Virus-Induced Gene Silencing (VIGS) in Hydrangea macrophylla and Functional Analysis of HmF3′5′H

<i>Hydrangea macrophylla</i>, renowned for its large inflorescences and a diverse range of colors, highlights a significant limitation in current gene function research, which is the lack of effective molecular genetic tools. This study utilized a <i>tobacco rattle virus</i> (TRV)-based virus-induced gene silencing (VIGS) system to investigate gene function through posttranscriptional gene silencing in <i>H. macrophylla</i> for the first time. The ortholog of <i>phytoene desaturase</i> (<i>PDS</i>) in <i>H. macrophylla</i>, termed <i>HmPDS</i>, was identified. Infection of tissue-cultured seedlings with TRV-<i>HmPDS</i> led to photobleaching of the leaves. Additionally, infection with TRV containing the <i>HmCHS1</i> fragment in the flowers resulted in decreased anthocyanin production in sepals and a lightening of sepal coloration in the infected flowers. The phenomena and RT-qPCR results proved that the <i>PDS</i> and <i>CHS</i> genes of hydrangea were successfully silenced via the vacuum infiltration method. Furthermore, the introduction of TRV-<i>HmF3'5'H</i> revealed a decrease in delphinidin-3-glucoside content in sepals and caused a color change in the sepals from blue to pink. This study demonstrated that the TRV-VIGS system was successfully established in <i>H. macrophylla</i> and effectively applied to the function analysis of <i>HmF3'5'H</i>.