Biotechnological approaches to improve C3-photosynthesis: establishment of a complete glycolate pathway in C3 chloroplasts and overexpression of C4 single enzymes in A. thaliana

MAURINO, VG; H FAHNENSTICH; SAIGO, MARIANA; MARIA FABIANA DRINCOVICH; FLUGGE, U.

Cambridge, UK

Congreso; Satellite Meeting of XIV Internacional Congreso of Photosynthesis: C4 and CAM: from molecular diversity to ecological convergence; 2007

The photosynthetic cycle of C4-plants provides a CO2 pump, which leads to increased CO2/O2 ratio at the site of Rubisco and thus results in a decreased oxygenase activity. In this way, C4-plants display a high photosynthetic capacity. By introducing a complete glycolate catabolic cycles into C3-chloroplasts, it is attempted to create an autoregulatory cycle which results in an attenuation of photorespiration and an expected improvement in the efficiency of CO2 assimilation. Arabidopsis thaliana was used to set up and characterized the novel pathway. Other approach to improve C3-photosynthesis is the introduction of single C4-activities in C3-plants, expecting that it will led to the desired redirection of fluxes. C4-NADP-ME was overexpressed in A. thaliana leading to 6 to 30 fold higher activities. There were no beneficial impacts in the photosynthetic performance in the transgenic plants. However, plants growing in short days displayed a pale green phenotype. In these conditions, MEm plants have a decreased fresh weight/area ratio and thinner leaf sections. No differences in morphology and development were evident in long days. Analysis of data showed that MEm transgenic plants entered dark induced senescence more rapidly due to an accelerated starvation caused by extremely low levels of malate and fumarate. Thus, in prolonged darkness these metabolites are consumed faster than in the wild-type and, as a consequence, MEm plants enter irreversible senescence more rapidly. In addition, our data point out that malate and fumarate are important form of fixed carbon that can be rapidly metabolized at least in Arabidopsis thaliana.