Blue light receptor CRY1 regulates HSFA1d nuclear localization to promote plant thermotolerance.

Temperature increases as light intensity rises, but whether light signals can be directly linked to high temperature response in plants is unclear. Here, we find that light pre-treatment enables plants to survive better under high temperature, designated as light-induced thermotolerance (LIT). With short-term light treatment, plants induce light-signaling pathway genes and heat shock genes. Blue light photoreceptor cryptochrome 1 (CRY1) is required for LIT. We also find that CRY1 physically interacts with the heat shock transcription factor A1d (HsfA1d) and that HsfA1d is involved in thermotolerance under light treatment. Furthermore, CRY1 promotes HsfA1d nuclear localization through importin alpha 1 (IMPα1). Consistent with this, CRY1 shares more than half of the chromatin binding sites with HsfA1d. Mutation of CRY1 (cry1-304) diminishes a large number of HsfA1d binding sites that are shared with CRY1. We present a model where, by coupling light sensing to high-temperature stress, CRY1 confers thermotolerance in plants via HsfA1d.