Nicotiana tabacum NADP-Malic Enzyme: Cloning, Characterization and Analysis of Biological Role

GABRIELA LETICIA MÜLLER; MARÍA FABIANA DRINCOVICH; CARLOS SANTIAGO ANDREO; MARÍA VALERIA LARA

PLANT AND CELL PHYSIOLOGY

Oxford University Press

Año: 2008 vol. 49 p. 469 - 480

0032-0781

NADP-malic enzyme (NADP-ME) catalyzes the oxidativedecarboxylation of L-malate, producing pyruvate, CO2and NADPH. The photosynthetic role of this enzyme in C4and Crassulacean acid metabolism (CAM) plants has beenwell established; however, the biological role of several nonphotosyntheticisoforms described in C3, C4 and CAM plantsis still speculative. In this study, the characterization ofthe NADP-ME isoforms from Nicotiana tabacum wasperformed. Three different nadp-me transcripts were identifiedin this C3 plant, two of which encode for putativecytosolic isoforms (DQ923118 and EH663836), while thethird encodes for a plastidic counterpart (DQ923119).Although the three transcripts are expressed in vegetative aswell as in reproductive tissues, they display different levels ofexpression. With regards to enzyme activity, root is the tissuethat displays the highest NADP-ME activity. RecombinantNADP-MEs encoded by DQ923118 and DQ923119 wereexpressed in Escherichia coli and their kinetic parameters andresponse to different metabolic effectors were analyzed.Studies carried out with crude extracts and with therecombinant proteins indicate that the cytosolic and plastidicisoforms aggregate as tetramers of subunits of 65 and 63 kDa,respectively. Real-time reverse transcription–PCR studiesshow that the three nadp-me tobacco transcripts responddifferently to several biotic and abiotic stress stimuli. Finally,the physiological role of each isoform is discussed in terms ofthe occurrence, kinetic properties and response to stress. Thestructure of the NADP-ME family in tobacco is comparedwith those of other C3 species.