[Quantitative trait locus (QTL) mapping and candidate gene analysis of heat tolerance of rice at heading stage]

Rice (Oryza sativa L.) is one of the major food crops in China, and high-temperature stress has become one of the key abiotic stressors threatening stable rice production and food security. Rice is most sensitive to high temperatures at the heading stage. Heat stress can lead to the accumulation of reactive oxygen species, damage to cell membranes, and a reduction in seed-setting rate, thereby seriously affecting rice yields and quality. To identify quantitative trait loci (QTLs) associated with heat tolerance during the panicle emergence stage of rice and to gain deeper insights into the genetic basis of heat tolerance, in this study, the indica rice cultivar 'HZ', the japonica cultivar 'Nekken2', and their 120 recombinant inbred lines (RILs) were used as experimental materials. The seed-setting rate and heat tolerance coefficient of the population at the heading stage were evaluated for three consecutive years from 2023 to 2025. On the basis of the previously constructed high-density genetic linkage map, QTLs associated with heat tolerance of rice at the heading stage were identified. A total of 43 QTLs related to seed-setting rate and heat tolerance coefficient were identified, among which the QTL qSSRIII-12.2 showed the highest logarithm of odds (LOD) value of 4.51. Chromosome 5 were identified with the most QTLs (9). In addition, some QTLs were overlapped. According to the QTL mapping intervals, 12 candidate genes were screened out. qRT-PCR was performed to analyze the expression patterns of these candidate genes. The results showed that the expression levels of most genes were significantly different between the parental lines. Among them, LOC_Os05g30480, LOC_Os05g31040, LOC_Os05g31062, and LOC_Os07g37580 were upregulated after heat stress, which suggested that these genes might play a positive role in rice heat tolerance. In contrast, the expression levels of LOC_Os10g28000, LOC_Os10g30680, LOC_Os12g25660, and LOC_Os12g26030 decreased after heat stress, which indicated that these genes may negatively regulate heat tolerance in rice. The results of this study provide a theoretical basis and important genetic resources for the mining and functional verification of heat tolerance genes in rice at the heading stage.