Functions Of NAD(H) Kinases In Arabidopsis Thaliana Under Abiotic Stress

Environmental stress such as salt, drought, chilling, waterlogging are the main restriction factors of crop production. Plant can produce and accumulated reactive oxygen species that cause oxidative stress, they are highly reactive and toxic, and can lead to the oxidative destruction of cells.NAD(H) kinase may play an important role in the synthesis of NADPH. Three distinct NADK isoforms (NADK1, NADK2 and NADK3) have been identified in Arabidopsis. However, the physiological roles of NADKs under environmental stress remain unclear. In present study, we investigated the physiological role of Arabidiposis NADKs. The subcellular localization and expression pattern of NAD(H) kinase under stress were analyzed through molecular methods. The function of NAD(H) kinase in abiotic stress response was invesgated using the Arabidopsis mutant of NAD(H) kinase.A comparison of the sequence data gained from bacteria and yeast NAD kinases with the Arabidopsis genome reveals three genes encoding putative NAD(H) kinases. The expression pattern of NADKs shows the transcription of NADK3 was induced significantly by cold, MVor ABA treatment, this suggests that NADK3 may take part in the response to stress of plant.NADK2 protein was predicted to have a chloroplast targeting sequence in the N-terminal region. 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 nadk.2 plants. The nadk.2 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. The analysis of NADK3 mutant suggests that the loss of NADK3 may make plants be sensitive to oxidative stress.So that, NAD(H)K is a key kinase family in ROS scavenging system. Our work will make us understand oxidative stress further.