In a landmark discovery poised to reshape our understanding of plant biochemistry, researchers have unveiled a highly conserved three-step pathway responsible for the biosynthesis of salicylic acid (SA) across diverse seed plants. Salicylic acid, a phenolic compound widely recognized as a pivotal plant defense hormone, has long been studied for its integral role in systemic acquired resistance and immunity. However, the precise molecular origins of SA outside model plants such as Arabidopsis remained enigmatic until now. This breakthrough elucidates new enzymatic players and metabolic steps fundamental to SA production, revealing evolutionary conservation and offering transformative insights with implications reaching far beyond botany.
Salicylic acid’s prominence extends beyond plant physiology; it represents the biochemical bedrock of aspirin, humanity’s most iconic and historically impactful pharmaceutical. Given aspirin’s derivation from SA, deepening our grasp of SA biosynthesis in plants potentially bridges gaps in both agricultural science and medicinal chemistry. The crux of this investigation harnessed the increasingly popular and genetically tractable model Nicotiana benthamiana, a species outside the Brassicaceae family, aiming to illuminate the elusive SA biosynthetic route operating in many angiosperms.
The study identifies a sequential enzymatic cascade catalyzing SA production, beginning from benzoyl coenzyme A (benzoyl-CoA). The first step involves a unique transferase enzyme, benzoyl-CoA:benzyl alcohol benzoyl transferase (BEBT), which conjugates benzoyl-CoA with benzyl alcohol to yield benzyl benzoate. This biochemical conjugation signifies an intriguing divergence from known SA synthesis routes, highlighting nature’s adeptness at evolving alternative metabolic solutions in discrete plant lineages.
Following the formation of benzyl benzoate, the pathway proceeds with its hydroxylation mediated by benzyl benzoate oxidase (BBO). This oxidation step produces benzyl salicylate, a key intermediate that has remained largely obscured in plant metabolic studies prior to this work. The identification and functional characterization of BBO fills a critical gap in the metabolic sequence leading toward SA formation, enriching our understanding of hydroxylation mechanisms in secondary metabolite biosynthesis.
The piloting enzyme cascade culminates with benzyl salicylate hydrolase (BSH), which cleaves benzyl salicylate to release free salicylic acid. This final hydrolysis step liberates the biologically active SA molecule, ready to fulfill its diverse defensive roles within the plant system. Intriguingly, the coordinated activity of BEBT, BBO, and BSH appears to be a widespread biochemical module conserved across angiosperms, transcending both dicot and monocot taxa.
To validate this pathway’s ubiquity, the researchers identified genes encoding BEBT, BBO, and BSH in a phylogenetically broad spectrum of seed plants, including economically and ecologically relevant species such as willow, poplar, soybean, and rice. Functional complementation assays demonstrated that these genes from diverse plants could rescue the SA-deficient phenotype of Nicotiana benthamiana mutants, underscoring the biochemical equivalency and evolutionary conservation of this pathway.
Further substantiating the pathway’s significance, knockout studies in Oryza sativa (rice) revealed that null mutants of OsBEBT, OsBBO, and OsBSH genes exhibited impaired SA biosynthesis and consequently exhibited weakened immune responses. Rice’s reliance on this pathway cements the concept that this alternative SA biosynthetic route is not an isolated curiosity but a central and indispensable metabolic process within monocotyledonous crops vital for global food security.
This discovery recasts the canonical understanding of salicylic acid biosynthesis predominantly derived from Arabidopsis, which utilizes chorismate-derived pathways, indicating that plants have evolved parallel or complementary biosynthetic strategies tailored to their ecological niches and evolutionary trajectories. The demonstration of a benzoyl-CoA-based conserved pathway heralds a new paradigm in plant hormone biosynthesis research.
The implications of this study are multifold. By clarifying the universality of this three-step pathway, researchers and crop scientists now possess molecular targets to manipulate SA levels, enabling tailored enhancement of disease resistance in crops through precision breeding or biotechnological interventions. The modulation of SA biosynthesis could offer an environmentally friendly strategy to reduce agrochemical reliance by fortifying innate plant immunity.
Moreover, the biochemical intermediates characterized here, such as benzyl benzoate and benzyl salicylate, may harbor unexplored bioactivities or industrial applications, potentially inspiring novel uses beyond their physiological context. Understanding their biosynthesis opens avenues for metabolic engineering to produce these compounds at scale for pharmaceuticals, fragrances, or natural preservatives.
From an evolutionary perspective, the conservation of this pathway across distant plant lineages raises intriguing questions about the selective pressures shaping secondary metabolism diversification in plants. It also invites renewed exploration into the existence of other, as yet unrecognized, metabolic routes for critical defense compounds, hinting at untapped enzymatic biodiversity within the plant kingdom.
In summary, this study provides a compelling vista into the metabolism of one of plant biology’s most essential hormones. Through elegant biochemical dissection and cross-species validation, Liu, Xu, Wu, and colleagues have demystified a long-standing question about how plants synthesize salicylic acid outside the Brassicaceae family. Their work not only deepens fundamental botanical knowledge but also sows seeds for transformative agricultural innovations and broader biotechnological applications.
As scientific investigation continues to illuminate the intricate pathways mediating plant defense and adaptation, the delineation of this three-step biosynthetic route stands as a testament to the power of integrative molecular biology approaches. It reaffirms the importance of studying diverse model organisms and underscores the evolutionary ingenuity encoded within plant genomes. With salicylic acid at the nexus of plant immunity and human health, this discovery carries profound significance, promising to influence multiple scientific disciplines for years to come.
Subject of Research: Biosynthesis and metabolic pathway elucidation of salicylic acid in seed plants
Article Title: Three-step biosynthesis of salicylic acid from benzoyl-CoA in plants
Article References:
Liu, Y., Xu, L., Wu, M. et al. Three-step biosynthesis of salicylic acid from benzoyl-CoA in plants.
Nature (2025). https://doi.org/10.1038/s41586-025-09185-7
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