Integrated analyses of transcriptome and metabolomic profiles of terpenoid and volatile compounds reveal terpenoid...

Terpenoids play a crucial role in determining grape fruit quality, yet a comprehensive evaluation of their metabolic dynamics remains lacking. This study examined 'Shine Muscat' grape fruits across developmental stages to elucidate terpenoid synthesis alterations and underlying mechanisms at cellular, physiological, transcriptional, and metabolic levels. Our findings reveal that fruit development involves a reduction in epidermal and subepidermal cell numbers, loose cell arrangement, and cell membrane shrinkage and collapse. Cell organelles undergo disintegration and vacuolization, with pronounced plasmolysis as the fruit matures. The total phenol and flavonoid contents showed no significant variation across the developmental stages. Conversely, transcriptomic analysis revealed that key enzymes in the mevalonate (MVA) and methylerythritol phosphate (MEP) pathways, such as 1-deoxy-D-xylulose-5-phosphate synthase (DXS), geranylgeranyl diphosphate synthase (GGPPS), Farnesyl Pyrophosphate Synthase (FPPS), and 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGR), exhibited the highest activities at berries harvest-ripe (P3) stage, correlating with variations in IPP content. MVA levels surged at berry softening begins (P2) before declining at the P3 stage. Analysis of terpenoid metabolism and transcriptomics revealed a significant correlation in the carotenoid biosynthesis pathway, which is associated with abscisic acid (ABA) and phaseic acid (PA). The correlation between the metabolome of volatile substances and transcriptome was mainly enriched in the monoterpenoid biosynthesis pathway, with neomenthol and beta-glucosidase 44 (BGL44) showing the highest correlation. Metabolome of volatile components also identified 25 terpenoid substances with the odor activity values (OAV) values greater than 1 at the P3 stage. Linalool mainly accumulated at the P3 stage, while geraniol mainly accumulated at berry development (P1) stage. Comprehensive analysis of multi-omics revealed that VvABA2, regulated by BR, directly influences the levels of important terpenoids, like geraniol, ABA, and PA, suggesting a connection between volatile and non-volatile terpenoids. VvHMGR3 and VvDXS1 are found correlated with the levels of geraniol and neomenthol but not with nerolidol. These results reveal terpenoids' vital role in the development process of 'Shine Muscat', advance our understanding of grape aroma metabolic pathways, and fill the gap in the comprehensive evaluation of terpenoids.