GEX1-mediated semigamy induces both maternal and paternal haploids in cotton.

A mutation in Gamete Expressed 1 (GEX1) in cotton disrupts nuclear membrane fusion during double fertilization, enabling maternal haploids, paternal haploids, and chimeric progeny.

• Why it matters: Semigamy’s long-standing mechanism for producing haploids during double fertilization has been unclear for over six decades, limiting rational haploid breeding strategies.
• What they did: The study identified GEX1 as the semigamy gene, then used cytology to show delayed or incomplete karyogamy and applied CRISPR-Cas9 disruption to reproduce the fusion defects.
• The result: Delayed karyogamy lets closely apposed but unfused gametic nuclei divide independently, and GEX1 disruption enables dual-origin haploid induction in a single generation for rapid doubled-haploid production.

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