Soybean is a worldwide crop that offers valuable proteins, fatty acids, and phytonutrients to humans but is always damaged by insect pests or pathogens. Plants have captured sophisticated defense mechanisms in resisting the attack of insects and pathogens. How to protect soybean in an environment- or human-friendly way or how to develop plant-based pest control is a hotpot. Herbivore-induced plant volatiles that are released by multiple plant species have been assessed in multi-systems against various insects, of which (E)-β-ocimene has been reported to show anti-insect function in a variety of plants, including soybean. However, the responsible gene in soybean is unknown, and its mechanism of synthesis and anti-insect properties lacks comprehensive assessment. In this study, (E)-β-ocimene was confirmed to be induced by Spodoptera litura treatment. A plastidic localized monoterpene synthase gene, designated as GmOCS, was identified to be responsible for the biosynthesis of (E)-β-ocimene through genome-wide gene family screening and in vitro and in vivo assays. Results from transgenic soybean and tobacco confirmed that (E)-β-ocimene catalyzed by GmOCS had pivotal roles in repelling a S. litura attack. This study advances the understanding of (E)-β-ocimene synthesis and its function in crops, as well as provides a good candidate for further anti-insect soybean improvement.

Proanthocyanidins (PAs), anthocyanins, and flavonols are key flavonoids that play diverse roles in plant physiology and human health. Despite originating from a shared biosynthetic pathway, the regulatory mechanisms of PA biosynthesis and the cooperative regulation of different kinds of flavonoids remain elusive, particularly in flower tissues or organs. Here, we elucidated the regulatory network governing PA biosynthesis in Freesia hybrida ‘Red River®’ by characterizing four TT2-type MYB transcription factors, designated FhMYBPAs. Phylogenetic analysis, subcellular localization, and transactivation assays predicted their roles as PA-related activators. Pearson correlation analysis revealed significant correlations between FhMYBPAs and PA accumulation in various floral tissues and development stages. Functional studies demonstrated that FhMYBPAs activated PA biosynthesis by directly binding to the promoters of target genes, which can be enhanced by FhTT8L. Additionally, a hierarchical and feedback regulatory model involving FhTTG1, FhMYB27, and FhMYBx was proposed for PA biosynthesis. Furthermore, comparative analysis of flavonoid-related MYB factors involving FhPAP1, FhMYB5, FhMYBF1, and FhMYB21L2 highlighted their roles in regulating PA, anthocyanin, and flavonol biosynthesis, with some exhibiting versatile regulations. Overall, our findings provide insights into the spatio-temporal regulation of flavonoids in flowers and expand our understanding of MYB-mediated transcriptional regulation of specialized metabolites in plants.