Identification of Mg-protoporphyrin IX as a chloroplast signal that mediates the expression of nuclear genes
Kropat, J.1, Oster, U.2, Rüdiger, W.2, Beck, C.F.1
1Institut für Biologie III, Universität Freiburg, Schänzlestraße 1, D-79100 Freiburg, Germany
2Botanisches Institut, Universität München, Menzinger Straße 67, D-80638 München, Germany
Coordination between the activities of organelles and nucleus requires the exchange of signals. One of these signals has been proposed to be a chloroplast generated factor that controls the activities of nuclear genes. 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-protoporphyrin IX or ist dimethyl ester to wild-type or mutant cells in the dark resulted in induction. Light was shown to cause an increase in chlorophyll precursor pools. Conditions that prevented this increase did not result in induction. The analysis of HSP70A promoter mutants that do or do not respond to light revealed that that these chlorophyll precursors specifically activate the light signaling pathway. Activation of gene expression was not observed when protoporphyrin IX, protochlorophyllide, or chlorophyllide were added. A specific interaction of defined chlorophyll precursors with factor(s) that regulate nuclear gene expression is suggested.
Kropat, J., Oster, U., Rü,diger,W., Beck, C.F. (1997) Chlorophyll precursors are signals of chloroplast origin involved in light induction of nuclear heat-shock genes. Proc. Natl. Acad. Sci. USA 94:14168-14172
| LOCATION |
DATE |
TIME |
| Lecture Hall I |
Monday, April 6 |
02:20 pm |