A plant porphyria related to defects in plastid import of protochlorophyllide oxidoreductase A

doi:10.1073/pnas.0610934104

A plant porphyria related to defects in plastid import of protochlorophyllide oxidoreductase A

*Université Joseph Fourier et Centre National de la Recherche Scientifique Unité Mixte de Recherche 5575, CERMO, BP53, F-38041 Grenoble Cedex 9, France;
^‡Lehrstuhl für Pflanzenphysiologie, Universität Bayreuth, Universitätsstrasse 30, D-95447 Bayreuth, Germany; and
^§Department of Crop and Soil Sciences, Washington State University, Pullman, WA 99164-6420

Contributed by Diter von Wettstein, December 12, 2006 (received for review November 11, 2006)

Abstract

The plastid envelope of higher plant chloroplasts is a focal point of plant metabolism. It is involved in numerous pathways, including tetrapyrrole biosynthesis and protein translocation. Chloroplasts need to import a large number of proteins from the cytosol because most are encoded in the nucleus. Here we report that a loss-of-function mutation in the outer plastid envelope 16-kDa protein (oep16) gene causes a conditional seedling lethal phenotype related to defects in import and assembly of NADPH:protochlorophyllide (Pchlide) oxidoreductase A. In the isolated knockout mutant of Arabidopsis thaliana, excess Pchlide accumulated in the dark operated as photosensitizer and provoked cell death during greening. Our results highlight the essential role of the substrate-dependent plastid import pathway of precursor Pchlide oxidoreductase A for seedling survival and the avoidance of developmentally programmed porphyria in higher plants.

Footnotes

^¶To whom correspondence may be addressed. E-mail: diter{at}wsu.edu or steffen.reinbothe{at}ujf-grenoble.fr
↵ ^†Present address: Lehrstuhl für Pflanzenphysiologie, Ruhr-Universität Bochum, Universitätsstrasse 150, D-44801 Bochum, Germany.
Author contributions: S.P., J.-M.B., G.T., C.R., and S.R. designed research; S.P., A.S., F.B., A.L., I.S., C.R., and S.R. performed research; D.v.W., C.R., and S.R. analyzed data; and S.R. wrote the paper.
The authors declare no conflict of interest.
This article contains supporting information online at www.pnas.org/cgi/content/full/0610934104/DC1.
Abbreviations:

Pchlide,

protochlorophyllide;

pPORA/B,

precursor Pchlide oxidoreductases A and B;

DHFR,

dihydrofolate reductase;

5-ALA,

5-aminolevulinic acid;

trans A,

transit peptide of pPORA.