Salicylic acid biosynthesis is not from phenylalanine in Arabidopsis

The Bursaphelenchus xylophilus Effector BxNMP1 Targets PtTLP-L2 to Mediate PtGLU Promoting Parasitism and Virulence in Pinus thunbergii

Pinus is an important economic tree species, but pine wilt disease (PWD) seriously threatens the survival of pine trees. PWD caused by Bursaphelenchus xylophilus is a major quarantine disease worldwide that causes significant economic losses. However, more information about its molecular pathogenesis is needed, resulting in a lack of effective prevention and treatment measures. In recent years, effectors have become a hot topic in exploring the molecular pathogenic mechanism of pathogens. Here, we identified a specific effector, BxNMP1, from B. xylophilus. In situ hybridization experiments revealed that BxNMP1 was specifically expressed in dorsal gland cells and intestinal cells, and RT-qPCR experiments revealed that BxNMP1 was upregulated in the early stage of infection. The sequence of BxNMP1 was different in the avirulent strain, and when BxNMP1-silenced B. xylophilus was inoculated into P. thunbergii seedlings, the disease severity significantly decreased. We demonstrated that BxNMP1 interacted with the thaumatin-like protein PtTLP-L2 in P. thunbergii. Additionally, we found that the β-1,3-glucanase PtGLU interacted with PtTLP-L2. Therefore, we hypothesized that BxNMP1 might indirectly interact with PtGLU through PtTLP-L2 as an intermediate mediator. Both targets can respond to infection, and PtTLP-L2 can enhance the resistance of pine trees. Moreover, we detected increased salicylic acid contents in P. thunbergii seedlings inoculated with B. xylophilus when BxNMP1 was silenced or when the PtTLP-L2 recombinant protein was added. In summary, we identified a key virulence effector of PWNs, BxNMP1. It positively regulates the pathogenicity of B. xylophilus and interacts directly with PtTLP-L2 and indirectly with PtGLU. It also inhibits the expression of two targets and the host salicylic acid pathway. This study provides theoretical guidance and a practical basis for controlling PWD and breeding for disease resistance.

Modulation of Photosystem II Function in Celery via Foliar-Applied Salicylic Acid during Gradual Water Deficit Stress

Water deficit is the major stress factor magnified by climate change that causes the most reductions in plant productivity. Knowledge of photosystem II (PSII) response mechanisms underlying crop vulnerability to drought is critical to better understanding the consequences of climate change on crop plants. Salicylic acid (SA) application under drought stress may stimulate PSII function, although the exact mechanism remains essentially unclear. To reveal the PSII response mechanism of celery plants sprayed with water (WA) or SA, we employed chlorophyll fluorescence imaging analysis at 48 h, 96 h, and 192 h after watering. The results showed that up to 96 h after watering, the stroma lamellae of SA-sprayed leaves appeared dilated, and the efficiency of PSII declined, compared to WA-sprayed plants, which displayed a better PSII function. However, 192 h after watering, the stroma lamellae of SA-sprayed leaves was restored, while SA boosted chlorophyll synthesis, and by ameliorating the osmotic potential of celery plants, it resulted in higher relative leaf water content compared to WA-sprayed plants. SA, by acting as an antioxidant under drought stress, suppressed phototoxicity, thereby offering PSII photoprotection, together with enhanced effective quantum yield of PSII photochemistry (ΦPSII) and decreased quantity of singlet oxygen (1O2) generation compared to WA-sprayed plants. The PSII photoprotection mechanism induced by SA under drought stress was triggered by non-photochemical quenching (NPQ), which is a strategy to protect the chloroplast from photo-oxidative damage by dissipating the excess light energy as heat. This photoprotective mechanism, triggered by NPQ under drought stress, was adequate in keeping, especially in high-light conditions, an equal fraction of open PSII reaction centers (qp) as of non-stress conditions. Thus, under water deficit stress, SA activates a regulatory network of stress and light energy partitioning signaling that can mitigate, to an extent, the water deficit stress on PSII functioning.

The genetic orchestra of salicylic acid in plant resilience to climate change induced abiotic stress: critical review

Climate change, driven by human activities and natural processes, has led to critical alterations in varying patterns during cropping seasons and is a vital threat to global food security. The climate change impose several abiotic stresses on crop production systems. These abiotic stresses include extreme temperatures, drought, and salinity, which expose agricultural fields to more vulnerable conditions and lead to substantial crop yield and quality losses. Plant hormones, especially salicylic acid (SA), has crucial roles for plant resiliency under unfavorable environments. This review explores the genetics and molecular mechanisms underlying SA's role in mitigating abiotic stress-induced damage in plants. It also explores the SA biosynthesis pathways, and highlights the regulation of their products under several abiotic stresses. Various roles and possible modes of action of SA in mitigating abiotic stresses are discussed, along with unraveling the genetic mechanisms and genes involved in responses under stress conditions. Additionally, this review investigates molecular pathways and mechanisms through which SA exerts its protective effects, such as redox signaling, cross-talks with other plant hormones, and mitogen-activated protein kinase pathways. Moreover, the review discusses potentials of using genetic engineering approaches, such as CRISPR technology, for deciphering the roles of SA in enhancing plant resilience to climate change related abiotic stresses. This comprehensive analysis bridges the gap between genetics of SA role in response to climate change related stressors. Overall goal is to highlight SA's significance in safeguarding plants and by offering insights of SA hormone for sustainable agriculture under challenging environmental conditions.

The Key Role of Plant Hormone Signaling Transduction and Flavonoid Biosynthesis Pathways in the Response of Chinese Pine (Pinus tabuliformis) to Feeding Stimulation by Pine Caterpillar (Dendrolimus tabulaeformis)

In nature, plants have developed a series of resistance mechanisms to face various external stresses. As understanding of the molecular mechanisms underlying plant resistance continues to deepen, exploring endogenous resistance in plants has become a hot topic in this field. Despite the multitude of studies on plant-induced resistance, how plants respond to stress under natural conditions remains relatively unclear. To address this gap, we investigated Chinese pine (Pinus tabuliformis) using pine caterpillar (Dendrolimus tabulaeformis) under natural conditions. Healthy Chinese pine trees, approximately 10 years old, were selected for studying induced resistance in Huangtuliangzi Forestry, Pingquan City, Chengde City, Hebei Province, China. Pine needles were collected at 2 h and 8 h after feeding stimulation (FS) via 10 pine caterpillars and leaf clipping control (LCC), to simulate mechanical damage caused by insect chewing for the quantification of plant hormones and transcriptome and metabolome assays. The results show that the different modes of treatments significantly influence the contents of JA and SA in time following treatment. Three types of differentially accumulated metabolites (DAMs) were found to be involved in the initial response, namely phenolic acids, lipids, and flavonoids. Weighted gene co-expression network analysis indicated that 722 differentially expressed genes (DEGs) are positively related to feeding stimulation and the specific enriched pathways are plant hormone signal transduction and flavonoid biosynthesis, among others. Two TIFY transcription factors (PtTIFY54 and PtTIFY22) and a MYB transcription factor (PtMYB26) were found to be involved in the interaction between plant hormones, mainly in the context of JA signal transduction and flavonoid biosynthesis. The results of this study provide an insight into how JA activates, serving as a reference for understanding the molecular mechanisms of resistance formation in conifers responding to mandibulate insects.

A peroxisomal cinnamate:CoA ligase-dependent phytohormone metabolic cascade in submerged rice germination

The mechanism underlying the ability of rice to germinate underwater is a largely enigmatic but key research question highly relevant to rice cultivation. Moreover, although rice is known to accumulate salicylic acid (SA), SA biosynthesis is poorly defined, and its role in underwater germination is unknown. It is also unclear whether peroxisomes, organelles essential to oilseed germination and rice SA accumulation, play a role in rice germination. Here, we show that submerged imbibition of rice seeds induces SA accumulation to promote germination in submergence. Two submergence-induced peroxisomal Oryza sativa cinnamate:CoA ligases (OsCNLs) are required for this SA accumulation. SA exerts this germination-promoting function by inducing indole-acetic acid (IAA) catabolism through the IAA-amino acid conjugating enzyme GH3. The metabolic cascade we identified may potentially be adopted in agriculture to improve the underwater germination of submergence-intolerant rice varieties. SA pretreatment is also a promising strategy to improve submerged rice germination in the field.

Multi-omics analyses of sid2 mutant reflect the need of isochorismate synthase ICS1 to cope with sulfur limitation in Arabidopsis thaliana

The SID2 (SA INDUCTION-DEFICIENT2) gene that encodes ICS1 (isochorismate synthase), plays a central role in salicylic acid biosynthesis in Arabidopsis. The sid2 and NahG (encoding a bacterial SA hydroxylase) overexpressing mutants (NahG-OE) have currently been shown to outperform wild type, presenting delayed leaf senescence, higher plant biomass and better seed yield. When grown under sulfate-limited conditions (low-S), sid2 mutants exhibited early leaf yellowing compared to the NahG-OE, the npr1 mutant affected in SA signaling pathway, and WT. This indicated that the hypersensitivity of sid2 to sulfate limitation was independent of the canonical npr1 SA-signaling pathway. Transcriptomic and proteomic analyses revealed that major changes occurred in sid2 when cultivated under low-S, changes that were in good accordance with early senescence phenotype and showed the exacerbation of stress responses. The sid2 mutants displayed a lower sulfate uptake capacity when cultivated under low-S and lower S concentrations in their rosettes. Higher glutathione concentrations in sid2 rosettes under low-S were in good accordance with the higher abundance of proteins involved in glutathione and ascorbate redox metabolism. Amino acid and lipid metabolisms were also strongly modified in sid2 under low-S. Depletion of total fatty acids in sid2 under low-S was consistent with the fact that S-metabolism plays a central role in lipid synthesis. Altogether, our results show that functional ICS1 is important for plants to cope with S limiting conditions.

Salicylic acid in plant immunity and beyond

As the most widely used herbal medicine in human history and a major defence hormone in plants against a broad spectrum of pathogens and abiotic stresses, salicylic acid (SA) has attracted major research interest. With applications of modern technologies over the past 30 years, studies of the effects of SA on plant growth, development, and defence have revealed many new research frontiers and continue to deliver surprises. In this review, we provide an update on recent advances in our understanding of SA metabolism, perception, and signal transduction mechanisms in plant immunity. An overarching theme emerges that SA executes its many functions through intricate regulation at multiple steps: SA biosynthesis is regulated both locally and systemically, while its perception occurs through multiple cellular targets, including metabolic enzymes, redox regulators, transcription cofactors, and, most recently, an RNA-binding protein. Moreover, SA orchestrates a complex series of post-translational modifications of downstream signaling components and promotes the formation of biomolecular condensates that function as cellular signalling hubs. SA also impacts wider cellular functions through crosstalk with other plant hormones. Looking into the future, we propose new areas for exploration of SA functions, which will undoubtedly uncover more surprises for many years to come.

Hollow Mesoporous Silica Nanoparticles as a New Nanoscale Resistance Inducer for Fusarium Wilt Control: Size Effects and Mechanism of Action

In agriculture, soil-borne fungal pathogens, especially Fusarium oxysporum strains, are posing a serious threat to efforts to achieve global food security. In the search for safer agrochemicals, silica nanoparticles (SiO2NPs) have recently been proposed as a new tool to alleviate pathogen damage including Fusarium wilt. Hollow mesoporous silica nanoparticles (HMSNs), a unique class of SiO2NPs, have been widely accepted as desirable carriers for pesticides. However, their roles in enhancing disease resistance in plants and the specific mechanism remain unknown. In this study, three sizes of HMSNs (19, 96, and 406 nm as HMSNs-19, HMSNs-96, and HMSNs-406, respectively) were synthesized and characterized to determine their effects on seed germination, seedling growth, and Fusarium oxysporum f. sp. phaseoli (FOP) suppression. The three HMSNs exhibited no side effects on cowpea seed germination and seedling growth at concentrations ranging from 100 to 1500 mg/L. The inhibitory effects of the three HMSNs on FOP mycelial growth were very weak, showing inhibition ratios of less than 20% even at 2000 mg/L. Foliar application of HMSNs, however, was demonstrated to reduce the FOP severity in cowpea roots in a size- and concentration-dependent manner. The three HMSNs at a low concentration of 100 mg/L, as well as HMSNs-19 at a high concentration of 1000 mg/L, were observed to have little effect on alleviating the disease incidence. HMSNs-406 were most effective at a concentration of 1000 mg/L, showing an up to 40.00% decline in the disease severity with significant growth-promoting effects on cowpea plants. Moreover, foliar application of HMSNs-406 (1000 mg/L) increased the salicylic acid (SA) content in cowpea roots by 4.3-fold, as well as the expression levels of SA marker genes of PR-1 (by 1.97-fold) and PR-5 (by 9.38-fold), and its receptor gene of NPR-1 (by 1.62-fold), as compared with the FOP infected control plants. Meanwhile, another resistance-related gene of PAL was also upregulated by 8.54-fold. Three defense-responsive enzymes of POD, PAL, and PPO were also involved in the HMSNs-enhanced disease resistance in cowpea roots, with varying degrees of reduction in activity. These results provide substantial evidence that HMSNs exert their Fusarium wilt suppression in cowpea plants by activating SA-dependent SAR (systemic acquired resistance) responses rather than directly suppressing FOP growth. Overall, for the first time, our results indicate a new role of HMSNs as a potent resistance inducer to serve as a low-cost, highly efficient, safe and sustainable alternative for plant disease protection.

MdWRKY71 promotes the susceptibility of apple to Glomerella leaf spot by controlling salicylic acid degradation

Glomerella leaf spot (GLS), a fungal disease caused by Colletotrichum fructicola, severely affects apple (Malus domestica) quality and yield. In this study, we found that the transcription factor MdWRKY71 was significantly induced by C. fructicola infection in the GLS-susceptible apple cultivar Royal Gala. The overexpression of MdWRKY71 in apple leaves resulted in increased susceptibility to C. fructicola, whereas RNA interference of MdWRKY71 in leaves showed the opposite phenotypes. These findings suggest that MdWRKY71 functions as a susceptibility factor for the apple-C. fructicola interaction. Furthermore, MdWRKY71 directly bound to the promoter of the salicylic acid (SA) degradation gene Downy Mildew Resistant 6 (DMR6)-Like Oxygenase 1 (DLO1) and promoted its expression, resulting in a reduced SA level. The sensitivity of 35S:MdWRKY71 leaves to C. fructicola can be effectively alleviated by knocking down MdDLO1 expression, confirming the critical role of MdWRKY71-mediated SA degradation via regulating MdDLO1 expression in GLS susceptibility. In summary, we identified a GLS susceptibility factor, MdWRKY71, that targets the apple SA degradation pathway to promote fungal infection.

Silica nanoparticles conferring resistance to bacterial wilt in peanut (Arachis hypogaea L.)

Peanut bacterial wilt (PBW) caused by the pathogen Ralstonia solanacearum severely affects the growth and yield potential of peanut crop. In this study, we synthesized silica nanoparticles (SiO2 NPs), a prospective efficient management approach to control PBW, and conducted a hydroponic experiment to investigate the effects of different SiO2 NPs treatments (i.e., 0, 100, and 500 mg L-1 as NP0, NP100, and NP500, respectively) on promoting plant growth and resistance to R. solanacearum. Results indicated that the disease indices of NP100 and NP500 decreased by 51.5 % and 55.4 % as compared with NP0 under R. solanacearum inoculation, respectively, while the fresh and dry weights and shoot length of NP100 and NP500 increased by 7.62-42.05 %, 9.45-32.06 %, and 2.37-17.83 %, respectively. Furthermore, SiO2 NPs induced an improvement in physio-biochemical enzymes (superoxide dismutase, peroxidase, catalase, ascorbate peroxidase, and lipoxygenase) which eliminated the excess production of hydrogen peroxide, superoxide anions, and malondialdehyde to alleviate PBW stress. Notably, the targeted metabolomic analysis indicated that SiO2 NPs enhanced salicylic acid (SA) contents, which involved the induction of systemic acquired resistance (SAR). Moreover, the transcriptomic analysis revealed that SiO2 NPs modulated the expression of multiple transcription factors (TFs) involved in the hormone pathway, such as AHLs, and the identification of hormone pathways related to plant defense responses, such as the SA pathway, which activated SA-dependent defense mechanisms. Meanwhile, the up-regulated expression of the SA-metabolism gene, salicylate carboxymethyltransferase (SAMT), initiated SAR to promote PBW resistance. Overall, our findings revealed that SiO2 NPs, functioning as a plant elicitor, could effectively modulate physiological enzyme activities and enhance SA contents through the regulation of SA-metabolism genes to confer the PBW resistance in peanuts, which highlighted the potential of SiO2 NPs for sustainable agricultural practices.

Biochemical Pathways of Salicylic Acid Derived from l-Phenylalanine in Plants with Different Basal SA Levels

As a plant hormone, salicylic acid (SA) has diverse regulatory roles in plant growth and stress resistance. Although SA is widely found in plants, there is substantial variation in basal SA among species. Tea plant is an economically important crop containing high contents of SA whose synthesis pathway remains unidentified. The phenylalanine ammonia-lyase (PAL) pathway is responsible for basal SA synthesis in plants. In this study, isotopic tracing and enzymatic assay experiments were used to verify the SA synthesis pathway in tea plants and evaluate the variation in phenylalanine-derived SA formation among 11 plant species with different levels of SA. The results indicated that SA could be synthesized via PAL in tea plants and conversion efficiency from benzoic acid to SA might account for variation in basal SA among plant species. This research lays the foundation for an improved understanding of the molecular regulatory mechanism for SA biosynthesis.

The cytosolic aminotransferase VAS1 coordinates aromatic amino acid biosynthesis and metabolism

The aromatic amino acids (AAAs) phenylalanine, tyrosine, and tryptophan are basic protein units and precursors of diverse specialized metabolites that are essential for plant growth. Despite their significance, the mechanisms that regulate AAA homeostasis remain elusive. Here, we identified a cytosolic aromatic aminotransferase, REVERSAL OF SAV3 PHENOTYPE 1 (VAS1), as a suppressor of arogenate dehydrogenase 2 (adh2) in Arabidopsis (Arabidopsis thaliana). Genetic and biochemical analyses determined that VAS1 uses AAAs as amino donors, leading to the formation of 3-carboxyphenylalanine and 3-carboxytyrosine. These pathways represent distinct routes for AAA metabolism that are unique to specific plant species. Furthermore, we show that VAS1 is responsible for cytosolic AAA biosynthesis, and its enzymatic activity can be inhibited by 3-carboxyphenylalanine. These findings provide valuable insights into the crucial role of VAS1 in producing 3-carboxy AAAs, notably via recycling of AAAs in the cytosol, which maintains AAA homeostasis and allows plants to effectively coordinate the complex metabolic and biosynthetic pathways of AAAs.

High air humidity dampens salicylic acid pathway and NPR1 function to promote plant disease

The occurrence of plant disease is determined by interactions among host, pathogen, and environment. Air humidity shapes various aspects of plant physiology and high humidity has long been known to promote numerous phyllosphere diseases. However, the molecular basis of how high humidity interferes with plant immunity to favor disease has remained elusive. Here we show that high humidity is associated with an "immuno-compromised" status in Arabidopsis plants. Furthermore, accumulation and signaling of salicylic acid (SA), an important defense hormone, are significantly inhibited under high humidity. NPR1, an SA receptor and central transcriptional co-activator of SA-responsive genes, is less ubiquitinated and displays a lower promoter binding affinity under high humidity. The cellular ubiquitination machinery, particularly the Cullin 3-based E3 ubiquitin ligase mediating NPR1 protein ubiquitination, is downregulated under high humidity. Importantly, under low humidity the Cullin 3a/b mutant plants phenocopy the low SA gene expression and disease susceptibility that is normally observed under high humidity. Our study uncovers a mechanism by which high humidity dampens a major plant defense pathway and provides new insights into the long-observed air humidity influence on diseases.

Influence of Exogenous 24-Epicasterone on the Hormonal Status of Soybean Plants

Brassinosteroids (BRs) are key phytohormones involved in the regulation of major processes of cell metabolism that guide plant growth. In the past decades, new evidence has made it clear that BRs also play a key role in the orchestration of plant responses to many abiotic and biotic stresses. In the present work, we analyzed the impact of foliar treatment with 24-epicastasterone (ECS) on the endogenous content of major phytohormones (auxins, salicylic acid, jasmonic acid, and abscisic acid) and their intermediates in soybean leaves 7 days following the treatment. Changes in the endogenous content of phytohormones have been identified and quantified by LC/MS. The obtained results point to a clear role of ECS in the upregulation of auxin content (indole-3-acetic acid, IAA) and downregulation of salicylic, jasmonic, and abscisic acid levels. These data confirm that under optimal conditions, ECS in tested concentrations of 0.25 µM and 1 µM might promote growth in soybeans by inducing auxin contents. Benzoic acid (a precursor of salicylic acid (SA)), but not SA itself, has also been highly accumulated under ECS treatment, which indicates an activation of the adaptation strategies of cell metabolism to possible environmental challenges.

Single-cell RNA sequencing profiles reveal cell type-specific transcriptional regulation networks conditioning fungal invasion in maize roots

Stalk rot caused by Fusarium verticillioides (Fv) is one of the most destructive diseases in maize production. The defence response of root system to Fv invasion is important for plant growth and development. Dissection of root cell type-specific response to Fv infection and its underlying transcription regulatory networks will aid in understanding the defence mechanism of maize roots to Fv invasion. Here, we reported the transcriptomes of 29 217 single cells derived from root tips of two maize inbred lines inoculated with Fv and mock condition, and identified seven major cell types with 21 transcriptionally distinct cell clusters. Through the weighted gene co-expression network analysis, we identified 12 Fv-responsive regulatory modules from 4049 differentially expressed genes (DEGs) that were activated or repressed by Fv infection in these seven cell types. Using a machining-learning approach, we constructed six cell type-specific immune regulatory networks by integrating Fv-induced DEGs from the cell type-specific transcriptomes, 16 known maize disease-resistant genes, five experimentally validated genes (ZmWOX5b, ZmPIN1a, ZmPAL6, ZmCCoAOMT2, and ZmCOMT), and 42 QTL or QTN predicted genes that are associated with Fv resistance. Taken together, this study provides not only a global view of maize cell fate determination during root development but also insights into the immune regulatory networks in major cell types of maize root tips at single-cell resolution, thus laying the foundation for dissecting molecular mechanisms underlying disease resistance in maize.

Repeated mechanical damage enhanced Aquilaria sinensis resistance to Heortia vitessoides through jasmonic acid

Introduction

The leaf-chewing pest Heortia vitessoides severely threatens the growth and development of Aquilaria sinensis. In our previous study, we found that mechanical damage (MD) to stem enhanced A. sinensis sapling resistance to H. vitessoides larvae.

Methods

To reveal the defense mechanisms underlying this observation, we analyzed the types and contents of volatile organic compounds (VOCs), phytohormone contents, and expression of phytohormone-related genes in response to MD and herbivory wounding(HW).

Results

Here, we identified several VOCs, such as the pesticides fenobucarb and 2,4-di-tert-butylphenol, in mature leaf (ML) of MD-treated plants. Compared with salicylic acid (SA) or the ethylene (ET) pathway, jasmonic acid (JA) content and JA-related genes were more strongly upregulated. Interestingly, we found a dramatic difference between JA-related upstream and downstream genes expression in YL and ML, which confirmed that JA-Ile accumulation in MD-ML and HW-ML could be derived from local damaged site.

Discussion

Taken together, we provide evidence that the JA pathway plays a dominant role in the A. sinensis response to MD and HW.

PIF8-WRKY42-mediated salicylic acid synthesis modulates red light induced powdery mildew resistance in oriental melon

Light signals and plant hormones are involved in regulating the growth, development and stress resistance of plants; however, it remains unclear whether light affects hormones and thus pathogen resistance in oriental melon. Here, we found that red light promoted salicylic acid (SA) accumulation and powdery mildew resistance by activating the transcription of CmICS, the key gene for SA biosynthesis, and silencing CmICS seriously weakened the induction effect of red light on powdery mildew resistance in oriental melon leaves. Further studies showed that red light induced the expression of CmWRKY42 under powdery mildew stress, and CmWRKY42 directly bound to the CmICS promoter to activate its expression and promote the accumulation of SA under red light. Furthermore, we found that PHYTOCHROME INTERACTING FACTOR 8 (PIF8), as a negative regulator of SA biosynthesis, inhibits CmWRKY42 transcriptional activation by binding to the CmWRKY42 promoter, and thus inhibits transcriptional activation of CmICS by CmWRKY42. Also, CmPIF8 binds to the CmICS promoter and directly inhibits its transcription. In conclusion, our study revealed a new molecular mechanism of the relationship between red light-SA-powdery mildew resistance and provided a theoretical basis for resistance breeding of oriental melon.

Gene enrichment and co-expression analysis shed light on transcriptional responses to Ralstonia solanacearum in tomato

BACKGROUND

Tomato (Solanum lycopersicum) is both an important agricultural product and an excellent model system for studying plant-pathogen interactions. It is susceptible to bacterial wilt caused by Ralstonia solanacearum (Rs), and infection can result in severe yield and quality losses. To investigate which genes are involved in the resistance response to this pathogen, we sequenced the transcriptomes of both resistant and susceptible tomato inbred lines before and after Rs inoculation.

RESULTS

In total, 75.02 Gb of high-quality reads were generated from 12 RNA-seq libraries. A total of 1,312 differentially expressed genes (DEGs) were identified, including 693 up-regulated and 621 down-regulated genes. Additionally, 836 unique DEGs were obtained when comparing two tomato lines, including 27 co-expression hub genes. A total of 1,290 DEGs were functionally annotated using eight databases, most of which were found to be involved in biological pathways such as DNA and chromatin activity, plant-pathogen interaction, plant hormone signal transduction, secondary metabolite biosynthesis, and defense response. Among the core-enriched genes in 12 key pathways related to resistance, 36 genotype-specific DEGs were identified. RT-qPCR integrated analysis revealed that multiple DEGs may play a significant role in tomato response to Rs. In particular, Solyc01g073985.1 (NLR disease resistance protein) and Solyc04g058170.1 (calcium-binding protein) in plant-pathogen interaction are likely to be involved in the resistance.

CONCLUSION

We analyzed the transcriptomes of both resistant and susceptible tomato lines during control and inoculated conditions and identified several key genotype-specific hub genes involved in a variety of different biological processes. These findings lay a foundation for better understanding the molecular basis by which resistant tomato lines respond to Rs.

Emerging Roles of Salicylic Acid in Plant Saline Stress Tolerance

One of the most important phytohormones is salicylic acid (SA), which is essential for the regulation of plant growth, development, ripening, and defense responses. The role of SA in plant-pathogen interactions has attracted a lot of attention. Aside from defense responses, SA is also important in responding to abiotic stimuli. It has been proposed to have great potential for improving the stress resistance of major agricultural crops. On the other hand, SA utilization is dependent on the dosage of the applied SA, the technique of application, and the status of the plants (e.g., developmental stage and acclimation). Here, we reviewed the impact of SA on saline stress responses and the associated molecular pathways, as well as recent studies toward understanding the hubs and crosstalk between SA-induced tolerances to biotic and saline stress. We propose that elucidating the mechanism of the SA-specific response to various stresses, as well as SA-induced rhizosphere-specific microbiome modeling, may provide more insights and support in coping with plant saline stress.