Maternal haploid induction in maize via mutation of <i>Gamete Expression protein 1</i>

Doubled haploid (DH) technology, based on haploid induction (HI), is a crucial tool in enhancing crop-breeding efficiency and has been successfully applied in various plant species. While many HI-related genes have been identified using diverse strategies, the genetic basis and molecular mechanisms underlying HI remain incompletely understood. In this study, we present a novel system for inducing haploid offspring through targeted mutagenesis of the Zea mays Gamete Expression protein 1 (ZmGEX1) gene in maize. Our findings reveal that zmgex1 heterozygous plants (zmgex1^+/-) induce maternal haploids via self- and cross-pollination as the female parent, with an average rate of 1.34%. This indicates that the haploid progeny is exclusively maternal in origin, carrying the maternal genome. We also demonstrate that ZmGEX1 is expressed in both female spikelets and anthers, localizing to the cytoplasm, nucleus and endoplasmic reticulum. Although the transmission efficiency of the zmgex1 allele is reduced in female gametophytes, ZmGEX1 does not affect embryo sac development but influences fertilization. We propose that defective fusion of the sperm and egg nuclei may lead to haploid formation. Finally, a schematic that illustrates the potential application of the new gene ZmGEX1 in maize breeding programs is proposed. Collectively, this study identifies ZmGEX1 as a novel gene involved in maternal HI and provides a promising strategy for breeding improvements.