gene ZmNBS42 enhances disease resistance in Arabidopsis.

Expression of the ZmNBS42 in Arabidopsis plants conferred resistance to bacterial pathogens, providing potential resistance enhancement of maize in further genetic breeding. Nucleotide-binding site (NBS) domain proteins play critical roles in disease resistance. In this study, we isolate a novel NBS gene ZmNBS42 from maize and systematically investigate its function on disease resistance. We find that the expression levels of ZmNBS42 in maize leaf were strikingly increased in response to Bipolaris maydis inoculation and SA treatment. The spatial expression pattern analysis reveals that, during development, ZmNBS42 is ubiquitously highly expressed in maize root, leaf, stem, internode and seed, but lowly expressed in pericarp and embryo. To better understand the roles of ZmNBS42, we overexpressed ZmNBS42 in heterologous systems. Transient overexpression of ZmNBS42 in the leaves of Nicotiana benthamiana induces a hypersensitive response. ZmNBS42 overexpression (ZmNBS42-OE) Arabidopsis plants produced more SA content than Col-0 plants, and increased the expression levels of some defense-responsive genes compared to Col-0 plants. Moreover, the ZmNBS42-OE Arabidopsis plants displayed enhanced resistance against Pseudomonas syringae pathovar tomato DC3000 (Pst DC3000). These results together suggest that ZmNBS42 can serve as an important regulator in disease resistance, thus better understanding of ZmNBS42 would benefit the resistance enhancement in maize breeding programs.

Brassinosteroids-mediated regulation of ABI3 is involved in high-temperature induced early flowering in plant

The interplay of plant hormones is one of the essential mechanisms for plant growth and development. A recent study reported that Brassinosteroids (BR) and ABSCISIC ACID (ABA) interact antagonistically in early seedling developments through the BR-mediated epigenetic repression of ABSCISIC ACID-INSENSITIVE 3 (ABI3). However, the other physiological roles of the BR-mediated regulation of ABI3 and ABA responses beyond early seedling developments remain largely unknown. Here, we showed that the activation of BR signaling by high temperatures promotes flowering time through the suppression of ABI3 expressions. Elevated ambient temperature induced early flowering in wild type Col-0 plants, but not in BR-defective bri1-116 mutant plants. Conversely, a hyper BR biosynthetic dwf4-D mutant displayed more sensitive thermomorphic long shoot elongation and early flowering. Both expression patterns and physiological responses supported the biological roles of ABI3 in the regulation of floral transition and reproduction under high temperature conditions. Finally, we confirmed that the lowered expressions of the transcript and protein levels of ABI3 brought on by elevated temperature were correlated with warmth-induced early flowering phenotypes. In conclusion, our data suggest that the BR- and warmthmediated regulation of ABI3 are important in thermomorphic reproductive phase transitions in plants.

Melatonin induction and its role in high light stress tolerance in Arabidopsis thaliana

In plants, melatonin is a potent bioactive molecule involved in the response against various biotic and abiotic stresses. However, little is known of its defensive role against high light (HL) stress. In this study, we found that melatonin was transiently induced in response to HL stress in Arabidopsis thaliana with a simultaneous increase in the expression of melatonin biosynthetic genes, including serotonin N-acetyltransferase1 (SNAT1). Transient induction of melatonin was also observed in the flu mutant, a singlet oxygen (1 O2 )-producing mutant, upon light exposure, suggestive of melatonin induction by chloroplastidic 1 O2 against HL stress. An Arabidopsis snat1 mutant was devoid of melatonin induction upon HL stress, resulting in high susceptibility to HL stress. Exogenous melatonin treatment mitigated damage caused by HL stress in the snat1 mutant by reducing O2- production and increasing the expression of various ROS-responsive genes. In analogy, an Arabidopsis SNAT1-overexpressing line showed increased tolerance of HL stress concomitant with a reduction in malondialdehyde and ion leakage. A complementation line expressing an Arabidopsis SNAT1 genomic fragment in the snat1 mutant completely restored HL stress susceptibility in the snat1 mutant to levels comparable to that of wild-type Col-0 plants. The results of the analysis of several Arabidopsis genetic lines reveal for the first time at the genetic level that melatonin is involved in conferring HL stress tolerance in plants.

Overexpression of Constitutively Active OsRab11 in Plants Enhances Tolerance to High Salinity Levels

Rab proteins are key regulators of intracellular trafficking between specific compartments in a cell. Among them, Rab11, a widely conserved sub-group, mainly regulates plasma membrane (PM) trafficking. Previously, we reported that Oryza sativa Rab11 (OsRab11) plays an important role in the intracellular trafficking from the trans-Golginetwork (TGN) to the plasma membrane (PM) and prevacuolar compartments (PVCs), and in the plant’s response to high salt stress. In this study, when the constitutively active mutant of OsRab11, (CA OsRab11(Q73L)) was co-transformed with Arabidopsis Ca2+-ATPase8-GFP (ACA8-GFP) or sporamin-GFP (Spo-GFP) into Arabidopsis protoplasts, the PM or vacuolar trafficking proportion of the reporter proteins was highly increased. Transgenic Arabidopsis plants overexpressing (OE) CA OsRab11(Q73L) exhibited enhanced tolerance to high salt stress and exogenous abscisic acid (ABA) compared to Col plants. Moreover, certain stress-responsive genes were expressed under high salt stress and ABA treatment in OEOsRab11(Q73L) plants. Thus, these results suggest that the active conformation of OsRab11 may be required to modulate plant responses to salt and ABA via the regulation of the expression of stress-responsive genes.

Inoculation with Bacillus subtilis and Azospirillum brasilense Produces Abscisic Acid That Reduces Irt1-Mediated Cadmium Uptake of Roots.

Cadmium (Cd) contamination of agricultural soils represents a serious risk to crop safety. A new strategy using abscisic acid (ABA)-generating bacteria, Bacillus subtilis or Azospirillum brasilense, was developed to reduce the Cd accumulation in plants grown in Cd-contaminated soil. Inoculation with either bacterium resulted in a pronounced increase in the ABA level in wild-type Arabidopsis Col-0 plants, accompanied by a decrease in Cd levels in plant tissues, which mitigated the Cd toxicity. As a consequence, the growth of plants exposed to Cd was improved. Nevertheless, B. subtilis and A. brasilense inoculation had little effect on Cd levels and toxicity in the ABA-insensitive mutant snrk 2.2/2.3, indicating that the action of ABA is required for these bacteria to reduce Cd accumulation in plants. Furthermore, inoculation with either B. subtilis or A. brasilense downregulated the expression of IRT1 (iron-regulated transporter 1) in the roots of wild-type plants and had little effect on Cd levels in the IRT1-knockout mutants irt1-1 and irt1-2. In summary, we conclude that B. subtilis and A. brasilense can reduce Cd levels in plants via an IRT1-dependent ABA-mediated mechanism.

The Role of Programmed Cell Death Regulator LSD1 in Nematode-Induced Syncytium Formation.

Cyst-forming plant-parasitic nematodes are common pests of many crops. They inject secretions into host cells to induce the developmental and metabolic reprogramming that leads to the formation of a syncytium, which is the sole food source for growing nematodes. As in other host-parasite models, avirulence leads to rapid and local programmed cell death (PCD) known as the hypersensitive response (HR), whereas in the case of virulence, PCD is still observed but is limited to only some cells. Several regulators of PCD were analyzed to understand the role of PCD in compatible plant–nematode interactions. Thus, Arabidopsis plants carrying recessive mutations in LESION SIMULATING DISEASE1 (LSD1) family genes were subjected to nematode infection assays with juveniles of Heterodera schachtii. LSD1 is a negative and conditional regulator of PCD, and fewer and smaller syncytia were induced in the roots of lsd1 mutants than in wild-type Col-0 plants. Mutation in LSD ONE LIKE2 (LOL2) revealed a pattern of susceptibility to H. schachtii antagonistic to lsd1. Syncytia induced on lsd1 roots compared to Col0 showed significantly retarded growth, modified cell wall structure, increased vesiculation, and some myelin-like bodies present at 7 and 12 days post-infection. To place these data in a wider context, RNA-sequencing analysis of infected and uninfected roots was conducted. During nematode infection, the number of transcripts with changed expression in lsd1 was approximately three times smaller than in wild-type plants (1440 vs. 4206 differentially expressed genes, respectively). LSD1-dependent PCD in roots is thus a highly regulated process in compatible plant–nematode interactions. Two genes identified in this analysis, coding for AUTOPHAGY-RELATED PROTEIN 8F and 8H were down-regulated in syncytia in the presence of LSD1 and showed an increased susceptibility to nematode infection contrasting with lsd1 phenotype. Our data indicate that molecular regulators belonging to the LSD1 family play an important role in precise balancing of diverse PCD players during syncytium development required for successful nematode parasitism.

The common bean COK-4 and the Arabidopsis FER kinase domain share similar functions in plant growth and defence.

Receptor-like kinases are membrane proteins that can be shared by diverse signalling pathways. Among them, the Arabidopsis thaliana FERONIA (FER) plays a role in the balance between distinct signals to control growth and defence. We have found that COK-4, a putative kinase encoded in the common bean anthracnose resistance locus Co-4, which is transcriptionally regulated during the immune response, is highly similar to the kinase domain of FER. To assess whether COK-4 is a functional orthologue of FER, we expressed COK-4 in the wild-type Col-0 and the fer-5 mutant of Arabidopsis and evaluated FER-associated traits. We observed that fer-5 plants show an enhanced apoplastic and stomatal defence against Pseudomonas syringae. In addition, the fer-5 mutant shows reduced biomass, smaller guard cell size, greater number of stomata per leaf area, fewer leaves, faster transition to reproductive stage and lower seed weight per plant than the wild-type Col-0. Except for the stomatal complex length and number of stomata, COK-4 expression in fer-5 lines partially or completely rescued both defence and developmental defects of fer-5 to the wild-type level. Notably, COK-4 may have an additive effect to FER, as the expression of COK-4 in Col-0 resulted in enhanced defence and growth phenotypes in comparison with wild-type Col-0 plants. Altogether, these findings indicate that the common bean COK-4 shares at least some of the multiple functions of the Arabidopsis FER kinase domain, acting in both the induction of plant growth and regulation of plant defence.

AtMyb56 Regulates Anthocyanin Levels via the Modulation of AtGPT2 Expression in Response to Sucrose in Arabidopsis.

Sucrose is a crucial compound for the growth and development of plants, and the regulation of multiple genes depends on the amount of soluble sugars present. Sucrose acts as a signaling molecule that regulates a proton-sucrose symporter, with its sensor being the sucrose transporter. Flavonoid and anthocyanin biosynthesis are regulated by sucrose, and sucrose signaling can affect flavonoid and anthocyanin accumulation. In the present study, we found a Myb transcription factor affecting accumulation of anthocyanin. AtMyb56 showed an increase in its expression in response to sucrose treatment. Under normal conditions, anthocyanin accumulation was similar between Col-0 (wild type) and atmyb56 mutant seedlings; however, under sucrose treatment, the level of anthocyanin accumulation was lower in the atmyb56 mutant plants than in Col-0 plants. Preliminary microarray analysis led to the investigation of the expression of one candidate gene, AtGPT2, in the atmyb56 mutant. The phosphate translocator, which is a plastidial phosphate antiporter family, catalyzes the import of glucose-6-phosphate (G-6-P) into the chloroplast. AtGPT2 gene expression was altered in atmyb56 seedlings in a sucrose-dependent manner in response to circadian cycle. Furthermore, the lack of AtMyb56 resulted in altered accumulation of maltose in a sucrose-dependent manner. Therefore, the sucrose responsive AtMyb56 regulates AtGPT2 gene expression in a sucrose-dependent manner to modulate maltose and anthocyanin accumulations in response to the circadian cycle.

Accession-specific life strategies affect responses in leaves of Arabidopsis thaliana plants exposed to excess Cu and Cd

The natural accession Columbia (Col-0) is considered as the reference genome of the model plant Arabidopsis thaliana. Nonetheless, Col-0 plants are more sensitive to excess copper (Cu) and cadmium (Cd) than other widely used accessions such as Wassilewskija (Ws) plants. In the current study, this accession-specific metal sensitivity is further explored by comparing the responses in leaves of Col-0 and Ws plants exposed to excess Cu and Cd.Our results suggest that different life strategies favored by both accessions under physiological conditions affect their response to metal exposure. While Col-0 plants mainly invest in metal detoxification, Ws plants center on nutrient homeostasis. In particular, the higher expression of genes related to Cu homeostasis genes in non-exposed conditions indicates that Ws plants possess a constitutively efficient metal homeostasis. On the other hand, oxidative stress-related MAPK signaling appears to be boosted in leaves of Col-0 plants exposed to excess Cu. Furthermore, the upregulation of the glutathione (GSH) biosynthesis GSH2 gene and the increased GSH concentration after Cd exposure suggest the activation of detoxification mechanisms, such as phytochelatin production, to counteract the more severe Cd-induced oxidative stress in leaves of Col-0 plants. Exposure to Cd also led to a more pronounced ethylene signaling response in leaves of Col-0 as compared to Ws plants, which could be related to Cd-induced GSH metabolism. In conclusion, accession-specific life strategies clearly affect the way in which leaves of A. thaliana plants cope with excess Cu and Cd.