A Positive Feedback Loop between HSP101 and HSA32 Modulates Long-term Acquired Thermotolerance Illustrating Diverse Heat Stress Responses in Rice Varieties

Heat stress is an important factor that has a negative impact on rice production. To alleviate this problem, it is necessary to extensively understand the genetic basis of heat tolerance and adaptability to heat stress in rice. Here, we report the molecular mechanism underlying heat acclimation memory that confers long-term acquired thermotolerance (LAT) in this monocot plant. Our results showed that a positive feedback loop formed by two heat-inducible genes, HSP101 and HSA32, at the posttranscriptional level prolongs the effect of heat acclimation in rice seedlings. The interplay between HSP101 and HSA32 also affects basal thermotolerance of rice seeds. These findings are similar to those reported for the dicot plant Arabidopsis thaliana, suggesting a conserved function in plant heat stress response. Comparison between a japonica rice cultivar, Nipponbare, and an indica cultivar, N22, showed opposite performance in basal thermotolerance and LAT assays. N22 seedlings have a higher basal thermotolerance level than Nipponbare, and vice versa at the LAT level, indicating that these two types of thermotolerance can be decoupled. The HSP101 and HSA32 protein levels were substantially higher in Nipponbare than in N22 after a long recovery following heat acclimation treatment, at least partly explaining the difference in the LAT phenotype. Our results point out the complexity of thermotolerance diversity in rice cultivars, which may need to be taken into consideration when breeding for heat tolerance for different climate scenarios.


Co-researchers:Meng-yi Lin, Kuo-hsing Chai, Swee-suak Ko, Lin-yun Kuang, Huu-Sheng Lur, and Yee-yung Charng