Research Focus

Plant Heat Stress Response and Thermotolerance Mechanisms

The primary interest of our research is to understand how plants cope with high-temperature stress. High-temperature stress reduces the productivity of crops, which is a big challenge to food security because of global warming. Improving the thermal adaptability of plants is essential to mitigate the problem, and identification of the significant genetic factors involved in thermal versatility will facilitate achievement of this goal.

In our lab, Arabidopsis and rice are the primary species for studying the protective roles of plant genes under various high-temperature regimes. Biochemical, molecular biological, physiological, and genetic tools are applied to decipher the underlying mechanisms of thermotolerance and regulation of heat-stress response:

I. Functional Analysis of Heat Shock Factor (HSF)– HSF is the major transcription regulator of heat stress responsive (HSR) proteins, such as heat shock proteins. In Arabidopsis, members of the HSFA1 subgroup are required for up-regulation of transcription of HSR genes in response to multiple stresses, including high temperature, salt, osmolyte, and oxidative agents. HSFA1s control the heat-induction of several important transcription factors, such as HSFA2, HSFB1, DREB2A, and bZIP28. Together, they form a complex heat stress response signaling network. We found that four HSFA1s and HSFA2 in Arabidopsis have evolved specific functions in response to different environmental factors, probably by preferentially targeting to different downstream genes.

II. Modulation of Heat Acclimation Memory– Heat acclimation triggers the expression of HSR genes mediated by HSF and enhances tolerance to noxious high temperature, a phenomenon known as acquired thermotolerance. Once normal conditions are restored, acquired thermotolerance gradually disappears. We discovered two pathways that extend the effect of heat acclimation in Arabidopsis: HSFA2-mediated and HSP101-HSA32-mediated pathways.

The former involves a HSFA1 and HSFA2 transcription cascade, which prolongs the transcriptional activities of HSR genes. The latter involves a positive feedback loop at post-transcriptional level between two heat-inducible proteins, HSP101 and HSA32. Our evidence suggests that HSP101 promotes the synthesis of HSA32, and HSA32 retards the degradation of HSP101, an important factor of acquired thermotolerance. Prolonging heat acclimation “memory” is likely to be an important strategy for coping with repetitive heat stress or temperature fluctuation.

III. The Molecular Basis of Thermotolerance Diversity– In the natural environment, plants face different types of heat stress. For example, heat stress caused by exposure to extremely high temperature is different from that caused by prolonged moderately high temperature. Recently, we have shown that plants employ different sets of genes to overcome the challenge of four heat stress regimes, resulting in four types of thermotolerance (basal thermotolerance; short-term acquired thermotolerance; long-term acquired thermotolerance; and thermotolerance to moderately high temperature). Realizing the existence of diverse thermotolerance responses in plants facilitates studies of gene function and provides insight into thermal adaptability.