J. Kropat et al., CHLOROPHYLL PRECURSORS ARE SIGNALS OF CHLOROPLAST ORIGIN INVOLVED IN LIGHT INDUCTION OF NUCLEAR HEAT-SHOCK GENES, Proceedings of the National Academy of Sciences of the United Statesof America, 94(25), 1997, pp. 14168-14172
Coordination between the activities of organelles and the nucleus requ
ires the exchange of signals, Using Chlamydomonas, we provide evidence
that plastid-derived chlorophyll precursors may replace light in the
induction of two nuclear heat-shock genes (HSP70A and HSP70B) and thus
qualify as plastidic signal. Mutants defective in the synthesis of Mg
-protoporphyrin IX were no longer inducible by light. Feeding of Mg-pr
otoporphyrin IX or its dimethyl ester to wild-type or mutant cells in
the dark resulted in induction. The analysis of HSP70A promoter mutant
s that do or do not respond to light revealed that these chlorophyll p
recursors specifically activate the light signaling pathway. Activatio
n of gene expression was not observed when protoporphyrin IX, protochl
orphyllide, or chlorophyllide were added: A specific interaction of de
fined chlorophyll precursors with factor(s) that regulate nuclear gene
expression is suggested.