Differential regulation of chlorophyll a oxygenase genes in rice.
Chlorophyll b is synthesized from chlorophyll a by chlorophyll a oxygenase. We have identified two genes (OsCAO1 and OsCAO2) from the rice genome that are highly homologous to previously studied chlorophyll a oxygenase (CAO) genes. They are positioned in tandem, probably resulting from recent gene duplications. The proteins they encode contain two conserved functional motifs - the Rieske Fe-sulfur coordinating center and a non-heme mononuclear Fe-binding site. OsCAO1 is induced by light and is preferentially expressed in photosynthetic tissues. Its mRNA level decreases when plants are grown in the dark. In contrast, OsCAO2 mRNA levels are higher under dark conditions, and its expression is down-regulated by exposure to light. To elucidate the physiological function of the CAO genes, we have isolated knockout mutant lines tagged by T-DNA or Tos17. Mutant plants containing a T-DNA insertion in the first intron of the OsCAO1 gene have pale green leaves, indicating chlorophyll b deficiency. We have also isolated a pale green mutant with a Tos17 insertion in that OsCAO1 gene. In contrast, OsCAO2 knockout mutant leaves do not differ significantly from the wild type. These results suggest that OsCAO1 plays a major role in chlorophyll b biosynthesis, and that OsCAO2 may function in the dark.
Lee
Sichul
S
National Research Laboratory of Plant Functional Genomics, Division of Molecular and Life Sciences, Pohang University of Science and Technology (POSTECH), Pohang, 790-784, Korea.
Kim
Jin-Hong
JH
Yoo
Eun Sang
ES
Lee
Choon-Hwan
CH
Hirochika
Hirohiko
H
An
Gynheung
G
D002734:Chlorophyll / Q000737:chemistry / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D004269:DNA, Bacterial / Q000235:genetics; D005453:Fluorescence; D020869:Gene Expression Profiling; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D005838:Genotype; D005966:Glucuronidase / Q000235:genetics / Q000378:metabolism; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D016254:Mutagenesis, Insertional; D009154:Mutation; D012275:Oryza / Q000737:chemistry / Q000201:enzymology / Q000235:genetics*; D010105:Oxygenases / Q000235:genetics* / Q000378:metabolism; D010641:Phenotype; D010802:Phylogeny; D010860:Pigments, Biological / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D030821:Plants, Genetically Modified; D018749:RNA, Plant / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013050:Spectrometry, Fluorescence / Q000379:methods
D004269:DNA, Bacterial; D007527:Isoenzymes; D010860:Pigments, Biological; D010940:Plant Proteins; D018749:RNA, Plant; C036483:T-DNA; D002734:Chlorophyll; D010105:Oxygenases; C115272:chlorophyll a oxygenase; D005966:Glucuronidase