Gabor Jakab

Dissecting the β-aminobutyric acid-induced priming phenomenon in Arabidopsis ?

Plants treated with the nonprotein amino acid β-aminobutyric acid (BABA) develop an enhanced capacity to resist biotic and abiotic stresses. This BABA-induced resistance (BABA-IR) is associated with an augmented capacity to express basal defense responses, a phenomenon known as priming. Based on the observation that high amounts of BABA induce sterility in Arabidopsis thaliana, a mutagenesis screen was performed to select mutants impaired in BABA-induced sterility (ibs). Here, we report the isolation and subsequent characterization of three T-DNA–tagged ibs mutants. Mutant ibs1 is affected in a cyclin-dependent kinase–like protein, and ibs2 is defective in AtSAC1b encoding a polyphosphoinositide phosphatase. Mutant ibs3 is affected in the regulation of the ABA1 gene encoding the abscisic acid (ABA) biosynthetic enzyme zeaxanthin epoxidase. To elucidate the function of the three IBS genes in plant resistance, the mutants were tested for BABA-IR against the bacterium Pseudomonas syringae pv tomato, the oomycete Hyaloperonospora parasitica, and BABA-induced tolerance to salt. All three ibs mutants were compromised in BABA-IR against H. parasitica, although to a different extent. Whereas ibs1 was reduced in priming for salicylate (SA)-dependent trailing necrosis, mutants ibs2 and ibs3 were affected in the priming for callose deposition. Only ibs1 failed to express BABA-IR against P. syringae, which coincided with a defect in priming for SA-inducible PR-1 gene expression. By contrast, ibs2 and ibs3 showed reduced BABA-induced tolerance to salt, which correlated with an affected priming for ABA-inducible gene expression. For all three ibs alleles, the defects in BABA-induced sterility and BABA-induced protection against P. syringae, H. parasitica, and salt could be confirmed in independent mutants. The data presented here introduce three novel regulatory genes involved in priming for different defense responses.

Enhancing Arabidopsis Salt and Drought Stress Tolerance by Chemical Priming for Its Abscisic Acid Responses

Drought and salt stress tolerance of Arabidopsis (Arabidopsis thaliana) plants increased following treatment with the nonprotein amino acid β-aminobutyric acid (BABA), known as an inducer of resistance against infection of plants by numerous pathogens. BABA-pretreated plants showed earlier and higher expression of the salicylic acid-dependent PR-1 and PR-5 and the abscisic acid (ABA)-dependent RAB-18 and RD-29A genes following salt and drought stress. However, non-expressor of pathogenesis-related genes 1 and constitutive expressor of pathogenesis-related genes 1 mutants as well as transgenic NahG plants, all affected in the salicylic acid signal transduction pathway, still showed increased salt and drought tolerance after BABA treatment. On the contrary, the ABA deficient 1 and ABA insensitive 4 mutants, both impaired in the ABA-signaling pathway, could not be protected by BABA application. Our data demonstrate that BABA-induced water stress tolerance is based on enhanced ABA accumulation resulting in accelerated stress gene expression and stomatal closure. Here, we show a possibility to increase plant tolerance for these abiotic stresses through effective priming of the preexisting defense pathways without resorting to genetic alterations.

β-Aminobutyric Acid-induced Resistance in Plants

Thehe broad sprectrum protective effect of the non-protein amino acid β-aminobutyric acid (BABA) against numerous plant diseases has been well-documented in the literature. Here, we present an overview of BABA-induced protection in various pathosystems. Contriidictory reports concerning the mechanism of action underlying this type of protection incited us to take advantage of Arabidopsis/pathogen interactions as model systems to investigate the action of BABA at the genetic and molecular level. We present evidence that the protective effect of BABA is due to a potentiation of natural defense mechanisms against biotic and abiotic stresses. In order to dissect the pathways involved in potentiation by BABA describe the use of a mutational approach based on BABA-induced female sterility in Arabidopsis.

β-Aminobutyric Acid-Induced Resistance Against Downy Mildew in Grapevine Acts Through the Potentiation of Callose Formation and Jasmonic Acid Signaling

beta-Aminobutyric acid (BABA) was used to induce resistance in grapevine (Vitis vinifera) against downy mildew (Plasmopara viticola). This led to a strong reduction of mycelial growth and sporulation in the susceptible cv. Chasselas. Comparing different inducers, the best protection was achieved with BABA followed by jasmonic acid (JA), whereas benzo (1,2,3)-thiadiazole-7-carbothionic acid-S-methyl ester (a salicylic acid [SA] analog) and abscisic acid (ABA) treatment did not increase the resistance significantly. Marker genes for the SA and JA pathways showed potentiated expression patterns in BABA-treated plants following infection. The callose synthesis inhibitor 2-deoxy-D-glucose partially suppressed BABA- and JA-induced resistance against P viticola in Chasselas. Application of the phenylalanine ammonia lyase inhibitor 2-aminoindan-2-phosphonic acid and the lipoxygenase (LOX) inhibitor 5, 8, 11, 14-eicosatetraynoic acid (ETYA) also led to a reduction of BABA-induced resistance (BABA-IR), suggesting that callose deposition as well as defense mechanisms depending on phenylpropanoids and the JA pathways all contribute to BABA-IR. The similar phenotype of BABA- and JA-induced resistance, the potentiated expression pattern of JA-regulated genes (LOX-9 and PR-4) following BABA treatment, and the suppression of BABA-IR with ETYA suggest an involvement of the JA pathway in BABA-IR of grapevine leading to a primed deposition of callose and lignin around the infection sites.

Molecular Characterization of a Novel Lipase-Like Pathogen-Inducible Gene Family of Arabidopsis

In a differential screening between Arabidopsis plants pretreated with the resistance-inducer β-aminobutyric acid and untreated control plants, we have identified a gene encoding a novel lipase-like protein, PRLIP1. The abundance of PRLIP1 mRNAs in Arabidopsis leaves was up-regulated by application of β-aminobutyric acid, salicylic acid (SA), and ethylene as well as by various pathogens. Induction of PRLIP1 depended on a functioning SA and ethylene signal transduction pathway but was independent of jasmonate signaling. This novel pathogenesis-related (PR) gene of Arabidopsis belongs to a gene family consisting of six (PRLIP1, PRLIP2, PRLIP4, PRLIP5, PRLIP6, and PRLIP7) closely related members in tandem position on chromosome 5. Among these genes, PRLIP2 also was induced in leaves by SA and infections by pathogens but on a much lower level than PRLIP1. The PRLIP1 family showed a tissue-specific expression pattern. Both PRLIP1 and PRLIP2 were specifically expressed in leaves and siliques, PRLIP1 additionally in stems and flowers. The expression of PRLIP6 and PRLIP4 was root specific, whereas mRNA of PRLIP5 and PRLIP7 were not detected in any of these tissues. The more distantly related genes PRLIP3, PRLIP9, and PRLIP8 were found on chromosomes 2, 4, and 5, respectively. The expression level of PRLIP3 was checked and found constitutive during the different stress conditions tested. The PRLIP1 gene was overexpressed in Escherichia coli, and the resulting PRLIP1 protein showed esterase activity on p-nitrophenyl-butyrate and allowed the growth of the bacteria on lipidic substrates such as Tween20 or Tween80.

Environmental plasticity of Pinot noir grapevine leaves: A trans-European study of morphological and biochemical changes along a 1,500-km latitudinal climatic gradient

A 2-year study explored metabolic and phenotypic plasticity of sun-acclimated Vitis vinifera cv. Pinot noir leaves collected from 12 locations across a 36.69-49.98°N latitudinal gradient. Leaf morphological and biochemical parameters were analysed in the context of meteorological parameters and the latitudinal gradient. We found that leaf fresh weight and area were negatively correlated with both global and ultraviolet (UV) radiation, cumulated global radiation being a stronger correlator. Cumulative UV radiation (sumUVR) was the strongest correlator with most leaf metabolites and pigments. Leaf UV-absorbing pigments, total antioxidant capacities, and phenolic compounds increased with increasing sumUVR, whereas total carotenoids and xanthophylls decreased. Despite of this reallocation of metabolic resources from carotenoids to phenolics, an increase in xanthophyll-cycle pigments (the sum of the amounts of three xanthophylls: violaxanthin, antheraxanthin, and zeaxanthin) with increasing sumUVR indicates active, dynamic protection for the photosynthetic apparatus. In addition, increased amounts of flavonoids (quercetin glycosides) and constitutive β-carotene and α-tocopherol pools provide antioxidant protection against reactive oxygen species. However, rather than a continuum of plant acclimation responses, principal component analysis indicates clusters of metabolic states across the explored 1,500-km-long latitudinal gradient. This study emphasizes the physiological component of plant responses to latitudinal gradients and reveals the physiological plasticity that may act to complement genetic adaptations.

Foliar exposure of grapevine (Vitis vinifera L.) to TiO2 nanoparticles under field conditions: Photosynthetic response and flavonol profile

In the past decade, utilization of nanostructured materials has increased intensively in a wide range of applications. Titanium dioxide nanoparticles (TiO2 NPs), for instance, can be applied for the inactivation of various pathogens through photo-induced generation of reactive oxygen species. Although TiO2 NPs with high antimicrobial activity are of great importance, in practice, their phytotoxic effects have not yet been fully clarified. In this study, we investigated the potential phytotoxicity of TiO2 NPs on grapevine (Vitis vinifera L.) under field conditions. After foliar exposure, two particularly stress-sensitive parameters, photosynthetic function and the flavonol profile, were examined. Micro- and macroelement composition of the leaves was also studied by ICP-AES measurements. We found that TiO2 NPs significantly decreased the net CO2 assimilation and increased stomatal conductance, indicating metabolic (nonstomatal) inhibition of the photosynthesis. The lower electron transport rate and lower nonphotochemical quenching in treated leaves are indicative of diminished photoprotective processes.

Contrasting acclimation mechanisms of berry color variant grapevine cultivars (Vitis vinifera L. cv. Furmint) to natural sunlight conditions

The acclimation mechanisms of two berry color variant grapevine leaves, Furmint White (FW) and Furmint Red (FR), to natural sunlight conditions were investigated comparing leaves from two distinct locations: at canopy surface (sun-exposed leaves) and in the inner layers (shaded leaves). We found that in contrast to FR leaves, sun-exposed FW leaves were thicker than shaded leaves due to thicker palisade tissues. Confocal laser scanning microscopy of Naturstoff-treated leaf segments revealed that flavonoids were accumulated in nuclei, cell walls, cytoplasm, and chloroplasts of the adaxial epidermal and palisade layers of sun-exposed leaves in both cultivars. High-performance liquid chromatography analysis showed that the main phenolic components in both cultivars were caftaric acid and various glycosylated flavonols. Among the latter, the dominant component was quercetin glucuronide in both cultivars, unaffected by light conditions. However, caftaric acid and quercetin glucoside were present in significantly higher amounts in sun-exposed than in shaded leaves of both cultivars, but the effect of light conditions on caftaric acid contents was more pronounced in FR than in FW. Accordingly, the total polyphenol content of leaf extracts characterized by Folin-reagent reactivity was more enhanced in sun-exposed leaves of FR, than in FW. Our data suggest two different sunlight acclimation strategies to protect photosynthetic mesophyll tissues from potential photo-oxidative damage. One is realized in FW leaves as stronger shading by thicker palisade layer accompanied by enhanced chemical defense. The other is achieved in FR leaves via a more pronounced increase in caftaric acid and total polyphenol content but without morphological adjustments.