Biology subjects

Narayanan, A. K.

Publications and source records attributed to Narayanan, A. K..

4 recordsLinked to original sources

bioRxiv2025

Distinct Microbial Communities Within and On Seep Carbonates Support Long-term Anaerobic Oxidation of Methane and Novel pMMO Diversity

At methane seeps worldwide, syntrophic anaerobic methane-oxidizing archaea and sulfate-reducing bacteria (ANME-SRB) promote carbonate precipitation and rock formation, acting as methane and carbon sink. While maintenance of active anaerobic oxidation of methane (AOM) within seep carbonates has been documented, the ANME-SRB reactivity to methane exposure remains uncertain. Surface-associated microbes may metabolize AOM-derived sulfide, maintain carbonate anoxia, and contribute to carbonate dissolution and higher trophic levels; however, these microbial communities are poorly described thus far. Here we provide new insights into microbial diversity, metabolic potential, activity, and resiliency within and on Southern Californian methane seep carbonates, by combining 16S rRNA and metagenomic sequencing, laboratory incubations, and BONCAT-FISH. Ca. Methanophaga (ANME-1) dominated the carbonate interiors across different seepage activities, based on sequencing, while the dominant SRB was Ca. Desulfaltia, potentially a new ANME partner. BONCAT-FISH revealed differences in ANME-1 cell activity, suggesting cell dormancy or DNA preservation at less active seep sites. Carbonate incubations from low activity seeps ([≥]24 months) showed an exponential AOM reactivation (44-day doubling time), suggesting seep carbonates remain potential methane sinks over dynamic seepage conditions. The surface-associated communities were distinct from the carbonate interior and other seep habitats, and highly heterogeneous. Surface ANME-SRB biofilms and sulfide-oxidizing bacterial mats were associated with high and intermediate AOM carbonates, potentially influencing carbonate precipitation/dissolution. Carbonate surfaces shared diverse aerobic methanotrophs with invertebrates, potentially serving as pool for animal epibionts. Besides particulate methane monooxygenases from aerobic methanotrophs, we found divergent forms including within a Methylophagaceae (GCA-002733105) MAG suggesting a new function within Methylophagaceae.

ecology↗

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↗