title: Clp protease controls chlorophyll b synthesis by regulating the level of chlorophyllide a oxygenase.
abstract: Chlorophyll b is one of the major light-harvesting pigments in green plants and it is essential for optimal light harvesting. Chlorophyll b is synthesized from chlorophyll a by chlorophyllide a oxygenase (CAO) which consists of A, B and C domains. Previously, we demonstrated that the C domain alone has a catalytic function, while the A and B domains control the level of CAO protein in response to chlorophyll b accumulation. We hypothesized that the accumulation of chlorophyll b triggers the proteolytic degradation of CAO. In this study, in order to gain further insight into this regulatory mechanism we screened for mutants that have defects in the control of CAO accumulation. Seeds from a transgenic line of Arabidopsis which overexpressed a CAO-GFP fusion were mutagenized and their progenies were screened by laser-scanning confocal microscopy for mutants showing an elevated level of GFP fluorescence. One particular mutant (dca1) exhibited stronger GFP fluorescence and accumulated a GFP-CAO fusion protein at a higher level. Concomitantly, the chlorophyll a to b ratio decreased in this mutant. The mutation in the dca1 mutant was mapped to the ClpC1 gene, thereby indicating that a chloroplast Clp protease is involved in regulating chlorophyll b biosynthesis through the destabilization of CAO protein in response to the accumulation of chlorophyll b.
authors.affiliation: Institute of Low Temperature Science, Hokkaido University, N19 W8 Kita-ku, Sapporo, Japan.
authors.forename: Eiki
authors.initials: E
authors.lastname: Nakagawara
authors.forename: Yasuhito
authors.initials: Y
authors.lastname: Sakuraba
authors.forename: Akihiro
authors.initials: A
authors.lastname: Yamasato
authors.forename: Ryouichi
authors.initials: R
authors.lastname: Tanaka
authors.forename: Ayumi
authors.initials: A
authors.lastname: Tanaka
mesh_terms: D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000378:metabolism*; D002734:Chlorophyll / Q000096:biosynthesis*; D002735:Chlorophyllides / Q000378:metabolism; D002736:Chloroplasts / Q000201:enzymology / Q000378:metabolism; D003001:Cloning, Molecular; D018548:Cotyledon / Q000378:metabolism; D049071:Endopeptidase Clp / Q000235:genetics / Q000378:metabolism*; D005816:Genetic Complementation Test; D049452:Green Fluorescent Proteins / Q000235:genetics; D009154:Mutation; D010105:Oxygenases / Q000378:metabolism*; D030821:Plants, Genetically Modified; D021122:Protein Subunits; D011993:Recombinant Fusion Proteins / Q000235:genetics; D012639:Seeds / Q000201:enzymology / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D002735:Chlorophyllides; D021122:Protein Subunits; D011993:Recombinant Fusion Proteins; D002734:Chlorophyll; D049452:Green Fluorescent Proteins; C037184:chlorophyll b; D010105:Oxygenases; D049071:Endopeptidase Clp