The ga3ox1b mutation reveals the crosstalk between gibberellin and other phytohormones in controlling the growth and development of female flowers in Cucurbita pepo.

Cucurbita pepo produces female and male unisexual flowers on the same plant, and their large size makes the species a good model for studying regulation of sex-associated traits. As male flowers appear earlier during plant development than females, a system has evolved whereby female flowers grow and open faster than male flowers, allowing synchronization for proper pollination and fertilization. Our findings establish that gibberellin (GA) drives the divergent development of female and male flowers. We characterize a loss-of-function mutation in the GA biosynthetic gene CpGA3ox1B that causes GA deficiency in various organs. Cpga3ox1b, surprisingly, only impairs female flowers, rendering them small, unopened, and sterile. Male flowers develop normally, and are fertile, like male wild-type (WT) flowers. In the WT, CpGA3ox1B transcription is higher in female than male flowers, causing accumulation of GA and resulting in faster growth. The dwarf plant and flower phenotypes were rescued by GA3, but not by ethylene or jasmonic acid, indicating that the ga3ox1b flower never reached the appropriate size to be sensitive to these hormones, which control petal expansion and flower opening. The GA mutation affects corolla and pistil growth rather than ethylene-regulated sex determination in the floral meristem. Opposite transcriptomic shifts in ga3ox1b and ethylene-insensitive etr2b ovaries demonstrate the mutual exclusion of ethylene and GA signaling, highlighting the role of transcription factors such as MYB62 in integrating both pathways to regulate C. pepo development.