Change in gene expression in Chlamydomonas reinhardtii upon heat shock

This was an accompanying experiment. Previously, the expression of genes hsp70A and hsp70B had been established as being tetrapyrrole-dependent (Kropat et al., 1997, 2000). Since both are well-known heat-shock proteins, we performed a one-step heat shock treatment by shifting the temperatures from 23°C to 42°C for 45 min. Moreover, this experiment served as an additional global control to further test the reliability of the microarray and our general conditions since the heat shock response in general is quite well investigated. 3988 responding genes were identified. Among them are 22 genes known to be regulated by HS, selected examples are: the heat shock proteins 22A, 22B and 22C, here leading the list of top-regulated genes on place 1 with a FC of 91297 (22A), place 3 with a FC of 45023 (22B) and place 5 with a FC of 6570 (22C). Other examples are several DnaJ-like proteins or the ClpB chaperone, from the Hsp100 family. In total the analysis comprises 8 samples. For heat shock, a 20 ml culture with ~4 × 106 cells per ml in a 100 ml Erlenmeyer flask was incubated at 42°C for 45 min in the light with shaking. Control cultures were incubated in the light at 23°C (von Gromoff et al., 1989; Kropat et al., 2000). For harvest, cultures were chilled immediately by pouring them onto crushed ice, centrifuged (5 min, 3000 g, 4°C) and resuspended in 1 ml TAP. This procedure was repeated three times, resulting in 3 biological replicates.