Elevated CO2 alters photosynthesis, growth and susceptibility to powdery mildew of oak seedlings

Elevated CO2 (eCO2) is a determinant factor of climate change and is known to alter plant processes such as physiology, growth and resistance to pathogens. Quercus robur, a tree species integrated in most forest regeneration strategies, shows high vulnerability to powdery mildew (PM) disease at the seedling stage. PM is present in most oak forests and it is considered a bottleneck for oak woodland regeneration. Our study aims to decipher the effect of eCO2 on plant responses to PM. Oak seedlings were grown in controlled environment at ambient (aCO2, ∼400 ppm) and eCO2 (∼1000 ppm), and infected with Erysiphe alphitoides, the causal agent of oak PM. Plant growth, physiological parameters and disease progression were monitored. In addition, to evaluate the effect of eCO2 on induced resistance (IR), these parameters were assessed after treatments with IR elicitor β-aminobutyric acid (BABA). Our results show that eCO2 increases photosynthetic rates and aerial growth but in contrast, reduces root length. Importantly, under eCO2 seedlings were more susceptible to PM. Treatments with BABA protected seedlings against PM and this protection was maintained under eCO2. Moreover, irrespectively of the concentration of CO2, BABA did not significantly change aerial growth but resulted in longer radicular systems, thus mitigating the effect of eCO2 in root shortening. Our results demonstrate the impact of eCO2 in plant physiology, growth and defence, and warrant further biomolecular studies to unravel the mechanisms by which eCO2 increases oak seedling susceptibility to PM.

Mechanisms associated with the synergistic induction of resistance to tobacco black shank in tobacco by arbuscular mycorrhizal fungi and β-aminobutyric acid

Tobacco black shank (TBS), caused by Phytophthora nicotianae, is one of the most harmful diseases of tobacco. There are many studies have examined the mechanism underlying the induction of disease resistance by arbuscular mycorrhizal fungi (AMF) and β-aminobutyric acid (BABA) alone, but the synergistic effects of AMF and BABA on disease resistance have not yet been studied. This study examined the synergistic effects of BABA application and AMF inoculation on the immune response to TBS in tobacco. The results showed that spraying BABA on leaves could increase the colonization rate of AMF, the disease index of tobacco infected by P.nicotianae treated with AMF and BABA was lower than that of P.nicotianae alone. The control effect of AMF and BABA on tobacco infected by P.nicotianae was higher than that of AMF or BABA and P.nicotianae alone. Joint application of AMF and BABA significantly increased the content of N, P, and K in the leaves and roots, in the joint AMF and BABA treatment than in the sole P. nicotianae treatment. The dry weight of plants treated with AMF and BABA was 22.3% higher than that treated with P.nicotianae alone. In comparison to P. nicotianae alone, the combination treatment with AMF and BABA had increased Pn, Gs, Tr, and root activity, while P. nicotianae alone had reduced Ci, H₂O₂ content, and MDA levels. SOD, POD, CAT, APX, and Ph activity and expression levels were increased under the combined treatment of AMF and BABA than in P.nicotianae alone. In comparison to the treatment of P.nicotianae alone, the combined use of AMF and BABA increased the accumulation of GSH, proline, total phenols, and flavonoids. Therefore, the joint application of AMF and BABA can enhance the TBS resistance of tobacco plants to a greater degree than the application of either AMF or BABA alone. In summary, the application of defense-related amino acids, combined with inoculation with AMF, significantly promoted immune responses in tobacco. Our findings provide new insights that will aid the development and use of green disease control agents.

Distinct chemical resistance-inducing stimuli result in common transcriptional, metabolic, and nematode community signatures in rice root and rhizosphere

Induced resistance (IR), a phenotypic state induced by an exogenous stimulus and characterized by enhanced resistance to future (a)biotic challenge, is an important component of plant immunity. Numerous IR-inducing stimuli have been described in various plant species, but relatively little is known about 'core' systemic responses shared by these distinct IR stimuli and the effects of IR on plant-associated microbiota. In this study, rice (Oryza sativa) leaves were treated with four distinct IR stimuli (β-aminobutyric acid, acibenzolar-S-methyl, dehydroascorbic acid, and piperonylic acid) capable of inducing systemic IR against the root-knot nematode Meloidogyne graminicola and evaluated their effect on the root transcriptome and exudome, and root-associated nematode communities. Our results reveal shared transcriptional responses-notably induction of jasmonic acid and phenylpropanoid metabolism-and shared alterations to the exudome that include increased amino acid, benzoate, and fatty acid exudation. In rice plants grown in soil from a rice field, IR stimuli significantly affected the composition of rhizosphere nematode communities 3 d after treatment, but by 14 d after treatment these changes had largely reverted. Notably, IR stimuli did not reduce nematode diversity, which suggests that IR might offer a sustainable option for managing plant-parasitic nematodes.

Transcriptional profiling of defense responses to Botrytis cinerea infection in leaves of Fragaria vesca plants soil-drenched with β-aminobutyric acid

Grey mold caused by the necrotrophic fungal pathogen Botrytis cinerea can affect leaves, flowers, and berries of strawberry, causing severe pre- and postharvest damage. The defense elicitor β-aminobutyric acid (BABA) is reported to induce resistance against B. cinerea and many other pathogens in several crop plants. Surprisingly, BABA soil drench of woodland strawberry (Fragaria vesca) plants two days before B. cinerea inoculation caused increased infection in leaf tissues, suggesting that BABA induce systemic susceptibility in F. vesca. To understand the molecular mechanisms involved in B. cinerea susceptibility in leaves of F. vesca plants soil drenched with BABA, we used RNA sequencing to characterize the transcriptional reprogramming 24 h post-inoculation. The number of differentially expressed genes (DEGs) in infected vs. uninfected leaf tissue in BABA-treated plants was 5205 (2237 upregulated and 2968 downregulated). Upregulated genes were involved in pathogen recognition, defense response signaling, and biosynthesis of secondary metabolites (terpenoid and phenylpropanoid pathways), while downregulated genes were involved in photosynthesis and response to auxin. In control plants not treated with BABA, we found a total of 5300 DEGs (2461 upregulated and 2839 downregulated) after infection. Most of these corresponded to those in infected leaves of BABA-treated plants but a small subset of DEGs, including genes involved in 'response to biologic stimulus', 'photosynthesis' and 'chlorophyll biosynthesis and metabolism', differed significantly between treatments and could play a role in the induced susceptibility of BABA-treated plants.

L-Aspartate and L-Glutamine Inhibit Beta-Aminobutyric Acid-Induced Resistance in Tomatoes

Plant diseases caused by pathogens lead to economic and agricultural losses, while plant resistance is defined by robustness and timing of defence response. Exposure to microbial-associated molecular patterns or specific chemical compounds can promote plants into a primed state with more robust defence responses. β-aminobutyric acid (BABA) is an endogenous stress metabolite that induces resistance, thereby protecting various plants' diverse stresses by induction of non-canonical activity after binding into aspartyl-tRNA synthetase (AspRS). In this study, by integrating BABA-induced changes in selected metabolites and transcript data, we describe the molecular processes involved in BABA-induced resistance (BABA-IR) in tomatoes. BABA significantly restricted the growth of the pathogens P. syringae pv. tomato DC3000 and was related to the accumulation of transcripts for pathogenesis-related proteins and jasmonic acid signalling but not salicylic acid signalling in Arabidopsis. The resistance was considerably reduced by applying amino acids L-Asp and L-Gln when L-Gln prevents general amino acid inhibition in plants. Analysis of amino acid changes suggests that BABA-IR inhibition by L-Asp is due to its rapid metabolisation to L-Gln and not its competition with BABA for the aspartyl-tRNA synthetase (AspRS) binding site. Our results showed differences between the effect of BABA on tomatoes and other model plants. They highlighted the importance of comparative studies between plants of agronomic interest subjected to treatment with BABA.

MADS2 regulates priming defence in postharvest peach through combined salicylic acid and abscisic acid signaling

MADS-box genes play well-documented roles in plant development, but relatively little is known regarding their involvement in defence responses. In this study, pre-treatment of peach (Prunus persica) fruit with β-aminobutyric acid (BABA) activated resistance against Rhizopus stolonifer, leading to a significant delay in the symptomatic appearance of disease. This was associated with an integrated defence response that included a H2O2 burst, ABA accumulation, and callose deposition. cDNA library screening identified nucleus-localized MADS2 as an interacting partner with NPR1, and this was further confirmed by yeast two-hybrid, luciferase complementation imaging, and co-immunoprecipitation assays. The DNA-binding activity of NPR1 conferred by the NPR1-MADS2 complex was required for the transcription of SA-dependent pathogenesis-related (PR) and ABA-inducible CalS genes in order to gain the BABA-induced resistance, in which MAPK1-induced post-translational modification of MADS2 was also involved. In accordance with this, overexpression of PpMADS2 in Arabidopsis potentiated the transcription of a group of PR genes and conferred fungal resistance in the transgenic plants. Conversely, Arabidopsis mads2-knockout lines showed high sensitivity to the fungal pathogen. Our results indicate that MADS2 positively participates in BABA-elicited defence in peach through a combination of SA-dependent NPR1 activation and ABA signaling-induced callose accumulation, and that this defence is also related to the post-translational modification of MADS2 by MAPK1 for signal amplification.

pekinensis) Seedlings with Improved Photosynthetic Performance and Antioxidant System

Heat stress is one of the major abiotic factors that limit the growth, development, and productivity of plants. Both glycine betaine (GB) and β-aminobutyric acid (BABA) have received considerable attention due to their roles in stimulating tolerance to diverse abiotic stresses. In order to understand how GB and BABA biostimulants alleviate heat stress in a cool-weather Chinese cabbage (Brassica rapa L. ssp. pekinensis) plant, we investigated the GB- and BABA-primed heat-stressed plants in terms of their morpho-physiological and biochemical traits. Priming with GB (15 mM) and BABA (0.2 mM) was conducted at the third leaf stage by applying foliar sprays daily for 5 days before 5 days of heat stress (45 °C in 16 h light/35 °C in 8 h dark) on Chinese cabbage seedlings. The results indicate that GB and BABA significantly increased chlorophyll content, and the parameters of both gas exchange and chlorophyll fluorescence, of Chinese cabbage under heat stress. Compared with the unprimed heat-stressed control, the dry weights of GB- and BABA-primed plants were significantly increased by 36.36% and 45.45%, respectively. GB and BABA priming also greatly mitigated membrane damage, as indicated by the reduction in malondialdehyde (MDA) and electrolyte leakage through the elevation of proline content, and increased activity levels of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX). Taken together, GB and BABA have great potential to enhance the thermotolerance of Chinese cabbage through higher photosynthesis performance, osmoprotection, and antioxidant enzyme activity.

Activation of the BABA-induced priming defence through redox homeostasis and the modules of TGA1 and MAPKK5 in postharvest peach fruit

The priming of defence responses in pathogen-challenged model plants undergoes a preparation phase and an expression phase for defence function. However, the priming response in postharvest fruits has not been elucidated. Here, we found that 50 mM β-aminobutyric acid (BABA) treatment could induce two distinct pathways linked with TGA1-related systemic acquired resistance (SAR), resulting in the alleviation of Rhizopus rot in postharvest peach fruit. The first priming phase was elicited by BABA alone, leading to the enhanced transcription of redox-regulated genes and posttranslational modification of PpTGA1. The second phase was activated by an H₂ O₂ burst via up-regulation of PpRBOH genes and stimulation of the MAPK cascade on pathogen invasion, resulting in a robust defence. In the MAPK cascade, PpMAPKK5 was identified as a shortcut interacting protein of PpTGA1 and increased the DNA binding activity of PpTGA1 for the activation of salicylic acid (SA)-responsive PR genes. The overexpression of PpMAPKK5 in Arabidopsis caused the constitutive transcription of SA-dependent PR genes and as a result conferred resistance against the fungus Rhizopus stolonifer. Hence, we suggest that the BABA-induced priming defence in peaches is activated by redox homeostasis with an elicitor-induced reductive signalling and a pathogen-stimulated H₂ O₂ burst, which is accompanied by the possible phosphorylation of PpTGA1 by PpMAPKK5 for signal amplification.

Alterations in Sucrose and Phenylpropanoid Metabolism Affected by BABA-Primed Defense in Postharvest Grapes and the Associated Transcriptional Mechanism

Defense elicitors can induce fruit disease resistance to control postharvest decay but may incur quality impairment. Our present work aimed to investigate the resistance against Botrytis cinerea induced by the elicitor β-aminobutyric acid (BABA) and to elucidate the specific transcriptional mechanism implicated in defense-related metabolic regulations. The functional dissection results demonstrated that, after inoculation with the fungal necrotroph B. cinerea, a suite of critical genes encoding enzymes related to the sucrose metabolism and phenylpropanoid pathway in priming defense in grapes were transcriptionally induced by treatment with 10 mM BABA. In contrast, more UDP-glucose, a shared precursor of phenylpropanoid and sucrose metabolism, may be redirected to the phenylpropanoid pathway for the synthesis of phytoalexins, including trans-resveratrol and ɛ-viniferin, in 100 mM BABA-treated grapes, resulting in direct resistance but compromised soluble sugar contents. An R2R3-type MYB protein from Vitis vinifera, VvMYB44, was isolated and characterized. VvMYB44 expression was significantly induced upon the grapes expressed defensive reaction. Subcellular localization, yeast two-hybrid, and coimmunoprecipitation assays revealed that the nuclear-localized VvMYB44 physically interacted with the salicylic acid-responsive transcription coactivator NPR1 in vivo for defense expression. In addition, VvMYB44 directly bound to the promoter regions of sucrose and phenylpropanoid metabolism-related genes and transactivated their expression, thus tipping the balance of antifungal compound accumulation and soluble sugar maintenance. Hence, these results suggest that 2R-type VvMYB44 might be a potential positive participant in BABA-induced priming defense in grape berries that contributes to avoiding the excessive consumption of soluble sugars during the postharvest storage.[Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Corrigendum: Heat Shock Protein HSP24 Is Involved in the BABA-Induced Resistance to Fungal Pathogen in Postharvest Grapes Underlying an NPR1-Dependent Manner

[This corrects the article DOI: 10.3389/fpls.2021.646147.].

Heat Shock Protein HSP24 Is Involved in the BABA-Induced Resistance to Fungal Pathogen in Postharvest Grapes Underlying an NPR1-Dependent Manner

Although heat shock proteins (HSPs), a family of ubiquitous molecular chaperones, are well characterized in heat stress-related responses, their function in plant defense remains largely unclear. Here, we report the role of VvHSP24, a class B HSP from Vitis vinifera, in β-aminobutyric acid (BABA)-induced priming defense against the necrotrophic fungus Botrytis cinerea in grapes. Grapes treated with 10 mmol L^-1 BABA exhibited transiently increased transcript levels of VvNPR1 and several SA-inducible genes, including PR1, PR2, and PR5. Additionally, phytoalexins accumulated upon inoculation with the gray mold fungus B. cinerea, which coincided with the action of a priming mode implicated in pathogen-driven resistance. Intriguingly, electrophoretic mobility shift (EMSA), yeast two-hybrid (Y2H) and His pull-down assays demonstrated that the nuclear chaperone VvHSP24 cannot modulate the transcript of PR genes but does directly interact with VvNPR1 in vivo or in vitro. Furthermore, we found that VvHSP24 overexpression enhanced the transcript levels of NPR1 and SA-responsive genes (PR1, PR2, and PR5) and increased the resistance of transgenic Arabidopsis thaliana to B. cinerea compared with wildtype Col-0. An opposite trend between CRISPR mutants of AtHSFB1 (the orthologous gene of VvHSP24 in Arabidopsis) and wildtype plants was observed. Hence, our results suggest that VvHSP24 has a potential role in NPR1-dependent plant resistance to fungal pathogen. BABA-induced priming defense in grapes may require posttranslational modification of the chaperone VvHSP24 to activate VvNPR1 transcript, leading to PR gene expressions and resistance phenotypes.

β-aminobutyric acid induces priming defence against Botrytis cinerea in grapefruit by reducing intercellular redox status that modifies posttranslation of VvNPR1 and its interaction with VvTGA1

Either NPR1 or TGA1 serve as master redox-sensitive transcriptional regulators for the transcription of PR genes in plants. The redox modification of the two co-activators involved in BABA-induced priming resistance against Botrytis cinerea in grapes was examined in this study. The results showed that 10 mmol L^-1 BABA could effectively trigger a priming defense in grapes as manifested by augmented expression levels of PR genes upon inoculation with B. cinerea. Moreover, transcriptome profiling analysis revealed that all of the sets of key genes in the enzymatic ROS scavenging system, the PPP and AsA-GSH cycle were in harmony and were transcriptionally induced in BABA-primed grapes with pathogenic infection; in addition, this enhanced expression caused the accelerated accumulation of reductive substances, namely, AsA, GSH and NADPH, resulting in reduced intercellular conditions. Under reduced conditions, the interaction of VvTGA1 and VvNPR1 in the Y2H assay implied that VvTGA1 can provide the DNA binding capacity required by VvNPR1 for activation of VvPR genes. Consequently, the transactivation of VvNPR1 by the promoters of VvPR1, VvPR2 and VvPR5 was determined via a DLR assay, and it induced the transcription of the VvPR genes. In parallel, the redox-modified reducing condition achieved with an abundant supply of reductive substances was closely associated with the translocation of NPR1 for interaction with TGA in the nucleus. Thus, the posttranslational modification and subsequent interaction of the two redox-sensitive co-activators of VvNPR1 and VvTGA1 under reduced conditions may be responsible for BABA-induced priming for effective disease resistance in grapes.

The IBI1 Receptor of β-Aminobutyric Acid Interacts with VOZ Transcription Factors to Regulate Abscisic Acid Signaling and Callose-Associated Defense

External and internal signals can prime the plant immune system for a faster and/or stronger response to pathogen attack. β-aminobutyric acid (BABA) is an endogenous stress metabolite that induces broad-spectrum disease resistance in plants. BABA perception in Arabidopsis is mediated by the aspartyl tRNA synthetase IBI1, which activates priming of multiple immune responses, including callose-associated cell wall defenses that are under control by abscisic acid (ABA). However, the immediate signaling components after BABA perception by IBI1, as well as the regulatory role of ABA therein, remain unknown. Here, we have studied the early signaling events controlling IBI1-dependent BABA-induced resistance (BABA-IR), using untargeted transcriptome and protein interaction analyses. Transcriptome analysis revealed that IBI1-dependent expression of BABA-IR against the biotrophic oomycete Hyaloperonospora arabidopsidis is associated with suppression of ABA-inducible abiotic stress genes. Protein interaction studies identified the VOZ1 and VOZ2 transcription factors (TFs) as IBI1-interacting partners, which are transcriptionally induced by ABA but suppress pathogen-induced expression of ABA-dependent genes. Furthermore, we show that VOZ TFs require nuclear localization for their contribution to BABA-IR by mediating augmented expression of callose-associated defense. Collectively, our study indicates that the IBI1-VOZ signaling module channels pathogen-induced ABA signaling toward cell wall defense while simultaneously suppressing abiotic stress-responsive genes.

Redox status regulates subcelluar localization of PpTGA1 associated with a BABA-induced priming defence against Rhizopus rot in peach fruit

This study attempted to characterize the involvement of a change in the redox status and subcellular localization in the BABA-induced priming resistance of peach fruit against Rhizopus rot. Specifically, 50 mM BABA primed the peaches for the enhanced disease resistance against R. stolonifer, as demonstrated by suppression of the disease development upon pathogen challenge accompanied by the clearly elevated level of TGA transcription factor (PpTGA1) and NPR1 gene (PpNPR1). In addition, the BABA elicitation enhanced the activities of a series of critical enzymes in the PPP and AsA-GSH cycle, and eventually promoted the NADPH and GSH pools, which altered the intracellular redox state towards a highly reductive condition. Additionally, PpTGA1-GFP was localized in the cytoplasm in the absence of BABA treatment or R. stolonifer inoculation, while BABA elicitation plus R. stolonifer inoculation caused PpTGA1-GFP to specifically translocate to the nucleus, where it interacted with PpNPR1 and regulated the positive expression of PR genes. Therefore, the observations implied that BABA could promote the reduction of the redox state, resulting in the translocation of PpTGA1 to the nucleus, which was a prerequisite for the induction of a priming defence against Rhizopus rot in peach.

Nitric Oxide Plays an Important Role in β-Aminobutyric Acid-Induced Resistance to Botrytis cinerea in Tomato Plants

β-Aminobutyric acid (BABA) has consistently been reported to enhance plant immunity. However, the specific mechanisms and downstream components that mediate this resistance are not yet agreed upon. Nitric oxide (NO) is an important signal molecule involved in a diverse range of physiological processes, and whether NO is involved in BABA-induced resistance is interesting. In this study, treatment with BABA significantly increased NO accumulation and reduced the sensitivity to Botrytis cinerea in tomato plants. BABA treatment reduced physical signs of infection and increased both the transcription of key defense marker genes and the activity of defensive enzymes. Interestingly, compared to treatment with BABA alone, treatment with BABA plus cPTIO (NO specific scavenger) not only significantly reduced NO accumulation, but also increased disease incidence and lesion area. These results suggest that NO accumulation plays an important role in BABA-induced resistance against B. cinerea in tomato plants.

Combination of β-Aminobutyric Acid and Ca2+ Alleviates Chilling Stress in Tobacco (Nicotiana tabacum L.)

Chilling is a major abiotic factor limiting the growth, development, and productivity of plants. β-aminobutyric acid (BABA), a new environmentally friendly agent, is widely used to induce plant resistance to biotic and abiotic stress. Calcium, as a signaling substance, participates in various physiological activities in cells and plays a positive role in plant defense against cold conditions. In this study, we used tobacco as a model plant to determine whether BABA could alleviate chilling stress and further to explore the relationship between BABA and Ca²⁺. The results showed that 0.2 mM BABA significantly reduced the damage to tobacco seedlings from chilling stress, as evidenced by an increase in photosynthetic pigments, the maintenance of cell structure, and upregulated expression of NtLDC1, NtERD10B, and NtERD10D. Furthermore, 0.2 mM BABA combined with 10 mM Ca²⁺ increased the fresh and dry weights of both roots and shoots markedly. Compared to that with single BABA treatment, adding Ca²⁺ reduced cold injury to the plant cell membrane, decreased ROS production, and increased antioxidant enzyme activities and antioxidant contents. The combination of BABA and Ca²⁺ also improved abscisic acid and auxin contents in tobacco seedlings under chilling stress, whereas ethylene glycol-bis (β-aminoethylether)-N,N,N',N'-tetraacetic acid (EGTA) reversed the effects of BABA. These findings suggested that BABA enhances the cold tolerance of tobacco and is closely related to the state of Ca²⁺ signaling.

β-Aminobutyric Acid Priming Acquisition and Defense Response of Mango Fruit to Colletotrichum gloeosporioides Infection Based on Quantitative Proteomics

β-aminobutyric acid (BABA) is a new environmentally friendly agent to induce disease resistance by priming of defense in plants. However, molecular mechanisms underlying BABA-induced priming defense are not fully understood. Here, comprehensive analysis of priming mechanism of BABA-induced resistance was investigated based on mango-Colletotrichum gloeosporioides interaction system using iTRAQ-based proteome approach. Results showed that BABA treatments effectively inhibited the expansion of anthracnose caused by C. gleosporioides in mango fruit. Proteomic results revealed that stronger response to pathogen in BABA-primed mango fruit after C. gleosporioides inoculation might be attributed to differentially accumulated proteins involved in secondary metabolism, defense signaling and response, transcriptional regulation, protein post-translational modification, etc. Additionally, we testified the involvement of non-specific lipid-transfer protein (nsLTP) in the priming acquisition at early priming stage and memory in BABA-primed mango fruit. Meanwhile, spring effect was found in the primed mango fruit, indicated by inhibition of defense-related proteins at priming phase but stronger activation of defense response when exposure to pathogen compared with non-primed fruit. As an energy-saving strategy, BABA-induced priming might also alter sugar metabolism to provide more backbone for secondary metabolites biosynthesis. In sum, this study provided new clues to elucidate the mechanism of BABA-induced priming defense in harvested fruit.

Effect of β-Aminobutyric Acid on Disease Resistance Against Rhizopus Rot in Harvested Peaches

The effect of β-aminobutyric acid (BABA) on Rhizopus rot produced by Rhizopus stolonifer in harvested peaches and the possible action modes were investigated. Treatment with 50 mmol L-1 of BABA resulted in significantly lower lesion diameter and disease incidence compared with the control. The activities of defense-related enzymes chitinase and β-1,3-glucanase were notably enhanced by this treatment. Meanwhile, BABA treatment also increased lignin accumulation and maintained higher energy status in peaches by enhancing activities of enzymes in the phenylpropanoid and energy metabolism pathways. Semiquantitative reverse transcription PCR results indicated that the transcription of four defense-related genes was substantially and rapidly enhanced only in that BABA-treated fruit upon inoculation with the pathogen. Thus, our results demonstrated that BABA was effective on controlling Rhizopus rot by inducing disease resistance, which includes the increase in gene transcription and activity of defense-related enzymes, the enhancement of cell wall strength, and the maintenance of high energy status in Prunus persica fruit. Moreover, the disease resistance induced by BABA was demonstrated through priming model rather than direct induction.

Benzothiadiazole and B-Aminobutyricacid Induce Resistance to Ectropis Obliqua in Tea Plants (Camellia Sinensis (L.) O. Kuntz)

In order to investigate the effect of benzothiadiazole (BTH) and β-aminobutyric acid (BABA) on the resistance of tea plants (Camellia sinensis) to tea geometrid (Ectropis obliqua), three levels each of benzothiadiazole (BTH) and β-aminobutyric acid (BABA) were sprayed on 10-year-old tea plants. Generally PPO and PAL activities increased with low concentrations of BTH and BABA treatments. Quantitative RT-PCR revealed a 1.43 and 2.72-fold increase in PPO gene expression, and 3.26 and 3.99-fold increase in PAL gene expression with 75 mg/L BTH and 400 mg/L BABA respectively. Analysis of hydrolysis of synthetic substrates also revealed that chymotrypsin-like enzyme activity present in larval midgut extracts was not significantly inhibited by BTH and BABA. However, proteinase activity was found to be inversely proportional to the age of tea geometrid. Larvae pupation rate decreased by 8.10, 10.81 and 21.62% when tea geometrid were fed with leaves treated with 25, 50 and 75 mg/L BTH solutions, while 100, 200 and 400 mg/L BABA solutions decreased same by 8.10, 16.21 and 13.51% respectively. Also, larvae development period delayed to 23.33 and 26.33 days with 75 mg/L BTH and 400 mg/L BABA treatments respectively. The results in this study; therefore, suggest that benzothiadiazole (BTH) and β-aminobutyric acid (BABA) play a role in inducing resistance in tea plants to tea geometrid, with the optimal effect achieved at BTH-3 (75 mg/L) and BABA-3 (400 mg/L), respectively.

Induction of Direct or Priming Resistance against Botrytis cinerea in Strawberries by β-Aminobutyric Acid and Their Effects on Sucrose Metabolism

The specific forms of disease resistance induced by β-aminobutyric acid (BABA) and their impacts on sucrose metabolism of postharvest strawberries were determined in the present research. Treatment with 10-500 mmol L(-1) BABA inhibited the Botrytis cinerea infection, possibly directly by suppressing the fungus growth and indirectly by triggering disease resistance. Moreover, BABA-induced resistance against B. cinerea infection in strawberries was associated with either one of two mechanisms, depending upon the concentration used: BABA at concentrations higher than 100 mmol L(-1) directly induced the defense response, including a H2O2 burst, modulation of the expression of PR genes, including FaPR1, FaChi3, Faβglu, and FaPAL, and increased activities of chitinase, β-1,3-glucanase, and PAL, whereas BABA at 10 mmol L(-1) activated a priming response because the BABA-treated fruits exhibited an increased capacity to express molecular defense only when the fruits were inoculated with B. cinerea. Activation of the priming defense appeared almost as effective against B. cinerea as inducing direct defense. However, the primed strawberries maintained higher activities of SS synthesis and SPS and SPP enzymes) and lower level of SS cleavage during the incubation; these activities contributed to higher sucrose, fructose, and glucose contents, sweetness index, and sensory scores compared to fruits exhibiting the direct defense. Thus, it is plausible that the priming defense, which can be activated by BABA at relatively low concentrations, represents an optimal strategy for combining the advantages of enhanced disease protection and soluble sugar accumulation.

β-aminobutyric acid mediated drought stress alleviation in maize (Zea mays L.)

The present study highlights the role of β-aminobutyric acid (BABA) in alleviating drought stress effects in maize (Zea mays L.). Chemical priming was imposed by pretreating 1-week-old plants with 600 μM BABA prior to applying drought stress. Specific activities of key antioxidant enzymes and metabolites (ascorbate and glutathione) levels of ascorbate-glutathione cycle were studied to unravel the priming-induced modulation of plant defense system. Furthermore, changes in endogenous ABA and JA concentrations as well as mRNA expressions of key genes involved in their respective biosynthesis pathways were monitored in BABA-primed (BABA+) and non-primed (BABA-) leaves of drought-challenged plants to better understand the mechanistic insights into the BABA-induced hormonal regulation of plant response to water-deficit stress. Accelerated stomatal closure, high relative water content, and less membrane damage were observed in BABA-primed leaves under water-deficit condition. Elevated APX and SOD activity in non-primed leaves found to be insufficient to scavenge all H2O2 and O2 (·-) resulting in oxidative burst as evident after histochemical staining with NBT and DAB. A higher proline accumulation in non-primed leaves also does not give much protection against drought stress. Increased GR activity supported with the enhanced mRNA and protein expressions might help the BABA-primed plants to maintain a high GSH pool essential for sustaining balanced redox status to counter drought-induced oxidative stress damages. Hormonal analysis suggests that in maize, BABA-potentiated drought tolerance is primarily mediated through JA-dependent pathway by the activation of antioxidant defense systems while ABA biosynthesis pathway also plays an important role in fine-tuning of drought stress response.

Comparative proteomic analysis of β-aminobutyric acid-mediated alleviation of salt stress in barley

The non-protein amino acid β-aminobutyric acid (BABA) is known to induce plant resistance to a broad spectrum of biotic and abiotic stresses. This is the first study describing the effect of BABA seed priming on physiological and proteomic changes under salt stress conditions in barley (Hordeum vulgare). The aim of our study was to investigate the changes of fresh weight, dry weight and relative water content (RWC) as well as root proteome changes of two barley lines contrasting in salt tolerance (DH14, DH 187) in response to salt stress after seed priming in water or in 800 μM BABA. Seed priming with BABA significantly increased (p ≤ 0.05) RWC in both barley lines, which indicates considerably lower water loss in BABA-primed plants than in the non-primed control plants. Dry and fresh matter increased significantly in line DH 187, whereas no changes were detected in line DH14. BABA-primed plants of both lines showed different proteomic patterns than the non-primed control plants. The root proteins exhibiting significant abundance changes (1.75-fold change, p ≤ 0.05) were separated by two-dimensional polyacrylamide gel electrophoresis (2D- PAGE). Thirty-one spots, representing 24 proteins, were successfully identified by MALDI TOF/TOF mass spectrometry. The most prominent differences include the up-regulation of antioxidant enzymes (catalase, peroxidase and superoxide dismutase), PR proteins (chitinase, endo-1,3-β-glucosidase), and chaperones (cyclophilin, HSC 70). Our results indicate that BABA induces defence and detoxification processes which may enable faster and more effective responses to salt stress, increasing the chances of survival under adverse environmental conditions.

Normoergic NO-dependent changes, triggered by a SAR inducer in potato, create more potent defense responses to Phytophthora infestans

In our experimental approach we examined how potato leaves exposed to a chemical agent might induce nitric oxide (NO) dependent biochemical modifications for future mobilization of an effective resistance to Phytophthora infestans. After potato leaf treatment with one of the following SAR inducers, i.e. β-aminobutyric acid (BABA), 2,6-dichloroisonicotinic acid (INA) or Laminarin, we observed enhanced NO generation concomitant with biochemical changes related to a slight superoxide anion (O2(-)) and hydrogen peroxide (H2O2) accumulation dependent on minimal NADPH oxidase and peroxidase activities, respectively. These rather normoergic changes, linked to the NO message, were mediated by the temporary down-regulation of S-nitrosoglutathione reductase (GSNOR). In turn, after challenge inoculation signal amplification promoted potato resistance manifested in the up-regulation of GSNOR activity tuned with the depletion of the SNO pool, which was observed by our team earlier (Floryszak-Wieczorek et al., 2012). Moreover, hyperergic defense responses related to an early and rapid O2(-)and H2O2 overproduction together with a temporary increase in NADPH oxidase and peroxidase activities were noted. BABA treatment was the most effective against P. infestans resulting in the enhanced activity of β-1,3-glucanase and callose deposition. Our results indicate that NO-mediated biochemical modifications might play an important role in creating more potent defense responses of potato to a subsequent P. infestans attack.

β-Aminobutyric acid increases abscisic acid accumulation and desiccation tolerance and decreases water use but fails to improve grain yield in two spring wheat cultivars under soil drying

A pot experiment was conducted to investigate the effect of the non-protein amino acid, β-aminobutyric acid (BABA), on the homeostasis between reactive oxygen species (ROS) and antioxidant defence during progressive soil drying, and its relationship with the accumulation of abscisic acid (ABA), water use, grain yield, and desiccation tolerance in two spring wheat (Triticum aestivum L.) cultivars released in different decades and with different yields under drought. Drenching the soil with 100 µM BABA increased drought-induced ABA production, leading to a decrease in the lethal leaf water potential (Ψ) used to measure desiccation tolerance, decreased water use, and increased water use efficiency for grain (WUEG) under moderate water stress. In addition, at severe water stress levels, drenching the soil with BABA reduced ROS production, increased antioxidant enzyme activity, and reduced the oxidative damage to lipid membranes. The data suggest that the addition of BABA triggers ABA accumulation that acts as a non-hydraulic root signal, thereby closing stomata, and reducing water use at moderate stress levels, and also reduces the production of ROS and increases the antioxidant defence enzymes at severe stress levels, thus increasing the desiccation tolerance. However, BABA treatment had no effect on grain yield of wheat when water availability was limited. The results suggest that there are ways of effectively priming the pre-existing defence pathways, in addition to genetic means, to improve the desiccation tolerance and WUEG of wheat.