Identification of genes expressed in response to light stress in leaves of Arabidopsis thaliana using RNA differential display.

The plant cell responds to light stress by the expression of genes encoding specific stress proteins with possible protective functions. Five genes, the mRNA levels of which increased drastically in response to light stress in mature green leaves of Arabidopsis thaliana were identified and isolated by the differential display technique. These genes were designated Lsr1-Lsr5 (light stress-regulated). Northern blot analysis demonstrated that the transcript level of Lsr1-Lsr5 increased 4- to 17-fold under light stress conditions as compared with leaves incubated at low intensity light. Further analysis of the Lsr1-Lsr5 transcript level under cold stress, heat shock, wounding, desiccation, salt stress, oxidative stress and UV-A irradiation showed that the expression of all five genes was triggered by more than one stress factor. Thus, it was expected that isolated genes encode proteins involved in general stress responses. Homology searches revealed that all of the isolated cDNAs were represented in the GenBank in genomic DNAs and expressed sequence tag (EST) cDNA clones. The Lsr1-Lsr4 genes encoded cytoplasmic proteins with assigned identities, such as ERD15 (early responsive to dehydration), ACT2 (actin 2), LEA14 (late embryogenesis abundant) and MT1a (metallothionein class 1a), respectively. Light stress had not yet been reported to induce or enhance the expression of these genes. The Lsr5 clone encoded a novel protein with high similarity to beta-1,3-galactosyltransferases from human and primates predicted to be located in the Golgi body. Three ORFs homologous to the Lsr5 gene were found on chromosome I and IV of Arabidopsis indicating that a multigene family of these proteins exists in plants. The possible role of Lsr gene products in light stress defences is discussed.