A genetic engineering approach to improve the carbon fixation in C3 plants by reducing the flux through the photorespiratory pathway. Consequences of the expression of novel activities in chloroplasts of A. thaliana

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Photorespiration results from the oxygenation reaction catalysed by ribulose 1,5-bisphosphate carboxylase/oxygenase. In this reaction glycolate 2-P is produced and subsequently metabolised in the photorespiratory pathway to form glycerate 3-P. During this process, CO2 and NH4+ are released and ATP and reducing equivalents are consumed, thus making photorespiration a wasteful process. By introducing two alternative and complete glycolate catabolic cycles into C3 chloroplasts, we attempt to create an autoregulatory cycle which results in an attenuation of photorespiration and an expected improvement in the efficiency of CO2 assimilation and consequently, faster biomass production. The model plant Arabidopsis thaliana will be used to set up and characterized the novel pathways. In a further step, the new glycolate cycles will be introduced into plants with agronomical interest, like tomato or potato. On the other hand, during our previous work the introduction of single activities for each pathway in A. thaliana rendered transgenic plants with interesting and unexpected phenotypes (e.g., salt resistance, photoperiod-dependent pale green rosettes and accelerated dark-induced senescence). A thorough metabolic characterization of these transgenic plants will be performed to clarify the physiological alterations introduced with the expression of the transgenes.