Biology subjects

Nagegowda, D. A.

Publications and source records attributed to Nagegowda, D. A..

8 recordsLinked to original sources

bioRxiv2025

A dual-localized geraniol synthase and a previously unreported cytosolic geranyl pyrophosphatase contribute to geraniol formation in lemongrass

Geraniol, a major constituent of many essential oils and precursor for geraniol-derived aldehydes and acetates, is produced in plants through the action of a terpene synthase encoding geraniol synthase or via terpene synthase-independent non-canonical pathway involving a Nudix hydrolase and a yet to be discovered pyrophosphatase. Here, we identify a geraniol synthase (Cymbopogon flexuosus geraniol synthase; CfGES) that catalyzes the conversion of geranyl pyrophosphate (GPP) (also known as geranly diphosphate) to geraniol, as well as a previously unreported geranyl pyrophosphatase (CfG(P)Pase) that acts on both GPP and geranyl monophosphate (GP), albeit with different efficiencies, to generate geraniol. Virus-induced gene silencing of CfGES or CfG(P)Pase resulted in a substantial reduction in geraniol and its immediate product citral in lemongrass leaves. Conversely, transient overexpression of CfGES or CfG(P)Pase resulted in enhanced production of geraniol and citral in lemon balm (Melissa officinalis) leaves, as well as geraniol, citronellol, and citral in rose (Rosa damascena) flower petals. Subcellular localization studies revealed that while CfGES exhibited dual cytosolic/plastidial localization, CfG(P)Pase was localized to the cytosol. This localization pattern was further supported by the significantly higher geraniol-forming activity observed in the purified cytosolic protein fraction compared to the chloroplast fraction. Our study uncovers the missing step in cytosolic geraniol formation via a TPS-independent non-canonical route and demonstrates that geraniol, required for citral production in lemongrass, is synthesized by cytosolic CfG(P)Pase and cytosol-/plastid-localized CfGES.

plant biology↗

bioRxiv2024

CrGEF1, CrGAP1, and CrGDI2 function as key regulators of ROP-GTPase mediated modulation of alkaloid biosynthesis in Catharanthus roseus

ROP-GTPase Regulatory Proteins (RGRPs) have been shown to control plant morphogenesis, development and immunity, however, their role in specialized metabolism is hitherto not known. Here, we demonstrate that specific RGRPs control monoterpene indole alkaloid (MIA) biosynthesis by interacting with distinct Rho of Plants (ROP) in Catharanthus roseus. Among the five Guanine nucleotide Exchange Factors (GEFs), four GTPase-activating proteins (GAPs), and two GDP dissociation inhibitors (GDIs) identified in the C. roseus genome, only CrGEF1, CrGAP1, and CrGDI2 specifically interacted with CrROP3 and CrROP5. These RGRPs displayed distinct cytosolic and/or membrane localization patterns, with their transcripts predominantly expressed in aerial tissues. Functional studies revealed that CrGEF1 acts as a positive regulator of MIA biosynthesis, as its silencing led to a reduction in MIA production, while overexpression enhanced MIA levels. Conversely, CrGAP1 and CrGDI2 function as negative regulators, with their silencing resulting in increased MIA production and their overexpression causing reduced MIA levels. Notably, terminal truncated forms of these RGRPs showed interaction with CrROP3 or CrROP5 but failed to influence MIA biosynthesis, underscoring the importance of these domains in their regulatory functions. Overall, our findings uncover a previously unexplored mechanism by which distinct RGRPs coordinate with specific ROPs to regulate transcription factors and fine-tune MIA biosynthesis in C. roseus. SignificancePlants fine-tune their metabolic pathways to adapt to environmental and physiological cues, balancing primary and specialized metabolism. Here, we uncover a feedback regulatory mechanism by which ROP-GTPase regulatory proteins (RGRPs) control alkaloid biosynthesis in Catharanthus roseus. We found that CrGEF1, CrGAP1, and CrGDI2 specifically interact with ROP-GTPases CrROP3 and CrROP5, modulating the monoterpene indole alkaloid (MIA) pathway. This RGRP-ROP module plays a crucial role in dynamically regulating MIA levels, where CrGEF1 promotes MIA production while CrGAP1 and CrGDI2 act as negative regulators. These findings highlight the importance of RGRP-ROP circuitry in control of alkaloid biosynthesis in C. roseus, and specialized metabolism in plants.

plant biology↗

bioRxiv2024

Phylogenetically distant enzymes localized in cytosol and plastids drive citral biosynthesis in lemongrass

Except for the genetic basis of citral-forming alcohol dehydrogenases (ADHs) in Litsea cubeba tree, and biochemical studies on citral-forming enzymes from select plants, knowledge regarding in-planta biosynthesis of citral and its metabolic origin remains limited. Here, we have elucidated the functions of an ADH (CfADH1) and an aldoketo-reductase (CfAKR2b) in citral biosynthesis in lemongrass (Cymbopogon flexuosus), one of the most cultivated aromatic crops for its citral-rich essential oil. Expression of both CfADH1 and CfAKR2b showed correlation with citral accumulation in different developmental stages. Recombinant CfADH1 and CfAKR2b, despite their sequence unrelatedness, exhibited similar kinetic properties and formed citral from geraniol with NADP cofactor. Virus-induced gene silencing in lemongrass, and transient expression in lemon balm (Melissa officinalis), demonstrated the in-planta involvement of CfADH1 and CfAKR2b in citral biosynthesis. While CfADH1 exhibited a dual cytosolic/plastidial localization, CfAKR2b was localized to cytosol. Moreover, feeding lemongrass seedlings with mevalonate- and methylerythritol-phosphate-pathway specific inhibitors combined with volatile profiling supported the role of both pathways in citral formation. Our results demonstrate phylogenetically distant enzymes localized in cytosol and plastids drive citral biosynthesis in lemongrass, indicating an evolutionary scenario aimed at maximizing the utilization of precursor pools from both cytosolic and plastidial pathways for high citral production.

plant biology↗

bioRxiv2024

Functional characterization of two glycosyltransferases from Withania somnifera illuminates their role in withanosides biosynthesis and defence against bacteria

The medicinal properties of Ashwagandha (Withania somnifera L. Dunal) are attributed to the presence of unique class of natural products called as withanolides and their glycosylated forms, withanosides. Withanosides are proposed to be formed from withanolides by the action of glycosyltransferases (GTs). This study reports the functional characterization of two GTs (WsGT4 and WsGT6) from W. somnifera that exhibited induced expression in response to methyl jasmonate treatment and showed highest expression in leaves compared to other tissues. Biochemical assays with recombinant WsGT proteins showed that WsGT4 and WsGT6 formed glycosylated products with four and one of the seven tested withanolides substrates, respectively. WsGT4 catalyzed product formation using withanolide A, withanolide B, withanone, and 12-deoxywithastramonolide as substrates, with UDP-glucose serving as the glucose donor, while WsGT6 catalyzed the product formation only with withaferin A as substrate employing either UDP-glucose or UDP-galactose as sugar donors. Moreover, in planta studies through virus-induced gene silencing and transient overexpression of WsGT4 and WsGT6 in W. somnifera leaves modulated the levels of withanolides and withanosides, indicating their role in withanosides biosynthesis. Furthermore, while individual silencing of both WsGT4 and WsGT6 in W. somnifera reduced the tolerance to Pseudomonas syringae DC3000 growth, their overexpression enhanced the tolerance to the bacterium in W. somnifera. Taken together, these results shed light on the roles of WsGT4 and WsGT6 in withanoside biosynthesis and defence against model bacterial pathogen in W. somnifera.

plant biology↗

bioRxiv2023

Analysis of root volatiles and functional characterization of a root-specific germacrene A synthase in Artemisia pallens

Davana (Artemisia pallens) is a valuable aromatic herb within the Asteraceae family, highly prized for its essential oil (EO) produced in the aerial parts. However, the root volatiles and their specific composition, and genes responsible for root volatiles have remained unexplored until now. Here, we show that A. pallens roots possess distinct oil bodies and yields [~]0.05% of EO, which is primarily composed of sesquiterpenes {beta}-elemene, neryl isovalerate, {beta}-selinene, and -selinene, and trace amounts of monoterpenes {beta}-myrcene, D-limonene. This shows that, besides aerial parts, roots of davana can also be a source of unique EO. Moreover, we functionally characterized a terpene synthase (ApTPS1) that exhibited high in silico expression in the root transcriptome. The recombinant ApTPS1 showed the formation of {beta}-elemene and germacrene A with E,E-farnesyl diphosphate (FPP) as a substrate. Further, detailed analysis of assay products revealed that {beta}-elemene was the thermal rearrangement product of germacrene A. Furthermore, the functional expression of ApTPS1 in Saccharomyces cerevisiae confirmed the in vivo {beta}-elemene/germacrene A synthase activity of ApTPS1. At the transcript level, ApTPS1 displayed predominant expression in root, with significantly lower level of expression in other tissues. This expression pattern of ApTPS1 positively correlated with the tissue-specific accumulation level of {beta}-elemene. Overall, these findings provide fundamental insights into the EO profile of davana roots, and the contribution of ApTPS1 in the formation of a major root volatile. Main conclusionThe study demonstrated that Artemisia pallens roots can be a source of terpene-rich essential oil and root-specific ApTPS1 forms germacrene-A contributing to major root volatiles.

plant biology↗

bioRxiv2023

The cytochrome P450 enzyme WsCYP71B35 from Withania somnifera has a role in withanolides biosynthesis and defense against bacteria

The medicinal properties of Ashwagandha (Withania somnifera L. Dunal) are attributed to withanolides, which belong to the triterpenoid steroidal lactones class of compounds. Though it is proposed that intermediates of the universal phytosterol pathway are utilized by cytochrome P450 (CYP450) enzymes to form withanolides, studies on functional characterization of these enzymes has been sparse. This study reports the functional characterization of a CYP450 candidate from W. somnifera (WsCYP71B35) that exhibited induced expression in response to methyl jasmonate treatment and showed higher expression in tissues that accumulate withanolides. Biochemical assay with yeast microsomal fraction expressing recombinant WsCYP71B35 indicated no activity when phytosterols and their intermediate 24-methylene cholesterol were used as substrates. However, WsCYP71B35 catalyzed product formation with withaferin A, withanolide A, withanolide B, and withanoside IV among the tested substrates. Moreover, virus-induced gene silencing (VIGS) and transient overexpression of WsCYP71B35 in W. somnifera leaves modulated the levels of withaferin A, withanolide A, and withanolide B, indicating the role of WsCYP71B35 in withanolides pathway. Furthermore, VIGS of WsCYP71B35 in W. somnifera reduced its tolerance to Pseudomonas syringae (DC3000) infection, whereas overexpression enhanced the tolerance to the bacterium in W. somnifera and transgenic tobacco. Overall, these results provide insights into the role of W. somnifera WsCYP71B35 in withanolides biosynthesis and bacterial defense.

plant biology↗

bioRxiv2023

Rho of plant GTPases with geranylgeranylation motif modulate monoterpene indole alkaloid biosynthesis in Catharanthus roseus

Rho Of Plant (ROP) GTPases function as molecular switches that control signaling processes essential for growth, development, and defense. However, their role in specialized metabolism is poorly understood. Previously, we demonstrated that inhibition of protein geranylgeranyl transferase (PGGT-I) negatively impacts the biosynthesis of monoterpenoid indole alkaloids (MIA) in Catharanthus roseus, indicating the involvement of prenylated proteins in signaling. Here, we show through biochemical, molecular and in planta approaches that specific geranylgeranylated ROPs modulate C. roseus MIA biosynthesis. Among the six C. roseus ROP GTPases (CrROPs), only CrROP3 and CrROP5, having a C- terminal CSIL motif, were specifically prenylated by PGGT-I. Additionally, both of their transcripts showed higher expression in most parts compared to other CrROPs. Protein- protein interaction studies revealed that both CrROP3 and CrROP5, but not CrROP2 (lacking CSIL motif), interacted with CrPGGT-I. Further, CrROP3 and CrROP5 exhibited nuclear localization, whereas CrROP2 was localized to plasma membrane. In planta functional studies revealed that silencing of CrROP3 and CrROP5 negatively affected MIA biosynthesis, while their overexpression upregulated MIA formation. In contrast, silencing and overexpression of CrROP2 had no effect on MIA biosynthesis. Moreover, overexpression of {Delta}CrROP3 and {Delta}CrROP5 mutants lacking the CSIL motif failed to enhance MIA biosynthesis. Taken together, these results implicate that CrROP3 and CrROP5 have positive regulatory role on MIA biosynthesis and thus shed light on how geranylgeranylated ROP GTPases mediate the modulation of specialized metabolism in C. roseus.

plant biology↗

bioRxiv2020

Antibacterial efficacy of Jackfruit rag extract against clinically important pathogens and validation of its antimicrobial activity in Shigella dysenteriae infected Drosophila melanogaster infection model

The aim of this study was to determine the antibacterial property of extract derived from a part of the Jackfruit called rag, that is generally considered as fruit waste. Morpho-physical characterization of the Jackfruit rag extract (JFRE) was performed using gas-chromatography, where peaks indicative of furfural; pentanoic acid; and hexadecanoic acid were observed. In vitro biocompatibility of JFRE was performed using the MTT assay, which showed comparable cellular viability between extract-treated and untreated mouse fibroblast cells. Agar well disc diffusion assay exhibited JFRE induced zones of inhibition for a wide variety of laboratory and clinical strains of gram-positive and gram-negative bacteria. Analysis of electron microscope images of bacterial cells suggests that JFRE induces cell death by disintegration of the bacterial cell wall and precipitating intracytoplasmic clumping. The antibacterial activity of the JFREs was further validated in vivo using Shigella dysenteriae infected fly model, where JFRE pre-fed flies infected with S. dysenteriae had significantly reduced mortality compared to controls. JFRE demonstrates broad antibacterial property, both in vitro and in vivo, possibly by its activity on bacterial cell wall. This study highlights the importance of exploring alternative sources of antibacterial compounds, especially from plant-derived waste, that could provide economical and effective solutions to current challenges in antimicrobial therapy.

microbiology↗