title: Effects of chlorophyllide a oxygenase overexpression on light acclimation in Arabidopsis thaliana.
abstract: Land plants change the compositions of light-harvesting complexes (LHC) and chlorophyll (Chl) a/b ratios in response to the variable light environments which they encounter. In this study, we attempted to determine the mechanism which regulates Chl a/b ratios and whether the changes in Chl a/b ratios are essential in regulation of LHC accumulation during light acclimation. We hypothesized that changes in the mRNA levels for chlorophyll a oxygenase (CAO) involved in Chl b biosynthesis are an essential part of light response of Chl a/b ratios and LHC accumulation. We also examined the light-intensity dependent response of CAO-overexpression and wild-type Arabidopsis thaliana plants. When wild-type plants were acclimated from low-light (LL) to high-light (HL) conditions, CAO mRNA levels decreased and the Chl a/b ratio increased. In transgenic plants overexpressing CAO, the Chl a/b ratio remained low under HL conditions; thereby suggesting that changes in the CAO mRNA levels are necessary for those in Chl a/b ratios upon light acclimation. Under HL conditions, the accumulation of Lhcb1, Lhcb3 and Lhcb6 was enhanced in plants overexpressing CAO. On the contrary, in a CAO-deficient mutant, chlorina 1-1, theaccumulation of Lhcb1, Lhcb2, Lhcb3, Lhcb6 and Lhca4 was reduced. In comparison to wild-type, beta-carotene levels were reduced in CAO-overexpressing plants, while they were elevated in chlorina 1-1 mutants. These results imply that the transcriptional control of CAO is a part of the regulatory mechanism for the accumulation of a distinct set of LHC proteins upon light acclimation.
authors.affiliation: Institute of Low Temperature Science, CREST, Hokkaido University, Japan Science and Technology Corporation, N19 W8, 060-0819 Sapporo, Kita-ku, Japan. rtanaka@lowtem.hokudai.ac.jp
authors.forename: Ryouichi
authors.initials: R
authors.lastname: Tanaka
authors.forename: Ayumi
authors.initials: A
authors.lastname: Tanaka
mesh_terms: D000064:Acclimatization; D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics / Q000528:radiation effects*; D002734:Chlorophyll / Q000378:metabolism; D000077194:Chlorophyll A; D018506:Gene Expression Regulation, Plant; D008027:Light; D045342:Light-Harvesting Protein Complexes / Q000378:metabolism; D010105:Oxygenases / Q000235:genetics* / Q000378:metabolism*; D030821:Plants, Genetically Modified; D012333:RNA, Messenger / Q000378:metabolism; D013997:Time Factors; D019207:beta Carotene / Q000378:metabolism
chemical_list: D045342:Light-Harvesting Protein Complexes; D012333:RNA, Messenger; D019207:beta Carotene; D002734:Chlorophyll; C037184:chlorophyll b; D010105:Oxygenases; C115272:chlorophyll a oxygenase; D000077194:Chlorophyll A