NADK2, an Arabidopsis chloroplastic NAD kinase, plays a vital role in both chlorophyll synthesis and chloroplast protection.
As one of terminal electron acceptors in photosynthetic electron transport chain, NADP receives electron and H(+) to synthesize NADPH, an important reducing energy in chlorophyll synthesis and Calvin cycle. NAD kinase (NADK), the catalyzing enzyme for the de novo synthesis of NADP from substrates NAD and ATP, may play an important role in the synthesis of NADPH. NADK activity has been observed in different sub-cellular fractions of mitochondria, chloroplast, and cytoplasm. Recently, two distinct NADK isoforms (NADK1 and NADK2) have been identified in Arabidopsis. However, the physiological roles of NADKs remain unclear. In present study, we investigated the physiological role of Arabidiposis NADK2. Sub-cellular localization of the NADK2-GFP fusion protein indicated that the NADK2 protein was localized in the chloroplast. The NADK2 knock out mutant (nadk2) showed obvious growth inhibition and smaller rosette leaves with a pale yellow color. Parallel to the reduced chlorophyll content, the expression levels of two POR genes, encoding key enzymes in chlorophyll synthesis, were down regulated in the nadk2 plants. The nadk2 plants also displayed hypersensitivity to environmental stresses provoking oxidative stress, such as UVB, drought, heat shock and salinity. These results suggest that NADK2 may be a chloroplast NAD kinase and play a vital role in chlorophyll synthesis and chloroplast protection against oxidative damage.
Chai
Mao-Feng
MF
National Laboratory of Plant Physiology and Biochemistry, College of Biological Sciences, China Agricultural University, 100094 Beijing, China.
Chen
Qi-Jun
QJ
An
Rui
R
Chen
Ye-Miao
YM
Chen
Jia
J
Wang
Xue-Chen
XC
D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000166:cytology / Q000201:enzymology* / Q000235:genetics; D002734:Chlorophyll / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D002736:Chloroplasts / Q000502:physiology*; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D006358:Hot Temperature; D008969:Molecular Sequence Data; D009249:NADP / Q000378:metabolism; D010641:Phenotype; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000235:genetics / Q000378:metabolism*; D018526:Plant Transpiration; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D012965:Sodium Chloride; D014466:Ultraviolet Rays
D002734:Chlorophyll; D012965:Sodium Chloride; D009249:NADP; D017853:Phosphotransferases (Alcohol Group Acceptor); C021844:NAD kinase