SA Accumulation Research Articles

Glycoside hydrolase PpGH28BG1 modulates benzaldehyde metabolism and enhances fruit aroma and immune responses in peach.

Benzaldehyde (BAld) is one of the most widely distributed volatiles that contributes to flavor and defense in plants. Plants regulate BAld levels through various pathways, including biosynthesis from trans-cinnamic acid (free BAld), release from hydrolysis of glycoside precursors (BAld-H) via multiple enzymatic action steps, and conversion into downstream chemicals. Here, we show that BAld-H content in peach (Prunus persica) fruit is up to 100-fold higher than that of free BAld. By integrating transcriptome, metabolomic and biochemical approaches, we identified glycoside hydrolase PpGH28BG1 as being involved in the production of BAld-H through the hydrolysis of glycoside precursors. Overexpressing and silencing of PpGH28BG1 significantly altered BAld-H content in peach fruit. Transgenic tomatoes heterologously expressing PpGH28BG1 exhibited a decrease in BAld-H content and an increase in SA accumulation, while maintaining fruit weight, pigmentation, and ethylene production. These transgenic tomato fruits displayed enhanced immunity against Botrytis cinerea compared to wild type (WT). Induced expression of PpGH28BG1 and increased SA content were also observed in peach fruit when exposed to Monilinia fructicola infection. Additionally, elevated expression of PpGH28BG1 promoted fruit softening in transgenic tomatoes, resulting in a significantly increased emission of BAld compared to WT. Most untrained taste panelists preferred the transgenic tomatoes over WT fruit. Our study suggests that it is feasible to enhance aroma and immunity in fruit through metabolic engineering of PpGH28BG1 without causing visible changes in the fruit ripening process.

Melatonin alleviates arsenic (As) toxicity in rice plants via modulating antioxidant defense system and secondary metabolites and reducing oxidative stress

The Arsenic (As) load on the environment has increased immensely due to large-scale industrial and agricultural uses of As in several synthetic products, such as fertilizers, herbicides, and pesticides. Melatonin is a plant hormone that has a key role in abiotic stress inhibition, but the mechanism of resilience to As stress remains unexplored in rice plants. In this study, we determined how As affects rice plant and how melatonin facilitate As stress tolerance in rice. Here we investigated that, exogenous melatonin reduced As stress by inducing anthocyanin biosynthesis. Melatonin induced the expression of anthocyanin biosynthesis genes such as PAL, CHS, CHI, F3H, DFR, and ANS, which resulted in 1659% and 389% increases in cyanidin and delphinidin, respectively. Similarly, melatonin application significantly induced SA and ABA accumulation in response to As stress in rice plant. Application of melatonin also significantly reduced expression of PT-2 and PT-8 (transporter genes) and reduced uptake of As and its translocation to other compartments. Melatonin and As analysis revealed that melatonin application significantly reduced As contents in the melatonin-supplemented plants, suggesting that As uptake is largely dependent on either the melatonin basal level or anthocyanin in rice plants. In this study, we investigated new symptoms on leaves, which can severely damage leaves and impair photosynthesis. However, anthocyanin as a chelating agent, detoxifies As in vacuole and reduces oxidative stress induced by As.

Efficacy of endophytic SB10 and glycine betaine duo in alleviating phytotoxic impact of combined heat and salinity in Glycine max L. via regulation of redox homeostasis and physiological and molecular responses

Adverse environmental stresses occurring simultaneously exhibit a lethal effect on crop productivity at the global level. Here, we investigated the individual and synergistic effects of endophytic T. virens SB10 and glycine betaine (GB) on the physiological and biochemical responses of Glycine max L. to alleviate the devastating effects of combined heat and salinity (HS) stress. Screening against HS stress tolerance showed that SB10 has significant tolerance against heat stress and produces hormones such as gibberellins and indole-3-acetic acid upon GB amendment of the growth medium under HS stress. Moreover, the current findings illustrated that the synergistic application of SB10 and GB was effective in alleviating the negative effects of HS stress on plant growth and physiology. The findings revealed that SB10 + GB led to a reduction in proline accumulation and Na+ uptake. It also maintained a high K+/Na + ratio by regulating GmHKT1 and GmSOS1 expression and enhanced macronutrient uptake (N, Ca, K) in plants. In turn, plants exhibited a higher growth rate and gaseous exchange attributes coupled with the upregulation of APX, SOD, POD, and GSH antioxidant activities and transcript accumulation of GmSOD1 and GmAPX1 to overcome HS-induced oxidative damage. Furthermore, SB10 + GB downregulated DREB2, DREB1B, and GmNCED3 expression and resulted in the reduced accumulation of endogenous ABA while enhancing endogenous SA accumulation via upregulation of PAL genes. In addition, enhanced accumulation of bioactive gibberellins (GA1, GA3, GA4, and GA7) was detected under HS stress in the SB10 + GB treatment group. Moreover, SB10 + GB also significantly regulated GmHsp90A2 and GmHsfA2 expression in tolerance against HS stress. The combination of SB10 and GB was shown to be an effective and alternative approach for growing G. max at high temperature coupled with saline conditions for sustainable agriculture.

POWERDRESSpositively regulates systemic acquired resistance in Arabidopsis.

PWR, an epigenetic regulator, and PIF4, a transcription factor coordinately regulate both local resistance and systemic acquired resistance in Arabidopsis. A plant that gets infected once becomes resistant to subsequent infections through the development of systemic acquired resistance (SAR). Primary-infected tissues generate mobile signals that travel to systemic tissues and cause epigenetic changes associated with the SAR activation. Epigenetic regulators and the process of infection memory development are largely obscure for plants. POWERDRESS (PWR), a SANT domain-containing histone deacetylation (HDAC) promoting gene, is essential for thermomorphogenesis. Here we show that PWR is required for the SAR activation in Arabidopsis. The pwr mutants in Ler and Col-0 background possess normal local resistance but are defective in SAR. PHYTOCHROME-INTERACTING FACTOR 4 (PIF4) genetically interacts with PWR for flowering and thermomorphogenesis and is a negative regulator of basal immunity. We found a cooperative function for suppressing basal immunity and SAR activation by PIF4 and PWR, respectively. PWR promotes the expression of SA biosynthesis genes and the accumulation of SA in the systemic tissues. RSI1/FLD, which influences histone methylation and acetylation, is essential to infection memory development in Arabidopsis. Our results show that PWR and RSI1 positively regulate each other's expression. Exogenous application of HDAC inhibitor sodium butyrate abolishes SAR-mediated SA accumulation, expression of PR1 gene, and protection against pathogens after challenge inoculation. The results indicate the possibility of the involvement of HDAC activity of PWR in the formation of infection memory development in Arabidopsis.

Overexpression of the Arabidopsis MACPF Protein AtMACP2 Promotes Pathogen Resistance by Activating SA Signaling.

Immune response in plants is tightly regulated by the coordination of the cell surface and intracellular receptors. In animals, the membrane attack complex/perforin-like (MACPF) protein superfamily creates oligomeric pore structures on the cell surface during pathogen infection. However, the function and molecular mechanism of MACPF proteins in plant pathogen responses remain largely unclear. In this study, we identified an Arabidopsis MACP2 and investigated the responsiveness of this protein during both bacterial and fungal pathogens. We suggest that MACP2 induces programmed cell death, bacterial pathogen resistance, and necrotrophic fungal pathogen sensitivity by activating the biosynthesis of tryptophan-derived indole glucosinolates and the salicylic acid signaling pathway dependent on the activity of enhanced disease susceptibility 1 (EDS1). Moreover, the response of MACP2 mRNA isoforms upon pathogen attack is differentially regulated by a posttranscriptional mechanism: alternative splicing. In comparison to previously reported MACPFs in Arabidopsis, MACP2 shares a redundant but nonoverlapping role in plant immunity. Thus, our findings provide novel insights and genetic tools for the MACPF family in maintaining SA accumulation in response to pathogens in Arabidopsis.

Histone acetyltransferase TaHAG1 interacts with TaPLATZ5 to activate TaPAD4 expression and positively contributes to powdery mildew resistance in wheat.

Plants have evolved a two-branched innate immune system to detect and cope with pathogen attack, which are initiated by cell-surface and intracellular immune receptors leading to pattern-triggered immunity (PTI) and effector-triggered immunity (ETI), respectively. A core transducer including PAD4-EDS1 node is proposed as the convergence point for a two-tiered immune system in conferring pathogen immunity. However, the transcriptional regulatory mechanisms controlling expression of these key transducers remain largely unknown. Here, we identified histone acetyltransferase TaHAG1 as a positive regulator of powdery mildew resistance in wheat. TaHAG1 regulates expression of key transducer gene TaPAD4 and promotes SA and reactive oxygen species accumulation to accomplish resistance to Bgt infection. Moreover, overexpression and CRISPR-mediated knockout of TaPAD4 validate its role in wheat powdery mildew resistance. Furthermore, TaHAG1 physically interacts with TaPLATZ5, a plant-specific zinc-binding protein. TaPLATZ5 directly binds to promoter of TaPAD4 and together with TaHAG1 to potentiate the expression of TaPAD4 by increasing the levels of H3 acetylation. Our study revealed a key transcription regulatory node in which TaHAG1 acts as an epigenetic modulator and interacts with TaPLATZ5 that confers powdery mildew resistance in wheat through activating a convergence point gene between PTI and ETI, which could be effective for genetic improvement of disease resistance in wheat and other crops.

Generation of the salicylic acid deficient Arabidopsis via a synthetic salicylic acid hydroxylase expression cassette

BackgroundSalicylic acid (SA) is one of the plant hormones, which plays crucial roles in signaling transduction in plant growth, disease resistance, and leaf senescence. Arabidopsis (Arabidopsis thaliana) SA 3-hydroxylase (S3H) and 5-hydroxylase (S5H) are key enzymes which maintain SA homeostasis by catalyzing SA to 2,3-dihydroxybenzoic acid (DHBA) and 2,5-DHBA, respectively.ResultsSA deficient transgenic Arabidopsis lines were generated by introducing two binary vectors S5Hpro::EGFP-S3H and 35Spro::EGFP-S3H respectively, in which the expression of S3H is under the control of the S5H promoter or CaMV 35S promoter. Compared with the constitutive expression of S3H gene under the control of 35S promoter, the S3H gene under the native S5H promoter is activated by endogenous SA and results in a dynamic control of SA catabolism in a feedback mode. The SA accumulation, growth, leaf senescence, and pathogen resistance of the S5Hpro::GFP-S3H transgenic plants were investigated in parallel with NahG transgenic plants. The SA levels in the S5Hpro::EGFP-S3H transgenic plants were similar to or slightly lower than those of NahG transgenic Arabidopsis and resulted in SA deficient phenotypes. The low-SA trait of the S5Hpro::EGFP-S3H transgenic lines was inherited stably in the later generations.ConclusionsCompared with NahG transgenic lines producing by-product catechol, S5Hpro::EGFP-S3H transgenic lines reduce SA levels by converting SA to a native product 2,3-DHBA for catabolism. Together, we provide new SA-deficient germplasms for the investigations of SA signaling in plant development, leaf senescence, and disease resistance.

Hypersensitivity-Related Genes HSR201 and HSR203J Are Regulated by Calmodulin-Binding Protein 60-Type Transcription Factors and Required for Pathogen Signal-Induced Salicylic Acid Synthesis.

Salicylic acid (SA) plays a key role in plant resistance to pathogens. In Arabidopsis, the isochorismate synthase pathway mainly contributes to pathogen-induced SA synthesis, and the expression of SA synthesis genes is activated by two calmodulin (CaM)-binding protein 60 (CBP60)-type transcription factors, CBP60g and SARD1. In tobacco, the mechanisms underlying SA synthesis remain largely unknown. SA production is induced by wounding in tobacco plants in which the expression of two stress-related mitogen-activated protein kinases is suppressed. Using this phenomenon, we identified genes whose expression is associated with SA synthesis. One of the genes, NtCBP60g, showed 23% amino acid sequence identity with CBP60g. Transient overexpression of NtCBP60g as well as NtSARD1, a tobacco homolog of SARD1, induced SA accumulation in Nicotiana benthamiana leaves. NtCBP60g and NtSARD1 bound CaM, and CaM enhanced SA accumulation induced by NtCBP60g and NtSARD1. Conversely, mutations in NtCBP60g and NtSARD1 that abolished CaM binding reduced their ability to induce SA. Expression profiling and promoter analysis identified two hypersensitivity-related genes, HSR201 and HSR203J as the targets of NtCBP60g and NtSARD1. Virus-induced gene silencing of both NtCBP60g and NtSARD1 homologs compromised SA accumulation and the expression of HSR201 and HSR203J homologs, which were induced by a pathogen-derived elicitor in N. benthamiana leaves. Moreover, elicitor-induced SA accumulation was compromised by silencing of the HSR201 homolog and the HSR203J homolog. These results suggested that HSR201 and HSR203J are regulated by NtCBP60g and NtSARD1 and are required for elicitor-induced SA synthesis.

Effect of Feeding Stage and Density of Whiteflies on Subsequent Aphid Performance on Tobacco Plants

Bemisia tabaci Middle East-Asia Minor 1 (MEAM1) is a cosmopolitan, highly polyphagous agricultural pest, which has the capacity to displace other native insect herbivores. Here, equipped with an integrated approach, the effect of developmental stages and feeding density of whiteflies on Myzus persicae performance in tobacco plants are investigated. Bioassay results showed that B. tabaci nymphs, but not adult, pre-infestation significantly reduced survival and fecundity of M. persicae, and the strongest resistance to M. persicae was detected at the medium density (9–10 nymphs/cm2). Neither low nor high feeding density of B. tabaci nymphs triggered visible resistance to aphids. However, no significant results were detected in salicylate-deficient NahG plants after B. tabaci nymph infestation. In addition to performance distinctions, hormone quantification and qPCR results revealed very different effects for nymph and adult whitefly stages on the defense responses in tobacco. B. tabaci nymph infestation significantly increased SA accumulation and SA-responsive genes (PR-1a, PR-2a) expression but suppressed JA-regulated responses. In contrast, tobacco plants responded to adult infestation by slightly increasing in both SA- and JA-regulated defenses. Furthermore, higher transcription level of Bt56, coding gene of a secretory salivary effector, was recorded in nymphs vs. adults, while silencing of Bt56 by virus-induced gene silencing (VIGS) partly impaired the aphid resistance induced by B. tabaci nymphs. These results proved that the induction of tobacco defense responses varied with the feeding stages of whiteflies: nymphs of B. tabaci, but not adults, induced a defense response against aphids, with a density threshold for this induced resistance.

SUMO E3 ligase SIZ1 connects sumoylation and reactive oxygen species homeostasis processes in Arabidopsis.

The ubiquitin-like modifying peptide SMALL UBIQUITIN-LIKE MODIFIER (SUMO) has become a known modulator of the plant response to multiple environmental stimuli. A common feature of many of these external stresses is the production of reactive oxygen species (ROS). Taking into account that SUMO conjugates rapidly accumulate in response to an external oxidative stimulus, it is likely that ROS and sumoylation converge at the molecular and regulatory levels. In this study, we explored the SUMO-ROS relationship, using as a model the Arabidopsis (Arabidopsis thaliana) null mutant of the major SUMO-conjugation enhancer, the E3 ligase SAP AND MIZ 1 (SIZ1). We showed that SIZ1 is involved in SUMO conjugate increase when primed with both exogenous and endogenous ROS. In siz1, seedlings were sensitive to oxidative stress imposition, and mutants accumulated different ROS throughout development. We demonstrated that the deregulation in hydrogen peroxide and superoxide homeostasis, but not of singlet O2 (1O2), was partially due to SA accumulation in siz1. Furthermore, transcriptomic analysis highlighted a transcriptional signature that implicated siz1 with 1O2 homeostasis. Subsequently, we observed that siz1 displayed chloroplast morphological defects and altered energy dissipation activity and established a link between the chlorophyll precursor protochlorophyllide and deregulation of PROTOCHLOROPHYLLIDE OXIDOREDUCTASE A (PORA), which is known to drive overproduction of 1O2. Ultimately, network analysis uncovered known and additional associations between transcriptional control of PORA and SIZ1-dependent sumoylation. Our study connects sumoylation, and specifically SIZ1, to the control of chloroplast functions and places sumoylation as a molecular mechanism involved in ROS homeostatic and signaling events.

Orchestration of plant development and defense by indirect crosstalk of salicylic acid and brassinosteorid signaling via transcription factor GhTINY2.

Salicylic acid (SA) and brassinosteroids (BRs) are well known to regulate diverse processes of plant development and stress responses, but the mechanisms by which these phytohormones mediate the growth and defense trade-off are largely unclear. In addition, little is known about the roles of DEHYDRATION RESPONSIVE ELEMENT BINDING transcription factors, especially in biotic stress and plant growth. Here, we identified a cotton (Gossypium hirsutum) APETALA2/ETHYLENE RESPONSIVE FACTOR gene GhTINY2 that is strongly induced by Verticillium dahliae. Overexpression of GhTINY2 in cotton and Arabidopsis enhanced tolerance to V. dahliae, while knockdown of expression increased the susceptibility of cotton to the pathogen. GhTINY2 was found to promote SA accumulation and SA signaling transduction by directly activating expression of WRKY51. Moreover, GhTINY2-overexpressing cotton and Arabidopsis showed retardation of growth, increased sensitivity to inhibitors of BR biosynthesis, down-regulation of several BR-induced genes, and up-regulation of BR-repressed genes, while GhTINY2-RNAi cotton showed the opposite effects. We further determined that GhTINY2 negatively regulates BR signaling by interacting with BRASSINAZOLE-RESISTANT 1 (BZR1) and restraining its transcriptional activation of the expression of INDOLE-3-ACETIC ACID INDUCIBLE 19 (IAA19). These findings indicate that GhTINY2 fine-tunes the trade-off between immunity and growth via indirect crosstalk between WRKY51-mediated SA biosynthesis and BZR1-IAA19-regulated BR signaling.

Overexpression of OsCM alleviates BLB stress via phytohormonal accumulation and transcriptional modulation of defense-related genes in Oryza sativa

Xanthomonas oryzae is a serious pathogen causing bacterial leaf blight (BLB) disease in rice, markedly reducing its yield. In this study, the rice chorismate mutase (OsCM) gene was overexpressed in a bacterial leaf blight-susceptible rice line to investigate the functional role of OsCM in response to bacterial leaf blight stress. We reported that overexpression of OsCM altered the downstream pathway of aromatic amino acids, mitigating pathogen stress by altering stress-responsive genes and hormonal accumulation. Phenotypic evaluation showed that the lesion length in the transgenic line was significantly lesser than that in the wild-type, suggesting greater resistance in the transgenic line. Further analysis revealed that OsCM expression induced phenylalanine accumulation and suppressed tyrosine accumulation in response to bacterial leaf blight stress. Furthermore, bacterial leaf blight stress induced genes downstream of the phenylpropanoid pathway in conjunction with OsCM, suggesting that the phenylpropanoid pathway is dependent on OsCM gene expression. We reported high SA and low JA accumulation in response to bacterial leaf blight stress in the transgenic line. This higher SA accumulation suggested that SA induces immune responses by functioning as a promoter of nonexpresser pathogenesis-related genes 1 (NPR1) transcriptional regulation. Xa7 expression was induced with increase in nonexpresser pathogenesis-related genes 1, which is thought to be responsible for Xa7 expression, which is responsible for mitigating bacterial leaf blight stress.

Developmental characteristics of grapevine seedlings root border cells and their response to ρ-hydroxybenzoic acid

ρ-hydroxybenzoic acid (4-HBA) is one of the major autotoxins that cause grapevine replant disease. Root border cells (RBCs) play an important role in plant defense. Although RBCs have been investigated in many plants, relevant information in grapevines is limited. In this study, we aimed to investigate the developmental characteristics of RBCs in the grapevine (Vitis riparia × Vitis labrusca) ‘Beta’ and their response to 4-HBA stress. RBCs were observed under a laser scanning confocal microscope. The phenolic acid composition of RBCs slime was determined by high-performance liquid chromatography. The level of gene expression was determined by quantitative real-time polymerase chain reaction. Grapevine RBCs have high biological activity, contain starch granules, and are surrounded by a mucilage layer. Root treatments using different concentrations of 4-HBA affected the development of RBCs and root growth, and induced the secretion of salicylic acid from the RBCs, which can stimulate, induce, and maintain the activity of antioxidant enzymes to some extent in the cells under 4-HBA stress. Grapevine RBCs may resist 4-HBA stress by increasing its number and enhancing their secondary metabolism and SA accumulation, which can induce the antioxidant defense system of the cells.

RSI1/FLD is a positive regulator for defense against necrotrophic pathogens

The reduced systemic immunity 1 (rsi1) mutant of Arabidopsis (allelic to fld; flowering locus D) is essential for systemic acquired resistance (SAR). RSI/FLD codes for putative histone-demethylase and modulates flowering and defense response. The rsi1/fld mutants are defective in systemic SA accumulation upon pathogen challenge and fail to respond to the SAR signals in the distal tissues. However, the role of RSI1/FLD in ethylene (ET)-jasmonic acid (JA) signaling was not known. Here we show that expression of RSI1/FLD is induced by methyl-jasmonate (MeJA). The rsi1 mutants are hyper-susceptible to necrotrophic pathogens Botrytis cinerea and Alternaria alternata. In contrary to the susceptibility phenotypes, these mutants are not defective in expression of ET/JA-inducible genes such as PR3, PDF1.2, ERF1, Thi1.2, and ORA59. However, pathogen-induced expression of MYC2 and VSP2 genes are compromised in the rsi1 mutant. Germination of seedlings in the presence of MeJA or amino-carboxy-cyclopropane (ACC, ET precursor) suggest that rsi1/fld mutants are partially defective in JA signaling but hyperactive in ethylene signaling. The results altogether demonstrate novel roles of FLD in controlling plant immune responses against necrotrophic pathogens.

A salivary effector enables whitefly to feed on host plants by eliciting salicylic acid-signaling pathway

Phloem-feeding insects feed on plant phloem using their stylets. While ingesting phloem sap, these insects secrete saliva to circumvent plant defenses. Previous studies have shown that, to facilitate their feeding, many phloem-feeding insects can elicit the salicylic acid- (SA-) signaling pathway and thus suppress effective jasmonic acid defenses. However, the molecular basis for the regulation of the plant's defense by phloem-feeding insects remains largely unknown. Here, we show that Bt56, a whitefly-secreted low molecular weight salivary protein, is highly expressed in the whitefly primary salivary gland and is delivered into host plants during feeding. Overexpression of the Bt56 gene in planta promotes susceptibility of tobacco to the whitefly and elicits the SA-signaling pathway. In contrast, silencing the whitefly Bt56 gene significantly decreases whitefly performance on host plants and interrupts whitefly phloem feeding with whiteflies losing the ability to activate the SA pathway. Protein-protein interaction assays show that the Bt56 protein directly interacts with a tobacco KNOTTED 1-like homeobox transcription factor that decreases whitefly performance and suppresses whitefly-induced SA accumulation. The Bt56 orthologous genes are highly conserved but differentially expressed in different species of whiteflies. In conclusion, Bt56 is a key salivary effector that promotes whitefly performance by eliciting salicylic acid-signaling pathway.

Cell Death Is Not Sufficient for the Restriction of Potato Virus Y Spread in Hypersensitive Response-Conferred Resistance in Potato

Hypersensitive response (HR)-conferred resistance to viral infection restricts the virus spread and is accompanied by the induction of cell death, manifested as the formation of necrotic lesions. While it is known that salicylic acid is the key component in the orchestration of the events restricting viral spread in HR, the exact function of the cell death in resistance is still unknown. We show that potato virus Y (PVY) can be detected outside the cell death zone in Ny-1-mediated HR in potato plants (cv. Rywal), observed as individual infected cells or small clusters of infected cells outside the cell death zone. By exploiting the features of temperature dependent Ny-1-mediated resistance, we confirmed that the cells at the border of the cell death zone are alive and harbor viable PVY that is able to reinitiate infection. To get additional insights into this phenomenon we further studied the dynamics of both cell death zone expansion and occurrence of viral infected cell islands outside it. We compared the response of Rywal plants to their transgenic counterparts, impaired in SA accumulation (NahG-Rywal), where the lesions occur but the spread of the virus is not restricted. We show that the virus is detected outside the cell death zone in all lesion developmental stages of HR lesions. We also measured the dynamics of lesions expansion in both genotypes. We show that while rapid lesion expansion is observed in SA-depleted plants, virus spread is even faster. On the other hand the majority of analyzed lesions slowly expand also in HR-conferred resistance opening the possibility that the infected cells are eventually engulfed by cell death zone. Taken altogether, we suggest that the HR cell death is separated from the resistance mechanisms which lead to PVY restriction in Ny-1 genetic background. We propose that HR should be regarded as a process where the dynamics of events is crucial for effectiveness of viral arrest albeit the exact mechanism conferring this resistance remains unknown.

Both Light-Induced SA Accumulation and ETI Mediators Contribute to the Cell Death Regulated by BAK1 and BKK1.

Receptor-like kinases BAK1 and BKK1 modulate multiple cellular processes including brassinosteroid signaling and PRR-mediated PTI in Arabidopsis. Our previous reports also demonstrated that bak1 bkk1 double mutants exhibit a spontaneous cell death phenotype under normal growth condition. With an unknown mechanism, the cell death in bak1 bkk1 is significantly suppressed when grown in dark but can be quickly induced by light. Furthermore, little is known about intrinsic components involved in BAK1 and BKK1-regulated cell death pathway. In this study, we analyzed how light functions as an initiator of cell death and identified ETI components to act as mediators of cell death signaling in bak1 bkk1. Cell death suppressed in bak1 bkk1 by growing in dark condition recurred upon exogenously treated SA. SA biosynthesis-related genes SID2 and EDS5, which encode chloroplast-localized proteins, were highly expressed in bak1-4 bkk1-1. When crossed to bak1-3 bkk1-1, sid2 or eds5 was capable of efficiently suppressing the cell death. It suggested that overly produced SA is crucial for inducing cell death in bak1 bkk1 grown in light. Notably, bak1-3 or bkk1-1 single mutant was shown to be more susceptible but bak1-3 bkk1-1 double mutant exhibited enhanced resistance to bacterial pathogen, suggesting immune signaling other than PTI is activated in bak1 bkk1. Moreover, genetic analyses showed that mutation in EDS1 or PAD4, key ETI mediator, significantly suppressed the cell death in bak1-3 bkk1-1. In this study, we revealed that light-triggered SA accumulation plays major role in inducing the cell death in bak1 bkk1, mediated by ETI components.

Improvement of shikimic acid production in Escherichia coli with growth phase-dependent regulation in the biosynthetic pathway from glycerol.

Shikimic acid is an important metabolic intermediate with various applications. This paper presents a novel control strategy for the construction of shikimic acid producing strains, without completely blocking the aromatic amino acid biosynthesis pathways. Growth phase-dependent expression and gene deletion was performed to regulate the aroK gene expression in the shikimic acid producing Escherichia coli strain, SK4/rpsM. In this strain, the aroL and aroK genes were deleted, and the aroB, aroG*, ppsA, and tktA genes were overexpressed. The relative amount of shikimic acid that accumulated in SK4/rpsM was 1.28-fold higher than that in SK4/pLac. Furthermore, a novel shikimic acid production pathway, combining the expression of the dehydroquinate dehydratase-shikimate dehydrogenase (DHQ-SDH) enzyme from woody plants, was constructed in E. coli strains. The results demonstrated that a growth phase-dependent control of the aroK gene leads to higher SA accumulation (5.33g/L) in SK5/pSK6. This novel design can achieve higher shikimic acid production by using the same amount of medium used by the current methods and can also be widely used for modifying other metabolic pathways.

Water Stress Responses of Tomato Mutants Impaired in Hormone Biosynthesis Reveal Abscisic Acid, Jasmonic Acid and Salicylic Acid Interactions.

To investigate the putative crosstalk between JA and ABA in Solanum lycopersicum plants in response to drought, suppressor of prosystemin-mediated responses2 (spr2, JA-deficient) and flacca (flc, ABA-deficient) mutants together with the naphthalene/salicylate hydroxylase (NahG) transgenic (SA-deficient) line were used. Hormone profiling and gene expression of key enzymes in ABA, JA and SA biosynthesis were analyzed during early stages of drought. ABA accumulation was comparable in spr2 and wild type (WT) plants whereas expression of 9-cis-epoxycarotenoid dioxygenase 1 (NCED1) and NCED2 was different, implying a compensation mechanism between NCED genes and an organ-specific regulation of NCED1 expression. JA levels and 12-oxo-phytodienoic acid reductase 3 (OPR3) expression in flc plants suggest that ABA regulates the induction of the OPR3 gene in roots. By contrast, ABA treatment to flc plants leads to a reduction of JA and SA contents. Furthermore, different pattern of SA accumulation (and expression of isochorismate synthase and phenylalanine ammonia lyase 1) was observed between WT seedlings and mutants, suggesting that SA plays an important role on the early response of tomato plants to drought and also that JA and ABA modulate its biosynthesis. Finally, hormone profiling in spr2 and NahG plants indicate a crosstalk between JA and SA that could enhance tolerance of tomato to water stress.

The mealybug Phenacoccus solenopsis suppresses plant defense responses by manipulating JA-SA crosstalk.

Induced plant defenses against herbivores are modulated by jasmonic acid-, salicylic acid-, and ethylene-signaling pathways. Although there is evidence that some pathogens suppress plant defenses by interfering with the crosstalk between different signaling pathways, such evidence is scarce for herbivores. Here, we demonstrate that the mealybug Phenacoccus solenopsis suppresses the induced defenses in tomato. We found that exogenous JA, but not SA, significantly decreased mealybug feeding time and reduced nymphal performance. In addition, constitutive activation of JA signaling in 35s::prosys plants reduced mealybug survival. These data indicate that the JA signaling pathway plays a key role in mediating the defense responses against P. solenopsis. We also found that mealybug feeding decreased JA production and JA-dependent defense gene expression, but increased SA accumulation and SA-dependent gene expression. In SA-deficient plants, mealybug feeding did not suppress but activated JA accumulation, indicating that the suppression of JA-regulated defenses depends on the SA signaling pathway. Mealybugs benefit from suppression of JA-regulated defenses by exhibiting enhanced nymphal performance. These findings confirm that P. solenopsis manipulates plants for its own benefits by modulating the JA-SA crosstalk and thereby suppressing induced defenses.