Downregulation of CSD2 by a heat-inducible miR398 is required for thermotolerance in Arabidopsis.

MicroRNAs (miRNAs) play important roles in plant growth and development and abiotic stress responses. We report here that heat stress rapidly induces miR398 and reduces transcript of its target gene CSD2. Transgenic plants overexpressing the miR398-resistant form of CSD2 are more sensitive to heat stress than transgenic plants overexpressing normal coding sequence of CSD2. Expression of heat stress transcription factors (HSFs) and heat shock proteins (HSPs) is reduced in the heat-sensitive transgenic plants overexpressing miR398-resistant form of CSD2. Our results suggest that downregulation of CSD2 by the heat-inducible miR398 is required for thermotolerance in Arabidopsis.