The HSP70 chaperone machines of Chlamydomonas are induced by cold stress

The responses of Chlamydomonas reinhardtii cells to low temperatures have not been extensively studied compared with other stresses. Like other organisms, this green alga has heat shock protein 70s (HSP70s) that are located in chloroplast, mitochondrion and cytosol. To test whether temperature downshifts affected HSP70s synthesis, we used real-time PCR and protein gel blot analysis. C. reinhardtii cells exposed to cold stress show increased HSP70s mRNA levels. Genes encoding other components of HSP70 chaperone machines (e.g. CGE1, CDJ1, HSP90C and HSP90A) are also up-regulated in response to decreased temperature. We demonstrated that the accumulation of all analyzed mRNA occur more slowly and with reduced amplitude in cells exposed to cold than in cells treated with heat. Furthermore, C. reinhardtii cells display the splicing of the CGE1 transcript that was dependent on low temperature. Finally, the transcription regulator of C. reinhardtii HSF1 is also cold-responsive, suggesting its role in the transcriptional regulation of HSP genes at low temperature.