| Photosynthetic organisms must acclimate under a sudden increase in photon flux density to prevent photooxidative damage. To identify genes induced by high-light stress in Chlamydomonas reinhardtii, a RT-PCR-based technique called Differential Display was used. Differential Display randomly amplifies the mRNA species of an organism under different environmental stresses enabling the detection of differentially expressed genes. Six light-stress inducible genes (Lsi7.1--Lsi12.1) were identified and cloned. Three of the clones (Lsi7.1, Lsi9.1 and Lsi11.1) showed significant matches with sequences in a Chlamydomonas EST database though only one of these showed similarity to a known protein. Of the six clones, only Lsi12.1 was detectable by Northern hybridization so its expression was further characterized. Lsi12 was induced within 1 hr under high-light, increased 4-fold in 12 hrs and returned to the unstressed level by 24 hrs. Although Lsi12 was clearly induced by high-light, there was a large (4-fold) and rapid (1 hr) increase in expression when cells were challenged with 200 mM NaCl stress suggesting that Lsi12 has a role in the response to stresses other than light; however, the role of Lsi12 in the process of light- and salt-acclimation is unknown. |
