PbGA20ox2 Regulates Fruit Set and Induces Parthenocarpy by Enhancing GA4 Content

Abstract

Fruit set and development occur following successful fertilization. Parthenocarpy, a valuable trait in some self-incompatible species, produces seedless fruit without fertilization. Gibberellin (GA) is a crucial hormone in fruit-set regulation and development. While investigating the development of parthenocarpy in pear (<i>Pyrus bretschneideri</i> Rehd.), we determined that GA 20-oxidases (GA20ox) may play key roles in seedless pear fruit development. Sequence analysis revealed three <i>PbGA20ox</i> genes: <i>PbGA20ox1, PbGA20ox2</i>, and <i>PbGA20ox3</i>. We analyzed the expression patterns of candidate genes and found that <i>PbGA20ox2</i> levels significantly changed in pollinated fruits. Tissue-specific expression assays revealed that <i>PbGA20ox2</i> is highly expressed in young fruit and leaves. Subcellular localization assays showed it was located in the cytoplasm, nucleus, and plasma membrane. Overexpressed <i>PbGA20ox2</i> tomato plants were taller and had longer hypocotyls and internodes, and the emasculated flowers produced parthenocarpic fruit. In pear, the transient overexpression of <i>PbGA20ox2</i> promoted fruit development and delayed the drop of nonpollinated fruit. Furthermore, the fruit of <i>PbGA20ox2-</i>overexpressing tomato and transient <i>PbGA20ox2-</i>overexpressing pear had increased GA₄ (but not GA₃ and GA₁) contents. This result provided evidence that <i>PbGA20ox2</i> was necessary for GA₄-dependent pear fruit development. Our study revealed that <i>PbGA20ox2</i> altered the GA biosynthetic pathway and enhanced GA₄ synthesis, thereby promoting fruit set and parthenocarpic fruit development.