ABSTRACT Land plants possess a unique system for responding to environmental stressors. How this system evolved during plant terrestrialization remains one of the major questions in plant evolutionary biology. To retrace this process, it is essential to study both land plants and their closest algal relatives, the zygnematophytes. Using the single-celled zygnematophyte Mesotaenium , we integrated physiological stress experiments with phosphoproteomics, genome-wide transcription factor binding analyses, and protein–protein interaction studies to investigate the architecture of a key stress response pathway: the signaling cascade homologous to the plant abscisic acid (ABA)-mediated pathway. Our results highlight the roles of histidine kinases (HKs) and calcium-dependent protein kinases (CDPKs) in osmotic stress signaling. Focusing on SnRK2 and ABF, key components at the downstream end of the canonical ABA signaling pathway, we provide evidence that ABF plays a central role in osmotic stress responses even in the absence of ABA. Together, our data reveal the coordinated action of parallel functional modules that were likely integrated into the ABA response cascade during plant terrestrialization.

Plant terrestrialization necessitated overcoming a barrage of stressors.1 Embryophytes (land plants) use an integrated response network to adjust their molecular physiology in response to terrestrial stressors2-one of the important stressors is UV irradiance. The zygnematophytes are the closest streptophyte algal relatives of embryophytes,3,4,5,6 renowned for their UV resilience7,8,9 and key for inferring the UV response toolkit of the earliest embryophytes.10,11 Throughout evolution, specialized metabolism radiated, yielding chemodiverse responses to environmental challenges12,13,14,15 ranging from UV-shielding flavonoids and coumarins to the polymer lignin of tracheophytes16; homologs of the underpinning core pathway occur in streptophyte algae.17 Here, we exposed the zygnematophyte Mesotaenium to UV-B irradiation and profiled its physiological, morphological, transcriptomic, and metabolomic features. After UV-B exposure, the cells showed rapid photophysiological responses and progressively growing terminal vacuoles. Our transcriptome data capture dynamic changes in gene expression in (1) core downstream homologs of phenol metabolic enzymes, photophysiological homeostats, and DNA repair factors and (2) upstream components featuring key homologs of kinase-mediated signaling cascades, as well as light quality and abscisic acid-mediated signaling components. To scrutinize the acclimatory chassis, we created a metabolite feature database specifically for the Mesotaenium metabolome. The metabolome displayed pronounced temporal shifts, with several phenolic features that accumulate along the UV-stress-acclimation kinetics. Overall, we capture chemodiverse responses, including various phenolics such as methoxypsoralen-like derivatives and coumarins. We establish an integrated model for UV responses in the closest algal relatives of embryophytes, illuminating the toolkit that allowed the progenitors of embryophytes to move out of a protective water column.

Sclerotinia sclerotiorum is a notorious soilborne fungal pathogen that causes serious yield losses in many economically important crops such as canola, beans, lettuce, and sunflower. The diseases it causes, commonly known as Sclerotinia stem rot or white mold, are difficult to control due to the pathogen's wide host range and the persistence of the sclerotia. Host-induced gene silencing (HIGS) has recently emerged as a promising strategy for managing fungal diseases, including those caused by S. sclerotiorum. However, effective HIGS targets are limited due to the incomplete knowledge about the pathogen's survival and virulence strategies. In this study, through combined forward and reverse genetic analyses, we identified and characterized four Ras guanine nucleotide exchange factors (RasGEFs) in S. sclerotiorum. These proteins were found to be essential for sclerotia development, compound appressoria functionality, and virulence to varying degrees. In parallel, four corresponding RasGEF homologs were characterized in Botrytis cinerea, a necrotrophic pathogen from the Sclerotiniaceae family, in which they contribute to fungal growth, conidiation, and virulence. Among them, RasGEFa plays a predominant role, as its deletion in both fungi resulted in the most severe developmental and virulence defects, and it appears to function upstream of the SMK1 MAPK pathway. Furthermore, plant hosts expressing double-stranded RNA targeting SsRasGEFa and SsRasGEFc showed significantly reduced disease symptoms, demonstrating the potential of HIGS as a strategy for controlling these pathogens. Taken together, our findings revealed that these RasGEFs play conserved and crucial roles in fungal development and virulence and represent promising molecular targets for durable HIGS-based crop protection. [Formula: see text] Copyright © 2026 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Many diverse bacteria can enter non- or slow-growing states where they are transiently tolerant to antibiotics. Despite its medical importance, the genetic mechanisms underlying this ‘persistence’ remain largely unknown, especially for spontaneous (type II) persistence that arises during exponential growth. To address this challenge, here we combine genomic, transcriptomic, and lipidomic analysis to explore the persistence mechanisms. We first analyzed the genome of the high-persistence mutant Escherichia coli DS1 ( hipQ ) to identify candidate genes for the high-persistence phenotype. We then compared the gene expression profile of these isolated persisters to that of normally growing cells with RNA-Seq and found that the activation of stress response mechanisms is likely not important in the entrance into hipQ -driven spontaneous persistence during exponential growth. Transcriptomic results also suggest that modifications in the cell membrane are closely linked to persistence, as further corroborated by lipidomic profiles showing a higher level of unsaturated fatty acids in persisters compared to normally growing cells. Taken together, our results indicate that changing membrane composition is associated with persistence, and further our understanding of spontaneous persister cells from the DS1 ( hipQ ) context.

Desaturases in plants are diverse. They vary in localization, source of reducing power, and substrate preference, accepting glycerolipids, long-chain bases, acyl-CoAs, and acyl-ACPs, in varying states of (un)saturation and chain length. Their products are incorporated into membrane glycerolipids, sphingolipids, or storage lipids. We previously characterized a desaturase from Physcomitrium patens that predominantly affects the monounsaturation of very-long-chain fatty acyl (VLCFA) moieties of sphingolipids, naming this desaturase SPHINGOLIPID FATTY ACYL DESATURASE (SFD). Among embryophytes, candidate SFDs were only identified in setaphytes, including one paralog in P. patens and an ortholog in Marchantia polymorpha. Here, we characterize the P. patens paralog, and clarify via mutant analysis that SFDs affect not only sphingolipid metabolism, but also glycerolipid metabolism. We express both paralogs, as well as the candidate gene from M. polymorpha, in Saccharomyces cerevisiae, and show they desaturate VLCFAs incorporated into sphingolipids, triacylglycerols, and acyl-CoAs. The simplest explanation is that "SFDs" likely accept an acyl-CoA, rather than a sphingolipid substrate as initially proposed. We suggest renaming these desaturases VERY-LONG-CHAIN FATTY ACYL DESATURASES (VFADs). The physiological functions of VFADs and functionally similar enzymes from other plant systems are discussed, as are the challenges with classifying desaturases.

Salinity stress is a growing global challenge. We investigated how Populus euphratica, a salinity-adapted tree, acclimates to NaCl from cellular to whole-plant levels. Photosynthesis and aboveground growth declined, but root length and biomass remained stable under salinity. Unlike lateral roots (LRs), main roots (MRs) displayed hyperplastic growth, with a twofold increase in tip diameter due to additional cortical cell layers but without changes in cell volume. This root thickening was Na*-specific and absent under KCl exposure. MRs accumulated high Na* levels, while LRs did not, consistent with strong Na* extrusion capacity and elevated expression of Na* transporters in LRs, indicating specialized ion management within the root system. Transcriptomic analysis revealed stronger salinity responses in LRs, with enrichment of transcripts involved in stress defense, transport, and transcriptional regulation. In contrast, MRs upregulated genes related to mitotic cell division, steroid biosynthesis, and cell wall organization, supporting hyperplasia. Root phytohormones showed increased ABA and JA, especially in MRs, while auxin declined. Long-term salinity led to downregulation of stress responses in MRs, suggesting acclimation, whereas LRs maintained active defense pathways. GO enrichment highlighted distinct developmental programs: MRs prioritized cell proliferation and structural remodeling, while LRs focused on stress tolerance and salt extrusion. These results suggest that P. euphratica employs a dual salt-coping strategy: MRs undergo hyperplastic growth for structural resilience and ion buffering, while LRs dynamically exclude Na* and transmit stress signals. This opens new perspectives on mechanisms of salt tolerance in plants, supporting that root-level specialization enables efficient salinity adaptation in halophytes.

Zygnematophytes emerged as the unexpected closest algal relatives of land plants despite their simple body plans, raising questions about the morphogenetic toolkit present in the last common ancestor of land plants and algae. Genomic analyses have revealed that zygnematophytes are cellular giants, sharing homologous frameworks for several phytohormones, secondary metabolites, and key morphogenetic and transcriptional regulatory processes. Zygnematophytes fall into 5 orders, each of which has charted its own evolutionary path. Here, we have sequenced a contiguous genome of Spirogyra pratensis, the eponymous representative of Spirogyrales and a classical model system for evolutionary cell biology in the green lineage. Building on this genome, we transcriptionally profiled the tractable life cycle of Spirogyra and its responses to a bifactorial gradient of light and temperature. Our data highlight the activation of quiescence and homeostatic programs. Yet what stands out most in Spirogyra is its spiral chloroplast-undulating intracellularly and abscising during mixed phragmoplast formation and furrowing. Leveraging the genome in tandem with co-expression network analyses, we describe the molecular underpinnings of the unique cytokinetic processes that govern both cell and plastid division. We find that Spirogyra deploys a molecular program characteristic of Phragmoplastophyta yet lacks the deeply conserved plastid division machinery found in other archaeplastid plastids.

The clubroot pathogen Plasmodiophora brassicae has an effector protein that can methylate the plant defense compound salicylic acid (SA), and the protein sequence is highly conserved in different isolates worldwide. Sequencing the full-length cDNA of P. brassicae Benzoic acid/Salicylic acid Methyltransferase (PbBSMT) from a small collection of clubs indicated the occurrence of a natural variation that differs by 18 amino acids, which was also found within the worldwide data collection for P. brassicae isolates. A search for more possible substrates including defense-inducing compounds revealed that PbBSMT was also able to convert a recently reported inductor of systemic defense, N-hydroxy pipecolic acid (NHP), to its methyl ester. PbBSMT showed much lower Km values for the substrates SA and NHP compared with the other two natural compounds previously identified to be methylated with high activities (benzoic and anthranilic acids), suggesting they are the most favored substrates in vitro. The two variants showed no difference in terms of being able to accept the four naturally occurring substrates. Mature clubs incubated for 21 d after inoculation with NHP or SA showed in vivo conversion to their respective methyl esters. The methyl ester of NHP was specifically detected in transgenic plants overexpressing PbBSMT under inductive conditions. Transgenic Arabidopsis with elevated NHP levels had reduced club weights, but no reduction in infection rate or disease severity was seen in these plants, or in mutants with decreased NHP levels. Treatment of infected plants with NHP did not reduce disease severity, and therefore a major function for NHP in defense against the clubroot pathogen is not apparent.

Plant pathogenic fungi pose a significant threat to global food security. Hence, discovering targeted (bio)chemical methods to combat plant diseases is a critical research avenue. Recent work has implicated copper radical oxidases (CROs) from Auxiliary Activity Family 5 (AA5) in fungal morphogenesis and pathogenesis, including in appressorium penetration by foliar phytopathogens in the genera Colletotrichum and Magnaporthe. We identified orthologous AA5-encoding genes in Verticillium species; however, it was not clear that the functions of the corresponding CROs would be conserved in these vascular wilt pathogens. Using Verticillium dahliae JR2 as an exemplar, recombinant protein production and detailed enzyme kinetic analyses revealed predominant aryl-alcohol oxidase activity of the AA5 subfamily 2 (AA5_2) homolog, and predominant aldehyde oxidase activity of the AA5 subfamily 1 (AA5_1) homolog. Transcriptomics and reverse genetics experiments on both CROs and three putative peroxidases/catalases (known activators of CROs) in V. dahliae JR2 failed to indicate direct roles in phytopathogenesis. Taken together, the data indicate that the biological roles of CROs and AA5_2 members, in particular, are not broadly conserved between foliar and vascular wilt phytopathogens. However, the biochemical characterization of an AA5_1 aldehyde oxidase and an AA5_2 aryl-alcohol oxidase from V. dahliae, as well as an AA5_2 ortholog from V. longisporum VL43, provides a foundation for further functional elucidation, as well as new biocatalysts for biotechnological applications.IMPORTANCEPlant pathogens constitute a considerable burden to human society by attacking crops and reducing agricultural yields. Oxidative enzymes are often key weapons in the arsenal deployed by phytopathogens in the effort to breach cell walls and extract nutrients. Here, the characterization of the biochemical specificities of copper radical oxidases (CROs) from Verticillium wilt/stripe fungi defines a range of possible alcohol and aldehyde substrates in vivo and outlines the potential of these enzymes for their biotechnological application for chemical valorization. Although specific gene knockouts did not reveal a biological function for these CROs, we now know that the molecular mechanism of CRO-mediated pathogenesis previously observed in foliar phytopathogens from the genera Colletotrichum and Magnaporthe is not conserved in the vascular wilt pathogen Verticillium.

Membrane lipid composition underpins the structural and functional identity of all plant membranes. This review examines membrane lipid metabolism and trafficking, with an emphasis on how lipid diversity and interorganelle movement support plant cell function. We explore the biophysical and biochemical specialization of subcellular membranes, with discussion of the endoplasmic reticulum, plasma membrane, apoplastic vesicles and barriers, tonoplast, peroxisomes, mitochondria, plastids, and thylakoids. We review both vesicular and nonvesicular lipid transport pathways, including membrane contact sites. Particular attention is given to glycerolipids, including phospholipids and galactolipids, sphingolipids, sterols, and, to a lesser extent, fatty acid exchange. By focusing on mechanisms of lipid transfer and remodeling, this review synthesizes our understanding of subcellular membrane lipid composition in the context of dynamic cellular processes including cell plate expansion, environmental stress responses, and photosynthetic membrane assembly.

Abstract Old Yellow Enzymes (OYEs) are a widely distributed family of ene -reductases that were first described in a Saccharomyces cerevisiae ferment. In plants, cis -12- oxo -phytodienoic acid ( cis -OPDA) reductase (OPR) is the best studied OYE. In Arabidopsis thaliana , the peroxisomal AtOPR3 was characterized as the major OPDA reductase, which generates 3- oxo -2-(2-pentenyl)-cyclopentane-1-octanoic acid in the jasmonic acid (JA) biosynthesis. In Atopr3 lines, only small amounts of JA are detectable after wounding. Here, we describe an OPR-like enzyme (named BnOPR) from the gram-positive Brevibacillus nitrificans . The sequence was identified in an early version of the Physcomitrium patens genome and is assumed to be a contamination by a bacterium growing in association with P. patens . In complementation experiments with an Atopr3 line, we demonstrate that expression of BnOPR, fused with a peroxisomal targeting signal, rescues the male infertile phenotype and increases JA and JA-Ile levels. The catalytic parameters of BnOPR were determined for a set of substrates, including cis -OPDA and prednisone. Interestingly, B. nitrificans, B. brevis , and Paenibacillus physcomitrellae were shown to have a positive effect on P. patens growth. Highlight The bacterial enzyme BnOPR rescues the male infertile phenotype of Atopr3 plants.

Research Conducted: To elucidate the functions of glycosylceramides, we generated and characterized mutants deficient in multiple steps contributing to their assembly in the model moss Physcomitrium patens. We mutagenized SPHINGOLIPID Δ8-DESATURASE, whose products are preferentially incorporated into glycosylceramides, and a suite of higher-order mutants combining sphingolipid Δ4-desaturase and glycosyl ceramide synthase. Methods: We used targeted lipidomics to describe the chemotypes of all mutants. We used quantitative phenotype analysis, transcriptomics, and phytohormone profiling to understand the effects of these chemotypes on development and physiology. Key Results: These mutants present a range of phenotypes that collectively indicate that in P. patens (1) glycosylceramide deficiency impairs development, largely due to imbalance in free ceramide homeostasis (2) the synthesis of glycosylceramides is dependent upon the presence of a specific free ceramide profile (3) the Δ4-, but not the Δ8-desaturation, is strictly required for glycosylceramide synthesis, (4) cell division and differentiation, but not cell expansion, are affected by sphingolipid imbalance, and (5) sphingolipid imbalance results in oxylipin accumulation. Conclusion: Collectively, our results elucidate the assembly and functions of glycosylceramides in a model bryophyte, and highlight conserved and specialized aspects of sphingolipid metabolism among plants.

The earliest land plants faced a significant challenge in adapting to environmental stressors. Stress on land is unique in its dynamics, entailing swift and drastic changes in light and temperature. While we know that land plants share with their closest streptophyte algal relatives key components of the genetic makeup for dynamic stress responses, their concerted action is little understood. Here, we combine time-course stress profiling using photophysiology, transcriptomics on 2.7 Tbp of data, and metabolite profiling analyses on 270 distinct samples, to study stress kinetics across three 600-million-year-divergent streptophytes. Through co-expression analysis and Granger causal inference we predict a gene regulatory network that retraces a web of ancient signal convergences at ethylene signaling components, osmosensors, and chains of major kinases. These kinase hubs already integrated diverse environmental inputs since before the dawn of plants on land.

Sinapine (O-sinapoyl choline) is the major phenolic metabolite typically found in the oil-rich seeds of Brassicaceae such as Camelina sativa and Brassica napus. It imparts a bitter taste to the seeds as a defence mechanism against herbivores, but it also renders them less palatable to livestock. To improve Camelina flour for human consumption or as animal feed, we reduced sinapine content through CRISPR/Cas9-based genome editing of REF1 (REDUCED EPIDERMAL FLUORESCENCE1), which encodes the NADP+-dependent coniferaldehyde/sinapaldehyde dehydrogenase (CALDH/SALDH), a key enzyme for sinapine biosynthesis in Arabidopsis thaliana and B. napus. Inactivation of all three homoeologues found in C. sativa lowered the sinapine content in seeds by an overall 56% in two cultivars indicating the presence of a REF1-independent pathway for sinapine biosynthesis. Most importantly however, crucial agronomic seed traits such as total lipid or protein content of the seeds, seed weight or germination were not affected. Hence, the ref1 mutant lines produced here provide a valuable trait, that can be combined with other traits through gene stacking to obtain crops with significantly improved product quality. Furthermore, metabolite fingerprinting by ultra-performance liquid chromatography-electrospray ionisation-quadrupole time-of-flight mass spectrometry of ref1 mutant lines revealed a contrasting phenylpropanoid profile in seeds and leaves, indicating that REF1 oxidises sinapaldehyde to sinapate in seeds and coniferyl aldehyde to ferulate in leaves. In contrast to Arabidopsis however, Camelina accumulates no comparable levels of sinapoyl malate, but substantial amounts of chlorogenic acid, of which an additional chlorogenic acid isomer distinguishes the two different Camelina cultivars as a metabolite marker.

Zygnematophytes emerged as the unexpected closest algal relatives of land plants despite their simple body plans, raising questions about the morphogenetic toolkit present in the last common ancestor of land plants and algae. Genomic analyses have revealed that zygnematophytes are cellular giants, sharing homologous frameworks for several phytohormones, secondary metabolites, and key morphogenetic and transcriptional regulatory processes. Zygnematophytes fall into five orders, each of which has charted its own evolutionary path. Here, we have sequenced a contiguous genome of Spirogyra pratensis , the eponymous representative of Spirogyrales and a classical model system for evolutionary cell biology in the green lineage. Building on this genome, we transcriptionally profiled the tractable life cycle of Spirogyra and its responses to a bifactorial gradient of light and temperature. Our data highlight the activation of quiescence and homeostatic programs. Yet what stands out most in Spirogyra is its spiral chloroplast—undulating intracellularly and abscising during mixed phragmoplast formation and furrowing. Leveraging the genome in tandem with co-expression network analyses, we describe the molecular underpinnings of the unique cytokinetic processes that govern both cell and plastid division. We find that Spirogyra deploys a molecular program characteristic of Phragmoplastophyta, yet lacks the deeply conserved plastid division machinery found in other archaeplastid plastids. ### Competing Interest Statement The authors have declared no competing interest. Deutsche Forschungsgemeinschaft, https://ror.org/018mejw64, RE-1697/18-1, RE-1697/19-1, RE-1697/20-1, 422691801, 440231723, 514060973 Deutsche Forschungsgemeinschaft, 528076711, Schw687/13-1, 407493903, 423957469 European Research Council, https://ror.org/0472cxd90, 852725 FWF Austrian Science Fund, 10.55776/P34181 Agencia Estatal de Investigación, https://ror.org/003x0zc53, MICIU/AEI/10.13039/501100011033 European Science Foundation, PID2021-125805OA-I00 Consejo Superior de Investigaciones Científicas, https://ror.org/02gfc7t72, JAE-PRE23-15 Agence Nationale de la Recherche, ANR-17-EUR-0007

We computed co-expression networks from more than 2200 samples of nine species across 600 million years of divergent streptophyte evolution and infer that the streptophyte algal ancestors of land plants already had a remarkable fraction of the embryophytic stress response system. Despite its phytohormone-independent origin, homologs of all core components of the drought hormone abscisic acid (ABA) subnetwork are present, and we find that most are co-expressed in streptophyte algae and land plants; this subnetwork was thus co-opted in embryophytes by bringing it under the regime of ABA. The last common ancestor of embryophytes and Zygnematophyceae algae had ancient stress-responsive pathways, enabling it to face the stresses typical of the land environment - even before the origin of land plants - while evolution on land led to the adaptive refinement of these responses.

Genome editing has the potential to enhance yield and quality traits of crops. However, standard genetic transformation methods are not always applicable to modern germplasm. To tackle this challenge in the widely cultivated variety Ligena of the oilseed crop camelina (Camelina sativa (L.) Crantz), an only recently established principle of adventitious shoot formation from immature zygotic embryos was employed to further improve its fatty acid profile. In this approach, the three subgenomic homeologs of the FATTY ACID ELONGASE 1 (FAE1) gene were subjected to targeted mutagenesis. To pre-validate the Cas9-interacting, target motif-specific guide (g)RNAs, a robust protoplast-based DNA transfection method was established. This assay demonstrated that the preselected gRNAs were capable of eliciting mutations across all three camelina FAE1 homeologs. Likewise, targeted mutagenesis was successful at the whole-plant level. Triple-homozygous fae1 knockout mutants were identified amongst a segregating generation M3 family. Gas chromatography of lipid extracts from M4 seeds revealed a significant increase in all unsaturated C18 fatty acids including the particularly valuable α-linolenic acid. This was accompanied by a near elimination of the C20 and C22 very long-chain fatty acids including the nutritionally problematic erucic acid. Altogether, we have developed camelina elite lines with two significantly improved properties of high relevance for a health-promoting human nutrition.

Developmental patterning and organ structure are elegantly simple in the moss Physcomitrium patens, which facilitates the cultivation and phenotypic characterization of severe mutant alleles. Essential membrane lipids, such as complex phosphosphingolipids (in plants, glycosyl inositol phosphorylceramides, GIPCs), are difficult to functionally characterize due to non-viable and pleiotropic phenotypes of mutants affected in their synthesis. Following the isolation and biochemical characterization of mutants affected in GIPC synthesis in P. patens, including sphinganine-C4-hydroxylase/sphingoid base hydroxylase (s4h/sbh) and inositol phosphorylceramide synthase (ipcs), we report some of their morphological, histological, and cytological phenotypes. We observed alterations in cell division, expansion, and differentiation. Specifically, the s4h knock-out mutant had abnormal cell division planes, as well as irregular depositions attached to cell walls. Severe ipcs mutant alleles showed frequent incomplete cell divisions, causing compromised cell autonomy as demonstrated by intercellular motility assays. These phenotypes suggest that sphingolipids impact both the orientation and proper formation of the cell plate during cytokinesis. Transmission electron microscopy revealed dramatic plasmodesmal structural defects in ipcs and s4h mutants, and these correlated with a macromolecule transport phenotype in s4h. Our methods can be used as a toolkit for quantifying growth, specifically cell division and plasmodesmal phenotypes in mosses, and our results illuminate key relationships between sphingolipid metabolism and fundamental cell functions. The severity of the observed defects in cell ultrastructure underscores both the resilience and the utility of P. patens as a model for investigating severe mutant phenotypes.

Oxylipin signaling has been suggested as a potential mechanism for the inter-partner recognition and homeostasis regulation of cnidarian-dinoflagellate symbiosis, which maintains the ecological viability of coral reefs. Here we assessed the effects of symbiosis and symbiont identity on a model cnidarian, the sea anemone Exaiptasia diaphana, using mass spectrometry to quantify octadecanoid oxylipins (i.e., 18-carbon-derived oxygenated fatty acids). A total of 84 octadecanoids were reported, and distinct stereospecificity was observed for the synthesis of R- and S-enantiomers for symbiont-free anemones and free-living cultured dinoflagellate symbionts, respectively. Symbiont-derived 13(S)-hydroxy-octadecatetraenoic acid (13(S)-HOTE) linked to a putative 13(S)-lipoxygenase was translocated to the host anemone with a 32-fold increase, suggesting it as a biomarker of symbiosis and as a potential agonist of host receptors that regulate inflammatory transcription. Only symbiosis with the native symbiont Breviolum minutum decreased the abundance of pro-inflammatory 9(R)-hydroxy-octadecadienoic acid (9(R)-HODE) in the host. In contrast, symbiosis with the non-native symbiont Durusdinium trenchii was marked by higher abundance of autoxidation-derived octadecanoids, corroborating previous evidence for cellular stress in this association. The putative octadecanoid signaling pathways reported here suggest foundational knowledge gaps that can support the bioengineering and selective breeding of more optimal host-symbiont pairings to enhance resilience and survival of coral reefs.