Phytochrome-regulated PIL1 derepression is developmentally modulated.
We define the photoresponsiveness, during seedling de-etiolation, of PHYTOCHROME-INTERACTING FACTOR 3-LIKE 1 (PIL1), initially identified by microarray analysis as an early-response gene that is robustly repressed by first exposure to light. We show that PIL1 mRNA abundance declines rapidly, with a half-time of 15 min, to a new steady-state level, 10-fold below the initial dark level, within 45 min of first exposure to red light. Analysis of phy-null mutants indicates that multiple phytochromes, including phyA and phyB, impose this repression. Conversely, PIL1 expression is rapidly derepressed by subsequent far-red irradiation of previously red light-exposed seedlings. However, the magnitude of this derepression is modulated over time, in a biphasic manner, in response to increasing duration of pre-exposure to continuous red light: (i) an early phase (up to about 6 h) of relatively rapidly increasing effectiveness of far-red reversal of repression, as declining phyA levels relieve initial very low fluence suppression of this response; and (ii) a second phase (beyond 6 h) of gradually declining effectiveness of far-red reversal, to only 20% of maximal derepression, within 36 h of continuous red light exposure, with no evidence of circadian modulation of this responsiveness, an observation in striking contrast to a previous report for entrained, green seedlings exposed to vegetative shade. These data, together with analysis of phytochrome signaling mutants and overexpressors with aberrant de-etiolation phenotypes, suggest that the second-phase decline in robustness of PIL1 derepression is an indirect consequence of the global developmental transition from the etiolated to the de-etiolated state, and that circadian coupling of derepression requires entrainment.
Hwang
Yong-Sic
YS
Department of Plant and Microbial Biology, University of California, Berkeley, CA 94720, USA.
Quail
Peter H
PH
D017360:Arabidopsis / Q000235:genetics* / Q000254:growth & development / Q000528:radiation effects; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental / Q000528:radiation effects; D018506:Gene Expression Regulation, Plant / Q000528:radiation effects; D005838:Genotype; D008027:Light; D008954:Models, Biological; D009024:Morphogenesis / Q000528:radiation effects; D009154:Mutation / Q000235:genetics; D010641:Phenotype; D051942:Phytochrome A / Q000378:metabolism*; D051939:Phytochrome B / Q000378:metabolism*; D012097:Repressor Proteins / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism
D029681:Arabidopsis Proteins; C456844:PIL1 protein, Arabidopsis; D051942:Phytochrome A; D012097:Repressor Proteins; D014157:Transcription Factors; D051939:Phytochrome B; C471983:AT2G32950 protein, Arabidopsis; D044767:Ubiquitin-Protein Ligases