Biology subjects

Pathak, P. K.

Publications and source records attributed to Pathak, P. K..

5 recordsLinked to original sources

bioRxiv2024

ELONGATED HYPOCOTYL 5 regulates light-mediated squalene biosynthesis and development in Arabidopsis thaliana

Terpenoids are diverse groups of metabolite families that are crucial for plant development and required in cosmetics and pharmacological industries. Various development processes and environmental factors, including light, have been shown to affect terpenoid biosynthesis. However, regulatory factors involved in such regulation have not been explored much. Squalene synthases (SQSs), key enzymes in the terpenoid pathway, are pivotal for sterol and triterpene biosynthesis across various organisms. In this study, we report that AtSQS1 expression and squalene content are higher in the dark, and light through ELONGATED HYPOCOTYL 5 (HY5) negatively regulates the AtSQS1 gene and squalene biosynthesis in Arabidopsis thaliana. Our study shows that the AtSQS1 gene is unaffected in the hy5-215 mutant during light and dark conditions, but it is down-regulated in WT and HY5OX lines. The histochemical GUS assays and GFP expression patterns indicate a negative regulation of squalene biosynthesis by AtHY5. Yeast one-hybrid assays, EMSA, and ChIP experiments have confirmed the physical binding of AtHY5 on light-responsive elements of the AtSQS1 promoter. We have validated our results by developing AtSQS1 promoter: reporter transgenic lines in WT, hy5-215 mutants, and HY5OX backgrounds and conducted expression, metabolite quantification, and histochemical GUS assays. The metabolites quantification of squalene and phytosterols through GC-MS further confirms that AtHY5 negatively regulates the squalene biosynthesis in a light-dependent manner in Arabidopsis.

plant biology↗

bioRxiv2024

MYB transcription factor, NtMYB308, regulates anthocyanin and lignin content, and fungal tolerance in tobacco

Anthocyanins are secondary metabolites synthesized through the phenylpropanoid pathway. They attract pollinators, possess antioxidant properties that scavenge free radicals during environmental stress, and provide protection against various stress conditions. Lignin, another secondary metabolite, plays crucial roles in providing mechanical support, facilitating water and solute transport, and protecting against pathogens. MYB transcription factors, particularly R2R3 MYBs, are key regulators of secondary metabolism, especially within the phenylpropanoid pathway. These factors act as both activators and repressors. The N-terminal region of R2R3-MYB repressors contains a conserved bHLH-binding domain, while the C-terminal domain is divergent and includes an EAR repressor domain. R2R3-MYB proteins notably target sequences such as the MYB-response element and AC elements. In this study, we identified and characterized the Nicotiana MYB transcription factor, NtMYB308, and explored its regulatory function in anthocyanin and lignin biosynthesis in tobacco. Our Virus Induced Gene Silencing (VIGS) and Protein-DNA interaction studies suggest that NtMYB308 is a negative regulator of anthocyanin and lignin biosynthesis by binding to the promoters of genes involved in these pathways. To validate our findings, we developed CRISPR/Cas9-based knockout mutant plants of tobacco, NtMYB308CR, which showed up-regulation of anthocyanin and lignin biosynthesis. Conversely, NtMYB308 overexpression (NtMYB308OX) plants exhibited the opposite effect. Enhanced anthocyanin and lignin levels in NtMYB308CR plants provided tolerance against the fungus Alternaria solani, while NtMYB308OX lines were susceptible. This study advances our understanding of the regulatory mechanisms governing anthocyanin and lignin biosynthesis and their role in biotic stress in tobacco. One Sentence SummaryA R2R3 MYB transcription factor, NtMYB308, negatively regulates anthocyanin and lignin content, and fungal tolerance in tobacco.

plant biology↗

bioRxiv2023

Autophagy Restricts Tomato Fruit Ripening Via a General Role in Ethylene Repression

Autophagy, a cellular degradation pathway, and the phytohormone ethylene function in plant development, senescence, and stress responses. However, the manner of their interaction is mostly unknown. We reasoned that this may be revealed by studying autophagy in a climacteric fruit ripening context, for which ethylene is crucial. During ripening, fruits undergo softening, color change, toxic compound degradation, volatile production, and sugar assembly by fine-tuning synthesis and degradation of their cellular content. For autophagy activity assessment, we analyzed autophagy-related 8 (ATG8) lipidation and GFP-ATG8-labeled autophagosome flux in tomato fruit cells. Autophagy activity increased sharply from ripening initiation, climaxed at its middle stage, and declined towards its end, resembling ethylene production dynamics. Silencing the core-autophagy genes SlATG2, SlATG7, and SlATG4 separately in mature fruits resulted in early ethylene production and ripening onset, which was abrogated by 1-methylcyclopropene (1-MCP), an ethylene signaling inhibitor. Beyond ripening, Arabidopsis atg5 and atg7 mutant seedlings exhibited elevated ethylene production and sensitivity to 1-Aminocyclopropane 1-carboxylic acid (ACC), ethylenes precursor, which induces autophagy. This research demonstrates that autophagy limits tomato fruit ripening via a general role in ethylene restriction, opening the path for a mechanistic understanding of autophagy-ethylene crosstalk and harnessing autophagy for fruit shelf-life extension.

plant biology↗

bioRxiv2020

Structure of the unique tetrameric STENOFOLIA homeodomain bound with DNA

Homeobox transcription factors are key regulators of morphogenesis and development in both animals and plants1. In plants, the WUSCHEL-related homeobox (WOX) family transcription factors function as central organizers of several developmental programs from embryo patterning to meristematic stem cell maintenance through transcriptional activation and repression2-4. The structure of WOX Homeodomain (HD) and the molecular mechanism of its interaction with DNA are unknown. Here, we report the 2.1 [A] crystal structure of the STENOFOLIA (STF) HD from Medicago truncatula in complex with DNA. STF binds DNA as a novel cooperative tetramer, enclosing nearly entire bound DNA surface. The STF tetramer is partially stabilized by docking of the C-terminal tail from one protomer onto a conserved hydrophobic surface on the head of another in a head-to-tail manner. Helix 3 not only serves a canonical role as a base reader in the major groove, but also provides extensive binding to DNA in the minor groove. Our structural and functional data reveal that STF specifically targets TGA sequence and the cooperative tetrameric binding with DNA is key to transcriptional repression in plants. Our data reveal an unprecedented HD:DNA recognition mechanism, representing the first plant HD structure from WOX family of transcription factors.

biochemistry↗

bioRxiv2018

Trichoderma asperelloides enhances local (LAR) and systemic acquired resistance (SAR) response under low nitrate nutrition in Arabidopsis

Nitrogen (N) is essential for growth, development and defense but, how low N affects defense and the role of Trichoderma in enhancing defense under low nitrate is not known. Low nitrate fed Arabidopsis plants displayed reduced growth and compromised local and systemic acquired resistance responses when infected with both avirulent and virulent Pseudomonas syringae DC3000. These responses were enhanced in the presence of Trichoderma. The mechanism of increased local and systemic acquired resistance mediated by Trichoderma involved increased N uptake and enhanced protein levels via modulation of nitrate transporter genes. The nrt2.1 mutant is compromised in local and systemic acquired resistance responses suggesting a link between enhanced N transport and defense. Enhanced N uptake was mediated by Trichoderma elicited nitric oxide (NO). Low NO producing nia1,2 mutant and nsHb+ over expressing lines were unable to induce nitrate transporters and thereby compromised defense in the presence of Trichoderma under low N suggesting a signaling role of Trichoderma elicited NO. Trichoderma also induced SA and defense gene expression under low N. The SA deficient NahG transgenic line and the npr1 mutant were also compromised in Trichoderma-mediated local and systemic acquired resistance responses. Collectively our results indicated that the mechanism of enhanced plant defense under low N mediated by Trichoderma involves NO, ROS, SA production as well as the induction of NRT and marker genes for systemic acquired resistance. One-sentence summaryTrichoderma enhances local and systemic acquired resistance under low nitrate nutrition

plant biology↗