Expression profiling and functional characterization of LoNCED gene in the pollen abortion of Lilium spp

Lilium spp. are widely cultivated for their ornamental value, but excessive pollen production poses significant commercial challenges. Male sterility, especially in pollenless cultivars, offers a promising breeding strategy to improve market appeal. This study demonstrates that abscisic acid (ABA) biosynthesis, mediated by 9-cis-epoxycarotenoid dioxygenase (NCED)‌-a rate-limiting enzyme in ABA production-constitutes the pivotal mechanism underlying complete male sterility in Lilium.

Through comparative transcriptomic analysis between fertile and sterile lily progenies, we identified significantly elevated ABA levels concomitant with upregulated LoNCED expression in the developing anthers of sterile plants. To investigate its role in male sterility, we isolated the LoNCED gene from both fertile and sterile lily progenies. Following cloning and tissue-specific expression analysis, we explored its function through homologous transient overexpression and heterologous expression. The LoNCED gene, with a 1812 bp open reading frame encoding 603 amino acids, encodes a hydrophilic protein (66.69 kDa) localized in chloroplasts and mitochondria. Sequence analysis revealed high similarity to NCED proteins from other species. Transient overexpression of LoNCED in Lilium anthers transformation downregulated key anther developmental genes (DYT1, TDF1, CYP703A2, CALS5 and DEX1), leading to tapetum degradation, microspore abortion, and complete pollen sterility. Our multispecies validation demonstrated conserved NCED-mediated sterility mechanisms across monocots and eudicots.

The LoNCED gene shows specific high expression during lily anther development. Its overexpression disrupts anther structure, arrests meiosis, and downregulates pollen development-related genes, revealing a conserved inhibitory role in male reproductive organ development.