Identification and Validation of qSTS5, a QTL Associated with Salt Tolerance at Seedling Stage in Dongxiang Wild Rice

Soil salinization severely restricts rice growth and global grain production, posing a serious threat to food security. Dongxiang wild rice serves as an important genetic resource for improving salt tolerance in rice. In this study, a backcross inbred line (BIL) population derived from Dongxiang wild rice DY80 and an indica restorer line R974 were used to detect QTLs for salt tolerance at the germination and seedling stages. Four QTLs related to germination-stage salt tolerance and three QTLs for seedling-stage salt tolerance were identified, among which qSTS5 on chromosome 5 showed the largest effect with a LOD score of 8.0 and a phenotypic contribution rate of 14.8%. An F_2:3 population was further constructed to validate qSTS5, which increased its LOD value to 10.4 and phenotypic variation explanation rate to 18.5%, and the locus was finally delimited to a 2.3 Mb interval. Transcriptome analysis identified eight differentially expressed genes (DEGs) within the qSTS5 region under salt stress. Sequence comparison between the parents revealed that three DEGs had no coding-region variations, while the other five showed nucleotide polymorphisms leading to amino acid changes. Among them, Os05g0349800 encodes a LEA protein, a typical stress-responsive gene, and harbors a frameshift mutation in DY80. Combined with its induced expression pattern under salt stress, this gene was considered the most promising candidate for qSTS5. This study not only provides a stable major QTL for rice breeding for salt tolerance but also lays a foundation for dissecting the molecular mechanism of salt tolerance in Dongxiang wild rice.