The phenylpropanoid pathway is essential for plant development and environmental adaptation, producing metabolites such as flavonoids, lignin, and salicylic acid. Phenylalanine ammonia-lyase (PAL) catalyzes the first committed step in this pathway and has long been viewed as a cytoplasmic enzyme. Here, we reveal that PAL responds to elevated flavonoid levels in Arabidopsis by undergoing phosphorylation and relocating to the nucleus. Nuclear sequestration of PAL reduces its cytoplasmic abundance and enzymatic activity, resulting in rapid suppression of phenylpropanoid metabolic flux. In parallel, nuclear-localized PAL interacts with the transcription factor TT8, disrupting MBW complex formation and down-regulating flavonoid biosynthetic genes. This dual mechanism enables PAL to act as a metabolic feedback regulator that dynamically adjusts flavonoid production in response to internal metabolic states. Our findings redefine PAL as both a biosynthetic enzyme and a responsive integrator of cellular metabolic status, establishing a previously unknown paradigm for feedback control in plant specialized metabolism.

Floral volatile terpenes play pivotal roles in plant-pollinator interactions and ecological adaptation, yet the genetic mechanisms underlying their diversification in Aquilegia remain poorly understood. This study integrates gas chromatography-mass spectrometry (GC/MS) and functional characterization assays to investigate how terpene synthase (TPS) diversity shapes floral scent evolution across Aquilegia species and populations. We identified (+)-limonene, linalool, β-pinene, and β-sesquiphellandrene as the dominant floral terpenes, with substantial inter- and intraspecific variation driven by differential expression and sequence divergence of key TPS genes, including TPS7, TPS8, TPS9 and TPS24. Functional characterization revealed that orthologous variants of TPS7 and TPS8 influence species-specific monoterpene and sesquiterpene production, while TPS24 variants exhibit substrate plasticity in linalool synthesis despite retaining conserved catalytic motifs. Population-level analyses of A. viridiflora revealed that frame-shift mutations and expression shifts in TPSs are associated with terpene profile divergence, while residue variations in allelic TPS variants may have driven functional novelty during evolution. Our findings highlight TPS diversity as a molecular mechanism for floral scent diversification, enabling adaptive radiation through pollinator-mediated selection and specialization within distinct ecological niches. This study provides crucial insights into the evolutionary interplay between genetic variation, enzymatic plasticity, and ecological adaptation in shaping plant biodiversity.

Floral coloration in Freesia hybrida is predominantly attributed to anthocyanins, with glycosylation playing a critical role in their stability and diversity. This study investigates the molecular mechanisms underlying color variation between F. hybrida cultivars, focusing on anthocyanin 5-O-glucosyltransferases (An5GTs). HPLC analysis revealed that ‘Pink Passion’ petals accumulate 3,5-O-diglucosidic anthocyanins, absent in ‘Red River^®’ and ‘Ambiance’. RNA-seq identified seven candidate Fh5GT genes, with phylogenetic and subcellular localization analyses confirming their classification as cytosolic glycosyltransferases. Expression profiling highlighted elevated transcript levels of Fh5GT1, Fh5GT3, and Fh5GT7 in ‘Pink Passion’, correlating with its di-glucosidic anthocyanin accumulation. In vitro enzymatic assays demonstrated that Fh5GT3 and Fh5GT7 preferentially glucosylate 3-O-monoglucosidic anthocyanins to form stable 3,5-O-diglucosides, with minimal activity on anthocyanidins to generate 5-O-glucosidic anthocyanins. Heterologous expression of Fh5GT3 and Fh5GT7 in Arabidopsis complemented anthocyanin deficiency in 5gt mutants, restoring pigmentation. These findings elucidate the potential role of 5GTs in modulating floral color diversity through anthocyanin modification, providing insights for targeted breeding strategies to enhance ornamental traits in horticultural species.

Floral scent is an essential and genetically complex trait in herbaceous peonies (Paeonia lactiflora Pall.); however, specific genes related to metabolic and regulatory networks remain scantily studied. Our study integrated metabolite profiling and RNA-sequencing to screen floral scent biosynthetic genes. Hence, the major molecules identified by headspace collection combined with cultivar-specific GC-MS analysis were geraniol, β-caryophyllene, 2-phenylethanol (2-PE), citronellol, and 1,8-cineole. Genes related to terpenoids and 2-PE biosynthesis were identified after the assembly and annotation of the P. lactiflora transcriptomes. Eight angiosperm-specific terpene synthases (TPSs) from the TPS-a and TPS-b clades, as well as enzymes linked to 2-PE synthesis such as aromatic amino acid decarboxylase (AADC), phenylacetaldehyde reductase (PAR), and geranial reductase (GER) were identified. The biochemical analysis of the enzymes encoded by PlPAR1 and PlGER1 generated 2-PE from phenylacetaldehyde (PAld). The pairwise alignment of AADC1 reveals a splice variant lacking a 124 bp fragment, thus highlighting the possible role of alternative splicing in modulating floral scent composition. This study offers insights into the molecular-level biosynthesis of terpenoids and 2-PE in Peonia taxa, and provides the basis for the functional characterization, breeding, and bioengineering of prospective candidate genes for the production of floral volatiles in the Paeonia genus.