SELF-PRUNING 6A promotes tuberization and heat tolerance but lowers immunity of potato ( <i>Solanum tuberosum</i> L.)

Potato (Solanum tuberosum L.) is a crucial global food crop, but high temperatures inhibit tuberization and reduce yield. To investigate heat tolerance genetics, a crossing population was created using the cultivars Annabelle (early tuber-forming, moderately heat tolerant) and Camel (mid-early tuber-forming, heat-sensitive). Screening over 500 progenies identified 10 contrasting individuals for further study. RNA-Seq analysis of parents and selected progeny confirmed the phenotypic heat tolerance classification. Tolerant genotypes exhibited earlier tuberization and significantly higher leaf expression of SELF-PRUNING 6A (SP6A), a key tuberization gene. Gene Ontology analysis revealed that under control conditions, heat-tolerant plants showed down-regulation of multiple defense-related pathways, particularly terpene synthases, leading to reduced terpene accumulation. This correlated with a diminished immune response, evident from lower ethylene production upon flgII-28 treatment. To explore the role of SP6A in the observed trade-off between tuberization and defense, transgenic SP6A overexpressing plants were studied. Like heat-tolerant progeny, SP6A overexpression led to down-regulation of defense genes, reduced terpene accumulation, and a weaker immune response. These findings suggest that SP6A-mediated assimilate redistribution plays a key role in the negative correlation between early tuberization and pathogen defense, providing insights into the genetic mechanisms underlying heat tolerance in potatoes.