title: Loss of nuclear gene expression during the phytochrome A-mediated far-red block of greening response.
abstract: We have examined the expression of the HEMA1 gene, which encodes the key chlorophyll synthesis enzyme glutamyl-tRNA reductase, during the phytochrome A-mediated far-red light (FR) block of greening response in Arabidopsis. Our results demonstrate that the FR block of greening comprises two separate responses: a white light (WL) intensity-independent response that requires 3 d of FR and is associated with a loss of expression of the nuclear genes HEMA1 and Lhcb following the transfer to WL (transcriptionally coupled response) and a WL intensity-dependent response that is induced by 1 d of FR and is transcriptionally uncoupled. Both responses required phytochrome A. The transcriptionally uncoupled response correlated with a deregulation of tetrapyrrole synthesis and potential photooxidative damage and was inhibited by cytokinin. The transcriptionally coupled FR response was additive with the loss of expression following Norflurazon-induced photobleaching and was absent in the presence of sucrose or after lower fluence rate (1 micromol m(-2) s(-1)) FR treatments. Both pathways leading to the loss of nuclear gene expression were inhibited by overexpression of NADPH:protochlorophyllide oxidoreductase, indicating a role for plastid signaling in the FR-mediated pathway. The significance of identifying a distinct phytochrome A-mediated plastid signaling pathway is discussed.
authors.affiliation: School of Biological Sciences, University of Southampton, Southampton SO16 7PX, United Kingdom.
authors.forename: Alex C
authors.initials: AC
authors.lastname: McCormac
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Terry
mesh_terms: D000445:Aldehyde Oxidoreductases / Q000235:genetics / Q000378:metabolism; D000622:Aminolevulinic Acid / Q000378:metabolism; D017360:Arabidopsis / Q000235:genetics* / Q000378:metabolism; D029681:Arabidopsis Proteins; D002734:Chlorophyll / Q000096:biosynthesis*; D002736:Chloroplasts / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D003583:Cytokinins / Q000494:pharmacology; D018506:Gene Expression Regulation, Plant / Q000187:drug effects / Q000528:radiation effects; D008027:Light; D045342:Light-Harvesting Protein Complexes; D009249:NADP / Q000378:metabolism; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D018384:Oxidative Stress; D010088:Oxidoreductases / Q000235:genetics / Q000378:metabolism; D044925:Oxidoreductases Acting on CH-CH Group Donors; D045322:Photosynthetic Reaction Center Complex Proteins / Q000235:genetics / Q000378:metabolism; D010834:Phytochrome / Q000378:metabolism*; D051942:Phytochrome A; D011401:Promoter Regions, Genetic / Q000235:genetics; D011724:Pyridazines / Q000494:pharmacology; D015398:Signal Transduction; D013395:Sucrose / Q000494:pharmacology; D015533:Transcriptional Activation
chemical_list: D029681:Arabidopsis Proteins; D003583:Cytokinins; D045342:Light-Harvesting Protein Complexes; D009687:Nuclear Proteins; C497973:PHYA protein, Arabidopsis; D045322:Photosynthetic Reaction Center Complex Proteins; D051942:Phytochrome A; D011724:Pyridazines; D010834:Phytochrome; D002734:Chlorophyll; D009249:NADP; D013395:Sucrose; D000622:Aminolevulinic Acid; D010088:Oxidoreductases; D000445:Aldehyde Oxidoreductases; C067282:glutamyl tRNA reductase; D044925:Oxidoreductases Acting on CH-CH Group Donors; C023886:protochlorophyllide reductase; C008677:norflurazone