Ectopic Expression of BABY BOOM Triggers a Conversion from Vegetative to Embryonic Growth

TLDR

The molecular mechanisms underlying the initiation and maintenance of the embryonic pathway in plants are largely unknown. The study aims to gain insight into embryonic pathway initiation and maintenance by identifying genes upregulated during in vitro embryo induction from immature pollen grains of Brassica napus. The authors used subtractive hybridization to isolate such genes during microspore embryogenesis. The identified gene BABY BOOM (BBM), an AP2/ERF transcription factor preferentially expressed in developing embryos and seeds, when ectopically expressed in Arabidopsis and Brassica, induces spontaneous somatic embryogenesis, cotyledon‑like structures, neoplastic growth, hormone‑free regeneration, and altered leaf and flower morphology, indicating a role in promoting cell proliferation and morphogenesis during embryogenesis.

Abstract

The molecular mechanisms underlying the initiation and maintenance of the embryonic pathway in plants are largely unknown. To obtain more insight into these processes, we used subtractive hybridization to identify genes that are upregulated during the in vitro induction of embryo development from immature pollen grains of Brassica napus (microspore embryogenesis). One of the genes identified, BABY BOOM (BBM), shows similarity to the AP2/ERF family of transcription factors and is expressed preferentially in developing embryos and seeds. Ectopic expression of BBM in Arabidopsis and Brassica led to the spontaneous formation of somatic embryos and cotyledon-like structures on seedlings. Ectopic BBM expression induced additional pleiotropic phenotypes, including neoplastic growth, hormone-free regeneration of explants, and alterations in leaf and flower morphology. The expression pattern of BBM in developing seeds combined with the BBM overexpression phenotype suggests a role for this gene in promoting cell proliferation and morphogenesis during embryogenesis.