Decoding TaSPX-7A's governance of wheat-mycorrhizal dependence from genome-wide association to molecular mechanism

Wheat (Triticum aestivum L.) establishes symbiotic relationships with arbuscular mycorrhizal (AM) fungi to improve mineral nutrient acquisition. Mycorrhizal dependence (MD) reflects the growth response to the symbiosis, but the biological mechanisms underlying wheat MD are still unclear. We used genome-wide association study (GWAS) and transcriptome analyses, and performed gene overexpression and dual luciferase assays to investigate the regulation of wheat MD. We identified 182 significant MD-associated quantitative trait loci (QTLs) and focused on TaSPX-7A in QTL173 as the key candidate gene. Overexpressing TaSPX-7A increased wheat MD, and TaMADS-5D repressed TaSPX-7A expression. The deletion of the TaMADS-5D binding site in the TaSPX-7A promoter was associated with higher TaSPX-7A expression in positive MD wheat. Promoter polymorphism-mediated differential expression of TaSPX-7A likely underlies natural MD variation in wheat. Our study reveals TaSPX-7A as a key regulator of MD and advances the mechanistic understanding of wheat AM symbiosis.