Some like It Hot; QTL and Rnaseq Investigation into the Basis of a Unique Form Resistance to Heat-Induced Seed Degradation.

Soybean reproductive structures are temperature sensitive, with a reproductive optimum of 22-24 °C. Ongoing climate change may also result in more widespread incidence of late season drought and elevated temperatures during seed-fill in the future. Currently, certain regions of the US soybean growing region (notably the Mississippi Delta) experience consistent late season elevated temperature and drought stress, which has shifted planting practices in favor of earlier maturity groups planted earlier in the season. This approach, the Early Soybean Production System, boosted on-farm revenue. However, seed also develop under very elevated temperatures (often >32°C during the day) resulting in decreased seed quality and unacceptable seed germination rates. The ancestors of all modern high yielding soybean lines lack substantial resistance to heat-induced-seed degradation, but Plant introduction PI587982A, maintains ~95% quality and germination under conditions that injure and devalue seed of high yielding elite cultivars. This source of temperature tolerance is being used in ongoing germplasm development and has been used to generate genetic mapping recombinant inbred line (RIL) populations. A major effect tolerance QTL, derived from PI 587982A, was detected in two field experiments, as well as two greenhouse heat stress experiments. RNAseq analysis performed with contrasting sensitive/tolerant genotypes revealed a common set of heat-responsive genes, as well unique transcriptomic signatures specific to the heat-tolerant genotype. Together, these results give insight into the biological mechanisms responsible for a unique form of genetic resistance to heat-induced seed degradation.