Poster: Photosynthesis
Abs #
348: Chlamydomonas Mutants Affecting Regulation of the cabII-1 Promoter by High Light
Transfer from low light to high light conditions represses accumulation of mRNAs of genes encoding light-harvesting chlorophyll a/b-binding proteins of photosystem II in Chlamydomonas reinhardtii. In other green algae, this regulation appears to involve a chloroplast-nucleus signal transduction pathway that responds to the redox state of plastoquinone. We have taken a molecular genetic approach to investigate how expression of the cabII-I gene is regulated by light intensity and to identify components of this signal transduction pathway. Following EMS mutagenesis, we isolated mutants with aberrant expression of a transcriptional fusion of the cabII-1 promoter with a reporter gene encoding arylsulfatase (ARS). The parental strain exhibited light intensity-dependent ARS expression, with decreased ARS activity in high light (HL; 500 mmol photons m-2 s-1) compared to low light (LL; 50 mmol photons m-2 s-1). In contrast, the lex1 mutant exhibited no decrease in ARS activity when grown in HL. Genetic analysis showed that the lex1 mutation affects a single nuclear gene. To facilitate the identification of genes such as LEX1, we isolated insertional mutants obtained with a plasmid harboring the ble gene. These mutants exhibited higher ARS activities when grown in HL, and mRNA levels of the endogenous cabII-1 gene were also altered upon transfer of cells from LL to HL. Determination of genomic sequences flanking the inserts in these mutants by TAIL PCR will enable us to identify genes that regulate cabII-I expression in response to changes in light intensity.
