Biology subjects

Gase, K.

Publications and source records attributed to Gase, K..

7 recordsLinked to original sources

bioRxiv2026

An auxiliary protein tunes reductase activity in alkaloid biosynthesis

Monoterpene indole alkaloids encompass a diverse class of plant natural products. Many of these valuable compounds, including the anticancer medicines vinblastine and vincristine (Catharanthus roseus) and the antiaddiction treatment ibogaine (Tabernanthe iboga) utilize a common biosynthetic intermediate, 19E-geissoschizine, which is produced by the medium-chain dehydrogenase/reductase geissoschizine synthase (GS). Herein we report the discovery of a non-catalytic auxiliary protein (facilitator of geissoschizine synthase, FoGS) that improves formation of 19E-geissoschizine by acting in combination with GS. The discovery of a FoGS orthologue that works with GS to produce 19Z-geissoschizine shows how this protein also controls the stereochemistry of the product. We demonstrate that FoGS and GS interact to form a stable heterodimer, and show through mutagenesis that FoGS likely modulates the structure of the GS active site. Microscopy studies suggest that FoGS also changes the subcellular localization of GS. The discovery of FoGS will enable efforts to heterologously reconstitute commercially important geissoschizine-derived monoterpene indole alkaloids, and moreover, highlights how metabolic pathways utilize proteins that are not essential for production of the products, but nevertheless enhance the efficiency and specificity of the catalytic biosynthetic pathway components.

biochemistry↗

bioRxiv2025

Discovery of iridoid cyclase completes the iridoid pathway in asterids

Iridoids are specialized monoterpenes ancestral to asterid flowering plants (Albach et al, 2001; Stull et al, 2018). Iridoids play key roles in plant defense and are also essential precursors for pharmacologically important alkaloids (Dobler et al, 2011; Eisner, 1964). The biosynthesis of all iridoids involves the cyclization of a reactive enol intermediate. While this cyclization occurs spontaneously at low yields, it has long been hypothesized that a dedicated enzyme is involved in this process (Geu-Flores et al, 2012; Lichman et al, 2019b). Here, we report the discovery of asterid iridoid cyclases (ICYC). We show that these enzymes catalyze cyclization of the reactive intermediate to form the two major iridoid stereoisomers found in plants. Our work uncovers the last missing key step in the otherwise well-characterized iridoid biosynthesis pathway in asterids. This discovery unlocks the possibility to generate previously inaccessible iridoid stereoisomers, which will enable metabolic engineering for the sustainable production of valuable iridoid and iridoid-derived compounds.

plant biology↗

bioRxiv2024

Divergent biosynthesis of monoterpene indole alkaloids from geissoschizine

Plants can generate structural diversity by enzymatic rearrangement of a central intermediate. 19E-geisssochizine is one such chemically versatile intermediate that plays a central role in the biosynthesis of monoterpene indole alkaloids such as strychnine, ibogaine and vinblastine. Here we report how 19E-geissoschizine undergoes oxidative transformations to generate four distinct alkaloid scaffolds through the action of three biosynthetic enzymes. Using in vitro enzymatic assays and gene silencing, we demonstrate how these three cytochrome P450 enzymes in the medicinal plant Catharanthus roseus transform 19E-geisssochzine into strychnos, sarpagan, akuammiline-type, and mavacurane-type alkaloids. We use mutational analysis to show how minimal changes to the active site of these similar enzymes modulate product specificity. This work highlights how substrate reactivity and enzyme mutations work synergistically to generate chemical diversity.

biochemistry↗

bioRxiv2024

QTL mapping in field plant populations reveals a genetic basis for frequency- and spatially-specific fungal pathosystem resistance

Fungal pathogens pose significant challenges to agro-ecosystem productivity. The wild tobacco, Nicotiana attenuata, has been grown for over two decades at an experimental field station in its native habitat, leading to the emergence of a high-mortality sudden wilt disease caused by a Fusarium-Alternaria pathosystem. By using an Advanced Intercross Recombinant Inbred Line (AI-RIL) mapping population of N. attenuata planted in the infected field site, we found two significant loci associated with plant susceptibility to the fungi. A functional characterization of several genes in these loci identified RLXL (intracellular ribonuclease LX-like) as an important factor underlying plant pathogen resistance. Virus-induced silencing of RLXL reduced leaf wilting in plants inoculated with an in vitro culture of Fusarium species. Assessing the significance of the RLXL-associated allele in mixed field populations indicated that, among 4-plant subpopulations, those harboring a single plant with the RLXL-deficiency allele exhibited the highest survival rates. Within these populations, a living RLXL-deficient plant improved the survival of RLXL-producing plants located diagonally, while the mortality of the adjacent plants remained as high as in all other subpopulations. Taken together, these findings provide evidence for the genetic basis for a frequency- and spatially-dependent population pathogen resistance mechanism. Significance statementPlant pathogen resistance studies predominantly focus on single genes that reduce pathogenicity in individual plants, aiming to apply these findings to agricultural monocultures. On the other hand, ecologists have observed for decades that greater diversity drives plant population resistance and resilience to pathogens. More studies are needed to identify and characterize loci with positive effects conferred through their frequency in plant populations. We combine quantitative genetics, molecular techniques, and ecologically-informed mixed field populations to identify a novel intracellular ribonuclease LX-like (RLXL) gene with a frequency- and position-dependent effect for plant resistance. To our knowledge, this is the first detailed link between plant population protection and various percentages of plants with an allele representing RLXL presence or absence.

plant biology↗

bioRxiv2023

Pre-zygotic mate selection affects progeny fitness and is only partially correlated with the expression of NaS-like RNases

O_LINicotiana attenuata styles preferentially select pollen from accessions with corresponding expression patterns of NaS-like-RNases (SLRs), and the post-pollination ethylene burst (PPEB) is an accurate predictor of seed siring success. However, the ecological consequences of mate selection, its effect on the progeny, and the role of SLRs in the control of ethylene signaling are still not well understood. C_LIO_LIWe explored the link between the magnitude of the ethylene burst and transcript and protein abundance of the SLRs in a set of recombinant inbred lines (RILs) and investigated the fitness consequences of mate selection for the next generation. Genome Wide Association Study (GWAS) identified novel candidate genes potentially involved in the control of mate selection. C_LIO_LIWe found that high levels of PPEB are associated with the absence of SLR2 but not with the expression of SLR1 in most of the tested RILs. Maternal genotypes that favor certain pollen produce offspring with longer roots when pollinated with these donors, but the selection for beneficial traits is abolished when the maternal genotype selects only against certain pollen donors. C_LIO_LIWe conclude that mate selection mechanisms affect the offspring number and performance in ways that might be adaptive. C_LI

ecology↗

bioRxiv2020

Specific decorations of 17-hydroxygeranyllinalool diterpene glycosides solve the autotoxicity problem of chemical defense in Nicotiana attenuata

17-hydroxygeranyllinalool diterpene glycosides (HGL-DTGs) are abundant and potent anti-herbivore defense metabolites in Nicotiana attenuata whose glycosylation and malonylation biosynthetic steps are regulated by jasmonate signaling. To characterize the biosynthetic pathway of HGL-DTGs, we conducted a genome-wide analysis of uridine diphosphate glycosyltransferases (UGTs) and identified 107 members of family-1 UGTs. Tissue-specific time-course transcriptional profiling revealed that the transcripts of three UGTs were highly correlated with two HGL-DTG key biosynthetic genes: geranylgeranyl diphosphate synthase (NaGGPPS) and geranyllinalool synthase (NaGLS). NaGLSs role in HGL-DTG biosynthesis was confirmed by virus-induced gene-silencing. Silencing the UDP-rhamnosyltransferase, UGT91T1, indicated its role in the rhamnosylation of HGL-DTGs. In vitro enzyme assays revealed that UGT74P3 and UGT74P4 use UDP-glucose for the glucosylation of 17-hydroxygeranyllinalool (17-HGL) to lyciumoside I. UGT74P3 and UGT74P5 stably silenced plants were severely developmentally deformed, suggesting a phytotoxic effect of 17-HGL. Applications of synthetic 17-HGL and silencing of these UGTs in HGL-DTG-free plants confirmed the phytotoxic effect of 17-HGL. Feeding assays with Manduca sexta larvae revealed the defensive functions of the glucosylation and rhamnosylation steps in HGL-DTG biosynthesis. Glucosylation is a critical step that contributes to the metabolites defensive function and solves the autotoxicity problem of this potent chemical defense.

plant biology↗

bioRxiv2017

Wild tobacco genomes reveal the evolution of nicotine biosynthesis

Nicotine, the signature alkaloid of Nicotiana species responsible for the addictive properties of human tobacco smoking, functions as a defensive neurotoxin against attacking herbivores. However, the evolution of the genetic features that contributed to the assembly of the nicotine biosynthetic pathway remains unknown. We sequenced and assembled genomes of two wild tobaccos, Nicotiana attenuata (2.5 Gb) and N. obtusifolia (1.5 Gb), two ecological models for investigating adaptive traits in nature. We show that after the Solanaceae whole genome triplication event, a repertoire of rapidly expanding transposable elements (TEs) bloated these Nicotiana genomes, promoted expression divergences among duplicated genes and contributed to the evolution of herbivory-induced signaling and defenses, including nicotine biosynthesis. The biosynthetic machinery that allows for nicotine synthesis in the roots evolved from the stepwise duplications of two ancient primary metabolic pathways: the polyamine and nicotinic acid dinucleotide (NAD) pathways. While the duplication of the former is shared among several Solanaceous genera which produce polyamine-derived tropane alkaloids, the innovation and efficient production of nicotine in the genus Nicotiana required lineage-specific duplications within the NAD pathway and the evolution of root-specific expression of the duplicated Solanaceae-specific ethylene response factor (ERF) that activates the expression of all nicotine biosynthetic genes. Furthermore, TE insertions that incorporated transcription factor binding motifs also likely contributed to the coordinated metabolic flux of the nicotine biosynthetic pathway. Together, these results provide evidence that TEs and gene duplications facilitated the emergence of a key metabolic innovation relevant to plant fitness.

genomics↗