Project description:Aim: To discover the target genes of Golden2-like transcription factors in Arabidopsis. Background: The Golden2-like (GLK) family of transcription factors is essential for proper chloroplast development in several plant species. In Arabidopsis, there are two largely redundant GLK genes, GLK1 and GLK2. Double mutant plants are pale green and reduced in stature. Their most notable chloroplast-related phenotype is impaired thylakoid membrane appression and reduction in steady-state levels of Photosystem II components. GLK proteins group within the GARP family of myb transcription factors; however, the genes they regulate remain unknown. Experimental Design: We have employed a two-component dexamethasone-inducible expression system [1]. An overexpressed fusion protein comprising the glucocorticoid receptor (GR), the lac repressor and the Gal4 activation domain resides in the plant cytoplasm. This protein, termed LHGR-N, enters the nucleus once dexamethasone binds to the GR domain. It then activates transcription from the lac operator promoter sequences present on separate transgenes which carry the cDNA to be induced. Since overexpression of either GLK1 or GLK2 is sufficient to complement the mutant phenotype, we reasoned that induction of expression of GLK1 and GLK2 cDNAs in the glk1;glk2 double mutant background should allow determination of their downstream genetic targets. In the first case, we decided to focus on GLK1 only. Genetic lines: Plants carrying a single copy of the LHGR-N transgene, conferring kanamycin resistance, were crossed with glk1;glk2 double mutant plants. A single homozygous F3 line was selected on the basis of pale green mutant phenotype and kanamycin resistance. This line was transformed with a construct carrying the GLK1 cDNA downstream of six repeats of the lac operator (pOp6) and a single CaMV minimal promoter. This construct confers hygromycin resistance. Transformants were confirmed by PCR and Southern blot, before being selected on the basis of transcript accumulation following induction by dexamethasone. The line with the strongest induction response was chosen for microarray experiments. Tissues: Approx. 100 10-day-old seedlings were grown on MS plates and transferred to 100 ml liquid MS for two further days prior to induction. Whole seedlings were harvested. Treatment: Either a) 10 uM dexamethasone dissolved in DMSO (INDUCED samples) or b) 0.1% v/v DMSO (CONTROL samples). Samples were harvested 4 and 24 hours post-treatment. Separate vessels were used for each time point and treatment. Two complete replicates were performed. Reference1. Craft, J. et al. (2005) Plant J. 41 899-918. 10 samples were used in this experiment.

Project description:Aim: To discover the target genes of Golden2-like transcription factors in Arabidopsis. Background: The Golden2-like (GLK) family of transcription factors is essential for proper chloroplast development in several plant species. In Arabidopsis, there are two largely redundant GLK genes, GLK1 and GLK2. Double mutant plants are pale green and reduced in stature. Their most notable chloroplast-related phenotype is impaired thylakoid membrane appression and reduction in steady-state levels of Photosystem II components. GLK proteins group within the GARP family of myb transcription factors; however, the genes they regulate remain unknown. Experimental Design: We have employed a two-component dexamethasone-inducible expression system [1]. An overexpressed fusion protein comprising the glucocorticoid receptor (GR), the lac repressor and the Gal4 activation domain resides in the plant cytoplasm. This protein, termed LHGR-N, enters the nucleus once dexamethasone binds to the GR domain. It then activates transcription from the lac operator promoter sequences present on separate transgenes which carry the cDNA to be induced. Since overexpression of either GLK1 or GLK2 is sufficient to complement the mutant phenotype, we reasoned that induction of expression of GLK1 and GLK2 cDNAs in the glk1;glk2 double mutant background should allow determination of their downstream genetic targets. In the first case, we decided to focus on GLK1 only. Genetic lines: Plants carrying a single copy of the LHGR-N transgene, conferring kanamycin resistance, were crossed with glk1;glk2 double mutant plants. A single homozygous F3 line was selected on the basis of pale green mutant phenotype and kanamycin resistance. This line was transformed with a construct carrying the GLK1 cDNA downstream of six repeats of the lac operator (pOp6) and a single CaMV minimal promoter. This construct confers hygromycin resistance. Transformants were confirmed by PCR and Southern blot, before being selected on the basis of transcript accumulation following induction by dexamethasone. The line with the strongest induction response was chosen for microarray experiments. Tissues: Approx. 100 10-day-old seedlings were grown on MS plates and transferred to 100 ml liquid MS for two further days prior to induction. Whole seedlings were harvested. Treatment: Either a) 10 uM dexamethasone dissolved in DMSO (INDUCED samples) or b) 0.1% v/v DMSO (CONTROL samples). Samples were harvested 4 and 24 hours post-treatment. Separate vessels were used for each time point and treatment. Two complete replicates were performed. Reference1. Craft, J. et al. (2005) Plant J. 41 899-918.

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Shade represses photosynthetic genes by disrupting the DNA binding of GOLDEN2-LIKE1

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