Biology subjects

Zerbe, P.

Publications and source records attributed to Zerbe, P..

7 recordsLinked to original sources

bioRxiv2026

Discovery of the rosalexin pathway expands the modular network of maize diterpenoid chemical defenses.

The evolutionary expansion of specialized metabolism has shaped the ability of plants to adapt to combined pathogen, pest, and other environmental pressures. For instance, the duplication and divergence of ancestral gibberellin pathway genes have given rise to specialized kauralexin and dolabralexin diterpenoids in maize (Zea mays) that serve as core components of disease resistance and stress adaptation. Here, we describe the biosynthesis and elicited production of rosalexins as a previously unrecognized component of the maize chemical defense network. By integrating genomics-enabled gene discovery, combinatorial enzyme assays, and AI-assisted enzyme mechanistic studies we show that maize rosalexin biosynthesis proceeds via a distinct 5-rosanol scaffold formed by the pairwise activity of two diterpene synthases, ZmTPS38/CPS2/AN2 and ZmTPS42/KSL1, recruited from gibberellin metabolism. Further oxygenation by the promiscuous P450 enzyme, ZmCYP71Z18, yields epoxyrosanol that, in turn, can undergo epoxide ring opening to form trihydroxyrosanol. Epoxyrosanol, but not 5-rosanol or trihydroxyrosanol, display strong inhibitory activity on fungal pathogen growth in vitro, highlighting the contribution of the epoxide group to antibiotic efficacy. Large variation in rosalexin presence and abundance exists across maize genotypes due to expansive ZmTPS42/KSL1 gene sequence variation and pseudogenization. Transcriptomics and targeted metabolomics demonstrated the pathogen-elicited accumulation of rosalexins in maize lines featuring functional ZmTPS42/KSL1 genes. However, no dominant pathogen resistance phenotype was observed in association with rosalexin abundance. These collective findings expand our knowledge of how multiple interconnected diterpenoid pathways arose in maize via duplication of hormone-metabolic genes and enable the utilization of a common precursor to form modular chemical defense layers. Significance StatementPlant diterpenoids play critical roles in crop development, stress defense and ecological adaptation. In maize, diterpenoids serve as key components of chemical defenses against pests and diseases with direct impact on crop immunity and vigor. Enzymes of the diterpene synthase and cytochrome P450 families largely drive diterpenoid chemical diversity. This study reports the discovery and characterization of the pathway forming rosalexin diterpenoids in maize. Pathogen-elicited accumulation and in vitro antifungal activity of rosalexin metabolites supports a physiological function in maize chemical defense.

plant biology↗

bioRxiv2025

Structure of Photosystem I-FCP from giant kelp uncovers drivers of antenna evolution across the red lineage

Brown algae and other red-algae-derived organisms such as diatoms are major contributors to global CO2 fixation via photosynthesis. To understand the photosynthetic function of brown algae, we obtained the structure of giant kelp Macrocystis pyrifera photosystem I (PSI) with a fucoxanthin-chlorophyll-protein (FCP) antenna and compared it to known structures from the red-algal lineage. We identified differences in M. pyriferas antenna composition, architecture and chlorophyll networks, as well as a pronounced variation in transmembrane hydrophobic thickness across the PSI-FCP supercomplex, with implications for photochemical function. Our work lays the foundation to understand kelps high photosynthetic productivity, reveals new drivers of antenna conservation and diversification, and sheds light on evolutionary relationships between organisms of the red lineage.

biochemistry↗

bioRxiv2025

Genome-Wide Discovery and Characterization of Terpene Synthases Contributing to Strawberry Aroma Metabolism

Strawberry (Fragaria X ananassa) is a globally cultivated fruit crop valued for its unique flavor and aroma. Major groups of volatile organic compounds that contribute to strawberry aroma include terpenes, fatty acid esters, furanones, and benzenoids. Understanding the biosynthetic genes and pathways underlying strawberry terpene metabolism provides resources for developing precision breeding strategies to improve strawberry aroma traits. Here we describe the genome-wide identification and functional analysis of the terpene synthase (TPS) family that governs terpene chemical diversity in strawberries. Mining of the allo-octoploid genome of the cultivar Royal Royce identified 75 TPS gene candidates. Biochemical characterization of 27 predicted mono-, sesqui- and di-TPS enzymes via in vitro activity assays and in vivo enzyme co-expression studies demonstrated a range of TPS activities that are relevant for the biosynthesis of two thirds of known strawberry terpenes as well as products not previously described in octoploid strawberry. Complementary metabolomic and transcriptomic studies across a diversity panel of strawberry accessions demonstrated substantial variation in the composition and abundance of more than 30 detected accession-specific and common terpene aromas, nine of which matching characterized TPS products. Analysis of a developmental time series of two accessions with contrasting aroma further revealed accession-specific alterations of terpene metabolism during fruit ripening. These results expand our understanding of strawberry aroma metabolism and characterized terpene aroma genes as a resource for the molecular breeding of desirable aroma traits. One-sentence summaryDiscovery and characterization of the terpene synthase family that controls the diversity of terpene aroma metabolism in accessions of strawberry. Significance StatementThe diverse class of terpenoids contributes to complex crop traits, including plant growth, stress resilience, pollination, nutrition, and aroma. The discovery of terpene-biosynthetic pathways in octoploid strawberry (Fragaria X ananassa) provides foundational knowledge of the diversity of terpenoid metabolism in this important specialty crop toward applications in improving aroma traits.

plant biology↗

bioRxiv2022

A dolabralexin-deficient mutant provides insight into specialized diterpenoid metabolism in maize (Zea mays).

Two major groups of maize (Zea mays) specialized metabolites, termed kauralexins and dolabralexins, serve as known or predicted diterpenoid defenses against pathogens, herbivores, and other environmental stressors. To consider physiological roles of the recently discovered dolabralexin pathway, we examined dolabralexin structural diversity, tissue-specificity, and stress-elicited production in a defined biosynthetic pathway mutant. Metabolomics analyses support a larger number of dolabralexin pathway products than previously known. We identified dolabradienol as a previously undetected pathway metabolite and characterized its enzymatic production. Transcript and metabolite profiling showed that dolabralexin biosynthesis and accumulation predominantly occurs in primary roots and shows quantitative variation across genetically diverse inbred lines. Generation and analysis of CRISPR-Cas9-derived loss-of- function Kaurene Synthase-Like 4 (Zmksl4) mutants demonstrated dolabralexin production deficiency, thus supporting ZmKSL4 as the diterpene synthase responsible for the conversion of geranylgeranyl pyrophosphate precursors into dolabradiene and downstream pathway products. Zmksl4 mutants further display altered root-to-shoot ratios and root architecture in response to water deficit, consistent with an interactive role of maize dolabralexins in plant vigor during abiotic stress.

plant biology↗

bioRxiv2022

Comparative transcriptomics and metabolomics reveal specialized metabolite drought stress responses in switchgrass (Panicum virgatum L.)

O_LISwitchgrass (Panicum virgatum) is a bioenergy model crop valued for its energy efficiency and drought tolerance resilience. The related monocot species rice (Oryza sativa) and maize (Zea mays) deploy species-specific, specialized metabolites as core stress defenses. By contrast, specialized chemical defenses in switchgrass are largely unknown. C_LIO_LITo investigate specialized metabolic drought responses in switchgrass, we integrated tissue-specific transcriptome and metabolite analyses of the genotypes Alamo and Cave-in-Rock that feature different drought tolerance. C_LIO_LIThe more drought-susceptible Cave-in-Rock featured an earlier onset of transcriptomic changes and significantly more differentially expressed genes in response to drought compared to Alamo. Specialized pathways showed moderate differential expression compared to pronounced transcriptomic alterations in carbohydrate and amino acid metabolism. However, diterpenoid-biosynthetic genes showed drought-inducible expression in Alamo roots, contrasting largely unaltered triterpenoid and phenylpropanoid pathways. Metabolomic analyses identified common and genotype-specific flavonoids and terpenoids. Consistent with transcriptomic alterations, several root diterpenoids showed significant drought-induced accumulation, whereas triterpenoid abundance remained predominantly unchanged. Structural analysis of drought-responsive root diterpenoids verified these metabolites as oxygenated furanoditerpenoids. C_LIO_LIDrought-dependent transcriptome and metabolite profiles provide the foundation to understand the molecular mechanisms underlying switchgrass environmental resilience. Accumulation of specialized root diterpenoids and corresponding pathway transcripts supports a role in drought stress tolerance for these compounds. C_LI Significance statementWith an increasing demand for renewable energy opposed by rising climate-driven crop losses, understanding, and leveraging plant natural defenses can enable the development of sustainable crop production systems. Here, we integrated comparative transcriptomics and metabolomics analyses to gain a detailed understanding of the diversity and physiological relevance of specialized metabolites in upland and lowland switchgrass ecotypes and provide resources for future investigations of drought response mechanisms in switchgrass.

plant biology↗

bioRxiv2021

Furanoditerpenoid biosynthesis in the bioenergy crop switchgrass is catalyzed by an alternate metabolic pathway

Specialized diterpenoid metabolites are important mediators of stress resilience in monocot crops. A deeper understanding of how species-specific diterpenoid-metabolic pathways and functions contribute to plant chemical defenses can enable crop improvement strategies. Here, we report the genomics-enabled discovery of five cytochrome P450 monooxygenases (CYP71Z25-29) that form previously unknown furanoditerpenoids in the monocot bioenergy crop switchgrass (Panicum virgatum). Combinatorial pathway reconstruction showed that CYP71Z25-29 catalyze furan ring addition to diterpene alcohol intermediates derived from distinct class II diterpene synthases, thus bypassing the canonical role of class I diterpene synthases in plant diterpenoid metabolism. Transcriptional co-expression patterns and presence of select diterpenoids in droughted switchgrass roots support possible roles of CYP71Z25-29 in abiotic stress responses. Integrating molecular dynamics, structural analysis, and targeted mutagenesis, identified active site determinants controlling distinct CYP71Z25-29 catalytic specificities and, combined with broad substrate promiscuity for native and non-native diterpenoids, highlights the potential of these P450s for natural product engineering. Significance StatementDiterpenoids play important roles in stress resilience and chemically mediated interactions in many plant species, including major food and bioenergy crops. Enzymes of the cytochrome P450 monooxygenase family catalyze the various functional decorations of core diterpene scaffolds that determine the large diversity of biologically active diterpenoids. This study describes the identification and mechanistic analysis of an unusual group of cytochrome P450 monooxygenases, CYP71Z25-29, from the bioenergy crop switchgrass (Panicum virgatum). These enzymes catalyze the furan ring addition directly to class II diterpene synthase products, thus bypassing the conserved pairwise reaction of class II and class I diterpene synthases in labdane diterpenoid metabolism. Insight into the distinct substrate-specificity of CYP71Z25-29 offers opportunity for engineering of furanoditerpenoid bioproducts.

plant biology↗

bioRxiv2020

Genetic elucidation of complex biochemical traits mediating maize innate immunity

Specialized metabolites constitute key layers of immunity underlying crop resistance; however, challenges in resolving complex pathways limit our understanding of their functions and applications. In maize (Zea mays) the inducible accumulation of acidic terpenoids is increasingly considered as a defense regulating disease resistance. To understand maize antibiotic biosynthesis, we integrated association mapping, pan-genome multi-omic correlations, enzyme structure-function studies, and targeted mutagenesis. We now define ten genes in three zealexin (Zx) gene clusters comprised of four sesquiterpene synthases and six cytochrome P450s that collectively drive the production of diverse antibiotic cocktails. Quadruple mutants blocked in the production of {beta}-macrocarpene exhibit a broad-spectrum loss of disease resistance. Genetic redundancies ensuring pathway resiliency to single null mutations are combined with enzyme substrate-promiscuity creating a biosynthetic hourglass pathway utilizing diverse substrates and in vivo combinatorial chemistry to yield complex antibiotic blends. The elucidated genetic basis of biochemical phenotypes underlying disease resistance demonstrates a predominant maize defense pathway and informs innovative strategies for transferring chemical immunity between crops.

plant biology↗