Evaluation of heat stress resistance and its molecular machanism of four indica rice cultivars at seedling stage

Objective To identify the variation in heat stress resistance among seedlings of four different indica rice cultivars grown in South China, and provide theoretical reference and technical support for the breeding and promotion of rice varieties.

Method We performed whole-genome re-sequencing, phenotype identification, and transcriptional level analysis to comprehensively evaluate the heat stress resistance for seedlings of high-yield conventional rice cultivar ‘Nan Xiu Mei Zhan’ (NXMZ), hybrid rice restorer cultivar ‘R5518’, and aromatic rice cultivars ‘Jiu Li Xiang’ (JLX) and ‘Nan Jing Xiang Zhan’ (NJXZ) in South China.

Result The ‘NJXZ’ was sensitive to heat stress. The ‘R5518’ showed medium resistance to heat stress. The resistances to heat stress of ‘JLX’ and ‘NXMZ’at seedling stage were relatively high in comparison to other two rice cultivars. We compared the haplotypes of heat resistance related genes, the relative expression levels and phenotypes, and found that many SNPs appeared in OsTT1 from‘JLX’, while the haplotypes of four cultivars with other heat-related QTLs remained relatively consistent, suggesting that the OsTT1 might contribute to partial heat stress resistance in ‘JLX’. The gene expression patterns in OsHSF7, OsHSP71.1 and OsHTS1 were consistent with the evaluation in heat stress resistance of rice cultivars, indicating that these three genes might associate with regulation in heat stress resistance of four indica rice cultivars.

Conclusion The gene expression difference, gene shift and transcript error in certain genes result in variations in heat stress resistance of different indica rice cultivars at seedling stage. These results can provide new ideas for genome-wide selection for heat tolerance breeding in rice.