Role of BABY BOOM Transcription Factor in Promoting Somatic Embryogenesis and Genetic Transformation in a Woody Magnoliid Liriodendron

ABSTRACT Somatic embryogenesis (SE) is a powerful biotechnological tool widely utilized for large‐scale propagation and genetic transformation. Morphogenic genes like BABY BOOM ( BBM ) and WUSCHEL ( WUS ) play crucial roles in SE and are extensively applied to improve SE‐based genetic transformation. However, the transcriptome profiling and key regulatory factors of SE in the woody magnoliid Liriodendron hybrid remain unclear. Here, we depicted the time‐series transcriptome profiling of SE in Liriodendron hybrid, highlighting the temporal significance of morphogenic genes like BBM in embryogenic callus and developing somatic embryos. Expression patterns were validated using qRT‐PCR and transgenic lines expressing β‐glucuronidase (GUS) and red fluorescent protein mCherry driven by the LhBBM promoter. Overexpression of LhBBM , both constitutive (CaMV 35S promoter) and SE‐specific ( Liriodendron WOX9 promoter), enhanced SE and embryonic callus induction. Conversely, CRISPR/Cas9‐mediated knockout of LhBBM reduces SE efficiency without compromising callus induction. Furthermore, we developed a secondary callus induction method that minimized the heterogeneity of a transgenic callus line, confirming the sufficiency and necessity of LhBBM in SE. Notably, LhBBM significantly improved genetic transformation efficiency in Liriodendron . These findings establish LhBBM as a promising target for enhancing SE capacity and SE‐based transformation efficiency, particularly in forest trees.