Functional analysis of isoforms of NADPH: protochlorophyllide oxidoreductase (POR), PORB and PORC, in Arabidopsis thaliana.
NADPH:protochlorophyllide oxidoreductase (POR) catalyzes the light-dependent reduction of protochlorophyllide. To elucidate the physiological function of three differentially regulated POR isoforms (PORA, PORB and PORC) in Arabidopsis thaliana, we isolated T-DNA tagged null mutants of porB and porC. The mature seedlings of the mutants had normal photosynthetic competencies, showing that PORB and PORC are interchangeable and functionally redundant in developed plants. In etiolated seedlings, only porB showed a reduction in the photoactive protochlorophyllide and the size of prolamellar bodies (PLBs), indicating that PORB, as well as PORA, functioned in PLB assembly and photoactive protochlorophyllide formation in etiolated seedlings. When illuminated, the etiolated porB seedling was able to green to a similar extent as the wild type, whereas the greening was significantly reduced under low light conditions. During greening, high light irradiation increased the level of PORC protein, and the greening of porC was repressed under high light conditions. The porB, but not porC, etiolated seedling was more sensitive to the far-red block of greening than the wild type, which is caused by depletion of endogenous POR proteins resulting in photo-oxidative damage. These results suggest that, at the onset of greening, PLBs are important for efficient capture of light energy for photoconversion under various light conditions, and PORC, which is induced by high light irradiation, contributes to photoprotection during greening of the etiolated seedlings.
Masuda
Tatsuru
T
Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama, 226-8501 Japan. tmasuda@bio.titech.ac.jp
Fusada
Naoki
N
Oosawa
Naoki
N
Takamatsu
Ken'ichi
K
Yamamoto
Yoshiharu Y
YY
Ohto
Masaaki
M
Nakamura
Kenzo
K
Goto
Koji
K
Shibata
Daisuke
D
Shirano
Yumiko
Y
Hayashi
Hiroaki
H
Kato
Tomohiko
T
Tabata
Satoshi
S
Shimada
Hiroshi
H
Ohta
Hiroyuki
H
Takamiya
Ken-ichiro
K
D017360:Arabidopsis / Q000201:enzymology*; D004269:DNA, Bacterial / Q000235:genetics; D018744:DNA, Plant / Q000235:genetics; D017353:Gene Deletion; D007527:Isoenzymes / Q000378:metabolism*; D016296:Mutagenesis; D044925:Oxidoreductases Acting on CH-CH Group Donors / Q000235:genetics / Q000378:metabolism*; D010788:Photosynthesis; D018087:Plastids / Q000201:enzymology / Q000648:ultrastructure
D004269:DNA, Bacterial; D018744:DNA, Plant; D007527:Isoenzymes; C036483:T-DNA; D044925:Oxidoreductases Acting on CH-CH Group Donors; C023886:protochlorophyllide reductase