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MOLECULAR AND GENETIC ANALYSIS OF A RETROGRADE SIGNALING PATHWAY FROM THE PLASTID TO THE NUCLEUS
Author(s) -
Chory J.,
Larkin R.,
Surpin M.,
Mochizuki N.,
Brusslan J.
Publication year - 2000
Publication title -
journal of phycology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.85
H-Index - 127
eISSN - 1529-8817
pISSN - 0022-3646
DOI - 10.1046/j.1529-8817.1999.00001-40.x
Subject(s) - biology , nuclear gene , chloroplast , mutant , plastid , genetics , microbiology and biotechnology , gene , genome
Chloroplast development requires coordinate nuclear and chloroplast gene expression. A putative signal from the chloroplast couples the transcription of certain nuclear genes encoding photosynthesis‐related proteins with chloroplast function. We have identified five Arabidopsis nuclear genes ( GUN 1‐ GUN 5) necessary for coupling the expression of some nuclear genes to the functional state of the chloroplast. Homozygous recessive gun mutations allow nuclear gene expression in the absence of chloroplast development. GUN 1 mutants have no visible phenotype in white light, but GUN 1 mutations interfere with the switch from heterotrophic to photosynthetic growth in young seedlings. GUN 2‐5 are pale. Double mutant studies suggest that gun1 affects a separate pathway from GUN 2, 3, 4, and 5. GUN 2 and GUN 3 are allelic to the known photomorphogenetic mutants, hy1 and hy2, involved in phytochromobilin biosynthesis downstream from heme. GUN 5 encodes the ChlH subunit of Mg‐chelatase, and GUN 4 encodes a novel chloroplast protein that is essential for chlorophyll accumulation. GUN 4 does not appear to be required for the synthesis of protochlorophyllide from 5‐aminolevulinic acid, which suggests that GUN 4 might be required for the early steps and/or the late steps of chlorophyll synthesis or another process that is required for chlorophyll accumulation. Our data suggest that certain perturbations of the tetrapyrrole biosynthetic pathway generate a signal from chloroplasts that causes transcriptional repression of nuclear genes encoding plastid‐localized proteins. The precise nature of this signal and the mechanism by which this signal is transduced to the nucleus is under investigation.