Institutional Publications

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Author: search.filters.author.Sharma, Namisha

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    Geminivirus-induced reprogramming of plant defense mechanisms: molecular insights and research frontiers
    (Annual Reviews, 2026) Sharma, Namisha; Sett, Susmita; Prasad, Manoj
    Geminiviruses employ multifunctional protein ammunition to evade robust plant defense pathways. Key viral proteins effectively manipulate host signaling mechanisms to create a permissive environment for viral replication. Rapid evolutionary adaptation of geminiviruses, synergized by the proliferation of insect vectors, creates a challenge for effective disease control. Current plant resistance against geminiviruses primarily relies on antiviral RNA silencing and the localized cell death mechanism as an outcome of the hypersensitive response. To win the escalating arms race between geminivirus manipulation and subsequent plant counteracting strategies and effectively restrict viral invasion, these defense strategies need to be updated or supplemented with novel engineering approaches. In this review, we provide a critical contemporary understanding of viral reprogramming pathways and host counter-defense responses that provide new avenues to improve plant immunity against geminiviruses.
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    Decoding the functionality of plant transcription factors
    (Oxford University Press, 2024) Dhatterwal, Pinky; Sharma, Namisha; Prasad, Manoj
    Transcription factors (TFs) intricately govern cellular processes and responses to external stimuli by modulating gene expressions. TFs help plants to balance the trade-off between stress tolerance and growth, thus ensuring their long-term survival in challenging environments. Understanding the factors and mechanisms that define the functionality of plant TFs is of paramount importance for unravelling the intricate regulatory networks governing development, growth, and responses to environmental stimuli in plants. The article provides a comprehensive understanding of these factors and mechanisms defining the activity of TFs. Understanding the dynamic nature of TFs has practical implications for modern molecular breeding programs, as it provides insights into how to manipulate gene expression to optimize desired traits in crops. Moreover, recent studies also report the functional duality of transcription factors, highlighting their ability to switch between activation and repression modes, this represents an important mechanism for attuning gene expression. Here we discuss what possible reasons for dual nature of TFs are and how this duality instructs the cell fate decision during development, and fine-tunes stress responses in plants, enabling them to adapt to various environmental challenges.
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    Histone deacetylase 9 interacts with SiHAT3.1 and SiHDA19 to repress dehydration responses through H3K9 deacetylation in foxtail millet
    (Oxford University Press, 2024) Kumar, Verandra; Singh, Babita; Singh, Roshan Kumar; Sharma, Namisha; Muthamilarasan, Mehanathan; Sawant, Samir V; Prasad, Manoj
    Climate change inflicts several stresses on plants, of which dehydration stress severely affects growth and productivity. C4 plants possess better adaptability to dehydration stress; however, the role of epigenetic modifications underlying this trait is unclear. Particularly, the molecular links between histone modifiers and their regulation remain elusive. In this study, genome-wide H3K9 acetylation (H3K9ac) enrichment using ChIP-seq was performed in two foxtail millet cultivars contrastingly differing in dehydration tolerance (IC403579; cv. IC4 – tolerant, and IC480117; cv. IC41 – sensitive). It revealed that a histone deacetylase, SiHDA9, was significantly up-regulated in the sensitive cultivar. Further characterization indicated that SiHDA9 interacts with SiHAT3.1 and SiHDA19 to form a repressor complex. SiHDA9 might be recruited through the SiHAT3.1 recognition sequence onto the upstream of dehydration-responsive genes to decrease H3K9 acetylation levels. The silencing of SiHDA9 resulted in the up-regulation of crucial genes, namely, SiRAB18, SiRAP2.4, SiP5CS2, SiRD22, SiPIP1;4 and SiLHCB2.3, which imparted dehydration tolerance in the sensitive cultivar (IC41). Overall, the study provides mechanistic insights into SiHDA9-mediated regulation of dehydration stress response in foxtail millet.
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    DNA methylation dynamics in response to abiotic and pathogen stress in plants
    (Springer Nature Publishing AG, 2022) Arora, Heena; Singh, Roshan Kumar; Sharma, Shambhavi; Sharma, Namisha; Panchal, Anurag; Das, Tuhin; Prasad, Ashish; Prasad, Manoj
    DNA methylation is a dynamic epigenetic mechanism that plays a significant role in gene expression and also maintains chromatin stability. The process is conserved in both plants and animals, and crucial for development and stress responses. Differential DNA methylation during adverse environmental conditions or pathogen attack facilitates the selective expression of defense-related genes. Both stress-induced DNA hypomethylation and hypermethylation play beneficial roles in activating the defense response. These DNA marks may be carried to the next generation making the progenies ‘primed’ for abiotic and biotic stress responses. Over the recent years, rapid advancements in the area of high throughput sequencing have enabled the detection of methylation status at genome levels in several plant species. Epigenotyping offers an alternative tool to plant breeders in addition to conventional markers for the selection of the desired offspring. In this review, we briefly discuss the mechanism of DNA methylation, recent understanding of DNA methylation-mediated gene regulation during abiotic and biotic stress responses, and stress memory in plants.
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    Role of Sw5 gene cluster in the fight against plant viruses
    (American Society for Microbiology, 2022) Sharma, Namisha; Prasad, Ashish; Prasad, Manoj
    The Sw5 gene cluster furnishes robust resistance to Tomato spotted wilt virus in tomato, which has led to its widespread applicability in agriculture. Among the five orthologs, Sw5b functions as a resistance gene against a broad-spectrum Tospovirus and is linked with Tospovirus resistance. However, its paralog, Sw5a, has been recently implicated in providing resistance against Tomato leaf curl New Delhi virus, broadening the relevance of the Sw5 gene cluster in promoting defense against plant viruses. We propose that plants have established modifications within the homologs of R genes that permit identification of different effector proteins and provide broad and robust resistance against different pathogens through activation of hypersensitive response and cell death.
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    The sly-miR166-SlyHB module acts as a susceptibility factor during ToLCNDV infection
    (Springer Nature Publishing AG, 2022) Prasad, Ashish; Sharma, Namisha; Chirom, Oceania; Prasad, Manoj
    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.
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    OsPSKR15, a phytosulfokine receptor from rice enhances abscisic acid response and drought stress tolerance
    (John Wiley & Sons, 2022) Nagar, Preeti; Sharma, Namisha; Jain, Muskan; Sharma, Gauri; Prasad, Manoj; Mustafiz, Ananda
    Abscisic acid (ABA) is a major phytohormone that acts as stimuli and plays an important role in plant growth, development, and environmental stress responses. Membrane-localized receptor-like kinases (RLKs) help to detect extracellular stimuli and activate downstream signaling responses to modulate a variety of biological processes. Phytosulfokine receptor (PSKR), a Leu-rich repeat (LRR)-RLK, has been characterized for its role in growth, development and biotic stress. Here, we observed that OsPSKR15, a rice PSKR, was upregulated by ABA in Oryza sativa. We demonstrated OsPSKR15 is a positive regulator in plant response to ABA. Ectopic expression of OsPSKR15 in Arabidopsis thaliana increased the sensitivity to ABA during germination, growth and stomatal closure. Consistently, the expression of ABA-inducible genes was significantly upregulated in these plants. OsPSKR15 also regulated reactive oxygen species (ROS)-mediated ABA signaling in guard cells, thereby governing stomatal closure. Furthermore, the constitutive expression of OsPSKR15 enhanced drought tolerance by reducing the transpirational water loss in Arabidopsis. We also reported that OsPSKR15 directly interacts with AtPYL9 and its orthologue OsPYL11 of rice through its kinase domain in the plasma membrane and nucleus. Altogether, these results reveal an important role of OsPSKR15 in plant response toward abiotic stress in an ABA-dependent manner.
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    The Sw5a gene confers resistance to ToLCNDV and triggers an HR response after direct AC4 effector recognition
    (PNAS, USA, 2021) Sharma, Namisha; Sahu, Pranav Pankaj; Prasad, Ashish; Muthamilarasan, Mehanathan; Waseem, Mohd; Khan, Yusuf; Thakur, Jitendra K.; Chakraborty, Supriya; Prasad, Manoj
    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.
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    Role of ubiquitination enzymes in abiotic environmental interactions with plants
    (Elsevier B.V., 2021) Sharma, Shambhavi; Prasad, Ashish; Sharma, Namisha; Prasad, Manoj
    Ubiquitination, a post-translational modification, plays a crucial role in various aspects of plant development and stress responses. Protein degradation by ubiquitination is well established and ubiquitin is the main underlying component directing the turnover of proteins. Recent reports have also revealed the non-proteolytic roles of ubiquitination in plants. In the past decade, ubiquitination has emerged to be one of the most important players in modulating plant's responses to abiotic stresses, which led to identification of specific E3 ligases and their targets involved in the process. Most of the E3 ligases play regulatory roles by modifying the stability and accumulation of stress responsive regulatory proteins, such as transcription factors, thus, modifying the downstream responses, or by degrading the proteins involved in the downstream cascade itself. In this review, we summarize and highlight the recent advances in the field of ubiquitination-mediated regulation of plant's responses to various abiotic stresses including limited nutrient availability and metal toxicity. The non-proteolytic role of ubiquitination in epigenetic regulation of abiotic stress induced response has also been discussed.
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    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
    (Elsevier B.V., 2021) Sharma, Namisha; Muthamilarasan, Mehanathan; Dulani, Priya; Prasad, Manoj
    In the present study, genes encoding for six major classes of enzymatic antioxidants, namely superoxide dismutase (SOD), catalase (CAT), glutathione reductase (GR), Peroxidase (Prx) and glutathione S-transferase (GST) are identified in tomato. Their expression was studied in tomato cultivars contrastingly tolerant to ToLCNDV during virus infection and different hormone treatments. Significant upregulation of SlGR3, SlPrx25, SlPrx75, SlPrx95, SlGST44, and SlGST96 was observed in the tolerant cultivar during disease infection. Virus-induced gene silencing of SlGR3 in the tolerant cultivar conferred disease susceptibility to the knock-out line, and higher accumulation (~80%) of viral DNA was observed in the tolerant cultivar. Further, subcellular localization of SlGR3 showed its presence in cytoplasm, and its enzymatic activity was found to be increased (~65%) during ToLCNDV infection in the tolerant cultivar. Knock-out lines showed ~3- and 3.5-fold reduction in GR activity, which altogether underlines that SlGR3 is vital component of the defense mechanism against ToLCNDV infection.