ABSTRACT: The responses of the transcriptome of Synechocystis PCC 6803 to UV-irradiation were measured at time points over 36 h. Irradiation was provided by Sylvania soft white DuluzR compact fluorescent 23W bulbs (Osram Sylvania Ltd, Mississauga, Canada), a 20W RS UV-B medical light with a spectral maximum at 310 nm (model ‘TL’, Philips, Holland), and 15W black lights each with a spectral maximum at 368 nm (model F15T8-BL, General Electric, USA). Total quantum scalar irradiance was measured with a model QSL-100 meter (Biospherical Instruments Inc., San Diego, CA). The flux densities of the UV-A and UV-B components of the spectrum were measured with DIX series UV-B and 365A sensors, respectively, with a Spectroline DRC-100X digital radiometer (Spectronics Corporation, Westbury, NY). In these experiments full illumination represented a continuous photon flux density in the visible range of 330 μmol photons m-2 s-1, with UV-A and UV-B maxima of 3.8 x 10^6 and 0.8 x 10^6 mW m-2, respectively. All values reported were the incident fluxes within culture vessels at the immediate surface of the cell suspensions. Aliquot cultures (in duplicate) were harvested after 0, 15 min, 1 h, 3 h, 6 h, 12 h, 24 h and 36 h of UV-irradiation. For each time point, total RNA were isolated from stressed and unstressed cells, reverse-transcribed, differentially labelled (dye swapped), hybridized together (stressed versus unstressed samples) and analyzed with DNA glass microarrays (two slides per each time point) (Custom-commercial array : CyanoCHIP version 2.0, TAKARA). To identify differentially expressed genes, the median of the normalized ratio of Cy5/Cy3 intensity was calculated for each spot of the replicated dye-swap. The results of the analysis were carefully examined to exclude the dye effect between the 2 Cy-swapped arrays. Keywords: UV-irradiation, desiccation, Synechocystis PCC 6803, cyanobacteria, time course, transcription
