title: The light stress-induced protein ELIP2 is a regulator of chlorophyll synthesis in Arabidopsis thaliana.
abstract: The early light-induced proteins (ELIPs) belong to the multigenic family of pigment-binding light-harvesting complexes. ELIPs accumulate transiently and are believed to play a protective role in plants exposed to high levels of light. Constitutive expression of the ELIP2 gene in Arabidopsis resulted in a marked reduction of the pigment content of the chloroplasts, both in mature leaves and during greening of etiolated seedlings. The chlorophyll loss was associated with a decrease in the number of photosystems in the thylakoid membranes, but the photosystems present were fully assembled and functional. A detailed analysis of the chlorophyll-synthesizing pathway indicated that ELIP2 accumulation downregulated the level and activity of two important regulatory steps: 5-aminolevulinate synthesis and Mg-protoporphyrin IX (Mg-Proto IX) chelatase activity. The contents of glutamyl tRNA reductase and Mg chelatase subunits CHLH and CHLI were lowered in response to ELIP2 accumulation. In contrast, ferrochelatase activity was not affected and the inhibition of Heme synthesis was null or very moderate. As a result of reduced metabolic flow from 5-aminolevulinic acid, the steady state levels of various chlorophyll precursors (from protoporphyrin IX to protochlorophyllide) were strongly reduced in the ELIP2 overexpressors. Taken together, our results indicate that the physiological function of ELIPs could be related to the regulation of chlorophyll concentration in thylakoids. This seems to occur through an inhibition of the entire chlorophyll biosynthesis pathway from the initial precursor of tetrapyrroles, 5-aminolevulinic acid. We suggest that ELIPs work as chlorophyll sensors that modulate chlorophyll synthesis to prevent accumulation of free chlorophyll, and hence prevent photooxidative stress.
authors.affiliation: CEA/Cadarache, IBEB, Service de Biologie Végétale et de Microbiologie Environnementales, UMR 6191 CNRS-CEA-Aix Marseille Univ., F-13108 Saint-Paul-lez-Durance, France.
authors.forename: Tzvetelina
authors.initials: T
authors.lastname: Tzvetkova-Chevolleau
authors.forename: Fabrice
authors.initials: F
authors.lastname: Franck
authors.forename: Ali E
authors.initials: AE
authors.lastname: Alawady
authors.forename: Luca
authors.initials: L
authors.lastname: Dall'Osto
authors.forename: Frédéric
authors.initials: F
authors.lastname: Carrière
authors.forename: Roberto
authors.initials: R
authors.lastname: Bassi
authors.forename: Bernhard
authors.initials: B
authors.lastname: Grimm
authors.forename: Laurent
authors.initials: L
authors.lastname: Nussaume
authors.forename: Michel
authors.initials: M
authors.lastname: Havaux
mesh_terms: D017360:Arabidopsis / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000096:biosynthesis / Q000235:genetics* / Q000528:radiation effects; D002734:Chlorophyll / Q000096:biosynthesis*; D005294:Ferrochelatase / Q000235:genetics / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D008027:Light / Q000009:adverse effects; D018384:Oxidative Stress; D010788:Photosynthesis; D018515:Plant Leaves / Q000502:physiology; D030821:Plants, Genetically Modified / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; C481743:ELIP2 protein, Arabidopsis; D002734:Chlorophyll; D005294:Ferrochelatase