Malate and fumarate emerges as key players in primary metabolism: Arabidopsis thaliana overexpressing C4-NADP-ME offer a way to manipulate the levels of malate and to analyze the physiological consequences

VERÓNICA MAURINO; HOLGER FAHNENSTICH; MARIANA SAIGO; MARÍA FABIANA DRINCOVICH; MARÍA INÉS ZANOR; ALISDAIR FERNI; ULF-INGO FLÜGGE

Glasgow, Reino Unido

Congreso; 14th Photosynthesis Congress; 2007

International Society of Photosynthesis Research

Maize C4 NADP-malic enzyme was expressed under control of the CamV35S promoter in Arabidopsis thaliana. An increase in the plastidic NADP-ME activity led to a pale green phenotype in plants growing in short days. Under these conditions, MEm plants have a decreased fresh weight/area ratio and thinner leaf sections. Measurements of chlorophyll content and chlorophyll fluorescence indicated an altered photosynthetic metabolism. While no differences in morphology and development were evident in long-day growth conditions, a parallel analysis of metabolite levels of rosettes from transgenic plants grown in different photoperiods revealed that plants grown in both long and short days showed a disturbed metabolic profile. Dark-induced senescence of intact plants progressed more rapidly in MEm plants compared to the wild-type. Interestingly, a retardation of senescence in the transgenic lines was gains by exogenous supply of glucose, sucrose and malate, suggesting that the lack of a rapid energy source is likely to be the initial factor leading to the induction of senescence in these plants. A fairly complete picture of primary metabolism assessed by GC-MS and the in vitro metabolic complementation assays allow us to conclude that MEm transgenic plants entered dark induced senescence more rapidly due to an accelerated starvation. Comparison of the data obtained for the MEm transformants and the wild-type indicated that extremely low levels of malate and fumarate are responsible for the accelerated dark-induced senescence encountered in the MEm plants. Reinforcing previous results, our data indicate that malate and fumarate are key players in the primary metabolism of Arabidopsis thaliana.