Genomic dissection of ROS detoxifying enzyme encoding genes for their role in antioxidative defense mechanism against Tomato leaf curl New Delhi virus infection in tomato

Salinity Stress Resilience in Sorghum bicolor through Pseudomonas-Mediated Modulation of Growth, Antioxidant System, and Eco-Physiological Adaptations

Increased soluble salts in soil and irrigation water threaten the sustainability of crops. This causes food insecurity directly by reducing the staple crop yield and indirectly by limiting fodder and forage production. Recently, plant-growth-promoting rhizosphere microorganism utilization improved crop productivity under stress. Therefore, this research was conducted to find the Sorghum bicolor growth improvement potential by exogenous application of five different Pseudomonas strains under salinity in a pot experiment. The salinity was applied with a 1/2-strength Hoagland's nutrient solution as 0 and 100 mM NaCl for 30 days. Results indicated that salinity reduced the vegetative growth parameters and stress-responsive biochemicals in nonbacterial treated plants. However, Pseudomonas strains applied to plants exhibited notable increases in growth, relative water content, antioxidant enzyme activities, osmolytes, and photosynthetic pigments under salinity. The ionic imbalance was also reduced due to Pseudomonas strains by improving K+ and K+/Na+ ratios under salinity. P. aeruginosa strain SAHK (OQ194056) and P. putida strain AHK_SHA007 (OR468335) were found to be promising compared to other strains in increasing growth and stress tolerance. The augmentation of the plant's antioxidant system and maintenance of ion homeostasis by Pseudomonas strains served as a strategy to enhance the plant salt tolerance.

Transcriptomic profiling reveals distinct responses to beet curly top virus (BCTV) infection in resistant and susceptible sugar beet genotypes

BACKGROUND

Sugar beets (Beta vulgaris L.) are grown worldwide and suffer economic loss annually due to curly top disease caused by the beet curly top virus (BCTV). The virus is spread by the beet leafhopper (BLH), Circulifer tenellus Baker. Current management strategies rely on chemical control and planting BCTV-resistant sugar beet genotypes. However, the genetic mechanism underlying BCTV resistance in sugar beet is unknown. This study aimed to determine these mechanisms by comparing a resistant (EL10) and susceptible (FC709-2) sugar beet genotype using host plant suitability (no-choice), host preference (choice) assays, and transcriptomic analysis.

RESULTS

Host plant suitability assays revealed no significant differences in adult survival or nymph production between viruliferous and non-viruliferous BLH on either genotype, suggesting that BCTV resistance is not directly associated with reduced beet leafhopper fitness. However, host preference assays showed that viruliferous BLH preferred settling on the susceptible genotype, FC709-2, compared to the resistant genotype, EL10 whereas the non-viruliferous BLH showed no preference. RNA-sequencing analysis of BCTV-inoculated (viruliferous BLH-fed) and mock-inoculated (non-viruliferous BLH-fed) plants at day 1, 7, or 14 post-inoculations highlighted dynamic and contrasting responses between the two genotypes. The resistant genotype had differentially expressed transcripts (DETs) associated with jasmonic acid and abscisic acid biosynthesis and signaling. DETs associated with stress mitigation mechanisms and reduction in plant primary metabolic processes were also observed. In contrast, the susceptible genotype had DETs associated with opposing phytohormones like salicylic acid and auxin. Moreover, this genotype exhibited an upregulation in DETs involved in volatile organic compounds (VOCs) production and increased primary plant metabolic processes.

CONCLUSIONS

These results provide novel insight into the opposing transcriptional responses underlying BCTV resistance and susceptibility in sugar beet. Understanding and classifying the mechanisms of resistance or susceptibility to BCTV infection in sugar beet is beneficial to researchers and plant breeders as it provides a basis for further exploration of the host plant-virus-vector interactions.

Azolla filiculoides extract improved salt tolerance in wheat (Triticum aestivum L.) is associated with prompting osmostasis, antioxidant potential and stress-interrelated genes

The growth and productivity of crop plants are negatively affected by salinity-induced ionic and oxidative stresses. This study aimed to provide insight into the interaction of NaCl-induced salinity with Azolla aqueous extract (AAE) regarding growth, antioxidant balance, and stress-responsive genes expression in wheat seedlings. In a pot experiment, wheat kernels were primed for 21 h with either deionized water or 0.1% AAE. Water-primed seedlings received either tap water, 250 mM NaCl, AAE spray, or AAE spray + NaCl. The AAE-primed seedlings received either tap water or 250 mM NaCl. Salinity lowered growth rate, chlorophyll level, and protein and amino acids pool. However, carotenoids, stress indicators (EL, MDA, and H2O2), osmomodulators (sugars, and proline), antioxidant enzymes (CAT, POD, APX, and PPO), and the expression of some stress-responsive genes (POD, PPO and PAL, PCS, and TLP) were significantly increased. However, administering AAE contributed to increased growth, balanced leaf pigments and assimilation efficacy, diminished stress indicators, rebalanced osmomodulators and antioxidant enzymes, and down-regulation of stress-induced genes in NaCl-stressed plants, with priming surpassing spray in most cases. In conclusion, AAE can be used as a green approach for sustaining regular growth and metabolism and remodelling the physio-chemical status of wheat seedlings thriving in salt-affected soils.

Glutathione-the "master" antioxidant in the regulation of resistant and susceptible host-plant virus-interaction

The interaction between plant hosts and plant viruses is a very unique and complex process, relying on dynamically modulated intercellular redox states and the generation of reactive oxygen species (ROS). Plants strive to precisely control this state during biotic stress, as optimal redox levels enable proper induction of defense mechanisms against plant viruses. One of the crucial elements of ROS regulation and redox state is the production of metabolites, such as glutathione, or the activation of glutathione-associated enzymes. Both of these elements play a role in limiting the degree of potential oxidative damage in plant cells. While the role of glutathione and specific enzymes is well understood in other types of abiotic and biotic stresses, particularly those associated with bacteria or fungi, recent advances in research have highlighted the significance of glutathione modulation and mutations in genes encoding glutathione-associated enzymes in triggering immunity or susceptibility against plant viruses. Apparently, glutathione-associated genes are involved in precisely controlling and protecting host cells from damage caused by ROS during viral infections, playing a crucial role in the host's response. In this review, we aim to outline the significant improvements made in research on plant viruses and glutathione, specifically in the context of their involvement in susceptible and resistant responses, as well as changes in the localization of glutathione. Analyses of essential glutathione-associated enzymes in susceptible and resistant responses have demonstrated that the levels of enzymatic activity or the absence of specific enzymes can impact the spread of the virus and activate host-induced defense mechanisms. This contributes to the complex network of the plant immune system. Although investigations of glutathione during the plant-virus interplay remain a challenge, the use of novel tools and approaches to explore its role will significantly contribute to our knowledge in the field.

Uncovering the Role of Hormones in Enhancing Antioxidant Defense Systems in Stressed Tomato (Solanum lycopersicum) Plants

Tomato is one of the most important fruits worldwide. It is widely consumed due to its sensory and nutritional attributes. However, like many other industrial crops, it is affected by biotic and abiotic stress factors, reducing its metabolic and physiological processes. Tomato plants possess different mechanisms of stress responses in which hormones have a pivotal role. They are responsible for a complex signaling network, where the antioxidant system (enzymatic and non-enzymatic antioxidants) is crucial for avoiding the excessive damage caused by stress factors. In this sense, it seems that hormones such as ethylene, auxins, brassinosteroids, and salicylic, jasmonic, abscisic, and gibberellic acids, play important roles in increasing antioxidant system and reducing oxidative damage caused by different stressors. Although several studies have been conducted on the stress factors, hormones, and primary metabolites of tomato plants, the effect of endogenous and/or exogenous hormones on the secondary metabolism is still poorly studied, which is paramount for tomato growing management and secondary metabolites production. Thus, this review offers an updated overview of both endogenous biosynthesis and exogenous hormone application in the antioxidant system of tomato plants as a response to biotic and abiotic stress factors.

Investigating the Interplay between Tomato Leaf Curl New Delhi Virus Infection, Starch Metabolism and Antioxidant Defence System in Potato (Solanum tuberosum L.)

The potato apical leaf curl disease is caused by tomato leaf curl New Delhi virus-potato (ToLCNDV-potato), which severely alters a plant's starch metabolism, starch hydrolysing enzymes, and antioxidant mechanism. In this study, the result suggested that ToLCNDV-potato significantly (p < 0.01) affected the morphological parameters and photosynthetic pigment system in both the cultivars of potato, viz., Kufri Pukhraj (susceptible) and Kufri Bahar (tolerant). However, the impact of ToLCNDV-potato was lower in Kufri Bahar. Moreover, the viral infection in potato showed significant (p < 0.01) enhancement in the leakage of plant oxidative metabolites such as proline and malondialdehyde (MDA) which was further confirmed with higher electrolyte leakage. The viral infection imbalance of starch metabolism in the leaves ultimately affects the carbohydrate profile. ToLCNDV-potato significantly lowered starch synthesis, enhanced the accumulation of sucrose, glucose, fructose and-which was further validated by enzymatic estimation of β-amylase-α-amylase and phosphorylase activity in the leaves of both cultivars. The antioxidant enzymes, viz., catalase, ascorbate peroxidase, and superoxide dismutase, were reported to be enhanced in both the cultivars due to ToLCNDV-potato infection. The higher enhancement of antioxidant enzyme activity was observed in Kufri Bahar, which signifies its resistant attributes. These findings in the potato plant broaden our understanding of the regulatory mechanisms of starch metabolism and antioxidant activity and provide proof of concept for breeding potato for ToLCNDV-potato tolerance.

The roles of microRNAs in horticultural plant disease resistance

The development of the horticultural industry is largely limited by disease and excessive pesticide application. MicroRNAs constitute a major portion of the transcriptomes of eukaryotes. Various microRNAs have been recognized as important regulators of the expression of genes involved in essential biological processes throughout the whole life cycle of plants. Recently, small RNA sequencing has been applied to study gene regulation in horticultural plants. In this review, we summarize the current understanding of the biogenesis and contributions of microRNAs in horticultural plant disease resistance. These microRNAs may potentially be used as genetic resources for improving disease resistance and for molecular breeding. The challenges in understanding horticultural plant microRNA biology and the possibilities to make better use of these horticultural plant gene resources in the future are discussed in this review.

Regulatory non-coding RNA: The core defense mechanism against plant pathogens

Plant pathogens damage crops and threaten global food security. Plants have evolved complex defense networks against pathogens, using crosstalk among various signaling pathways. Key regulators conferring plant immunity through signaling pathways include protein-coding genes and non-coding RNAs (ncRNAs). The discovery of ncRNAs in plant transcriptomes was first considered "transcriptional noise". Recent reviews have highlighted the importance of non-coding RNAs. However, understanding interactions among different types of noncoding RNAs requires additional research. This review attempts to consider how long-ncRNAs, small-ncRNAs and circular RNAs interact in response to pathogenic diseases within different plant species. Developments within genomics and bioinformatics could lead to the further discovery of plant ncRNAs, knowledge of their biological roles, as well as an understanding of their importance in exploiting the recent molecular-based technologies for crop protection.

Identification of Candidate Genes Associated With Tolerance to Apple Replant Disease by Genome-Wide Transcriptome Analysis

Apple replant disease (ARD) is a worldwide economic risk in apple cultivation for fruit tree nurseries and fruit growers. Several studies on the reaction of apple plants to ARD are documented but less is known about the genetic mechanisms behind this symptomatology. RNA-seq analysis is a powerful tool for revealing candidate genes that are involved in the molecular responses to biotic stresses in plants. The aim of our work was to find differentially expressed genes in response to ARD in Malus. For this, we compared transcriptome data of the rootstock ‘M9’ (susceptible) and the wild apple genotype M. ×robusta 5 (Mr5, tolerant) after cultivation in ARD soil and disinfected ARD soil, respectively. When comparing apple plantlets grown in ARD soil to those grown in disinfected ARD soil, 1,206 differentially expressed genes (DEGs) were identified based on a log2 fold change, (LFC) ≥ 1 for up– and ≤ −1 for downregulation (p < 0.05). Subsequent validation revealed a highly significant positive correlation (r = 0.91; p < 0.0001) between RNA-seq and RT-qPCR results indicating a high reliability of the RNA-seq data. PageMan analysis showed that transcripts of genes involved in gibberellic acid (GA) biosynthesis were significantly enriched in the DEG dataset. Most of these GA biosynthesis genes were associated with functions in cell wall stabilization. Further genes were related to detoxification processes. Genes of both groups were expressed significantly higher in Mr5, suggesting that the lower susceptibility to ARD in Mr5 is not due to a single mechanism. These findings contribute to a better insight into ARD response in susceptible and tolerant apple genotypes. However, future research is needed to identify the defense mechanisms, which are most effective for the plant to overcome ARD.

The potential inhibitory effect of ginsenoside Rh2 on mitophagy in UV-irradiated human dermal fibroblasts

Background

In addition to its use as a health food, ginseng is used in cosmetics and shampoo because of its extensive health benefits. The ginsenoside, Rh2, is a component of ginseng that inhibits tumor cell proliferation and differentiation, promotes insulin secretion, improves insulin sensitivity, and shows antioxidant effects.

Methods

The effects of Rh2 on cell survival, extracellular matrix (ECM) protein expression, and cell differentiation were examined. The antioxidant effects of Rh2 in UV-irradiated normal human dermal fibroblast (NHDF) cells were also examined. The effects of Rh2 on mitochondrial function, morphology, and mitophagy were investigated in UV-irradiated NHDF cells.

Results

Rh2 treatment promoted the proliferation of NHDF cells. Additionally, Rh2 increased the expression levels of ECM proteins and growth-associated immediate-early genes in ultraviolet (UV)-irradiated NHDF cells. Rh2 also affected antioxidant protein expression and increased total antioxidant capacity. Furthermore, treatment with Rh2 ameliorated the changes in mitochondrial morphology, induced the recovery of mitochondrial function, and inhibited the initiation of mitophagy in UV-irradiated NHDF cells.

Conclusion

Rh2 inhibits mitophagy and reinstates mitochondrial ATP production and membrane potential in NHDF cells damaged by UV exposure, leading to the recovery of ECM, cell proliferation, and antioxidant capacity.

Keap1 recognizes EIAV early accessory protein Rev to promote antiviral defense

The Nrf2/Keap1 axis plays a complex role in viral susceptibility, virus-associated inflammation and immune regulation in host cells. However, whether or how the Nrf2/Keap1 axis is involved in the interactions between equine lentiviruses and their hosts remains unclear. Here, we demonstrate that the Nrf2/Keap1 axis was activated during EIAV infection. Mechanistically, EIAV-Rev competitively binds to Keap1 and releases Nrf2 from Keap1-mediated repression, leading to the accumulation of Nrf2 in the nucleus and promoting Nrf2 responsive genes transcription. Subsequently, we demonstrated that the Nrf2/Keap1 axis represses EIAV replication via two independent molecular mechanisms: directly increasing antioxidant enzymes to promote effective cellular resistance against EIAV infection, and repression of Rev-mediated RNA transport through direct interaction between Keap1 and Rev. Together, these data suggest that activation of the Nrf2/Keap1 axis mediates a passive defensive response to combat EIAV infection. The Nrf2/Keap1 axis could be a potential target for developing strategies for combating EIAV infection.

The sly-miR166-SlyHB module acts as a susceptibility factor during ToLCNDV infection

The role of miRNAs during viral pathogenesis is poorly understood in plants. Here, we demonstrate a miRNA/target module that acts as a susceptibility factor during ToLCNDV infection. Tomato leaf curl New Delhi virus (ToLCNDV) is a devastating pathogen that causes huge crop loss. It is spreading to new geographical locations at a very rapid rate-raising serious concerns. Evolution of insecticidal resistance in Bemisia tabaci which acts as the carrier for ToLCNDV has made insect control very difficult in the recent years. Thus, it is important that the host molecular mechanisms associated with ToLCNDV resistance/susceptibility are investigated to develop management strategies. In our study, we have identified that sly-miR166/SlyHB module acts as a susceptibility factor to ToLCNDV in Solanum lycopersicum. Sly-miR166 is differentially regulated upon ToLCNDV infection in two contrasting tomato cultivars; H-88-78-1 (tolerant to ToLCNDV) and Punjab Chhuhara (susceptible to ToLCNDV). Expression analysis of predicted sly-miR166 targets revealed that the expression of SlyHB is negatively correlated with its corresponding miRNA. Virus-induced gene silencing of SlyHB in the susceptible tomato cultivar resulted in the decrease in disease severity suggesting that SlyHB is a negative regulator of plant defence. In summary, our study highlights a miRNA/target module that acts as a susceptibility factor during ToLCNDV infection. To the best of our knowledge, this is the first report that highlights the role of sly-miR166/SlyHB module in ToLCNDV pathogenesis.

The Sw5a gene confers resistance to ToLCNDV and triggers an HR response after direct AC4 effector recognition

Several attempts have been made to identify antiviral genes against Tomato leaf curl New Delhi virus (ToLCNDV) and related viruses. This has led to the recognition of Ty genes (Ty1-Ty6), which have been successful in developing virus-resistant crops to some extent. Owing to the regular appearance of resistance-breaking strains of these viruses, it is important to identify genes related to resistance. In the present study, we identified a ToLCNDV resistance (R) gene, SlSw5a, in a ToLCNDV-resistant tomato cultivar, H-88-78-1, which lacks the known Ty genes. The expression of SlSw5a is controlled by the transcription factor SlMyb33, which in turn is regulated by microRNA159 (sly-miR159). Virus-induced gene silencing of either SlSw5a or SlMyb33 severely increases the disease symptoms and viral titer in leaves of resistant cultivar. Moreover, in SlMyb33-silenced plants, the relative messenger RNA level of SlSw5a was reduced, suggesting SlSw5a is downstream of the sly-miR159-SlMyb33 module. We also demonstrate that SlSw5a interacts physically with ToLCNDV-AC4 (viral suppressor of RNA silencing) to trigger a hypersensitive response (HR) and generate reactive oxygen species at infection sites to limit the spread of the virus. The "RTSK" motif in the AC4 C terminus is important for the interaction, and its mutation completely abolishes the interaction with Sw5a and HR elicitation. Overall, our research reports an R gene against ToLCNDV and establishes a connection between the upstream miR159-Myb33 module and its downstream target Sw5a to activate HR in the tomato, resulting in geminivirus resistance.