Integrated Analysis of Transcriptome and Metabolome Provides Insights into Flavonoid Biosynthesis of Blueberry Leaves in Response to Drought Stress

Blueberries (<i>Vaccinium</i> spp.) are extremely sensitive to drought stress. Flavonoids are crucial secondary metabolites that possess the ability to withstand drought stress. Therefore, improving the drought resistance of blueberries by increasing the flavonoid content is crucial for the development of the blueberry industry. To explore the underlying molecular mechanism of blueberry in adaptation to drought stress, we performed an integrated analysis of the metabolome and transcriptome of blueberry leaves under drought stress. We found that the most enriched drought-responsive genes are mainly involved in flavonoid biosynthesis and plant hormone signal transduction pathways based on transcriptome data and the main drought-responsive metabolites come from the flavonoid class based on metabolome data. The <i>UDP-glucose flavonoid 3-O-glucosyl transferase</i> (<i>UFGT</i>), <i>flavonol synthase</i> (<i>FLS</i>), and <i>anthocyanidin reductase</i> (<i>ANR-2</i>) genes may be the key genes for the accumulation of anthocyanins, flavonols, and flavans in response to drought stress in blueberry leaves, respectively. Delphinidin 3-glucoside and delphinidin-3-O-glucoside chloride may be the most important drought-responsive flavonoid metabolites. <i>VcMYB1</i>, <i>VcMYBPA1</i>, <i>MYBPA1.2</i>, and <i>MYBPA2.1</i> might be responsible for drought-induced flavonoid biosynthesis and <i>VcMYB14, MYB14, MYB102</i>, <i>and MYB108</i> may be responsible for blueberry leaf drought tolerance. ABA responsive elements binding factor (<i>ABF</i>) genes, <i>MYB</i> genes, <i>bHLH</i> genes, and flavonoid biosynthetic genes might form a regulatory network to regulate drought-induced accumulation of flavonoid metabolites in blueberry leaves. Our study provides a useful reference for breeding drought-resistant blueberry varieties.