QTL mapping and identification of candidate genes for cold tolerance at the germination stage in wild rice

Background Cold damage stress significantly affects rice growth (germination and seedling) and causes serious losses in yield in temperate and high-altitude areas around the globe. Objective This study aimed to explore the cold tolerance (CT) locus of rice and create new cold-tolerant germplasm. We constructed a chromosome segment substitution line (CSSL) with strong CT and fine mapped quantitative trait loci (QTLs) associated with CT by performing the whole-genome resequencing of CSSL with phenotypes under cold treatment. Methods A chromosome CSSL, including 271 lines from a cross between the cold-tolerant wild rice Y11 ( Oryza rufipogon Griff.) and the cold-sensitive rice variety GH998, was developed to map QTLs conferring CT at the germination stage. The whole-genome resequencing was performed on CSSL for mapping QTLs of associated with CT at the germination stage. Results A high-density linkage map of the CSSLs was developed using the whole-genome resequencing of 1484 bins. The QTL analysis using 615,466 single-nucleotide polymorphisms (SNPs) led to the identification of 2 QTLs related to germination rate at low-temperature on chromosome 8 ( qCTG-8 ) and chromosome 11 ( qCTG-11 ). The qCTG-8 and qCTG-11 explained 14.55% and 14.31% of the total phenotypic variation, respectively. We narrowed down qCTG-8 and qCTG-11 to 195.5 and 78.83-kb regions, respectively. The expression patterns of important candidate genes in different tissues, and of RNA-sequencing (RNA-seq) in CSSLs, were identified based on gene sequences in qCTG-8 and qCTG-11 cold-induced expression analysis. LOC_Os08g01120 and LOC_Os08g01390 were identified as candidate genes in qCTG-8 , and LOC_Os11g32880 was identified as a candidate gene in qCTG-11 . Conclusions This study demonstrated a general method that could be used to identify useful loci and genes in wild rice and aid in the future cloning of candidate genes of qCTG-8 and qCTG-11 . The CSSLs with strong CT were supported for breeding cold-tolerant rice varieties.