Stemona genomes illuminate fatty acid partitioning between seeds and elaiosomes mediating wasp dispersal

Abstract Seed dispersal by wasps (vespicochory) is documented in five angiosperm families, with phylogenies suggesting that most vespicochorous lineages evolved from ant-dispersed (myrmecochorous) ancestors. While recent work has identified cues attracting wasp dispersers, the molecular basis remains unclear. To shed light on the molecular basis of vespicochory, we generated chromosome-level genomes for the wasp-dispersed Stemona tuberosa, and its close ant-dispersed relative S. mairei. Combining comparative genomic, transcriptomic, lipidomic, and functional analyses, we ask (i) how chemical elaiosome differentiation occurs during seed development, and (ii) how key mutualism-associated genes evolved in Stemona. We show that elaiosomes up-regulate stearoyl-ACP Δ9 desaturases (SAD) and accumulate oleic acid and 1,2-diolein, which serve both as food rewards and as precursors for CER1/3-mediated biosynthesis of (Z)-9-tricosene, the key wasp attractant. By contrast, high expression of FatB and DGAT1 in seeds is associated with medium-chain fatty acids (MCFAs) production. Comparative genomics indicates conservation of these genes across Stemona, with S. tuberosa-specific FatB expansion and SAD/CER1/3 repertoire divergence. Our work supports a model for elaiosome-seed fatty-acid differentiation linking recruitment and nourishment in vespicochory. Given that oleic acid and 1,2-diolein are also key cues in myrmecochory, this shared biochemical basis may help explain how vespicochory evolves from ant-dispersed ancestors. Competing Interest Statement The authors have declared no competing interest.