An unidentified ultraviolet-B-specific photoreceptor mediates transcriptional activation of the cyclobutane pyrimidine dimer photolyase gene in plants.

Cyclobutane pyrimidine dimers (CPDs) constitute a majority of DNA lesions caused by ultraviolet-B (UVB). CPD photolyase, which rapidly repairs CPDs, is essential for plant survival under sunlight containing UVB. Our earlier results that the transcription of the cucumber CPD photolyase gene (CsPHR) was activated by light have prompted us to propose that this light-driven transcriptional activation would allow plants to meet the need of the photolyase activity upon challenges of UVB from sunlight. However, molecular mechanisms underlying the light-dependent transcriptional activation of CsPHR were unknown. In order to understand spectroscopic aspects of the plant response, we investigated the wavelength-dependence (action spectra) of the light-dependent transcriptional activation of CsPHR. In both cucumber seedlings and transgenic Arabidopsis seedlings expressing reporter genes under the control of the CsPHR promoter, the action spectra exhibited the most predominant peak in the long-wavelength UVB waveband (around 310 nm). In addition, a 95-bp cis-acting region in the CsPHR promoter was identified to be essential for the UVB-driven transcriptional activation of CsPHR. Thus, we concluded that the photoperception of long-wavelength UVB by UVB photoreceptor(s) led to the induction of the CsPHR transcription via a conserved cis-acting element.