PARENT SESSION

Symposium S6D Crop photosynthesis, agricultural biotechnology
Thursday September 2nd, 2004 10:20 AM-12:20 PM Room 510A
Chair: Vince DeLuca
Co-Chair: Maurice Ku

Genetic engineering of photosynthetic C1 metabolism: (1) formaldehyde-assimilation and (2) augmentation of CO₂ fixation. Katsura Izui^*,1, Li-mei Chen¹, Kun-zhi Li¹, Hiroya Yurimoto², Yasuyoshi Sakai², Nobuo Kato², Tsuyoshi Furumoto¹, Masahiro Tamoi³, ¹ Graduate School of Biostudies, Kyoto University, Kyoto, Kyoto, Japan² Graduate School of Agriculture, Kyoto, Kyoto, Japan³ Graduate School of Advanced Life Science, Kinki University, Nara, Nara, Japan

ABSTRACT- To augment photosynthetic productivity of C3 plants by genetic engineering, we are trying to install either of the following two metabolic pathways in plants: (1) Direct reduction of CO₂ to HCHO, and then fixation of HCHO on ribulose-5-P to yield fructose-6-P by the ribulose monophosphate pathway inherent in methylotrophs, and (2) Pumping up of CO₂ into the chloroplast by the simplified C4 pathway, in which HCO₃^- is fixed on phosphoenolpyruvate (PEP) to yield oxaloacetate (OAA) in the cytoplasm by PEP carboxylase and OAA transported to the chloroplast is decarboxylated to supply CO₂ to the Calvin cycle by PEP carboxykinase (PCK).. Here we report several novel observations made during the course of this project. (1) The genes encoding 3-hexulose-6-phosphate synthase and 6-phospho-3-hexuloisomerase from Mycobacterium gastri MB19 (Mitsui et al. (2000) J. Bacteriol. 182:944-8) were introduced into Arabidopsis and tobacco under the control of tomato rbcS-3C promoter with its transit peptide. Their enzyme activities were highly expressed in the chloroplast. The transgenic plants were strongly tolerant to HCHO and showed an enhanced ability to absorb and assimilate HCHO. Thus these plants may be useful for remediation of the air polluted with HCHO, a sick-house gas, as they are. (2) Following our previous success in exerting the activity of PEP carboxylase from a cyanobacterium in Arabidopsis (Chen et al. (2004) Planta, in press), we undertook to express PCK from maize (Furumoto et al. (1999) Plant Mol. Biol. 41: 301-11) in the chloroplast of tobacco. Unexpectedly, the growth of transformants was enhanced maximally about two-fold by single introduction of the PCK gene. Preliminary data showed that maximum rates of photosynthetic CO₂ assimilation at saturated CO₂ and light intensity were both increased about 30% as compared with the control plants. The implications of results and possible usefulness of these transformants will be discussed.

KEY WORDS: Formaldehyde, C4 pathway, Metabolic engineering, Ribulose monophosphate pathway