Variations in Ecological Locations Induce Soybean Seed Wrinkles by Disrupting Source–Sink Relationship and Energy Metabolism at the Grain-Filling Stage

Defective seed filling, which manifests as seed wrinkling, severely impairs the yield and commercial quality of soybean crops. Soybean varieties independently developed in Heilongjiang Province exhibit distinct phenotypic variations in seed wrinkling across diverse ecological planting regions, whereas the molecular and physiological mechanisms driving such differences remain largely uncharacterized. In this study, two soybean genotypes with divergent heat resistance, namely, the heat-sensitive cultivar HH43 and the heat-tolerant cultivar HN76, were planted in three distinct ecological sites for comparative analysis. Statistical results indicated that ecological conditions serve as the predominant factor regulating seed-wrinkling variation, with high temperatures occurring during the seed-filling stage identified as the key abiotic stress trigger. Excessively high ambient temperatures triggered abnormal sucrose accumulation in the pod husks of heat-vulnerable HH43, disrupting the coupling relationship between sucrose metabolism and energy supply and thereby restricting starch biosynthesis in developing seeds. Transcriptome profiling combined with weighted gene co-expression network analysis (WGCNA) further demonstrated that heat stress significantly suppressed the expression of energy transport-related genes and induced the dysregulated expression of starch synthesis-associated genes in susceptible soybean plants, and these transcriptional alterations were further verified via qRT-PCR assays. Collectively, short-term extreme high temperatures interrupt the carbon transport and allocation process from pod husks to seeds in heat-sensitive soybean cultivars. By contrast, heat-tolerant genotypes can sustain a stable physiological metabolism and molecular regulatory networks to effectively cope with high-temperature stress during the seed-filling period.