Background: Glycosyltransferases (GTs) are principal post-reactive modifying enzymes responsible for establishing natural glycosidic bonds in secondary metabolites, playing a critical regulatory role in plant cellular metabolic homeostasis. Biphenyl, dibenzofuran, and their glycosides, the most abundant phytoalexins in the apple subfamily, are synthesized de novo after infection by bacteria or fungi. Nevertheless, the biological functions of GTs in Sorbus aucuparia remain largely uncharacterised. Purpose: This study systematically evaluated the impact of Sorbus aucuparia uridine diphosphate glycosyltransferases (SaUGTs) on biphenyl phytoalexin metabolism and growth patterns in Sorbus aucuparia suspension cells (SASCs) under yeast extract (YE)-induced biotic stress. Methods: The study established standardized SASCs cultures with controlled induction protocols using YE for biotic stress simulation. A multi-omics framework integrated phenotypic analyses, targeted metabolomics (UPLC-QTOF-MS), transcriptional profiling (quantitative PCR), and enzymatic functional assays. Results: YE treatment induced a biomass decline in SASCs, coinciding with substantial accumulation of biphenyl derivatives and glycosides. Temporal profiling revealed dynamic fluctuations in metabolite concentrations, reflecting sequential biosynthetic transformations. Stress exposure elevated soluble protein content and significantly up-regulated SaUGTs expression. YE-induced SaUGTs promote glycosylation of de novo-synthesised biphenyl phytoalexins (noraucuparin, aucuparin) and 2′-hydroxyaucuparin, with optimal cell growth occurring during metabolic equilibrium between aglycones and glycosides. Conclusion: These findings suggest a previously unrecognised regulatory strategy, whereby SASCs alleviate biotic stress through GT-mediated maintenance of phytoalexin-glycoside homeostasis, thus preventing detrimental over-activation of defence mechanisms.

The Bible of life is homeostasis. Plants respond to stresses by forming a coordinated defence process from a seemingly chaotic response. Plant molecular glycosylation is the most common and most extensive type of modification reaction in plants. Glycosylation is also an indispensable step for secondary metabolites to produce stable, soluble, storage, detoxification or inactive forms through conjugation with sugars. The present review adds to the description of glycosylation and corresponding glycosyltransferases (GTs) in plants during defence versus growth, which, in comparison to other plant defence regulations, are relatively uncharted. Growth inhibition under stress conditions is related to the redirection of plant resources (such as energy and metabolism) from primary metabolism and growth to activate defence mechanisms in resource-limited environments. A variety of small molecule compounds colored by GTs play an important role in buffering the effects of biotic and abiotic stresses on plants. Autotoxicity defense compounds are stored in the form of inactive glycosides in the defense reaction to release toxic aglycones and to produce cascade effects. All told, glycosylation of secondary metabolites is of first importance to balance growth and defence in an efficient and energy-saving way, but still far to go.