Reprogramming of microspore fate via BBM-BAR1 for highly efficient in vivo haploid induction

Haploid induction (HI) through stress-treated microspore culture has gained significant attention for over half a century, yet the molecular mechanism underlying microspore fate transition for androgenesis remains poorly understood. Here, we demonstrate that microspore-specific expression of BABY BOOM (BBM) is sufficient to induce microspore cell fate transition and in vivo androgenesis in both tobacco and rice, effectively bypassing the requirement for stress treatment. We further identify BBM-activated Androgenesis Regulator 1 (BAR1) as a novel downstream effector of BBM that promotes microspore reprogramming. Remarkably, both BBM and BAR1 can replace the role of stress treatment in reprogramming microspore development and triggering androgenesis. This study reveals a conserved regulatory module governing androgenesis, providing a transformative approach to overcome long-standing limitations and enable highly efficient in vivo HI across diverse crops.