Gibberellin-induced parthenocarpy in fruits of a prickly pear mutant

We explored the intricate dynamics of parthenocarpic fruit development in prickly pear Opuntia ficus-indica (Cactaceae) through the investigation of fruits of the Beer Sheva1 (BS1) a parthenocarpic mutant and its revertant non-parthenocarpic stems. BS1 fruits, characterized by parthenocarpy and enlarged unfertilized ovules, provide a unique model for investigating the regulatory mechanisms underlying fruit development in prickly pear. We hypothesized that elevated levels of gibberellins (GAs) in BS1 ovaries induce parthenocarpic fruit development. By integrating different approaches, including GA quantification and expression analysis of ovaries from BS1 and revertant flowers, we elucidated the pivotal role of biosynthetic, catabolic, and regulatory GA genes in orchestrating ovule development. Notably, our investigation revealed a complex interplay between GA biosynthesis and catabolic genes, particularly GID1, GA20ox, and GA2ox, which significantly influenced GA levels in BS1 ovaries. Quantification of endogenous GAs confirmed higher levels of bioactive GA1, GA3, and GA4 in BS1 compared to revertant ovules, indicating the central role of GAs in parthenocarpy. Furthermore, application of the GA inhibitor paclobutrazol (PBZ) to BS1 flower buds resulted in the reversion of BS1 fruits to the progenitor phenotype containing viable seeds, thereby validating the critical involvement of GAs in seed development. High-throughput RNA-sequencing analysis identified a total of 7,717 differentially expressed genes (DEGs) in BS1, among them GA-related genes. Overall, our findings shed light on the complex hormonal regulatory network governing parthenocarpic fruit development in prickly pear, paving the way for future studies aiming at understanding ovule development and development of commercially desirable seedless fruits.