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 (Pyrus bretschneideri Rehd.), we determined that GA 20-oxidases (GA20ox) may play key roles in seedless pear fruit development. Sequence analysis revealed three PbGA20ox genes: PbGA20ox1, PbGA20ox2, and PbGA20ox3. We analyzed the expression patterns of candidate genes and found that PbGA20ox2 levels significantly changed in pollinated fruits. Tissue-specific expression assays revealed that PbGA20ox2 is highly expressed in young fruit and leaves. Subcellular localization assays showed it was located in the cytoplasm, nucleus, and plasma membrane. Overexpressed PbGA20ox2 tomato plants were taller and had longer hypocotyls and internodes, and the emasculated flowers produced parthenocarpic fruit. In pear, the transient overexpression of PbGA20ox2 promoted fruit development and delayed the drop of nonpollinated fruit. Furthermore, the fruit of PbGA20ox2-overexpressing tomato and transient PbGA20ox2-overexpressing pear had increased GA4 (but not GA3 and GA1) contents. This result provided evidence that PbGA20ox2 was necessary for GA4-dependent pear fruit development. Our study revealed that PbGA20ox2 altered the GA biosynthetic pathway and enhanced GA4 synthesis, thereby promoting fruit set and parthenocarpic fruit development.
Highlights
Fruit set, a key developmental process that occurs following successful fertilization in higher plants, is the first step in fruit development (Joldersma and Liu, 2018)
We found that GA4+7 induced seedless pear fruit (Liu et al, 2018b); to investigate the mechanism by which GA induces parthenocarpy in pear, we analyzed the RNAseq data, which showed that pollination induced the expression of gibberellin biosynthesis pathway related genes, such as, PbGA3ox, Ent-Kaurene Synthase, Ent-Kaurene Oxidase, and PbGA20ox genes, and the expression of PbGA20ox2 was increased dramatically
The expression of PbGA2ox2, which transfers active GAs to inactive GAs, was downregulated by pollination at 9 DAA (Supplementary Table S1).These results indicated that pollination promoted GAs biosynthesis
Summary
A key developmental process that occurs following successful fertilization in higher plants, is the first step in fruit development (Joldersma and Liu, 2018). Fruit set and development represent the commitment of an angiosperm plant to the development of mature fruit (Joldersma and Liu, 2018). PbGA20ox Regulates Fruit Set and Development ‘Dangshansu’ (Pyrus bretschneideri Rehd.), a pear cultivar with fleshy fruits, is highly studied because of its considerable economic importance. Fruit set and development are triggered by pollination and fertilization. Many fruit species, including pear, exhibit natural self-incompatibility. Parthenocarpy, which induces seedless fruit, is independent of pollination and fertilization and is a valuable trait for some self-incompatible species
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